Borders' Dictionary of Health Physics

Return to menu

P-type semiconductor, hole semiconductor
An extrinsic semiconductor in which the mobile hole density exceeds the conduction electron density under conditions of thermal equilibrium.
(IEC 50-394-1993)

Pachygyria
Unusually thick convolutions of the cerebral cortex, related to defective development.
(ICRP 49)

Package
The packaging together with its radioactive contents as presented for transport.
(10CFR71.4)

Package
For radioactive materials, the packaging together with the contents as presented for transport.
(49CFR173.403)

Package
In Section 6 only of this standard: The packaging together with actual or simulated radioactive contents. In all other sections of this standard: The packaging together with its radioactive contents as presented for transport.
(ANSI N14.5-1987)

Package
Packaging together with its contents.
(ANSI N14.24-1985)

Package power reactor
A small nuclear power plant designed to be crated in packages small enough to be conveniently transported to remote locations.
(USAEC-1974)

Packaging
One or more receptacles and wrappers and their contents, excluding any special nuclear material, source material or byproduct material, but including absorbent material, spacing structures, thermal insulation, radiation shielding, devices for cooling and for absorbing mechanical shock, external fittings, neutron moderators, nonfissile neutron absorbers and other supplementary equipment.
(10CFR110.2)

Packaging
For radioactive materials, the assembly of components necessary to ensure compliance with the packaging requirements of this subpart. It may consist of one or more receptacles, absorbent material, spacing structures, thermal insulations, radiation shielding, and devices for cooling or absorbing mechanical shocks. The conveyance, tie-down system, and auxiliary equipment may sometimes be designated as part of the packaging.
(49CFR173.403)

Packaging
The assembly of components necessary to ensure compliance with the packaging requirements of this part. It may consist of one or more receptacles, absorbent materials, spacing structures, thermal insulation, radiation shielding, and devices for cooling or absorbing mechanical shocks. The vehicle, tie-down system, and auxiliary equipment may be designated as part of the packaging.
(10CFR71.4)

Packaging
A container to be used for the transpose of UF₆, including the outer protective packaging when utilized.
(ANSI N14.1-1990)

Packaging
The assembly of components necessary to ensure compliance with the package requirements as set forth in the applicable documents in 2.1.1 and 2.1.2 of this standard.
(ANSI N14.5-1987)

Packaging
The assembly of components, excluding contents, needed to ensure compliance with the requirements of 10 CFR 71 or comparable DOE Orders.
(ANSI N14.24-1985)

Packing density
Ratio of fiber or membrane volume of a filter to its total volume; also solidity.
(AM-1993)

Packing fraction
The ratio of the mass defect to the mass number of a nuclide.
(ANSI N1.1-1976)

Packing fraction
The difference between the actual mass of a nuclide and the nearest whole number, divided by the mass number, A; or (M-A)/A. An equivalent statement is that it is the mass defect divided by the mass number. It is positive for most nuclides with mass number less than 12 and more than 180, which therefore tend to be less stable, and negative for most other nuclides, which tend to be more stable.
(USAEC-1974)

Packing fraction
The ratio (D/A) of the mass defect (D) and mass number (A), of a nuclide.
(RHH)

Pair production
The simultaneous production of an electron and a positron by an interaction of a photon or a fast charged particle with the electronic field of a nucleus or other particle.
(NCRP 51)

Pair production
The transformation of the kinetic energy of a high energy photon or particle into mass, producing a particle and its antiparticle, such as an electron and positron. (See mass-energy equivalence.)
(USAEC-1974)

Pair production
An absorption process for x and gamma radiation in which the incident photon is annihilated in the vicinity of the nucleus of the absorbing atom, with subsequent production of an electron and positron pair. This reaction only occurs for incident photon energies exceeding 1.02 MeV.
(RHH)

Pair production (electron)
The simultaneous formation of a positive and negative electron as a result of the interaction of a photon of sufficient energy (>1.02 MeV) with the field of an atomic nucleus or electron.
(ANSI N1.1-1976)

Paleocortex
The ventrolateral area of the cerebral cortex. Phylogenetically this is the oldest portion of the cerebral cortex, and consequently differs most from the isocortex. It lies in the area adjacent to the corpus striatum and includes the primary olfactory cortex.
(ICRP 49)

Panoramic dry-source-storage irradiator
An irradiator in which the irradiations occur in air in areas potentially accessible to personnel and in which the sources are stored in shields made of solid materials. The term includes beam-type dry-source-storage irradiators in which only a narrow beam of radiation is produced for performing irradiations.
(10CFR36.2)

Panoramic irradiator
An irradiator in which the irradiations are done in air in areas potentially accessible to personnel. The term includes beam-type irradiators.
(10CFR36.2)

Panoramic wet-source-storage irradiator
An irradiator in which the irradiations occur in air in areas potentially accessible to personnel and in which the sources are stored under water in a storage pool.
(10CFR36.2)

Papilloma
A benign epithelial tumor with a fibrovascular stroma.
(ICRP 59)

Paralysis time
Constant predetermined value imposed on the resolving time by a paralysis circuit, usually in order to make the resolving time correction more accurate.
(IEC 50-394-1993)

Parameter
Any specific parameter or value affecting or describing the theoretical or measurable characteristics of a unit being considered which behaves as an independent variable or which depends upon some functional interaction of other quantities in a theoretically determinable manner.
(ANSI/ANS-3.8.1-1987)

Parameter
Any one of a set of variables in a model whose values determine model predictions.
(NUREG/CR 3332)

Parameter imprecision analysis
An analysis of uncertainty using error propagation techniques to produce a stochastically variable prediction of a function of stochastically variable parameters.
(NCRP 76)

Parameter imprecision analysis
An analysis of uncertainty in deterministic models, using error propagation techniques to produce a stochastically variable prediction as a function of stochastically variable parameters.
(NUREG/CR 3332)

Parameters
Any one of a set of independent variables in a model whose values determine the characteristics or behavior of the model.
(NCRP 123I)

Parameters
Any one of a set of independent variables in a model whose values determine the characteristics or behavior of the model.
(NCRP 76)

Parasitic capture
Any absorption (as in a reactor) of neutrons in reactions which do not cause further fission or the production of new fissionable material. In a reactor the process is undesirable. (See absorption, capture, neutron economy.)
(USAEC-1974)

Parent
A radionuclide which, upon disintegration, yields a specified nuclide - either directly or later as a member of a radioactive series.
(ENV RAD)

Parent
A radionuclide which, upon disintegration, yields a specified nuclide - either directly or later as a member of a radioactive series.
(ANSI N1.1-1976)

Parent
A radionuclide which, upon disintegration, yields a specified nuclide - either directly or later as a member of a radioactive series.
(HPJ 60)

Parent
A radionuclide that upon radioactive decay or disintegration yields a specific nuclide (the daughter), either directly or as a later member of a radioactive series. (See daughter, radioactive series.)
(USAEC-1974)

Parent
A radionuclide which, upon disintegration, yields a specified nuclide - either directly or later as a member of a radioactive series.
(RHH)

Parity
A symmetry property of a spatial wave function. The parity is said to be even (or +) if the wave function is left unchanged by reversing the sign of all the coordinates, odd (or -) if the sign of the wave function is thereby changed.
(ANSI N1.1-1976)

Parotid gland
Large serous salivary glands situated below and in front of the ear.
(HPJ 60)

Part 55 reviews
Those services provided by the Commission to administer requalification and replacement examinations and tests for reactor operators licensed pursuant to 10 CFR part 55 of the Commission's regulations and employed by part 50 licensees. These services also include related items such as the preparation, review, and grading of the examinations and tests.
(10CFR170.3)

Part 70 permit
Any permit issued pursuant to part 70 of this chapter.
(40CFR61.02)

Partial pressure
Pressure which a vapor would exert if it were the only component present in a volume of gas.
(AM-1993)

Participant
A person. identified in a hearing notice or other Commission order, who takes part in a hearing conducted by the Commission under this part, including any person to whom the Commission grants a hearing or leave to intervene in an export or import licensing hearing, either as a matter of right or as a matter of discretion.
(10CFR110.2)

Particle
A small discrete object, often having a density approaching the intrinsic density of the bulk material; it may chemically homogeneous or contain a variety of chemical species; it may consist of solid or liquid materials or both.
(AM-1993)

Particle
Minute portion of matter or energy.
(IEC 50-393-1993)

Particle
A minute constituent of matter, generally one with a measurable mass. The primary particles involved in radioactivity are a particle, b particles, neutrons, and protons.
(HPJ 60)

Particle
A photon, positive or negative electron, or an alpha particle.
(MIRD)

Particle
A minute constituent of matter, generally one with a measurable mass. The primary particles involved in radioactivity are alpha particles, beta particles, neutrons, and protons. (See charged particle, elementary particles, ion, radiation.)
(USAEC-1974)

Particle
An aggregate of molecules, forming a solid or liquid, ranging in size from a few molecular diameters to some tenths of millimeters (several hundred microns).
(ANSI N13.1-1969)

Particle (nuclear physics)
A neutron, proton, electron, ionized nucleus, neutrino, meson, pion, or other nuclear entity involved in and produced from nuclear reactions.
(ANSI N1.1-1976)

Particle accelerator
An accelerator.
(USAEC-1974)

Particle bounce
Rebound of particles that fail to adhere after impacting on a collecting surface.
(AM-1993)

Particle Clearance Velocity
Speed of clearance of particles deposited in the respiratory tract by mucous clearance, phagocytosis or dissolution and absorption.
(NCRP 125)

Particle current density
Vector such that its component along the normal to a surface equals the net number of particles crossing that surface in the positive direction per unit area and per unit time.
(IEC 50-393-1993)

Particle Dissolution Rate
Rate at which the change from a solid to a liquid form takes place.
(NCRP 125)

Particle fluence (f)
The quotient of dN by da, where dN is the number of particles incident on a sphere of cross-sectional area da.

(ICRP 51)

Particle fluence (f)
The quotient of dN by da, where dN is the number of particles incident on a sphere of cross-sectional area da.

(ICRU 33)

Particle fluence or fluence (f)
The number of particles which enter a small sphere divided by the cross sectional area of this sphere.
(ICRU 20)

Particle fluence or fluence (F)
The quotient DN by Da, where DN is the number of particles which enter a sphere of cross-sectional area Da.

(NBS 92)

Particle fluence or fluence (F)
The quotient DN by Da, where DN is the number of particles which enter a sphere of cross-sectional area Da.

(ICRU 10f)

Particle fluence or fluence (F)
The quotient DN by Da, where DN is the number of particles which enter a sphere of cross-sectional area Da.

(ICRU 10b)

Particle fluence rate (f)
The quotient of dF by dt, where dF is the incident of particle fluence in the time interval dt.
(ICRU 33)

Particle fluence rate indicator
Radiation indicator which gives an estimate of the quantity particle fluence rate.
(IEC 50-394-1993)

Particle fluence rate monitor
Radiation monitor designed to measure the quantity particle fluence rate provided with a means for giving perceptible warning that the particle fluence rate exceeds some predetermined value or that the measured value is outside some predetermined limits.
(IEC 50-394-1993)

Particle fluence ratemeter
Radiation meter designed to measure particle fluence rate.
(IEC 50-394-1993)

Particle flux ()
The quotient of dN by dt, where dN is the increment of particle number in the time interval dt.

(ICRP 51)

Particle flux ()
The quotient of dN by dt, where dN is the increment of particle number in the time interval dt.

(ICRU 33)

Particle flux density or flux density (f)
The quotient DF by Dt where DF is the particle fluence in time Dt.

Note: This quantity may also be referred to as particle fluence rate.
(NBS 92)

Particle flux density or flux density (f)
The quotient DF by Dt where DF is the particle fluence in time Dt.

Note: This quantity may also be referred to as particle fluence rate.
(ICRU 10b)

Particle flux density or flux density (f)
The quotient DF by Dt where DF is the particle fluence in time Dt.

Note: This quantity may also be referred to as particle fluence rate.
(ICRU 10f)

Particle number (n)
Total number of particles emitted, transferred, or received.
(IEC 50-393-1993)

Particle number (n)
The number of particles emitted, transferred or received.
(ICRU 33)

Particle radiance (p)
The quotient of df by dW, where df is the fluence rate of particles propagating in a specified direction within a solid angle dW.

(ICRU 33)

Particle size distribution
A relationship expressing the quantity of a particle property (activity) associated with particles in a given size range.
(AM-1993)

Particle transport
Processes that clear material from the respiratory tract to the GI tract and to the lymph nodes, and move material from one part of the respiratory tract to another.
(ICRP 68)

Particle transport
Processes that clear material from the respiratory tract to the GI tract and to the lymph nodes, and move material from one part of the respiratory tract to another.
(ICRP 66)

Particle, particulate
A minute piece of solid matter having measurable dimensions. Also a radioactive particle (alpha, beta) which can liberate ionizing radiation or (neutron) which can initiate a nuclear transformation.
(ERDA 76-21)

Particle-size distribution
The frequency of occurrence of particles of various sizes in a sample.
(TID-26608)

Particles
Particles are produced by mechanical means by the disintegration processes of grinding, crushing, drilling, blasting, and spraying; or by physiochemical reactions such as combustion, vaporization, distillation, sublimation, calcination, and condensation. Particles are classified as follows: dust, spray, fume, mist, fog, smoke.
(ANSI Z88.2-1980)

Particles, directly ionizing
Charge particles (electrons, protons, alpha particles, etc.) having sufficient kinetic energy to produce ionization by collision.
(ANSI N1.1-1976)

Particles, indirectly ionizing
Uncharged particles (neutrons, photons, etc.) which can liberate directly ionizing particles or can initiate a nuclear transformation.
(ANSI N1.1-1976)

Particles, ionizing
Directly or indirectly ionizing particles.
(ANSI N1.1-1976)

Particulate
A particle; this term is also used as an adjective indicating that the material in question has particle-like characteristics.
(AM-1993)

Particulate
Solid dry particles which remain in suspension individually in gases.
(IEC 50-393-1993)

Particulate matter
A suspension of fine solid or liquid particles in air, such as dust, fog, fume, mist smoke or sprays. Particulate matter suspended in air is commonly known as an aerosol.
(ANSI Z88.2-1980)

Pascal (pa)
The S.I. unit for pressure. 1 Pa = 1 newton per meter squared.
(NCRP 103)

Passive assay
Assay based on the observation of naturally occurring phenomena.
(ANSI N15.37-1981)

Passive detector
An instrument designed to estimate the concentration of radon or radon daughter products without any moving parts such as a sampling pump.
(NCRP 97)

Passive nda
An assay based on spontaneous nuclear radiation(s).
(ANSI N15.35-1983)

Passive sampling
Aerosol measurement using natural convection or diffusion to draw the air into the measurement device; as opposed to active sampling.
(AM-1993)

Path length
Total length of the path of a particle moving through a medium, measured along the actual path, whether of not rectilinear.
(NCRP 51)

Path, mean free
The average distance a particle travels between collisions.
(RHH)

Pathogen
A microorganism that causes disease.
(AM-1993)

Peak absorbed dose
The maximum value of the absorbed dose occurring along the central ray of a single fixed beam. The peak absorbed dose in water or soft tissue is situated at a depth of about 0.2 cm for ¹³⁷Cs gamma rays, 0.5 cm for ⁶⁰Co gamma rays, 1 cm for 4 MV x radiation and 4 cm for 25 MV x radiation. The exact position of the peak depends on the type of collimator, and on whether a secondary electron filter is used. It also depends on field size. source-surface distance and especially on source-diaphragm distance. (The depths given above assume that the number of secondary electrons arriving at the surface have been minimized.)
In an asymmetrical beam such as produced by a wedge filter, the peak absorbed dose may be less than the maximum absorbed dose which in this case will occur off the central ray.
(ICRU 24)

Peak scatter factor (backscatter factor)
The ratio of absorbed dose, at the depth of maximum electron buildup in a water phantom, on the central ray, to the absorbed dose at the same point in space with only sufficient medium around it for maximum electron buildup. For x rays with peak energies below 500 keV, the depth of maximum electron buildup is taken to be at the surface, and the peak scatter factor is often called the backscatter factor. Above 1 MeV, the peak scatter factor relates to a point beneath the surface, and includes some radiation scattered in the forward and side directions.
(NCRP 69)

Peak scatter factor (backscatter factor)
A special case of both tissue-air ratio (q.v.) and scatter factor. For x rays generated by potentials of 400 kV or less, the backscatter factor is the tissue-air ratio for which the reference point (q.v.) is taken at the intersection of the beam axis with the surface. The concept has been extended to radiation of higher energy by taking the reference point at a depth equal to that of the peak dose (q.v.). In the latter case the quantity should preferably be called peak scatter factor.
(ICRU 24)

Peak-to-compton ratio
In a pulse height spectrum of monoenergetic gamma radiation, ratio of counts per channel at the peak position of the total energy absorption peak to those at the flat portion of the Compton continuum.
(IEC 50-394-1993)

Peak-to-total ratio
In a monoenergetic gamma radiation pulse height spectrum, ratio of the number of counts contained in the total energy absorption peak to that contained in the whole spectrum.
(IEC 50-394-1993)

Pebble bed reactor
A reactor in which the fissionable fuel (and sometimes also the moderator) is in the form of packed or randomly placed pellets, which are cooled by gas or liquid.
(USAEC-1974)

Peclet number
Ratio of a particle's convective to diffusive transport.
(AM-1993)

Pegmatite
Igneous rock type that is usually found in dikes associated with granites. It can have a high uranium content.
(ENV RAD)

Penetrating radiation
A general term used to describe external radiations with sufficient penetrating power that the absorbed dose from exposures to man is delivered in significant quantities to tissues and organs other than the skin. It refers to gamma, x and neutron radiations.
(NCRP 65)

Penetrating radiation (p)
Those particles emitted in the source that contribute a significant dose to organs other than the source organ.
(MIRD)

Penetration
The measure of the quantity of a test agent that leaks through or around an air cleaning device when the device is tested with an agent of known characteristics under specified conditions; penetration is expressed as a percentage of the concentration of the test agent in the space upstream of the air cleaning device.
(ERDA 76-21)

Penetration
The complete passage of airborne contaminants through a filter or other collector.
(ANSI N13.1-1969)

Penetrometer
A simple device for measuring the penetrating power of a beam of X rays or other penetrating radiation by comparing transmission through various absorbers. (See absorber.)
(USAEC-1974)

Penumbra
The region, at the edge of a radiation beam, over which the dose rate changes rapidly as a function of distance from the axis is known as penumbra. It may be defined geometrically and dosimetrically.
(1) Geometric Penumbra: Geometric penumbra is the region in space which could be irradiated by primary photons or particles coming from part of the source only. By analogy, the transmission penumbra is the region irradiated by photons or particles which have traversed part of the thickness of the collimator, i.e., the outer edge.
(2) Geometric Penumbra Width: The width of the geometric penumbra in a plane perpendicular to the beam axis at any distance of interest from the source. It is a geometrical concept only and is calculated from the expression:

where s is the source diameter (or effective diameter), F + d is the distance from the source to the point of interest and F_D is the source-diaphragm distance.
(3) Physical Penumbra: Physical penumbra is a dosimetric concept and the physical penumbra width is the lateral distance between two specified isodose curves at a specified depth.
(ICRU 30)

Penumbra
The region of space which is partially shielded from the primary photons proceeding from the source. The penumbra has two components, only one of which is capable of precise definition:
(1) Geometrical Penumbra: The region of free space irradiated by primary photons coming from only part of the source. The geometrical penumbra width of the geometrical penumbra in a field may be given at any distance of interest from the source. For example, the geometrical penumbra width at the surface of a phantom is given by:
Geometrical penumbra width = a(a-b)/b
where:
a = diameter of front surface of source
s = source surface distance
b = distance from source to distal end of the limiting diaphragm.
(2) Transmission Penumbra: The region of space irradiated by primary photons which have traversed only part of the thickness of the collimator, i.e. the part of the collimator farthest from the source.
(ICRU 23)

Percentage depth dose
The ratio (expressed as a percentage) of the absorbed dose at any depth in a phantom to the absorbed dose at a fixed reference point on the beam axis. The reference depth is usually at the surface for x rays with peak energies below 500 keV and at a depth of maximum dose for higher energies.
(NCRP 69)

Percentage depth dose
The ratio, expressed as a percentage, of the absorbed dose rate at a point, at a depth along the beam axis, to the absorbed dose rate at a fixed point on the beam axis. For x rays generated by potentials up to 400 kV, the point of reference is at the surface while above 400 kV it is usually at the point of the peak absorbed dose. (For isocentric techniques the reference point is usually at the depth of the isocenter).
(ICRU 30)

Percentage depth dose
The ratio, expressed as a percentage, of the absorbed dose rate at a point, at a depth along the beam axis, to the absorbed dose rate at a fixed reference point on the beam axis. For x rays generated by potentials up to 400 kV, the point of reference is at the surface while above 400 kV it is usually at the point of the peak absorbed dose (q.v.). For isocentric techniques (q.v) the reference point is usually at the depth of the isocenter. For wedged beams the percentage depth doses are taken to be the same as those that apply to the same beam with the wedge filter omitted. This method is employed since it is difficult to determine the position of the reference dose.
(ICRU 24)

Percentage depth dose
The ratio (expressed as a percentage) of the absorbed dose, D_d, at any depth d in a phantom to the absorbed dose D₀ at any fixed reference point on the beam axis. Thus,
Percent depth dose = 100 D_d/D₀
For x rays up to 400 kV the reference point is usually at the surface. For x rays above 400 kV and for gamma rays, the reference point is usually at the position of the peak absorbed dose. However, any other arbitrary reference point on the beam axis may be chosen, provided that its position is specified.
(ICRU 23)

Percentage depth dose
Dose of radiation delivered at a specified depth in tissue, expressed as a percentage of the skin dose.
(RHH)

Percolation (infiltration)
The process of downward movement of water from the surface to underlying materials.
(NCRP 76)

Performance check
Following calibration, a source cheek carried out to ensure that the instrument response to radiation from a known source has not changed beyond acceptable bounds.
(NCRP 112)

Performance confirmation
The program of tests, experiments, and analyses which is conducted to evaluate the accuracy and adequacy of the information used to determine with reasonable assurance that the performance objectives for the period after permanent closure will be met.
(10CFR60.2)

Performance index (P_i)
The performance index of the ith dosimeter is defined as:

where (D_I)_i is the absorbed-dose index, assigned by testing laboratory to the irradiated dosimeters, and (D'_I)_i is the corresponding evaluated absorbed dose index reported by the processor.
(ANSI N13.15-1985)

Performance quotient (P_i)
For tests of protection dosimetry, the performance quotient of the ith dosimeter is defined as:

where (H_I)_i is the dose equivalent assigned by testing laboratory to the irradiated dosimeter, and (H'_I)_i is the corresponding evaluated dose equivalent reported by the processor. For tests of accident dosimetry, the same definition applies, with the absorbed dose, D, replacing the dose equivalent, H. Note: In this definition, H stands for H_s or H_d and D stands for D_d. No tests are performed for D_s.
(ANSI/HPS N13.11-1993)

Performance Testing
Testing conducted to verify a simulation facility's performance as compared to actual or predicted reference plant performance.
(10CFR55.4)

Period
The time required for one cycle of a regularly repeated series of events. In a nuclear reactor, it is the time required for the power level to change by the factor 2.718, which is known as e (the base of natural logarithms). (See Periodic Table.)
(USAEC-1974)

Period meter
Electronic assembly which, in association with one or more detectors, is used to indicate the time constant of a nuclear reactor.
(IEC 50-394-1993)

Period meter
An instrument for measuring the reactor time constant (reactor period). The instrument actually measures d(log neutron flux density)/dt.
(ANSI N1.1-1976)

Period range
A range of reactor power levels over which the reactor time constant (reactor period) rather than the reactor power is of primary importance for reactor control.
(ANSI N1.1-1976)

Periodic table
An arrangement of chemical elements in order of increasing atomic number. Elements of similar properties are placed one under the other, yielding groups and families of elements. Within each group there is a gradation of chemical and physical properties but, in general, a similarity of chemical behavior. From group to group, however, there is a progressive shift of chemical behavior from one end of the table to the other.
(RHH)

Periodic table (periodic chart)
A table or chart listing all the elements, arranged in order of increasing atomic numbers and grouped by similar physical and chemical characteristics into " periods". The table is based on the chemical law that the physical or chemical properties of the elements are periodic (regularly repeated) functions of their atomic weights, first proposed by the Russian chemist, Dmitri I. Mendeleev, in 1869.
(USAEC-1974)

Periphyton
The aquatic community of diatoms and other algae, bacteria, fungus and protozoa, which is attached to substrates.
(NCRP 76)

Permanent cessation of operation(s)
For a nuclear power reactor facility, a certification by a licensee to the NRC that it has permanently ceased or will permanently cease reactor operation(s), or a final legally effective order to permanently cease operation(s) has come into effect.
(10CFR50.2)

Permanent closure
Final backfilling of the underground facility and the sealing of shafts and boreholes.
(10CFR60.2)

Permanent fuel removal
For a nuclear power reactor facility, a certification by the licensee to the NRC that it has permanently removed all fuel assemblies from the reactor vessel.
(10CFR50.2)

Permanent radiographic installation
An enclosed shielded room, cell, or vault, not located at a temporary jobsite, in which radiography is performed.
(10CFR34.3)

Permanent radiographic installation
A shielded installation or structure designed or intended for radiography and in which radiography is regularly performed.
(10CFR34.2)

Permeability
The capacity of a solid to transmit a fluid. It is dependent on the porosity (volume of pores) as well as the extent of interconnection among pores.
(ENV RAD)

Permeability
The capacity of a porous rock, solid, or sediment to transmit a fluid without damage to the structure of the medium.
(RRM)

Permeability
The ratio of the magnetic flux density to the magnetic field strength at a point. Permeability is expressed in units of henry per meter (H/m).
(NCRP 67)

Permeability, relative
The ratio of the permeability of a medium at a point to that of vacuum.
(NCRP 67)

Permeable
Affording passage or penetration.
(RHH)

Permissible dose
See maximum permissible dose, radiation protection guide.
(USAEC-1974)

Permissible dose
The dose of radiation which may be received by an individual within a specified period of time with expectation of no significant harmful result.
(BEIR I)

Permissible dose
The dose of radiation which may be received by an individual within a specified period of time with expectation of no significant harmful result.
(RHH)

Permissible exposure limit (PEL)
The legally established time-weighted average (TWA) concentration or ceiling concentration of a contaminant that shall not be exceeded.
(ANSI Z88.2-1980)

Permissible level
That concentration of airborne material which has been established as a local guide or regulation to limit the quantity of radioactive materials inhaled. Permissible level may differ depending upon the nature of the airborne material, the duration of anticipated exposure, and the protection afforded by special clothing or other barriers.
(ANSI N13.1-1969)

Permissible organ burden
The quality of a radionuclide in any organ that just delivers the maximum permissible dose rate.
(NCRP 84)

Permit program
A comprehensive State operating permit system established pursuant to title V of the Act (42 U.S.C. 7661) and regulations codified in part 70 of this chapter and applicable to State regulations, or a comprehensive Federal operating permit system established pursuant to title V of the Act and regulations codified in this chapter.
(40CFR61.02)

Permitting authority
(1) The State air pollution control agency, local agency, other State agency, or other agency authorized by the Administrator to carry out a permit program under part 70 of this chapter; or
(2) The Administrator, in the case of EPA-implemented permit programs under title V of the Act (42 U.S.C. 7661).
(40CFR61.02)

Permittivity
The ratio of the electric flux density to the electric field strength at a point. Permittivity is expressed in units of farad per meter (F/m).
(NCRP 67)

Permittivity, relative
The ratio of the permittivity of a medium at a point to that of vacuum.
(NCRP 67)

Person
Has the same meaning as found in parts 30, 40, 50, and 70 of title 10 of the Code of Federal Regulations.
(10CFR170.3)

Person
(1) Any individual, corporation, partnership, firm, association, trust, estate, public or private institution, group, Government agency other than the Commission; any state or any political subdivision of, or any political entity within, a state; any foreign Government or nation or any political subdivision of any such government or nation; or other entity; and (2) any legal successor, representative, agent, or agency of the foregoing.
(10CFR171.5)

Person
(1) Any individual, corporation, partnership, firm, association, trust, estate, public or private institution, group, Government agency other than the Commission or the Department of Energy (DOE), except that the DOE shall be considered a person within the meaning of the regulations in this part to the extent that its facilities and activities are subject to the licensing and related regulatory authority of the Commission pursuant to section 202 of the Energy Reorganization Act of 1974, as amended (88 Stat. 1244), and Sections 131, 132, 133, 135, 137, and 141 of the Nuclear Waste Policy Act of 1982 (96 Stat. 2229, 2230, 2232, 2241);
(2) Any State, any political subdivision of a State, or any political entity within a State;
(3) Any foreign government or nation, or any political subdivision of any such government or nation, or other entity; and
(4) Any legal successor, representative, agent, or agency of the foregoing.
(10CFR72.3)

Person
(1) Any individual, corporation, partnership, firm, association, trust, estate, public or private institution, group, government agency other than the Commission or the Department of Energy (except that the Department of Energy is considered a person within the meaning of the regulations in this part to the extent that its facilities and activities are subject to the licensing and related regulatory authority of the Commission pursuant to law), any State or any political subdivision of or any political entity within a State, any foreign government or nation or any political subdivision of any such government or nation, or other entity; and
(2) any legal successor, representative, agent, or agency of the foregoing.
(10CFR61.2)

Person
(1) Any individual, corporation, partnership, firm, association, trust, estate, public or private institution, group, Government agency other than the Commission or the Department of Energy, except that the Department of Energy shall be considered a person within the meaning of the regulations in this part to the extent that its facilities and activities are subject to the licensing and related regulatory authority of the Commission pursuant to section 202 of the Energy Reorganization Act of 1974 (88 Stat. 1244), any state or any political subdivision of or any political entity within a state, any foreign government or nation or political subdivision of any such government or nation, or other entity; and
(2) Any legal successor, representative, agent, or agency of the foregoing.
(10CFR74.4)

Person
Any individual, corporation, partnership, firm, association, trust, estate, institution, group, Government agency other than the Commission or, with respect to imports, the Department of Energy; any State or political entity within a State; any foreign government or political entity of such government; and any authorized representative of the foregoing.
(10CFR110.2)

Person
Any individual, corporation, partnership, firm, association, trust, estate, public or private institution, group, agency, and State or any political subdivision of any political entity within a State, and any legal successor, representative, agent, or agency of the foregoing other than Government agencies;
(10CFR150.2)

Person
(1) any individual, corporation, partnership, firm, association, trust, estate, public or private institution, group, government agency other than the Commission or the Department, except that the Department shall be considered a person to the extent that its facilities are subject to the licensing and related regulatory authority of the Commission pursuant to section 202 of the Energy Reorganization Act of 1974, \1\ any State or any political subdivision of, or any political entity within a State, any foreign government or nation or any political subdivision of any such government or nation, or other entity; and (2) any legal successor, representative, agent, or agency of the foregoing.
(10CFR50.2)

Person
(1) Any individual, corporation, partnership, firm, association, trust, estate, public or private institution, group, Government agency other than the Commission or the Department of Energy (except that the Department shall be considered a person within the meaning of the regulations in 10 CFR chapter I to the extent that its facilities and activities are subject to the licensing and related regulatory authority of the Commission under section 202 of the Energy Reorganization Act of 1974 (88 Stat. 1244), the Uranium Mill Tailings Radiation Control Act of 1978 (92 Stat. 3021), the Nuclear Waste Policy Act of 1982 (96 Stat. 2201), and section 3(b)(2) of the Low-Level Radioactive Waste Policy Amendments Act of 1985 (99 Stat. 1842)), any State or any political subdivision of or any political entity within a State, any foreign government or nation or any political subdivision of any such government or nation, or other entity; and
(2) Any legal successor, representative, agent, or agency of the foregoing.
(10CFR20.1003)

Person
Any individual, corporation, partnership, firm, association, trust, State, public or private institution, group or agency who is an NRC or NRC Agreement State licensed generator of low-level radioactive waste within the scope of §62.1(c) of this part; any Governor (or for any State without a Governor, the chief executive officer of the State) on behalf of any NRC or NRC Agreement State licensed generator or generators of low-level radioactive waste within the scope of §62.1(c) of this part located in his or her State; or their duly authorized representative, legal successor, or agent.
(10CFR62.2)

Person
(1) Any individual, corporation, partnership, firm, association, trust, estate, public or private institution, group, Government agency other than the Commission or the Department, except that the Department shall be considered a person within the meaning of the regulations in this part to the extent that its facilities and activities are subject to the licensing and related regulatory authority of the Commission pursuant to section 202 of the Energy Reorganization Act of 1974 (88 Stat. 1244), any State or any political subdivision of or any political entity within a State, any foreign government or nation or any political subdivision of any such government or nation, or other entity; and
(2) any legal successor, representative, agent, or agency of the foregoing.
(10CFR30.4)

Person
(1) Any individual, corporation, partnership, firm, association, trust, estate, public or private institution, group, Government agency other than the Commission or the Department, except that the Department shall be considered a person within the meaning of the regulations in this part to the extent that its facilities and activities are subject to the licensing and related regulatory authority of the Commission pursuant to section 202 of the Energy Reorganization Act of 1974 (88 Stat. 1244), any State or any political subdivision of or any political entity within a State, any foreign government or nation or any political subdivision of any such government or nation, or other entity; and
(2) any legal successor, representative, agent, or agency of the foregoing.
(10CFR70.4)

Person
(1) Any individual, corporation, partnership, firm, association, trust, estate, public or private institution, group, government agency other than the Commission or the Department of Energy (DOE), (except that the DOE shall be considered a person to the extent that its facilities are subject to the licensing and related regulatory authority of the Commission pursuant to section 202 of the Energy Reorganization Act of 1974 and sections 104, 105, and 202 of the Uranium Mill Tailings Radiation Control Act of 1978), any state or political subdivision of a state, or any political subdivision of any government or nation, or other entity; and
(2) any legal successor, representative, agent, or agency of the foregoing.
(10CFR73.2)

Person
Any individual, corporation, partnership, firm, association, trust, estate, public or private institution, group, Government agency, any State or political subdivision of, or any political entity within a State; or any foreign government or nation or other entity and any legal successor, representative, agent, or agency of the foregoing; however, person does not include the Department of Energy.
(10CFR834.2)

Person
Any individual, corporation, partnership, firm, association, trust, estate, public or private institution, group, Government agency, any State or political subdivision of, or any political entity within a State, any foreign government or nation or other entity, and any legal successor, representative, agent or agency of the foregoing provided that person does not include the Department or the United States Nuclear Regulatory Commission.
(10CFR835.2-1993)

Person
(1) Any individual, corporation, partnership, firm, association, trust, estate, public or private institution, group, Government agency other than the Commission or the Department, except that the Department shall be considered a person within the meaning of the regulations in this part to the extent that its facilities and activities are subject to the licensing and related regulatory authority of the Commission pursuant to section 202 of the Energy Reorganization Act of 1974 (88 Stat. 1244), any State or any political subdivision of or any political entity within a State, any foreign government or nation or any political subdivision of any such government or nation, or other entity; and
(2) any legal successor, representative, agent, or agency of the foregoing.
(10CFR20.3)

Person in charge
Contractor management or their specific designee responsible for the DOE activity such as operation of the facility.
(10CFR834.2)

Person-gray
Unit of population dose obtained by summing individual dose values for all people in the exposed population. Thus, the number of person-grays contributed by 1 person exposed to 1 Gy is equal to that contributed by 100,000 people each exposed to 10 µGy.
(ICRP 59)

Person-gray
Unit of population exposure obtained by summing individual dose-equivalent values for all people in the exposed population. Thus, the number of person-grays contributed by 1 person exposed to 1 Gy is equal to that contributed by 100,000 people each exposed to 10 µGy.
(BEIR IV)

Person-related environmental monitoring
Environmental monitoring in circumstances where there may be several sources irradiating the same group of people. The main objective is to assess dose equivalents from all sources. Person-related environmental monitoring is not concerned with optimization and will usually by carried out by appropriate national authorities.
(ICRP 43)

Person-rem
Unit of population exposure obtained by summing individual dose equivalent values for all people in the population. Thus, the number of person-rems contributed by 1 person exposed to 100 rems is equal to that contributed by 100,000 people each exposed to 1 mrem.
(BEIR III)

Person-rems
The product of the average individual dose in a population times the number of individuals in the population. Syn: man-rems.
(BEIR I)

Person-years-at-risk
The number of persons exposed times the number of years after exposure minus some lag period during which the dose is assumed to be unexpressed (latent period).
(ICRP 59)

Person-years-at-risk
The number of persons exposed times the number of years after exposure minus some lag period during which the dose is assumed to be unexpressed (latent period).
(NCRP 98)

Person-years-at-risk (PYAR)
The number of persons exposed times the number of years after exposure minus some lag period during which the dose is assumed to be unexpressed (latent period).
(BEIR IV)

Personal dose equivalent
The dose equivalent in soft tissue at an appropriate depth, d, below a specified point on the body. Any statement of personal dose equivalent should include a specification of the reference depth, d, with the value expressed in mm. For penetrating radiation, a depth of 10 mm is employed; thus the notation is Hp(10). For weakly penetrating radiation, a depth of 0.07 mm for the skin and 3 mm for the eye are employed; thus the notations are Hp(0.07) and Hp(3), respectively.
(HPS N13.41-1997)

Personal dosemeter
Dosemeter of small size designed to be worn on a person for determining the dose equivalent received by that person.
(IEC 50-394-1993)

Personal protective equipment
Personnel protective equipment consists of items that in design or construction provide an appropriate degree of protection against toxic materials or physical agents. For example, such an item as a respirator is personal protective equipment.
(ANSI N7.2-1963)

Personal sampler
A device attached to a person in order to sample air in the person's immediate vicinity.
(AM-1993)

Personal supervision
Guidance and instruction by a logging supervisor, who is physically present at a temporary jobsite, who is in personal contact with logging assistants, and who can give immediate assistance.
(10CFR39.2)

Personnel dosimeter
A small radiation detector that is worn by an individual. Common types include film badges, TLD badges, pocket dosimeters and pocket ionization chambers.
(NCRP 105)

Personnel dosimeters
Devices designed to be worn or carried by an individual for the purpose of determining the dose equivalent received (e.g., film badges, pocket chambers, pocket dosimeters, ring badges, thermoluminescent dosimeters, etc.)
(NCRP 107)

Personnel meter
A device to be worn or carried by a person for the purpose of detecting or measuring radiation received by him.
(NBS 51)

Personnel monitor
Also known as personal monitor. An appropriately sensitive device used to estimate the absorbed dose or effective dose equivalent received by an individual.
(NCRP 107)

Personnel monitor
Also known as personal monitor. An appropriately sensitive device used to estimate the absorbed dose received by an individual.
(NCRP 102)

Personnel monitor
See monitor.
(NCRP 48)

Personnel monitoring
Periodic or continuous determination of the exposure received by a person, or the measurement of personal contamination levels.
(NCRP 111)

Personnel monitoring
Monitoring any part of individuals, their breaths, or excretions or any part of their clothing to determine the amount of radioactivity present in or on an individual.
(HPJ 60)

Personnel monitoring
Determination by either physical or biological measurement of the amount of ionizing radiation to which an individual has been exposed, such as by measuring the darkening of a film badge or performing a radon breath analysis. (See hand and foot counter.)
(USAEC-1974)

Personnel monitoring
The systematic periodic estimate of radiation dose received by personnel during working hours.
(NBS 55)

Personnel monitoring equipment
Devices designed to be worn or carried by an individual for the purpose of measuring the dose received (e.g., film badges, pocket chambers, pocket dosimeters, film rings, etc.)
(10CFR20.202)

Personnel neutron dosimeter (or dosimeter)
One or more devices worn on the body for the purpose of estimating the whole-body neutron dose equivalent received by an individual.
(ANSI N319-1976)

Persons
(1) Any individual, corporation, partnership, firm, association, trust, estate, public or private institution, group, Government agency other than the Commission or the Department of Energy except that the Department of Energy shall be considered a person within the meaning of the regulations in this part to the extent that its facilities and activities are subject to the licensing and related regulatory authority of the Commission pursuant to section 202 of the Energy Reorganization Act of 1974 (88 Stat. 1244) and the Uranium Mill Tailings Radiation Control Act of 1978 (92 Stat. 3021), any State or any political subdivision of, or any political entity within a State, any foreign government or nation or any subdivision of any such government or nation, or other entity; and
(2) any legal successor, representative, agent or agency of the foregoing.
(10CFR40.4)

Phagocytic Cells
Cells with the ability to engulf solid material.
(NCRP 125)

Phagocytosis
The engulfing and usually destruction of particulate matter by phagocytes.
(HPJ 60)

Phantom
A simulated person or part of a person used for calibration of in vivo measurement systems. A phantom is constructed to allow placement of radionuclides in a geometry approximating internal depositions.
(HPS N13.42-1997)

Phantom
A volume of material that approximates as closely as possible to the density and effective atomic number of tissue. Ideally a phantom should behave in respect to absorption of radiation in the same manner as tissue. Radiation dose measurements made within or on a phantom provide a means of determining the radiation dose within or on a body under similar exposure conditions. Some of the materials commonly used as phantoms are water, masonite, pressed wood, beeswax, and polyurethane plastics.
(HPJ 60)

Phantom
When a volume of a tissue substitute is used to simulate radiation interactions, this volume is called a phantom. A phantom may also simulate a body tissue with regard to anatomical details such as shape and spatial mass density distribution.
(ICRU 44)

Phantom
A simulated person or part of a person used for calibration of in-vivo measurement systems. A phantom is constructed to allow placement of radionuclides in a geometry approximating internal depositions.
(ANSI N13.30-1989D)

Phantom
An object used to simulate the absorption and scatter characteristics of the patient's body for radiation protection purposes.
(NCRP 102)

Phantom
In experimental dosimetry, a phantom is a physical model constructed of some non-living material such as plastic, wood, rubber, or the like and which simulates the morphological characteristics of a human or animal. Some phantoms consist of hollow plastic shells filled with a radioactive solution. It is desirable that a phantom not only simulate the size, shape, and location of the various tissues of interest, but that its composition be tissue equivalent with respect to radiation absorption and scatter parameters for the type of radiation being studied. By extension, for calculational dosimetry, the term is used to refer to models that exist only as mathematical descriptions of the boundaries, density, and radiation absorption characteristics that a physical system would have.
(NCRP 83)

Phantom
An object used to simulate the absorption and scatter characteristics of the patient's body.
(NCRP 66)

Phantom
A volume of tissue-equivalent material, usually large enough to provide full scatter conditions for the beam being used. Anatomical phantoms in the shape of the animal body are frequently used.
Homogeneous phantom: A phantom made of one material only. The most common phantom material is water.
Body phantom: A phantom in the shape of an animal body or part of it, where the various tissues have been simulated with respect to size, shape, position, and radiation interaction.
(ICRU 30)

Phantom
A volume of tissue-equivalent material either large enough to provide full backscatter or constructed to resemble some special object, such as a human body, for the purpose of measuring a dose distribution.
(ANSI N1.1-1976)

Phantom
A volume of tissue-equivalent material, usually large enough to provide full scatter conditions for the beam being used. In some cases anatomical phantoms in the shape of the human body are used.
Homogeneous phantom: A phantom made of one material only. The most common phantom material is water.
Body phantom: A phantom in the shape of a human body or part of it, where the various tissues have been simulated with respect to size, shape, position, and radiation interaction.
Standard phantom: A soft tissue-equivalent phantom, cubic in shape and at least 30 cm on a side.
(ICRU 24)

Phantom
A volume of tissue-equivalent material used to simulate the absorption and scatter characteristics of a patient's body or parts thereof.
(NCRP 49)

Phantom
A volume of tissue-equivalent material used to simulate the absorption and scatter characteristics of a patient's body or parts thereof.
(NCRP 48)

Phantom
A volume of material approximating as closely as possible the density and effective atomic number of living tissue, used in biological experiments involving radiation.
(USAEC-1974)

Phantom
A volume of tissue-equivalent material large enough to provide full scatter in the beam being used. Water is sufficiently tissue equivalent for present purposes.
Homogeneous Phantom: A phantom made of one material only.
Standard Phantom: A homogeneous phantom of 30 cm x 30 cm square cross section and 20 cm deep.
(ICRU 23)

Phantom particles
Particles that appear in a measured distribution that are due to coincidence or other nonideal aspects of the measurement process and not due to real particles.
(AM-1993)

Pharmacist
An individual registered by a state or territory of the United States, the District of Columbia or the Commonwealth of Puerto Rico to compound and dispense drugs, prescriptions and poisons.
(10CFR40.4)

Pharmacist
An individual licensed by a State or Territory of the United States, the District of Columbia, or the Commonwealth of Puerto Rico to practice pharmacy.
(10CFR35.2)

Pharynx
Passageway for air from the nasal cavity to the larynx and for food from the mouth to the esophagus and also acts as a resonating cavity for sound. (The upper portion is lined with pseudostratified ciliated Columnar epithelium, middle portion with stratified columnar epithelium, and the lower portion with stratified squamous epithelium).
(NCRP 125)

Phase coefficient (phase constant)
The imaginary part (b) of the propagation coefficient that describes the change of phase of a field component with distance in the direction of propagation. The phase coefficient is expressed in unit of radian per meter (rad/m) or degree per meter. See propagation coefficient.
(NCRP 67)

Phase transfer function (PTF)
The phase of the optical transfer function. The PTF represents the phase shift, expressed as a function of spatial frequency, of an output corresponding to a sinusoidal input (Metz and Doi, 1989).
(ICRU 54)

Phased disposal
A method of tailings management and disposal which uses lined impoundments which are filled and then immediately dried and covered to meet all applicable Federal standards.
(40CFR61.251)

Phases of an operation
The pre-operational, commissioning, operational, decommissioning and post-operational phases.
(ICRP 43)

Phasor
A spatially dependent complex scalar or vector field parameter. A phasor is commonly used to represent electromagnetic fields under single frequency, steady state conditions. Phasor notation greatly facilitates mathematical manipulation in field problems and in the graphical representation of field quantities.
(NCRP 67)

Phenotype
Characteristics observable in the individual in question (as opposed to genotype).
(ICRU 30)

F _m
Modifying Factor. Amount by which a parameter should be multiplied in order to calculate doses for a specific individual or group for which the modifying factor is recommended. Transient factors apply only during exposure to the factor and are relevant only to acute intakes. Permanent factors are relevant to chronic intake.
(ICRP 66)

Phosphate rock
An ore from which phosphorus is extracted and which often contains low concentrations of uranium.
(NCRP 118)

Phosphogypsum
The solid waste byproduct which results from the process of wet acid phosphorus production.
(40CFR61.201)

Phosphogypsum stacks or stacks
Piles of waste resulting from wet acid phosphorus production, including phosphate mines or other sites that are used for the disposal of phosphogypsum.
(40CFR61.201)

Phosphogypsum stacks or stacks
Piles of waste from phosphorus fertilizer production containing phosphogypsum. Stacks shall also include phosphate mines that are used for the disposal of phosphogypsum.
(40CFR61.201)

Phosphor
A luminescent substance; a material capable of emitting light when stimulated by radiation. (See scintillation.)
(USAEC-1974)

Phosphorescence
Luminescence persisting for an appreciable time after withdrawal of the exciting irradiation.
(IEC 50-394-1993)

Phosphorescence
Emission of radiation by a substance as a result of previous absorption of radiation of shorter wavelength. In contrast to fluorescence, the emission may continue for a considerable time after cessation of the exciting irradiation.
(RHH)

Phoswich
A low-energy photon detector consisting of two different types of scintillators coupled together (phosphor sandwich).
(HPJ 60)

Photocathode sensitivity
Quotient of the photoelectric emission current from the photocathode by the incident luminous flux under specified conditions of illumination.
(IEC 50-394-1993)

Photodisintegration
Any transformation of a nucleus induced by neutrons.
(NCRP 51)

Photoelectric effect
Complete absorption of a photon by an atom with the emission of an orbital electron.
(IEC 50-393-1993)

Photoelectric effect
The interaction of a photon with an atom, resulting in the absorption of the incident photon and the release of a bound electron from that atom with energy equal to the photon energy less the electron binding energy.
(NCRP 51)

Photoelectric effect
The complete absorption of a photon by an atom with the emission of an orbital electron. (Also called photoelectric absorption.)
(ANSI N1.1-1976)

Photoelectric effect
Process by which a photon ejects an electron from an atom. All the energy of the photon is absorbed in ejecting the electron and in imparting kinetic energy to it.
(RHH)

Photoelectric peak
In X or gamma radiation measurement, that portion of the spectral response curve corresponding to the absorption, in a detecting material, by a photoelectric effect, of the photon energy.
(IEC 50-394-1993)

Photoelectron
Electron ejected from an atom as a result of the photoelectric effect.
(IEC 50-393-1993)

Photofission
Fission of a nucleus induced by photons.
(NCRP 51)

Photofission
Nuclear fission induced by photons.
(ANSI N1.1-1976)

Photofraction
For a given photon energy, ratio of the number of photons detected in the total absorption peak to the total number of photons detected in the same time interval.
(IEC 50-394-1993)

Photoluminescence dosemeter
Dosemeter comprising a photoluminescent detectors a separate reader unit being used to read out the dose.
(IEC 50-394-1993)

Photometer
An instrument that measures the amount of light scattered from a particle cloud; also called a nephelometer.
(AM-1993)

Photomultiplier
A device that produces electrical pulses when struck by light pulses (such as from a scintillator).
(ENV RAD)

Photomultiplier tube
A light-sensitive vacuum tube using secondary emission from a number of electrodes in sequence to obtain increased current output; the electron stream is reflected and multiplied, in turn, from one electrode to the next.
(HPJ 60)

Photomultiplier tube
A photon detector in which electrons are generated by photoelectric emission and multiplied in successive stages by secondary emission. (Also called multiplier tube.)
(ANSI N1.1-1976)

Photomultiplier tube, multiplier phototube, PMT
Vacuum tube intended to convert light into an electrical signal and which essentially contains a photocathode and an electron multiplier.
(IEC 50-394-1993)

Photon
Quantum of electromagnetic radiation considered as a particle of energy hv, where h is the Planck constant and v the frequency of the radiation.
(IEC 50-393-1993)

Photon
For purposes of this report photon refers to ionizing electro-magnetic radiation, specifically x rays or gamma rays.
(NCRP 112)

Photon
An energy quantum of electromagnetic radiation. See gamma radiation.
(NCRP 111)

Photon
The carrier of a quantum of electromagnetic energy. Photons have an effective momentum but no mass or electrical charge.
(HPJ 60)

Photon
Ionizing electromagnetic radiation, irrespective of origin.
(ANSI N42.17A-1989)

Photon
Ionizing electromagnetic radiation, irrespective of origin.
(ANSI N42.17B-1989)

Photon
Ionizing electromagnetic radiation, irrespective of origin.
(ANSI N42.17C-1989)

Photon
A quantum of electromagnetic radiation.
(NCRP 105)

Photon
A quantum of electromagnetic radiation irrespective of origin.
(ANSI N323-1978)

Photon
An energy quantum of electromagnetic radiation. In this report, an x-ray or gamma-ray photon.
(NCRP 51)

Photon
A quantum of electromagnetic radiation.
(ANSI N1.1-1976)

Photon
The carrier of a quantum of electromagnetic energy. Photons have an effective momentum but no mass or electrical charge. (See radiation, quantum.)
(USAEC-1974)

Photon emission curve (of a scintillator)
Curve representing the variation with time of the photon emission rate corresponding to a single excitation of a scintillator.
(IEC 50-394-1993)

Photon Energy (Mev)
A quantity of electromagnetic energy whose value in ergs is the product of its frequency in cycles per second and Planck's constant.
(NCRP 125)

Photon equilibrium
Such equilibrium is said to exist in a volume element if the number and energy distribution of photons entering and leaving the volume element are the same.
(ICRU 17)

Photon propulsion
Use of the directional emission of photons for propulsion. The "exhaust" velocity is the velocity of light.
(ANSI N1.1-1976)

Photoneutron
Neutron ejected from an atomic nucleus as a result of the interaction of a photon with an atomic nucleus.
(IEC 50-393-1993)

Photoneutron
A neutron released from a nucleus by a photonuclear reaction.
(NCRP 51)

Photoneutron
A neutron released from a nucleus by a photonuclear reaction.
(ANSI N1.1-1976)

Photons
Units of energy of electromagnetic radiations.
(ENV RAD)

Photonuclear
Pertaining to the interaction of a photon with a nucleus.
(NCRP 51)

Photonuclear reaction
Nuclear reaction resulting from the interaction between a photon and a nucleus.
(IEC 50-393-1993)

Photonuclear reaction
The interaction of a photon with a nucleus, usually with the release of a charged particle or neutron.
(ANSI N1.1-1976)

Photophoresis
Particle motion under the influence of asymmetric light absorption within a particle.
(AM-1993)

Photoproton
A proton released from a nucleus by a photonuclear reaction.
(ANSI N1.1-1976)

Photosynthesis
The production of carbohydrates by green plants in the presence of sunlight through the agency of chlorophyll.
(RHH)

Phototiming
A method for timing radiographic examinations, the duration of the exposure being controlled by the amount of radiation which reaches a radiation-sensitive phototube behind the cassette.
(NCRP 66)

Physical Barrier
(1) Fences constructed of No. 11 American wire gauge, or heavier wire fabric, topped by three strands or more of barbed wire or similar material on brackets angled inward or outward between 30 deg. and 45 deg. from the vertical, with an overall height of not less than eight feet, including the barbed topping;
(2) Building walls, ceilings and floors constructed of stone, brick, cinder block, concrete, steel or comparable materials (openings in which are secured by grates, doors, or covers of construction and fastening of sufficient strength such that the integrity of the wall is not lessened by any opening), or walls of similar construction, not part of a building, provided with a barbed topping described in paragraph (1) of this definition of a height of not less than 8 feet; or
(3) Any other physical obstruction constructed in a manner and of materials suitable for the purpose for which the obstruction is intended.
(10CFR73.2)

Physical decay constant, l
The fraction of the nuclei of a particular radionuclide that decays per unit time.
(MIRD)

Physical field
Physical field is a dosimetric concept and is usually defined as being outlined by the 50% isodose curve at the depth of peak absorbed dose or at the isocenter, if one exists. It is generally slightly larger that the geometrical field. In some instances the (physical) field is defined by the 80 or 90 percent isodose curve. In this case the physical field will be considerably smaller than the geometrical field, with the amount depending on the flatness of the beam.
(ICRU 24)

Physical half-life
The time required for a radioactive substance to lose 50 percent of its activity by decay. It is the radioactive half-life.
(NCRP 65)

Physical half-life (T_p)
The time required for the level of radioactivity of a radionuclide to decrease by 50 percent due only to natural radioactive decay processes.
(HPJ 60)

Physical half-life (T_p)
The time required for the level of radioactivity of a radionuclide to decrease by 50 percent due only to natural radioactive decay processes.
(NCRP 87)

Physical half-life, T
The time in which one-half the nuclei of a particular radionuclide decay, hence the time in which the activity decreases to one-half its initial value.
(MIRD)

Physical inventory
Determination on a measured basis of the quantity of special nuclear material on hand at a given time. The methods of physical inventory and associated measurements will vary depending on the material to be inventoried and the process involved.
(10CFR74.4)

Physical model
A description of how measurements are influenced by physical factors such as temperature, composition, density, and the like. Physical models may be as simple as a list of variables and their constraints or as complicated as a set of equations that describe in detail the effect each variable has on the measurement.
(ANSI N15.54-1988)

Physical power (of a nuclear reactor)
Conventional value used in the reactor technology to express the neutron production of the nuclear reactor in terms of neutron per second.
(IEC 50-393-1993)

Physical security
Measures to reasonably ensure that source or special nuclear material will only be used for authorized purposes and to prevent theft or sabotage.
(10CFR110.2)

Physical separation
1 - Separation by geometry, such as distance, orientation.
2 - Separation by appropriate barriers.
3 - Separation by a combination thereof.
(IEC 50-393-1993)

Physical-Chemical Form
Form relating to the physics and chemistry of its source.
(NCRP 125)

Physician
An individual licensed by a State or territory of the United States, the District of Columbia or the Commonwealth of Puerto Rico to dispense drugs in the practice of medicine.
(10CFR55.4)

Physician
A medical doctor or doctor of osteopathy licensed by a State or Territory of the United States, the District of Columbia, or the Commonwealth of Puerto Rico to prescribe drugs in the practice of medicine.
(10CFR35.2)

Phytohemagglutinin
A proteinaceous hemagglutinin of plant origin used especially to induce mitosis.
(HPJ 60)

Phytoplankton
The plant organisms of plankton.
(NCRP 76)

Pi-meson
See pion.
(USAEC-1974)

Pia (pial surface)
The delicate fibrous membrane closely enveloping the brain and spinal cord.
(ICRP 49)

Pico
A prefix that divides a basic unit by one trillion (10¹²). Same as micromicro.
(USAEC-1974)

Picocurie
See curie.
(HPJ 60)

Picocurie (pCi)
A one trillionth (10^-12) part of a Curie or 0.037 nuclear transformations per second.
(NCRP 65)

Pig
A heavily shielded container (usually lead) used to ship or store radioactive materials.
(USAEC-1974)

Pile
Old term for nuclear reactor. This name was used because the first reactor was built by piling up graphite blocks and natural uranium.
(USAEC-1974)

Pile-up
Random coincidence summing, the superposition of successive electronic pulses due to their finite width and random distribution in time.
Pile-up inspection: sensing for pulses that have suffered pile-up.
Pile-up-inspection period: the minimum event-free time interval before and after a specific pulse necessary to prevent distortion of the signal amplitude by neighbouring pulses.
Pile-up rejector: a device that senses pulses perturbed in amplitude and helps to reject them.
(ICRU 52)

Pile-up (in a counting assembly)
Phenomenon where a pulse occurs on the tail of the preceding pulse so as to result in an incorrect indication of pulse amplitude.
(IEC 50-394-1993)

Pinch effect
In controlled fusion experiments, the effect obtained when an electric current, flowing through a column of plasma, produces a magnetic field that confines and compresses the plasma. (See controlled thermonuclear reaction, plasma, Sherwood.)
(USAEC-1974)

Pion
A cosmic particle with a mass about 280 times that of an electron. Positive, negative and neutral pions exist.
(NCRP 94)

Pion
A cosmic particle with a mass about 280 times that of an electron. Positive, negative and neutral pions exist.
(NCRP 45)

Pion
An elementary particle (contraction of Pi-meson). The mass of a charged (positive or negative) pion is about 273 times that of an electron; that of an electrically neutral pion is 264 times that of an electron. (See meson.)
(USAEC-1974)

Pion, pi meson
Meson having a rest mass approximately 270 times that of the electron, zero spin and one positive, negative or zero elementary electric charge.
(IEC 50-393-1993)

Piscivorous
Feeding on fish.
(NCRP 76)

Pitot tube
A device used to measure velocity pressure in a flow stream.
(AM-1993)

Pixel
A two-dimensional picture element in the presented image.
(NCRP 102)

Placer
A deposit of clay, silt, sand or gravel from glacial action or running water.
(NCRP 94)

Placer
A deposit of clay, silt, sand or gravel from glacial action or running water.
(NCRP 45)

Plan
The identification of a single audit or sequence of audits with an integral scope, depth of review, and frequency necessary to evaluate and report the adequacy of compliance and effectiveness of the safeguards system or systems within the scope of an audit responsibility.
(ANSI N15.38-1982)

Planar semiconductor detector
Semiconductor detector whose sensitive volume is in the form of a flat layer.
(IEC 50-394-1993)

Planck constant
A natural constant of proportionality (h) relating the frequency of a quantum of energy to the total energy of the quantum:

(RHH)

Planck's constant (H)
Constant approximately equal to 6.62608 x 10^-34 Js, used in the formula E = hn where E is the energy of a photon and n is the frequency of its associated wave.
(IEC 50-393-1993)

Plane wave
See wave, plane.
(NCRP 67)

Plankton
Aquatic organisms, usually microscopic, which float passively or exhibit limited locomotor activity.
(NCRP 76)

Planned release
A deliberate release of radioactive material into the environment (e.g., and effluent discharge) subject to authorized release limits.
(ICRP 29)

Planned special exposure
An infrequent exposure to radiation, separate from and in addition to the annual dose limits.
(10CFR20.1003)

Planning target volume (PTV)
A geometrical concept, and it is defined to select appropriate beam sizes and beam arrangements, taking into consideration the net effect of all the possible geometrical variations and inaccuracies in order to ensure that the prescribed dose is actually absorbed in the CTV.
(ICRU 50)

Plant factor
The ratio of the average power load of an electric power plant to its rated capacity. Sometimes called capacity factor.
(USAEC-1974)

Plant-Referenced Simulator
A simulator modeling the systems of the reference plant with which the operator interfaces in the control room, including operating consoles, and which permits use of the reference plant's procedures. A plant-referenced simulator demonstrates expected plant response to operator input, and to normal, transient, and accident conditions to which the simulator has been designed to respond.
(10CFR55.4)

Plant-referenced simulator
A simulator modeling the systems of the reference plant with which the operator interfaces in the control room, including operating consoles, and which permits use of the reference plant's procedures. A plant-referenced simulator demonstrates expected plant response to operator input, and to normal, transient, and accident conditions to which the simulator has been designed to respond.
(10CFR55.2)

Plasma
An electrically neutral gaseous mixture of positive and negative ions. Sometimes called the "fourth state of matter", since it behaves differently from solids, liquids and gases. High-temperature plasmas are used in controlled fusion experiments. (See charged particle.)
(USAEC-1974)

Plastic mantle
That zone of the earth extending from the bottom of the crust, at a depth of tens of kilometers, to a depth of 3,480 km. The mantle is under sufficient stress and at a temperature sufficient to make it plastic and subject to slow flow and deformation.
(NCRP 94)

Plate out
A thermal, electrical, chemical, or mechanical action that results in a loss of material by deposition on surfaces between sampling point and detector.
(ANSI N42.18-1974)

Plate out
A thermal, electrical, chemical, or mechanical action that results in a loss of material by deposition on surfaces between sampling point and detector.
(ANSI N13.10-1974)

Plateau
Portion of the characteristic curve of any Geiger-Muller counter tube over which the counting rate is substantially independent of the applied voltage.
(IEC 50-394-1993)

Plateau
A period of above-normal, relatively uniform incidence of morbidity in response to a given biologic insult.
(BEIR III)

Plateau
A period of above-normal, relative uniform, incidence of morbidity or mortality in response to a given biological insult.
(BEIR I)

Plateau
As applied to radiation detector chambers, the level portion of the counting rate-voltage curve where changes in operating voltage introduce minimum changes in the counting rate.
(RHH)

Plateau relative slope
Slope of the plateau expressed as the percentage change in counting rate per one hundred volts change in applied voltage.
(IEC 50-394-1993)

Plateau slope, relative
The relative increase in the number of counts as function of voltage expressed in percentage per 100 volts increase above the Geiger threshold.
(RHH)

Platelet
A minute flattened body (as of ice or a mineral), especially, blood platelet.
(HPJ 60)

Platelet
A small colorless corpuscle present in large numbers in the blood of all mammals, believed to play a role in the clotting of blood.
(NBS 63)

Plateout
The deposition of radon progeny on indoor surfaces, causing their removal from room air.
(ENV RAD)

Pleura
Serous membrane enveloping the lungs and lining the walls of the thoracic cavity.
(NCRP 125)

Plowshare
The Atomic Energy Commission program of research and development on peaceful uses of nuclear explosives. The possible uses include large-scale excavation, such as for canals and harbors, crushing ore bodies, and producing heavy transuranic isotopes. The term is based on a Biblical reference: Isaiah 2:4.
(USAEC-1974)

Plug
1 - Part used for plugging a hole in a screen of protective material so as to prevent the passage of radiation.
2 - Part welded to the clad, so as to make it radiation proof.
(IEC 50-393-1993)

Plume
An elongated, usually open, and mobile column of smoke or exhaust gas.
(ANSI/HPS N13.45-1998)

Plume
Flow of visible effluent from an outlet, e.g., a stack or vent.
(AM-1993)

Plume EPZ
An area of approximately 10 miles radius surrounding a nuclear power plant where the principal exposure sources would be whole body external exposure to gamma radiation from the plume and from deposited material and inhalation exposure from the passing radioactive plume.
(ANSI/ANS-3.8.1-1987)

Plutonium
Symbol Pu. A heavy, radioactive, man-made metallic element with atomic number 94. Its most important isotope is fissionable ²³⁹Pu, produced by neutron irradiation of ²³⁸U. It is used for reactor fuel and in weapons.
(HPJ 60)

Plutonium credit
The value of plutonium in irradiated uranium. This term refers to plutonium formed by conversion.
(ANSI N1.1-1976)

Plutonium processing and fuel fabrication plant
A plant in which the following operations or activities are conducted:
(1) Operations for manufacture of reactor fuel containing plutonium including any of the following: (i) Preparation of fuel material; (ii) formation of fuel material into desired shapes; (iii) application of protective cladding; (iv) recovery of scrap material; and (v) storage associated with such operations; or
(2) research and development activities involving any of the operations described in paragraph (r)(1) of this section, except for research and development activities utilizing unsubstantial amounts of plutonium.
(10CFR70.4)

Plutonium reactor
Reactor fueled with fissionable material, of which plutonium is the fissionable constituent.
(IEC 50-393-1993)

Plutonium-239
Plutonium-239 is one of the artificially produced isotopes of element 94, with the symbol Pu. Pu-239 decays by a emission, emitting a particles with an average energy of 5.15 mev, and has a half life of 24,400 years. Pure Pu-239 has a specific a activity of 1.36 x 10⁸ dpm per mg. There are only two excited states, 0.051 and 0.013 Mev, known from observations of a particle energies, but gamma rays observed are:

0.039 MeV	2 x 10^-5 gammas per decay
0.053 MeV	7 x 10^-5 gammas per decay
0.100 MeV	5.5 x 10^-5 gammas per decay
0.124 MeV	2.5 x 10^-5 gammas per decay
0.384 MeV	1.5 x 10^-5 gammas per decay

It has been calculated that these g-rays would produce a surface dose rate of 0.056 rad per hour. In addition, three L shell x-rays are known to follow internal conversion. Their energies are 0.0136, 0.0174, and 0.0205 MeV. Their respective intensities are 1.2 x 10^-2, 1.4 x 10^-2, and 0.3 x 10^-2 x-rays per decay. The contribution from spontaneous fission is negligible. The daughter of Pu-239 is U-235. Plutonium used for fuel fabrication may contain other isotopes such as Pu-238, Pu-240, and Pu-241. The isotopic concentration of fuel fabrication feed material vary, depending upon the conditions under which it is produced. The addition of these isotopes will change the surface dose rate and will also increase the yield of spontaneous fission neutrons.
(ANSI N7.2-1963)

Pn junction
A junction between P and N type semiconductor regions.
(IEC 50-394-1993)

Pneumatic (bubbler) probe
Tube used in pneumatic liquid height and density measurement systems.
(ANSI N15.19-1989)

Pneumoconiosis
Disease of the lungs, characterized by fibrosis and caused by the chronic inhalation of mineral dusts, especially silica and asbestos.
(NCRP 125)

Pneumoconiosis - producing dust
Dust, which when inhaled, deposited, and retained in the lungs, may produce signs, symptoms, and findings of pulmonary disease.
(ANSI Z88.2-1980)

Pneumoconiosis - producing dust
Dust, which when inhaled, deposited, and retained in the lungs, may produce signs, symptoms, and findings of pulmonary disease.
(ANSI Z88.2-1969)

PNL
Pacific Northwest Laboratory, operated for DOE by Battelle Memorial Institute at Richland, Washington. Sometimes also "BNW" for Battelle-Northwest.
(RAH)

Pocket chamber
A small condenser ionization chamber used for determining radiation exposure. An auxiliary charging and reading device is usually necessary.
(NBS 73)

Pocket chamber
A pocket-sized condenser ionization chamber used for monitoring radiation dose received by persons. An auxiliary charging and reading device is usually necessary.
(NBS 54)

Pocket dosimeter
A small ionization instrument which indicates radiation exposure directly. An auxiliary charging device is usually necessary.
(NBS 73)

Pocket dosimeter
A pocket-sized ionization instrument by means of which quantity of radiation is directly indicated. An auxiliary charging and reading device is usually necessary.
(NBS 54)

Pocket-sized alarm dosimeter
An instrument designed to be carried on the person that provides an alarm at a preset or selectable exposure. In addition, it may have a visual display or exposure or exposure rate, or both.
(ANSI N13.27-1981)

Pocket-sized alarm ratemeter
An instrument designed to be carried on the person that provides an alarm at a preset or selectable exposure rate. In addition, it may have a visual display or exposure or exposure rate, or both.
(ANSI N13.27-1981)

Pocket-sized chirper
An instrument designed to be carried on the person that produces a qualitative audible signal whose frequency or volume, or both, vary a function of radiation exposure rate.
(ANSI N13.27-1981)

Podiatric use
The intentional external administration of the radiation from byproduct material to human beings in the practice of podiatry in accordance with a license issued by a State or Territory of the United States, the District of Columbia, or the Commonwealth of Puerto Rico.
(10CFR35.2)

Podiatrist
An individual licensed by a State or Territory of the United States, the District of Columbia, or the Commonwealth of Puerto Rico to practice podiatry.
(10CFR35.2)

Podiatrist
An individual licensed by a State or Territory of the United States, the District of Columbia, or the Commonwealth of Puerto Rico to practice podiatry.
(10CFR30.4)

Poikilothermic
Cold-blooded animals or animals whose body tem-perature fluctuates with that of the environment.
(NCRP 109)

Point Isotropic Specific Absorbed Fraction
Fraction of the energy emitted by a point isotropic source that is absorbed per gram at a distance from the source.
(NCRP 125)

Point isotropic specific absorbed fraction
The fraction of the energy emitted by a point isotropic source that is absorbed per gram at a distance from the source.
(NUREG/CR 3332)

Point source
Any radiation source measured from a distance that is much greater than the linear size of the source. In this report, a source whose linear dimensions are less than 10% of the measurement distance may be considered a point source.
(NCRP 111)

Point source
A source whose dimensions are small compared to the distance from the source to the detector. If radiation emission from the source is also isotropic and unattenuated, the radiation fluence rate varies inversely as the square of the distance from the source. With respect to sources used in calibration of beta dose responsive instruments, a source is considered a point source when the source-to-detector distance is greater than two times the largest dimen-sion of the source or the largest dimension of the detector, which-ever is greater.
(NCRP 112)

Point source
Any radiation source measured from a distance that is much greater than the linear size of the source. In this report, a source whose linear dimensions are less than 10 percent of the measurement distance may be considered a point source for shielding purposes.
(NCRP 51)

Point spread function (PSF)
The radiant exposure distribution in the image of an infinitely small aperture (point source) of unit radiant energy.
(ICRU 54)

Point-to-plane precipitator
An electrostatic precipitator using a corona from a single point to deposit particles on a flat grounded plane.
(AM-1993)

Pointer
Information in a field of a record that links that record to another in the same or a different file.
(NCRP 114)

Poiseuille flow
Laminar flow with a parabolic velocity profile occurring in a circular duct; the gas velocity in the center of the tube equals twice the average velocity in the tube.
(AM-1993)

Poison
Any material that tends to decrease the effectiveness of an adsorbent by occupying adsorption sites on the surface of the adsorbent or by reacting with the impregnants in the adsorbent.
(ERDA 76-21)

Poison
Any material of high absorption cross section that absorbs neutrons unproductively and hence removes them from the fission chain reaction in a reactor, decreasing its reactivity.
(USAEC-1974)

Poison
Material of high absorption cross section which absorbs neutrons unproductively and reduces the reactivity of a reactor.
(RHH)

Poison, burnable
A nuclear poison purposely introduced into a reactor to help control long-term reactivity changes by its progressive burnup.
(ANSI N1.1-1976)

Poison, fixed
Nuclear poison, in the form of a solid material, attached to a process vessel, a reactor component, or experimental device, e.g., borosilicate glass (Pyrex, etc.) rings in an aqueous storage tank, to reduce reactivity or to prevent criticality.
(ANSI N1.1-1976)

Poison, homogeneous
Nuclear poison in the form of a solution or intimate mixture.
(ANSI N1.1-1976)

Poison, nuclear
A substance which, because of its high neutron absorption cross section, can reduce reactivity. The term is commonly called "poison".
(ANSI N1.1-1976)

Poisson distribution
Mathematical function relating the number of particles in a given volume element to the average concentration of randomly distributed particles in the entire volume.
(AM-1993)

Pokeweed mitogen
Extract of pokeweed that stimulates lymphocytes to enter mitosis, that is, cell division.
(HPJ 60)

Polarization (electromagnetic wave)
The directional and time characteristics of the electric field vector associated with a propagating wave.
(NCRP 67)

Polarization, electric
See electric polarization.
(NCRP 67)

Polarization, magnetic
See magnetization.
(NCRP 67)

Polarization, plane of
The plane containing the electric field of a propagating wave.
(NCRP 67)

Pole-zero cancellation
Technique of electronical circuits used to prevent overshoot or undershoot in RC pulse shaping networks used for unipolar pulses.
(IEC 50-394-1993)

Polycarbonate film
A plastic used as a neutron dosimeter and alpha particle detector. Following irradiation, the track damaged plastic is etched chemically to enhance the track damage. The tracks are counted and the dose is determined from the number of tracks.
(NCRP 101)

Polycythemia
A disease characterized by the over-production of red blood cells.
(RHH)

Polydisperse
Composed of particles with a range of sizes.
(AM-1993)

Polydisperse aerosol
An aerosol that is not monodisperse.
(TID-26608)

Polydisperse Aerosols
Aerosols composed of particles with a range of sizes.
(NCRP 125)

Polyenergetic
Possessing many different energies, either in a continuous spectrum or in groups of energy bands.
(NCRP 51)

Polymerization
Union of two or more molecules of a compound to form a more complex molecule.
(RHH)

Polymicorgyria
The presence of numerous abnormally narrow cerebral convolutions.
(ICRP 49)

Pool irradiator
Any irradiator at which the sources are stored or used in a pool of water including panoramic wet-source-storage irradiators and underwater irradiators.
(10CFR36.2)

Pool reactor
A reactor in which the fuel elements are suspended in a pool of water that serves as the reflector, moderator, and coolant. Popularly caged a swimming pool reactor, it is usually used for research and training.
(USAEC-1974)

Population
The people that may be affected by the change in environmental conditions due to the construction, operation, or decommissioning of an ISFSI or MRS.
(10CFR72.3)

Population
The totality of items or units of mate rial under consideration.
(ANSI N15.54-1988)

Population center distance
The distance from the reactor, to the nearest boundary of a densely populated center containing more than about 25,000 residents.
(10CFR100.3)

Population mean
The expected value of the random variable for the totality of items or units under consideration; that is, the first moment of the random variable about zero.
(ANSI N15.54-1988)

Population mean
The expected value of the random variable; i,e., the first moment about zero.
(ANSI N15.41-1984)

Population variance
The expected value of the square of the difference between a random variable and its own expected value; that is, the second moment of the random variable about the mean.
(ANSI N15.54-1988)

Population variance
The expected value of the square of the difference between a random variable and its own expected value; i.e., the second moment about the mean.
(ANSI N15.41-1984)

Pore velocity, seepage velocity
The average rate of flow in the pores of a given ground water medium. This is approximated by dividing the flux by the effective porosity.
(NCRP 123I)

Pore velocity, seepage velocity
The average rate of flow in the pores of a given ground water medium. This is approximated by dividing the flux by the effective porosity.
(NCRP 76)

Porosity
The property of containing interstices. Total porosity is expressed as the ratio of the volume of interstices to total volume. Effective porosity refers to the porosity through which flow occurs.
(NCRP 123I)

Porosity
(1-packing density).
(AM-1993)

Porosity
Property of a solid which contains many minute channels or open spaces that are capable of absorbing liquids.
(RRM)

Porosity
Total porosity is expressed as the ratio of the volume of interstices to total volume.
(NUREG/CR 3332)

Porous flow
Ground water flow which is predominantly through pores in the medium, or through the interstitial spaces between small grains of material (as opposed to fracture flow, defined previously).
(NCRP 123I)

Port
An opening in a research reactor through which objects are inserted for irradiation or from which beams of radiation emerge for experimental use.
(USAEC-1974)

Portable
Capable of being carried by hand to a specific facility or location for use and usually less than a nominal 22.5 kg in weight.
(ANSI N42.17C-1989)

Portable
Capable of being carried by hand to a specific facility or location for use and usually less than a nominal 22.5 kg in weight.
(ANSI N42.17A-1989)

Portable survey meter
An instrument intended to be operated while being carried by a person.
(ANSI N42.17A-1989)

Portable survey meter
An instrument intended to be operated while being carried by a person.
(ANSI N42.17C-1989)

Portable x- or gamma-radiation survey instrument
An instrument with a self-contained energy source (for example, batteries) designed to measure exposure rate while being carried. Such instruments may also have the capability to measure integral exposure, but instruments with the capability of measuring integral exposure only are specifically excluded from this definition.
(ANSI 13.4-1971)

Position-sensitive semiconductor detector
A semiconductor detector in which the center of the area of impact of ionizing radiation at the surface of the detector can be measured in one or two dimensions.
(IEC 50-394-1993)

Positive pressure respirator
A respirator in which the air pressure inside the respiratory inlet covering is positive in relation to the air pressure of the outside atmosphere during exhalation and inhalation.
(ANSI Z88.2-1980)

Positive temperature coefficient
See temperature coefficient of reactivity.
(USAEC-1974)

Positron
Elementary particle with one positive elementary electric charge and the same rest mass as the electron.
(IEC 50-393-1993)

Positron
[Symbol b⁺ (beta-plus)] An elementary particle with the mass of an electron but charged positively. It is the "antielectron". It is emitted in some radioactive disintegrations and is formed in pair production by the interaction of high-energy gamma rays with matter. (See antimatter, electron, pair production.)
(USAEC-1974)

Positron
A particle of equal mass to the electron and having an equal but positive charge.
(RHH)

Postclosure Controlled Area
A surface location, to be marked by suitable monuments, extending horizontally no more than 10 kilometers in any direction from the outer boundary of the underground facility, and the underlying subsurface, which area has been committed to use as a geologic repository and from which incompatible activities would be restricted following permanent closure.
(10CFR60.2)

Postulated initiating events
Events, or their credible combinations, such as equipment failures, operator errors, earthquakes and their consequences which are postulated as part of the design basis and which could lead to anticipated operational occurrences or accident conditions.
(IEC 50-393-1993)

Potential alpha activity
The total amount of alpha-particle radiation to be expected from a unit volume of air containing a mixture of radon and its progeny.
(ENV RAD)

Potential alpha energy
The total energy emitted during alpha decays if a quantity of radon progeny is allowed to decay through the entirety of the decay chain.
(ENV RAD)

Potential alpha energy (e_p)
The potential alpha energy e _p of an atom is the total a energy emitted during the decay of this atom along the decay chain up to ²¹⁰Pb (RaD) or ²⁰⁸Pb respectively. The total potential alpha energy per Bq of activity of a radionuclide becomes e _p/l _r, where the decay constant l _r is expressed in s^-1.
(ICRP 47)

Potential alpha energy (e _p)
The potential alpha energy e _p of an atom is the total a energy emitted during the decay of this atom along the decay chain up to ²¹⁰Pb (RaD) or ²⁰⁸Pb respectively. The total potential alpha energy per Bq of activity of a radionuclide becomes e _p/l _r, where the decay constant l _r is expressed in s^-1.
(ICRP 32)

Potential alpha energy concentration (PAEC)
This is the energy that would eventually be released in a specified volume of undisturbed air by the short-lived decay products of radon through the emission of alpha particles. PAEC is expressed in units of Working Level (WL) or J per cubic meter.
(NCRP 103)

Potential alpha energy concentration (PAEC)
The concentration of radon daughter products, in air, in terms of the alpha energy that will be released during complete decay through ²¹⁴Po.
(NCRP 97)

Potential alpha energy concentration in air
The potential a-energy concentration of any mixture of short-lived ²²²Rn- or ²²⁰Rn-daughters is the sum of the potential alpha energy of all daughter atoms present per unit volume of air.
(ICRP 50)

Potential alpha energy concentration in air
The potential alpha-energy concentration of any mixture of short-lived ²²²Rn- or ²²⁰Rn decay products is the sum of the potential alpha energy of all decay product atoms present per unit volume of air.
(ICRP 47)

Potential alpha energy concentration, c_p
The concentration of short-lived radon progeny in air in terms of the alpha energy released during complete decay through polonium-214.
(ICRP 65)

Potential alpha energy exposure (E)
The potential a-energy exposure of an individual to ²²²Rn or ²²⁰Rn decay products is the time-integral over the potential alpha-energy concentration of the decay product mixture to which the individual is exposed during a definite period of time. The quantity can be expressed in the unit J h m^-3.
(ICRP 47)

Potential alpha energy exposure (E)
The potential a energy exposure of an individual to ²²²Rn or ²²⁰Rn-daughters is the time-integral over the potential a-energy concentration of the daughter mixture to which the individual is exposed during a definite period of time. The quantity can be expressed in the unit J-h-m^-3 or WL h.
(ICRP 32)

Potential alpha energy exposure, P_p(T)
The time integral of the potential alpha energy concentration in air, c_p to which an individual is exposed over a given time period T, e.g. one year.
(ICRP 65)

Potential alpha energy intake by inhalation
The potential a energy intake of an individual by inhalation of radon decay products is the inhaled potential alpha energy of the decay product mixture during a definite period of time.
(ICRP 47)

Potential alpha energy intake by inhalation
The potential a energy intake of an individual by inhalation of radon-daughters is the inhaled potential alpha energy of the daughter mixture during a definite period of time.
(ICRP 32)

Potential alpha energy meter
Radiation meter which measures the total amount of alpha particle energy released, usually in air, by the short lived daughters of radon.
(IEC 50-394-1993)

Potential alpha energy monitor
Radiation monitor which measures the total amount of alpha particle energy released, usually in air, by the short-lived daughter of radon.
(IEC 50-394-1993)

Potential alpha energy of radon daughters
The potential alpha energy e_p of a radon daughter atom in the decay chain of ²²²Rn (radon) or ²²⁰Rn (thoron) is the total alpha energy emitted during the decay of this atom to ²¹⁰Pb or ²⁰⁸Pb respectively. Consequently, the potential alpha energy per unit of activity (Bq) of a daughter nuclide is
e_p/l_r = e_pT_r /ln 2
where l_r is the decay constant and T_r is the radioactive half-life of the considered radionuclide.
(ICRP 50)

Potential difference
Work required to carry a unit positive charge from one point to another.
(RHH)

Potential dose
Calculated dose based on a postulated set of exposure conditions that have a high probability of occurrence.
(10CFR834.2)

Potential ionization
The potential necessary to separate one electron from an atom, resulting in the formation of an ion pair.
(RHH)

Potentially exposed
In this report, all monitored and unmonitored personnel who have the potential for being exposed to radiation in the course to their duties.
(NCRP 107)

Potentially lethal damage
Potentially lethal damage is damage, the lethal expression of which may be modified by alterations in postirradiation conditions. In a cell system, potential lethal damage may involve communication between cells and hence, it expression could depend upon the relative configuration of the cells. In an organism, potentially lethal damage could involve the interaction of two or more cell systems. Potentially lethal damage might even be modifiable by preirradiation conditions.
(ICRU 30)

Power
The rate of thermal energy generation by a sample of material.
(ANSI N15.54-1988)

Power
The time rate of doing work; the unit of power is watt.
(NCRP 81)

Power
The time rate of doing work; the unit of power is watt.
(NCRP 75)

Power
The rate of change of energy with time. Typically used to describe the rate of energy flow across a surface or the rate of change of energy from one form to another. Power is expressed in units of watt (W).
(NCRP 67)

Power
The time rate of doing work; the unit of power is watt.
(NCRP 62)

Power coefficient, reactivity
The change of reactivity per unit change of reactor thermal power when other variables are not independently changed.
(ANSI N1.1-1976)

Power cubicle
The cubicle containing the power equipment for the accelerator, such as the capacitors, the power transformers, the d-c rectifiers.
(NBS 55)

Power density
See energy flux density and Poynting vector.
(NCRP 67)

Power density
The power generated per unit volume of a reactor core.
(ANSI N1.1-1976)

Power density
The rate of heat generated per unit volume of a reactor core. (See specific power.)
(USAEC-1974)

Power density, plane-wave equivalent
A quantity that is associated with any electromagnetic wave that is equal in magnitude to the power density of a plane wave that has the same electric (E) or magnetic (H) field strength.

(NCRP 67)

Power gain (antenna)
The ratio of the power per unit solid angle radiated in a given direction and at a given frequency to the power per unit solid angle radiated by a hypothetical, isotropic, lossless radiator for the same input power to both antennas. Power gain is a function of direction, frequency, distance, and polarization. When "gain" is used without qualifications, the maximum value of power gain is usually implied, i.e., the asymptotic value approached with increasing distance in the direction of maximum power per unit solid angle.
(NCRP 67)

Power measuring assembly based on activation
Measuring assembly designed to determine the thermal power of a nuclear reactor by measuring the activation of an appropriate material.
(IEC 50-394-1993)

Power of detection
The probability that the critical value of a statistical test will be exceeded when there is an actual loss of a specific SSNM quantity.
(10CFR74.4)

Power range
Range of power level within which the control of a reactor is primarily based upon measurement of temperature or neutron fluence rate rather than time constant.
(IEC 50-393-1993)

Power reactor
A nuclear reactor designed to produce electrical or heat energy licensed by the Commission under the authority of section 103 or subsection 104b of the Act and pursuant to the provisions of §50.21(b) or §50.22 of this chapter.
(10CFR170.3)

Power reactor
A nuclear reactor of a type described in § 50.21(b) or §50.22 of this chapter designed to produce electrical or heat energy.
(10CFR100.3)

Power Reactor
A nuclear reactor designed to produce electrical or heat energy and licensed by the Commission under the authority of section 103 or subsection 104b of the Atomic Energy Act of 1954, as amended, and pursuant to the provisions of Sec. 50.21(b) or Sec. 50.22 of this chapter.
(10CFR171.5)

Power reactor
Reactor whose primary purpose is to produce power.
(IEC 50-393-1993)

Power reactor
A reactor designed to produce useful nuclear power, as distinguished from reactors used primarily for research or for producing radiation or fissionable materials.
(USAEC-1974)

Power, nuclear
Useful power released in exothermic nuclear reactions.
(RHH)

Power, stopping
A measure of the effect of a substance upon the kinetic energy of a charged particle passing through it.
(RHH)

Powered-air purifying respirator
See respirator.
(ANSI Z88.2-1980)

Poynting vector
A field vector quantity, S, equal to the vector product of the electric field strength, E, and the magnetic field strength, H, that represents the magnitude and direction of the electromagnetic energy flux density.

When applied to a propagating wave, the integral of S over any surface represents the instantaneous power transmitted through the surface. S is in the direction of propagation. The Poynting vector is expressed in units of watt per square meter (W/m²).
(NCRP 67)

Practical Examination
A demonstration through practical application of the safety rules and principles in industrial radiography including use of all appropriate equipment and procedures.
(10CFR34.3)

Precision
A concept employed to describe dispersion of measurements with respect to a measure of location or central tendency.
(HPS N13.30-1996)

Precision
An indication of the degree of variation in the results of repeated measurements of a variable.
(AM-1993)

Precision
The extent of reproducibility of the measurements, commonly quantified by the standard deviation of a group of measure-ments about the mean.
(NCRP 112)

Precision
The degree of mutual agreement characteristic of independent measurements as the result of repeated application of the process under specified conditions. It is concerned with the closeness of results.
(HPJ 60)

Precision
The degree of agreement of repeated measurements of the same parameter.
(ANSI N42.17B-1989)

Precision
The degree of agreement of repeated measurements of the same parameter.
(ANSI N42.17A-1989)

Precision
A concept employed to describe dispersion of measurement with respect to a measure of a location or central tendency.
(ANSI N13.30-1989D)

Precision
A concept employed to describe the dispersion of repeated measurements with respect to a measure of location of central tendency, usually the mean.
(ANSI N15.54-1988)

Precision
A measure of the reproducibility of results.
(ANSI N13.15-1985)

Precision
A qualitative term used to describe the dispersion of a set of numbers (measured values) with respect to its central tendency. The variance (or its square root, the standard deviation) is commonly used as a measure of precision.
(ANSI N15.36-1983)

Precision
The degree of agreement of repeated measurements of the same property, express quantitatively as the standard deviation computed from the results of the series of measurements.
(ANSI N317-1980)

Precision
The degree of agreement of repeated measurements of the same property, expressed in terms of dispersion of test results about the mean result obtained by repetitive testing of a homogeneous sample under specified conditions. The precision of a method is expressed quantitatively as the standard deviation computed from the results of a series of controlled determinations.
(ANSI N42.18-1974)

Precision Statistic
An estimator of precision calculated from a finite sample of data using a specified formula.
(HPS N13.30-1996)

Precision statistic
An estimator of precision calculated from a finite sample of data using a specified formula.
(ANSI N13.30-1989D)

Preclassifier
A device that removes particles ahead of an aerosol sensor, often in a manner similar to the particle removal occurring ahead of the respiratory region of interest; also called a preseparator or a precutter.
(AM-1993)

Preclosure Controlled Area
That surface area surrounding the geologic repository operations area for which the licensee exercises authority over its use, in accordance with the provisions of this part, until permanent closure has been completed.
(10CFR60.2)

Precursor
Any member of a radioactive decay chain preceding the member under consideration.
(NCRP 94)

Precursor
Of a nuclide, any radioactive nuclide which precedes that nuclide in a decay chain. The term is often restricted to the immediately preceding nuclide.
(ANSI N1.1-1976)

Precursor
Any member of a radioactive decay chain preceding the member under consideration.
(NCRP 45)

Precursor, delayed neutron
A nuclide whose nuclei undergo beta decay followed by neutron emission.
(ANSI N1.1-1976)

Prediction
A mathematical technique employed to calculate the equilibrium value of a calorimeter output, on the basis of an experimental determination of the baseline value and several measurements of the output at known times after insertion of the sample, but well before equilibrium has been attained. A substantial reduction in the time required to determine the thermal power of a sample can be achieved by using this method.
(ANSI N15.54-1988)

Prefilter
A filter unit installed ahead of another filter unit to protect the second unit from high dust concentrations or other environmental conditions. The prefilter usually has a lower efficiency for the finest particles present in the aerosol than the filter it protects. (See roughing filter).
(ERDA 76-21)

Preoperational
Occurring prior to operation of an installation or prior to major extension of such operations.
(ICRP 7)

Prescribed dosage
The quantity of radiopharmaceutical activity as documented:
(1) In a written directive; or
(2) Either in the diagnostic clinical procedures manual or in any appropriate record in accordance with the directions or the authorized user for diagnostic procedures.
(10CFR35.2)

Prescribed dose
(1) For gamma stereotactic radiosurgery, the total dose as documented in the written directive;
(2) For teletherapy, the total dose or dose per fraction as documented in the written directive; or
(3) For brachytheray, either the total source strength and exposure time or the total dose, as documented in the written directive.
(10CFR35.2)

Pressure coefficient, reactivity
The change of reactivity per unit change of pressure. In reactors with multiple pressure systems (e.g., moderator and coolant) their appropriate pressure must be specified.
(ANSI N1.1-1976)

Pressure driven flow
Physical transport of soil gas into a structure driven by depressurization of the structure. A dominant mechanism for radon entry into structures.
(ENV RAD)

Pressure head
The height above a standard datum of the surface of a column of water that can be supported by the pressure at a given point. The gradient of the pressure head is usually the driving force for ground water flow.
(NCRP 76)

Pressure relief system
The combination of a pressure relief device or devices, inlet and outlet piping, protective cavity and cavity cover, and any other component that may affect the relief pressure, flow capacity, or reseating pressure.
(ANSI N14.19-1986)

Pressure suppression
See vapor suppression.
(USAEC-1974)

Pressure vessel
A strong-walled container housing the core of most types of power reactors; it usually also contains moderator, reflector, thermal shield, and control rods.
(USAEC-1974)

Pressure vessel, reactor
A reactor vessel designed to withstand a substantial operating pressure.
(RHH)

Pressure-demand
See pressure-demand-type self-contained breathing apparatus and pressure-demand-type air-line respirator in ANSI Z88.2-1980.
(ANSI Z88.2-1980)

Pressure-tube reactor
A reactor in which the fuel elements are located inside tubes containing coolant circulating at high pressure. The tube assembly is surrounded by a tank containing the moderator at low pressure.
(USAEC-1974)

Pressurized water reactor
A nuclear reactor in which water is circulated under enough pressure to prevent it from boiling, while serving as moderator and coolant for the uranium fuel; the heated water is then used to produce steam for a power plant.
(NCRP 81)

Pressurized water reactor
A power reactor in which heat is transferred from the core to a heat exchanger by water kept under high pressure to achieve high temperature without boiling in the primary system. Steam is generated in a secondary circuit. Many reactors producing electric power are pressurized water reactors.
(USAEC-1974)

Prevalence
The number of cases of a disease in existence at a given time per unit population, usually 100,000 persons.
(NCRP 98)

Prevalence
The number of cases of a disease in existence at a given time per unit population, usually 100,000 persons.
(BEIR IV)

Prevalence
The rate of existing cases of disease in a population at a particular point in time.
(NCRP 80)

Prevalence
The number of cases of a disease in existence at a given time per unit population, usually 100,000 persons.
(BEIR III)

Prevalence
The number of cases of disease in existence at a certain time in a designated area.
(BEIR I)

Prewhitening matched filter (PWMF)
Observers which whiten, i.e., remove spatial correlations (or color), from image noise before analyzing the image. The ideal observer acts as a prewhitening matched filter.
(ICRU 54)

Price-Anderson Act
Federal legislation that provides that the Federal Government may grant indemnity to a varying extent to operators of nuclear facilities and carriers for liability caused by a nuclear incident.
(ANSI N14.24-1985)

Primary beam
Ionizing radiation from an x-ray tube anode or radioactive isotope which is allowed to pas by a direct path through an aperture in the radiation source housing for using in conducting x-ray measurements.
(ANSI N43.2-1977)

Primary beam
See radiation useful beam.
(NCRP 49)

Primary calibration
The determination of the electronic system accuracy when the detector is exposed to a known geometry to radiation from sources of known energies and activity levels traceable to the NBS.
(ANSI N42.18-1974)

Primary Chamber
Portion of the incinerator in which the actual combustion of waste occurs.
(ANSI/HPS N13.45-1998)

Primary coolant
The liquid or gas that flows over the reactor core, removing heat generated during the fission process.
(NUREG/CR 3332)

Primary coolant circuit
System for circulating a coolant used to remove heat from a primary heat source, such as a reactor core or a breeding blanket.
(IEC 50-393-1993)

Primary files
The complete set of records maintained for retrieval.
(NCRP 114)

Primary fission products
Fission fragments.
(USAEC-1974)

Primary fission yield
Fraction of fissions giving rise to a particular nuclide before any beta or gamma decay has occurred.
(IEC 50-393-1993)

Primary limit
A numerical limit on the annual or committed (effective) dose equivalent that may be received by a worker or member of the general public, as set forth in the 1987 or 1960 Federal guidances.
(FGR 11)

Primary particle
A particle introduced into the air in solid or liquid form.
(AM-1993)

Primary protective barrier
See protective barrier.
(NCRP 102)

Primary protective barrier
Barrier sufficient to attenuate the useful beam to the required degree. See protective barrier.
(NCRP 49)

Primary protective barrier
Barrier sufficient to attenuate stray radiation to the required level.
(NBS 73)

Primary protective barrier
Barrier sufficient to reduce the useful beam to the maximum permissible weekly dose.
(NBS 54)

Primary protective barriers
Barriers designed to reduce the dose rate produced by the useful beam in occupied spaces.
(NBS 55)

Primary radiation
Ionizing radiation emitted directly by a radiation source.
(IEC 50-393-1993)

Primary radiation
Ionizing radiation coming by a direct path from the x-ray tube anode or an isotope source.
(ANSI N43.2-1977)

Primary radiation
The radiation of earliest origin in the context of the situation considered. For example, electron radiation impinging on a shielding wall may be considered as "primary," from the standpoint of the shielding of electrons. The x rays produced from this impingement may be considered as "primary" from the standpoint of shielding against x rays.
(NCRP 51)

Primary radiation
Radiation coming directly from the source.
(NBS 73)

Primary radiation
Radiation coming directly from the source, including the useful beam (that part of the primary radiation that passes through the aperture or collimator of the radiation source enclosure).
(NBS 54)

Primary radiation
Radiation coming directly from the accelerator target, which includes X-rays (bremsstrahlung), electrons, and neutrons. It includes the useful-beam radiation and part of the leakage radiation.
(NBS 55)

Primordial
Formed or present at the origin of the earth.
(NCRP 94)

Primordial
Formed or present at the origin of the earth.
(NCRP 45)

Primordial radionuclides
Natural sources of radiation may be grouped in three types according to origin: Cosmic radiation, from the sun and from outer space, varies with altitude and latitude; Cosmogenic radionuclides (mainly carbon-14), produced through interaction of the cosmic rays with atoms in the atmosphere: and primordial radionuclides, which have existed in the earth's crust throughout it history (e.g., potassium-49 and nuclides in the uranium and thorium decay series).
(ICRP 39)

Principal activities
Activities authorized by the license which are essential to achieving the purpose(s) for which the license was issued or amended. Storage during which no licensed material is accessed for use or disposal and activities incidental to decontamination or decommissioning are not principal activities.
(10CFR70.4)

Principal activities
Activities authorized by the license which are essential to achieving the purpose(s) for which the license was issued or amended, excluding activities incidental to decontamination or decommissioning.
(10CFR72.3)

Principal plane
A plane which contains the central axis and, in the case of rectangular section beams, is parallel to one side of the rectangle.
(ICRU 30)

Principal plane
A plane which contains the central ray and, in the case of rectangular section beams, is parallel to one side of the rectangle.
(ICRU 24)

Principal plane
A plane which contains the beam axis and, in the case of rectangular section beams, is parallel to one side of the rectangle.
(ICRU 23)

Probabilistic model
See stochastic model.
(NCRP 123I)

Probabilistic model
See stochastic model.
(NCRP 76)

Probability
The likelihood of the occurrence of any particular form of an event, estimated as the ratio of the number of ways or times that the event may occur in that form to the total number of ways that it could occur in any form.
(HPJ 60)

Probability
See cross section.
(USAEC-1974)

Probe (of a radiation meter)
A radiation detector, with possibly a preamplifier and functional units, whose form permits its operation in places of difficult access, or remote from the associated apparatus.
(IEC 50-394-1993)

Probe sensitivity
The magnitude of the instrument with a given probe for a uniform area source.
(ANSI N42.17A-1989)

Probe separation
The vertical distance between the effective tips of the major and minor bubbler probes. The effective tip of the probe is the average elevation of the liquid-gas interface at the end of the probe.
(ANSI N15.19-1989)

Procedure
A document that specifies or describes how an activity is to be performed.
(ANSI N15.54-1988)

Procedure
A document that specifies or describes how an activity is to be performed.
(ANSI N15.41-1984)

Procedure
A document that specifies or describes how an activity is to be performed.
(ANSI N46.2-1978)

Process difference (PD)
The determination of an ID on a unit process level with the additional qualification that difficult to measure components may be modeled.
(10CFR74.4)

Process heat reactor
A reactor that produces heat for use in manufacturing processes.
(USAEC-1974)

Process yield
The quantity of SSNM actually removed from a unit process compared with the quantity predicted (based on a measured input) to be available for removal. Process yield differs from a process difference in that holdup and sidestreams are not measured or modeled.
(10CFR74.4)

Process, regenerative
The process by which damaged or destroyed cells are replaced by new ones of the same type.
(RHH)

Processing
The procedure of chemically developing the latent image of the incident radiation on the photographic emulsion into measurable optical densities and interpreting these to estimate the exposure.
(ANSI N13.7-1983)

Processing, radiochemical
The chemical processing of radioactive materials.
(ANSI N1.1-1976)

Processor
Supplier of personnel dosimetry services. These services include:
(1) Furnishing dosimeters to the user
(2) Evaluating the readings of the dosimeters after their return in terms of the shallow and the deep dose equivalent as prescribed in this standard
(3) Recording the results
(4) Reporting them to the user
(ANSI/HPS N13.11-1993)

Processor
The person or organization routinely performing personnel-monitoring services by means of TL dosimetry. Such services consist of supplying TL personnel-monitoring badges and evaluating their readings in terms of absorbed dose or dose equivalent. Processor and user may be, but not need be, members of the same organization.
(ANSI N13.15-1985)

Processor
Supplier of personnel dosimetry systems. These services include:
(1) Furnishing dosimeters to the users.
(2) Evaluating the readings of the dosimeters after their return in terms of shallow and the deep dose equivalent as prescribed in this standard.
(3) Recording the results.
(4) Reporting them to the user.
(ANSI N13.11-1983)

Procurement document
A contract that defines the requirements which facilities or basic components must meet in order to be considered acceptable by the purchaser.
(10CFR50.2)

Procurement document
Purchase requisitions, purchase orders, drawings, contracts, specifications or instructions used to define requirements for purchase.
(ANSI N46.2-1978)

Produce
When used in relation to special nuclear material, means
(1) to manufacture, make, produce, or refine special nuclear material;
(2) to separate special nuclear material from other substances in which such material may be contained; or
(3) to make or to produce new special nuclear material.
(10CFR70.4)

Product conveyor system
A system for moving the product to be irradiated to, from, and within the area where irradiation takes place.
(10CFR36.2)

Production facility
(1) Any nuclear reactor designed or used primarily for the formation of plutonium or uranium-233; or
(2) Any facility designed or used for the separation of the isotopes of uranium or the isotopes of plutonium, except laboratory scale facilities designed or used for experimental or analytical purposes only; or
(3) Any facility designed or used for the processing of irradiated materials containing special nuclear material, except (i) laboratory scale facilities designed or used for experimental or analytical purposes, (ii) facilities in which the only special nuclear materials contained in the irradiated material to be processed are uranium enriched in the isotope U-235 and plutonium produced by the irradiation, if the material processed contains not more than 10^-6, grams of plutonium per gram of U-235 and has fission product activity not in excess of 0.25 millicuries of fission products per gram of U-235, and (iii) facilities in which processing is conducted pursuant to a license issued under Parts 30 and 70 of this chapter, or equivalent regulations of an Agreement State, for the receipt, possession, use, and transfer of irradiated special nuclear material, which authorizes the processing of the irradiated material on a batch basis for the separation of selected fission products and limits the process batch to not more than 100 grams of uranium enriched in the isotope 235 and not more than 15 grams of any other special nuclear material.
(10CFR170.3)

Production facility
(1) Any equipment or device determined by rule of the Commission to be capable of the production of special nuclear material in such quantity as to be of significance to the common defense and security, or in such manner as to affect the health and safety of the public, including a uranium enrichment facility; or
(2) Any important component part especially designed for such equipment or device as determined by the Commission.
(10CFR150.2)

Production facility
Any nuclear reactor or plant specially designed or used to produce special nuclear material through the irradiation of source material or special nuclear material, the separation of isotopes or the chemical reprocessing of irradiated source or special nuclear material.
(10CFR110.2)

Production facility
Production facility as defined in the regulations contained in Part 50 of this chapter.
(10CFR30.4)

Production object
An object of unknown mass whose mass value is to be determined by the mass measurement process.
(ANSI N15.18-1988)

Production reactor
Reactor whose primary purpose is to produce fissile or other materials or to perform irradiation on an industrial scale.
(IEC 50-393-1993)

Production reactor
A reactor designed primarily for large-scale production of plutonium-239 by neutron irradiation of uranium-238. Also a reactor used primarily for the production of radioactive isotopes.
(USAEC-1974)

Production test
A test made on each item or a sample of items or product from a production run to verify that the item meets specification requirements.
(ERDA 76-21)

Profile plot
A plot of the residuals obtained by fitting a straight line to the data from one or more calibration runs.
(ANSI N15.19-1989)

Progeny
The decay products resulting after a series of radioactive decays. Progeny can also be radioactive, and the chain continues until a stable nuclide is formed.
(BEIR IV)

Program records
Those records, related to the radiation protection pro-gram that are currently in effect and all prior records of the same type.
(NCRP 114)

Programmed action safety assembly
Safety device which controls in a programmed way a limited decrease of power.
(IEC 50-394-1993)

Projected-area (equivalent) diameter
Diameter of a circle that has the same area as the projected area of a particle seen under a microscope.
(AM-1993)

Prompt critical
Qualifies the condition that a nuclear chain reacting medium is critical only while utilizing prompt neutrons.
(IEC 50-393-1993)

Prompt critical
Fulfilling the condition that a nuclear chain reacting medium is critical utilizing prompt neutrons only.
(ANSI N1.1-1976)

Prompt criticality
The state of a reactor when the fission chain reaction is sustained solely by prompt neutrons, that is, without the help of delayed neutrons. (See criticality.)
(USAEC-1974)

Prompt excretion
Removal of activity directly from blood to urinary bladder or to the gastrointestinal tract with the clearance half-time assigned to blood.
(ICRP 67)

Prompt gamma radiation
Gamma radiation accompanying the fission process without measurable delay.
(ANSI N1.1-1976)

Prompt gamma radiation
Gamma radiation accompanying the fission process without measurable delay.
(RHH)

Prompt neutron
Neutron accompanying the fission process without measurable delay.
(IEC 50-393-1993)

Prompt neutron fraction
The ratio of the mean number of prompt neutrons per fission to the mean total number of neutrons (prompt plus delayed) per fission.
(ANSI N1.1-1976)

Prompt neutrons
Neutrons that are emitted immediately following nuclear fission, as district from delayed neutrons, which are emitted for some time after fission has occurred. Prompt neutrons comprise more than 99% of fission neutrons.
(USAEC-1974)

Prompt radiation
Radiation produced by the primary fission or fusion process, as distinguished from the radiation from fission products, their decay chains and other later reactions.
(USAEC-1974)

Propagation coefficient (propagation constant)
A complex quantity, the real part of which (attenuation coefficient) describes the change in magnitude and the imaginary part of which (phase coefficient) describes the change in phase with the distance of a field component in the direction of propagation of an electromagnetic wave. See attenuation coefficient, phase coefficient.
(NCRP 67)

Property
Something owned or possessed, or to which a person has a legal title.
(10CFR834.2)

Proportional counter
See counter.
(HPJ 60)

Proportional counter
A chamber equipped with suitable electrodes and operated at a voltage high enough to produce ionization by collision and adjusted so that the total ionization per count is substantially proportional to the ionization produced by the absorption of the radiation event.
(NBS 51)

Proportional counter tube
Counter tube operating in the proportional mode.
(IEC 50-394-1993)

Proportional region
Range of applied voltage of a counter tube in which the gas multiplication factor is greater than one and practically independent of the total number of ion pairs initially produced in the sensitive volume as a result of an ionizing event, the pulse amplitude being proportional to this number.
(IEC 50-394-1993)

Proportional region
The range of applied voltage in a radiation counter tube in which the charge collected per ionizing event is proportional to the charge liberated by that event.
(ANSI N1.1-1976)

Proportional region
Voltage range in which the gas amplification is greater than one, and in which the charge collected is proportional to the charge produced by the initial ionizing event.
(RHH)

Prosencephalon
The forebrain, i.e., the part of the brain that develops rostral to the cephalic flexure. It comprises the diencephalon (interbrain) and the telencephalon (endbrain), and the latter gives rise to the right and left cerebral vesicles, i.e., the future cerebral hemispheres.
(ICRP 49)

Protected area
An area encompassed by physical barriers and to which access is controlled.
(10CFR73.2)

Protected area
The area within the site security fence and controlled under the security plan.
(ANSI/ANS-3.8.1-1987)

Protection
Provisions to reduce exposure of persons to radiation. For example, protective barriers to reduce external radiation or measures to prevent inhalation of radioactive materials. (See radiation protection.)
(USAEC-1974)

Protection
Provisions designed to reduce exposure of persons to radiation. For external radiation, this consists in the use of protective barriers of radiation-absorbing material, in insuring adequate distances from the radiation sources, in reducing exposure time, or in combinations of these. For internal sources, it involves measures to restrict inhalation, ingestion, or other modes of entry of radioactive materials into the body.
(NBS 54)

Protection
Provisions designed to reduce exposure of personnel to radiation. For external radiation this involves the use of protective barriers, the assignment of adequate distance from radiation sources, the reduction of operating time or beam intensity, or any combinations of these.
(NBS 55)

Protection dosimetry
Routine estimation of the shallow and deep dose equivalent received by personnel.
(ANSI/HPS N13.11-1993)

Protection dosimetry
Routine estimation of the shallow and deep dose equivalent for the purpose of providing one or the parameters for assessing the radiation protection measures in a given radiation facility.
(ANSI N13.11-1983)

Protection factor
The ratio of the ambient concentration of an airborne substance to the concentration of the substance inside the respirator at the breathing zone of the worker. The protection factor is a measure of the degree of protection provided by a respirator to the wearer.
(ANSI Z88.2-1980)

Protection survey
Evaluation of the radiation hazards incidental to the production, use, or presence or radioactive materials or other sources of radiation under a specified set of conditions. Such evaluation customarily includes a physical survey of the disposition of materials and equipment and measurements of the dose rates of radiation that may be involved.
(NBS 55)

Protection system (of a nuclear reactor)
System intended to prevent reactor conditions from exceeding specified safe limits, or to reduce the consequences of their being exceeded.
(IEC 50-394-1993)

Protective action
An action taken to avoid or reduce the projected dose to individuals.
(ANSI/ANS-3.8.1-1987)

Protective action guide
Those specified dose levels which, if projected to be exceeded for individuals in the population, cause preestablished protective actions to be recommended.
(ANSI/ANS-3.8.1-1987)

Protective action guide (PAG)
The absorbed dose of ionizing radiation to individuals in the general population which would warrant protective action following a contaminating event, such as a nuclear explosion. (See radiation protection guide.)
(USAEC-1974)

Protective action recommendation (PAR)
Recommendations to implement corrective actions.
(ANSI/ANS-3.8.1-1987)

Protective apron
An apron made of radiation absorbing material(s) used to reduce radiation exposure.
(NCRP 107)

Protective apron
An apron made of radiation absorbing materials, used to reduce radiation exposure.
(NCRP 102)

Protective barrier
A barrier of radiation absorbing material(s) used to reduce radiation exposure.
Primary protective barrier: A protective barrier used to attenuate the useful beam for radiation protection purposes.
Secondary protective barrier: A barrier sufficient to attenuate stray radiation (scattered plus leakage) for radiation protection purposes.
(NCRP 107)

Protective barrier
A barrier of radiation absorbing material(s) use to reduce radiation exposure.
Primary protective barrier: A barrier used to attenuate the useful beam for radiation (scattered or leakage) protection purposes.
Secondary protective barrier: A barrier sufficient to attenuate stray radiation (scattered plus leakage) for radiation protection purposes.
(NCRP 102)

Protective barrier
A barrier of radiation-attenuating material used to reduce radiation exposure.
(NCRP 48)

Protective barrier
A barrier of radiation attenuating material(s) used to reduce radiation exposure.
(NCRP 49)

Protective barrier
Barrier of attenuating material used to reduce radiation hazards.
(NBS 73)

Protective barrier
Barrier of radiation-absorbing material, such as lead, concrete, etc., used to reduce radiation hazards.
(NBS 54)

Protective barriers
Barriers of radiation-absorbing material, such as lead, concrete, or steel, that are used to reduce radiation hazards.
(NBS 55)

Protective clothing
Aprons, gloves, or other articles of clothing made of lead rubber or other material that absorbs radiation, which will reduce radiation exposure to parts of an individual covered by them.
(NCRP 48)

Protective clothing
Special clothing worn by a radiation worker to prevent contamination of his body or his personal clothing.
(USAEC-1974)

Protective clothing
Protective clothing consists of apparel that in design or construction provides a high degree of protection from contamination with toxic materials. For example, such items as rubber boots, jumpers, and heavy rubber gloves are protective clothing.
(ANSI N7.2-1963)

Protective function
A set of actions comprising the measurement of parameters of the plant, the signal-processing initiation and completion of the protective action, at values of the plant variables established in the design bases and associated with particular plant conditions.
(IEC 50-393-1993)

Protective glove
A glove made of radiation absorbing materials used to reduce radiation exposure.
(NCRP 102)

Protective packaging (overpack)
Outer packaging used to enclose cylinders containing enriched UF₆ exceeding 1 wt% ²³⁵U. Protective structural packaging that meets the criteria of the International Atomic Energy Agency (IAEA) for Type-B packaging for fissile radioactive materials is described in this standard
(ANSI N14.1-1990)

Protective source housing
An enclosure, for gamma-beam therapy source, so constructed that the leakage radiation does not exceed the limits specified in Section 5.3.4 (of NCRP 102).
(NCRP 102)

Protective source housing
An enclosure, for gamma-beam therapy source, so constructed that the leakage radiation dose not exceed specified limits with the source in the "OFF" and in the "ON" conditions.
(a) Beam "OFF" condition. The housing shall be so constructed that at one meter from the source, the maximum and average exposure rates do not exceed 10 mR h^-1 and 2 mr h^-1, respectively, when the beam control mechanism is in the "OFF" position.
(b) Beam "ON" condition. The leakage radiation measured at on meter from the source shall not exceed 0.1 percent of the useful beam exposure rate at that distance when the beam control mechanism is in the "ON position, except for the portion of the housing which includes the collimator zone. This limit, however, does not apply to source housings when the leakage radiation at one meter is less than 1 R h^-1, nor does it apply to apparatus used exclusively for whole-body irradiation.
(NCRP 49)

Protective survey
An evaluation of the radiation hazards incidental to the production, use, or existence of radioactive materials or other sources of radiation under a specific set of conditions.
(USAEC-1974)

Protective task
The least amount of those protective actions necessary to warrant that the safety task required by a given postulated initiating event is accomplished.
(IEC 50-393-1993)

Protium
A name sometimes applied to the hydrogen isotope of mass 1 to distinguish it from deuterium and tritium.
(RHH)

Proton
Stable particle with one positive elementary electric charge and a rest mass of approximately 1.672 62 x 10^-27 kg.
(IEC 50-393-1993)

Proton
An elementary particle with a single positive electrical charge and a mass approximately equal to 1837 times that of an electron. The nucleus of an ordinary or light hydrogen atom. Protons are constituents of all nuclei. The atomic number (Z) of an atom is equal to the number of protons in the nucleus.
(HPJ 60)

Proton
A stable elementary particle having a positive charge of 1.60219 x 10^-19 C and a rest mass of 1.67265 x 10^-27 kg.
(ANSI N1.1-1976)

Proton synchrotron
A type of particle accelerator for producing beams of very high energy protons (in the Bev range).
(USAEC-1974)

Protons
The proton is the nucleus of the hydrogen atom. Protons are positively charged.
(NCRP 98)

Prototype
The initial manufactured unit conforming in all vital characteristics to units manufactured subsequently.
(ANSI N432-1980)

Prototype source
Original of a model of a sealed source which serves as a pattern for the manufacture of all sources identified by the same model number.
(ANSI N542-1977)

Prototype source
A source used for type test of new designs.
(NBS 66)

Prototype testing
Performance testing of a new sealed source before sources of such design are put into actual use.
(ANSI N542-1977)

Protraction
Extending the length of exposure, for example, the continuous delivery of a radiation dose over some period of time.
(ICRP 59)

Protraction
Extending the length of exposure, for example, the continuous delivery of a radiation dose over some period of time.
(NCRP 98)

Prover
A calibrated device or system designed to measure and deliver a specified quantity of liquid.
(ANSI N15.19-1989)

Prover, gravimetric
A prover designed to measure and deliver a specified mass of liquid.
(ANSI N15.19-1989)

Prover, volumetric
A prover designed to measure and deliver a specified volume of liquid.
(ANSI N15.19-1989)

Proximal extremity
That end of the limb which is nearest to the point of attachment (the upper arms and thighs).
(HPS N13.41-1997)

Proximal lung
The region of the lung closest to the nose.
(ENV RAD)

Pseudo-coincidence counting
A method for measuring the concentration of long-lived a-particle emitters, such as plutonium or its compounds, collected on a filter, with differentiation of the a-particle emitters occurring naturally as the decay products of ²²²Rn (radon) and ²²⁰Rn (thoron). The detector senses and records the "pseudo-coincidence" of ²¹⁴Bi b-decay and its daughter, ²¹⁴Po a-decay, thus providing an index to the quantity of ²²²Rn present. The ²¹⁴Po decays with a half-life of 150 µs (microseconds), hence the parent-daughter decay is regarded and utilized as a "pseudo-coincidence". The same consideration holds true for the ²¹²Bi to ²¹²Po decay. These are members of the ²²⁰Rn decay chain.
(ANSI N13.1-1969)

Psu adsorber
An adsorber that is permanently installed in a system and that can be emptied of and refilled with adsorbent without removing it from the system.
(ERDA 76-21)

Public Document Room
The place at 2120 L Street NW., Washington, DC, at which records of the Commission will ordinarily be made available for public inspection and any other place, the location of which has been published in the Federal Register, at which public records of the Commission pertaining to a particular geologic repository are made available for public inspection.
(10CFR60.2)

Public document room
The place at 2120 L Street NW, Washington, D.C., where public records of the Commission are ordinarily available for inspection.
(10CFR110.2)

Public dose
The dose received by a member of the public from exposure to radiation or radioactive material released by a licensee, or to any other source of radiation under the control of a licensee. Public dose does not include occupational dose or doses received from background radiation, from any medical administration the individual has received, from exposure to individuals administered radioactive material and released in accordance with Sec. 35.75, or from voluntary participation in medical research programs.
(10CFR20.1003)

Public dose
The dose received by members of the public from exposure to radiation and to radioactive material released by a DOE activity whether the exposure is within a DOE site boundary or offsite.
(10CFR834.2)

Public health and safety
The public health and safety of the United States.
(10CFR110.2)

Public safety personnel
Government employees, including firemen, state highway patrolmen, etc, assigned the responsibility of protecting the health and safety of the public.
(ANSI N14.27-1986)

Pulmonary (P) Region
Gas exchange region of the lungs; consists of alveoli and respiratory bronchioles.
(NCRP 125)

Pulmonary Clearance Classification (Class)
A classification scheme for inhaled material according to its rate of clearance from the pulmonary region of the lung. Materials are classified as D (days), W (weeks), or Y (years) according to a range of clearance times: Class D - less than 1 0 d; Class W - 10 to 100 d; Class Y - greater than 100 d. The term pulmonary clearance class was selected for use in this standard, although it is used interchangeably with "lung class" and "inhalation class" in ICRP 30.
(HPS N13.42-1997)

Pulmonary compartment
Portion of the respiratory tract in which gas exchange occurs (includes alveoli and respiratory bronchioles).
(AM-1993)

Pulmonary Fibrosis
Formation of scar tissue within the connective tissue of the lungs following pulmonary disease or inflammation.
(NCRP 125)

Pulmonary Lymph Nodes
Lymph nodes found in the pulmonary parenchyma, usually at bifurcations of bronchi and bronchioles.
(NCRP 125)

Pulmonary Thromboembolism
Blockage of a blood vessel in the lungs, usually by a clot in the heart that has become detached from its site of formation.
(NCRP 125)

Pulmonary Tuberculosis
Infectious disease of the lung caused by tubercle bacillus and characterized pathologically by inflammatory infiltrations, formation of tubercles, caseation, necrosis, abscesses, fibrosis, and calcification.
(NCRP 125)

Pulsar
A star in a highly-condensed state that produces pulses of electromagnetic radiation, due to rapid rotation of the star and its associated magnetic fields.
(NCRP 45)

Pulse
An electrical signal arising from a single event of ionizing radiation.
(USAEC-1974)

Pulse amplifier
An amplifier designed specifically to amplify the intermittent signals of a radiation detection instrument, incorporating appropriate pulse-shaping characteristics.
(USAEC-1974)

Pulse coincidence
Arrival of pulses within a preselected time interval in two or more detection channels at the input of a coincidence circuit.
(IEC 50-394-1993)

Pulse height
The measure of the strength or signal amplitude of a pulse delivered by a detector; measured in volts.
(USAEC-1974)

Pulse height analyzer
An electronic circuit which sorts and records pulses according to height or voltage.
(USAEC-1974)

Pulse height discriminator
See discriminator.
(USAEC-1974)

Pulse height selector
A circuit designed to select and pass voltage pulses in a certain range of amplitudes.
(USAEC-1974)

Pulse ionization chamber
Ionization chamber producing an output pulse for each detected ionizing particle.
(IEC 50-394-1993)

Pulse ionization detector
Radiation detector which consists of a volume filled with a suitable gas, or gaseous mixture, in which an electric field is provided for the collection, at the electrodes, of charges associated with the ions and the electrons produced in the sensitive volume of the detector by individual ionizing events.
(IEC 50-394-1993)

Pulse shaper
Sub-assembly intended to produce an output pulse with specified shape characteristics in response to an input signal.
(IEC 50-394-1993)

Pulse-evolution time
Time from the point that a pulse rises above the baseline noise to the peak of the pulse.
(ICRU 52)

Pulse-pair resolution
The ability to detect successive pulses as separate ones in time.
(ICRU 52)

pulse-pair resolution period
The minimum time interval between successive pulses necessary to detect them as separate pulses.
(ICRU 52)

Pulsed reactor
A type of research reactor with which repeated short, intense surges of power and radiation can be produced. The neutron flux during each surge is much higher than could be tolerated during a steady-state operation.
(USAEC-1974)

Purchaser
The organization responsible for establishment of procurement requirements and the issuance, administration, or both, of procurement documents.
(ANSI N46.2-1978)

Purkinje cell
A large neuron of the cerebellar cortex situated on the boundary between the molecular and granular layers of the cerebellum with an extensive dendritic tree; it derives its name from Johannes Purkyne, a Bohemian anatomist and physiologist, who is credited with the first description of this layer of the cerebellum. These cells are the sole output channels of the cerebellar cortex, and the excitatory and inhibitory impulses converge on them from many sources.
(ICRP 49)

Purpura
Large hemorrhagic spots in or under the skin or mucous tissues.
(RHH)

Pyrometallurgical processing
Fuel reprocessing based on reactions involving molten metals at high temperatures.
(ANSI N1.1-1976)

Pyrophoric Liquid
Any liquid that ignites spontaneously in dry or moist air at or below 130 deg.F (54.5 deg.C). A pyrophoric solid is any solid material, other than one classed as an explosive, which under normal conditions is liable to cause fires through friction, retained heat from manufacturing or processing, or which can be ignited readily and when ignited burns so vigorously and persistently as to create a serious transportation, handling, or disposal hazard. Included are spontaneously combustible and water-reactive materials.
(10CFR61.2)

Note: References shown in ()