Borders' Dictionary of Health Physics

E_res, residual maximum beta energy
The maximum energy of the beta spectrum from all beta decay branches of a radionuclide at the calibration distance. E_res is less than the corresponding E_max as the spectrum is modified by absorption and scattering in the source material itself, the source holder, the source encapsulation and other media between the source and the calibration position.
(NCRP 112)

E(t)-committed effective dose
The time integral of the effective dose rate (defined similarly as the Committed Equivalent Dose).
(ICRP 66)

E-effective dose
The sum of the equivalent doses, weighted by the appropriate tissue weighting factors, in all the tissues and organs of the body.
(ICRP 66)

Early Site Permit
A Commission approval, issued pursuant to subpart A of part 52 of this chapter, for a site or sites for one or more nuclear power facilities.
(10CFR100.3)

Early site permit
A Commission approval, issued pursuant to Subpart A of this part, for a site or sites for one or more nuclear power facilities.
(10CFR52.3)

Early somatic effects
Radiation effects occuring shortly after exposure to high doses of radiatin; these include erythema, epilation, and anorexia.
(NCRP 105)

Ecosystem
A basic functional unit in ecology. An area which includes living organisms and nonliving substances interacting to produce an exchange of materials and which is self-sustaining with the exception of energy.
(NUREG/CR 3332)

ED₁₀
The dose (effective dose) that causes a specific effect in 10% of the population under study.
(ICRP 59)

ED₅₀
The dose that causes a specific effect in 50% of the population under study.
(ICRP 59)

Edge enhancement
In xeroradiography, the disproportionate attraction of toner particles toward the region of high residual charge to produce a region of increased perceptibility along an image boundary between two proximal structures.
(NCRP 102)

EDTA
Ethylenediaminetetraacetic acid - a chelating agent (followed by related agents, DTPA, DETA, and DFOA and their zinc or calcium salts)
(RAH)

Effective absorbed energy
A term, not now used, for the product of the energy released by a radionuclide, the relative biological effectiveness of the type of radiation emitted and other modifying factors such as the fraction of disintegrations having a given energy, the ratio of daughter atoms to parent atoms, the n factor (which see), etc.
(NCRP 84)

Effective area (antenna)
In a given direction, the ratio of the power available at the terminals of an antenna, to the power per unit area (power density) of a plane wave incident on the antenna from that direction, polarized coincident with the polarization that the antenna would radiate. Effective area is expressed in units of square meter (m²).
(NCRP 67)

Effective atomic number
Atomic number of a hypothetical element with which radiation of a specified kind would interact in the same way as it interacts with a compound or mixture of interest.
(IEC 50-393-1993)

Effective attenuation coefficient
An empirically determined coefficient expressing the fractional change in absorbed dose with respect to attenuation thickness.
(ICRU 24)

Effective center
The point within a detector that produces, for a given set of irradiation conditions, a response equivalent to that which would be produced if the entire detector were located at the point.
(ANSI N42.17A-1989)

Effective center
The point within a detector that produces, for a given set of irradiation conditions, an instrument response equivalent to that which would be produced if the entire detector were located at the point.
(ANSI N323-1978)

Effective date
The date of promulgation in the FEDERAL REGISTER of an applicable standard or other regulation under this part.
(40CFR61.02)

Effective density
Density of a particle with voids, in contrast to a compact particle's bulk material density.
(AM-1993)

Effective dose
The sum over all exposed tissues of the products of the equivalent dose in a tissue and the weighting factor for that tissue (NCRP, 1993).
(NCRP 118)

Effective dose
The effective dose is the sum of the weighted equivalent doses in all the tissues and organs of the body.
(ICRP 67)

Effective dose
The weighted equivalent dose (a doubly weighted absorbed dose) has been previously called the effective dose equivalent but this name is unnecessarily complicated, especially in more complex combinations such as collective committed effective dose equivalent. The Commission has now decided to use the simpler name effective dose, E. The unit of effective dose is J kg^-1, with the special name sievert (Sv). The effective dose, E, is the sum of the weighted equivalent doses in all the tissues or organs of the body. It is given by the expression:

where H_T is the equivalent dose in tissue or organ T and w_T is the weighting factor for tissue T. Evidently:

(ICRP 60)

Effective dose (E)
The sum of the weighted equivalent doses in all the tissues and organs of the body given by the expression:
E = S w_TH_T,R
where w_T is the weighting factor for organ or tissue, T; and H_T,R is the equivalent dose in tissue or organ T due to a given radiation, R.
(NCRP 121)

Effective dose (E)
The sum of the weighted equivalent doses in all tissues and organs of the body, given by the expression:

where H_T is the equivalent dose in tissue or organ, T, and w_T is the weighting factor for tissue T.
(ICRP 68)

Effective dose equivalent
The sum of the products of the dose equivalent to the body organ or tissue and the weighting factors applicable to each of the body organs or tissues that are irradiated. Weighting factors are: 0.25 for gonads, 0.15 for breast, 0.12 for red bone marrow, 0.12 for lungs, 0.03 for thyroid, 0.03 for bone surface, and 0.06 for each of the other five organs receiving the highest dose equivalent.
(10CFR70.4)

Effective dose equivalent
The sum of the products of the dose equivalent to the organ or tissue and the weighting factors applicable to each of the body organs or tissues that are irradiated. Weighting factors are: 0.25 for gonads, 0.15 for breast, 0.12 for red bone marrow, 0.12 for lungs, 0.03 for thyroid, 0.03 for bone surface, and 0.06 for each of the other five organs receiving the highest dose equivalent.
(10CFR30.4)

Effective dose equivalent
The sum of the products of absorbed dose and appropriate factors to account for differences in biological effectiveness due to the quality of radiation and its distribution in the body of reference man. The unit of the effective dose equivalent is the rem. For purposes of this subpart, doses caused by radon-222 and its respective decay products formed after the radon is released from the facility are not included. The method for calculating effective dose equivalent and the definition of reference man are outlined in the International Commission on Radiological Protection's Publication No. 26.
(40CFR61.91)

Effective dose equivalent
The sum of the products of absorbed dose and appropriate factors to account for differences in biological effectiveness due to the quality of radiation and its distribution in the body of reference man. The unit of the effective dose equivalent is the rem. For purposes of this subpart doses caused by radon-222 and its decay products formed after the radon is released from the facility are not included. The method for calculating effective dose equivalent and the definition of reference man are outlined in the International Commission on Radiological Protection's Publication No. 26.
(40CFR61.101)

Effective dose equivalent
The sum of the products of absorbed dose and appropriate factors to account for differences in biological effectiveness due to the quality of radiation and its distribution in the body of reference man. The unit of the effective dose equivalent is the rem. The method for calculating effective dose equivalent and the definition of reference man are outlined in the International Commission on Radiological Protection's Publication No. 26.
(40CFR61.21)

Effective dose equivalent
The sum over specified tissues of the products of the dose equivalent in a tissue (T) and the weighting factor for that tissue, (w_T), i.e., H_E = S W_TH_T = H_wb.
(NCRP 114)

Effective dose equivalent
The sum over specified tissues of the products of the dose equivalent in a tissue and the weighting factor for that tissue.
(NCRP 109)

Effective dose equivalent
The product of the dose equivalent in a tissue (T) and the weighting factor representing its proportion of the stochastic risk resulting from irradiation of tissue (T) to the total risk when the whole body is irradiated uniformly.
(NCRP 94)

Effective dose equivalent
The effective dose equivalent, H_E, is defined by the sum S _T w_T H_T where w_T is the weighting factor specified by the Commission to represent the proportion of the stochastic risk resulting from irradiation of tissue T to the total risk when the body is irradiated uniformly, and H_T is the mean dose equivalent in tissue T. The values of w_T recommended by the Commission are shown below.
(ICRP 51)

Effective dose equivalent
Quantity obtained by multiplying the dose equivalents to various organs and tissues by factors that reflect the probability of harm to each in relation to all and summing the products. Expressed in sieverts, symbol Sv. Appropriate factors are recommended by the Commission.
(ICRP 36)

Effective dose equivalent
The sum of the weighted mean organ dose equivalents is called the effective dose equivalent, H_E, when the weighting factors w_T are those recommended by the Commission.
(ICRP 33)

Effective dose equivalent (EDE)
The sum of the products of the dose equivalent received by specified tissues of the body and a tissue-specific weighting factor. The effective dose equivalent is expressed in units of rem (or sievert).
(10CFR834.2)

Effective dose equivalent (H_E)
The sum of the products of the dose equivalent to the organ or tissue (H_T) and the weighting factors (w_T) applicable to each of the body organs or tissues that are irradiated (H_E = S w_T H_T)
(10CFR20.1003)

Effective dose equivalent (H_E)
The sum over specified tissues of the products of the dose equivalent (H) in a tissue (T) and the weighting factor for that tissue (w_T), i.e., H_E = S w_TH_T. Also H_E = H_wb. (See whole body dose equivalent).
(NCRP 107)

Effective dose equivalent (H_E)
The sum over specified tissues, of the products of the dose equivalent in a tissue (T) and the weighting factors for that tissue, (w_T), H_E = Sw_TH_T.
(NCRP 101)

Effective dose equivalent (H_E)
The sum over specified tissues, of the products of the dose equivalent in a tissue (T) and the weighting factors for that tissue, (w_T), H_E = Sw_TH_T.
(NCRP 105)

Effective dose equivalent (H_E)
The sum over specified tissues, of the products of the dose equivalent in a tissue (T) and the weighting factors for that tissue, (w_T), H_E = S w_TH_T.
(NCRP 98)

Effective dose equivalent (H_E)
The sum over specified tissues of the products of the dose equivalent in a tissue or organ (T) and the weighting factor for that tissue, w_T, i.e., H_E = S w_T H_T.
(FGR 11)

Effective dose equivalent (H_E)
The weighted average of the dose equivalents in certain organs or tissues of the body, H_T, each weighted by an organ weighting factor, w_T; thus,

The organ weighting factors were chosen by the ICRP to reflect the relative risk of death from cancer or occurrence of sever hereditary effects in the first generations after uniform whole-body exposure. The values of w_T currently recommended by the ICRP are as shown below.

Organ or Tissue w_T

Gonads 0.25

Breast 0.15

Red Bone Marrow 0.12

Lung 0.12

Thyroid 0.03

Bone Surfaces 0.03

Remainder 0.30

Organ or Tissue	w_T
Gonads	0.25
Breast	0.15
Red Bone Marrow	0.12
Lung	0.12
Thyroid	0.03
Bone Surfaces	0.03
Remainder	0.30

(ICRU 43)

Effective dose equivalent (H_E)
The sum over the tissues of the product of the dose equivalent H_T in a tissue (T) and the weighting factor w_T representing it proportion of the total stochastic (cancer and genetic) risk resulting from irradiation of tissue (T) to the risk when the whole body is irradiated uniformly, i.e., H_E = S _Tw_TH_T = H_wb.
(NCRP 91)

Effective dose equivalent (H_E)
The product of the dose equivalent in a tissue (T) and the weighting factor representing its proportion of the stochastic risk resulting from irradiation of tissue (T) to the total risk when the whole body is irradiated uniformly.
(NCRP 84)

Effective Dose Equivalent (H_E)
The summation of the products of the dose equivalent received by specified tissues of the body (H_T) and the appropriate weighting factor (w_T)--that is, H_E = S w_TH_T. It includes the dose from radiation sources internal and/or external to the body. For purposes of compliance with this part, deep dose equivalent to the whole body may be used as effective dose equivalent for external exposures. The effective dose equivalent is expressed in units of rem (or sievert).
(10CFR835.2-1998)

Effective dose equivalent (H_E)
The sum of the product of the dose equivalent to the organ or tissue (H_T) and the weighting factor (w_T) applicable to each of the body organs or tissues that are irradiated. Or:

(HPS N13.41-1997)

Effective dose equivalent (H_E)
The summation of the products of the dose equivalent received by specified tissues of the body (H_T) and the appropriate weighting factor (w_T) - that is H_E = S w_TH_T. It includes the dose from radiation sources internal and/or external to the body. The effective dose equivalent is expressed in units of rem (or sievert).
(10CFR835.2-1993)

Effective dose equivalent conversion factor (h_50,E)
The committed effective dose equivalent per unit intake of radionuclide.
(FGR 11)

Effective dose equivalent, H_E
The summation, over all the significantly irradiated tissues of the body, of the products of the individual tissue stochastic risk weighting factors, w_T, and the dose equivalent to the respective tissue, H_T, i.e., H_E = Sw_TH_T
(NCRP 112)

Effective energy
In reference to bremsstrahlung radiation from an x-ray machine, the effective energy is the monoenergetic photon energy which exhibits the same first half-value thickness in a given material as the x-ray beam.
(NCRP 112)

Effective energy
The energy used to characterize a heterogeneous radiation field that behaves under specified conditions as if it were a monoenergetic field of the same energy.
(ANSI N42.17C-1989)

Effective energy
The energy of monochromatic photons which undergoes the same percentage attenuation in a specified filter as the heterogeneous beam under consideration. Aluminum is the filter specified for photon energies less than, or equal to, 100 keV, copper for photon energies between 100 keV and 1.5 MeV, and lead for photons with energies greater than 1.5 MeV.
(ANSI 13.4-1971)

Effective energy (of a photon beam)
The energy of monoenergetic photons whose total attenuation coefficient in aluminum or copper equals the photon beam's differential rate of absorption measured under good geometry conditions and extrapolated to zero thickness of the same material.
(ANSI N13.7-1983)

Effective half-life
See half-life, effective.
(USAEC-1974)

Effective half-life (T_E)
The time required for the amount of a radionuclide deposited in a living organism to be diminished by 50 percent as a result of the combined action of radioactive decay and biological elimination, i.e.,

(HPJ 60)

Effective half-life (T_eff)
The time required for a radionuclide contained in a biological system, such as in man, to reduce its activity by half, as a combined result of radioactive decay and biological elimination.
(NCRP 65)

Effective half-time
Time required for a radioactive element in an animal's body or organ to be diminished 50 percent as a result of the combined action of radioactive decay and biological elimination.

Effective half-time =
biologic half-time x radioactive half-time
biologic half-time + radioactive half-time
(NCRP 75)

Effective half-time =
biologic half-time x radioactive half-time
biologic half-time + radioactive half-time
(NCRP 62)

Effective half-time, (T_j)_eff
The time in which the activity of the j-th component of the radionuclide decreases by one half as a result of radioactive decay and biologic elimination, in a particular organ.
(MIRD)

Effective kilogram
(1) For the source material uranium in which the uranium isotope uranium-235 is greater than 0.005 (0.5 weight percent) of the total uranium present: 10,000 kilograms, and
(2) for any other source material: 20,000 kilograms.
(10CFR40.4)

Effective kilogram
A unit used in safeguarding nuclear material. The quantity is:
(1) For special nuclear material: The amount specified in Sec. 70.4 of this chapter.
(2) For source material: The amount specified in Sec. 40.4(q) of this chapter.
(10CFR75.4)

Effective kilograms of special nuclear material
(1) For plutonium and uranium-233 their weight in kilograms;
(2) For uranium with an enrichment in the isotope U-235 of 0.01 (1%) and above, its element weight in kilograms multiplied by the square of its enrichment expressed as a decimal weight fraction; and
(3) For uranium with an enrichment in the isotope U-235 below 0.01 (1%), by its element weight in kilograms multiplied by 0.0001.
(10CFR74.4)

Effective Kilograms of Special Nuclear Material
(1) For plutonium and uranium-233, their weight in kilograms;
(2) For uranium enriched 1 percent or greater in the isotope U-235, its element weight in kilograms multiplied by the square of its enrichment expressed as a decimal weight fraction; and
(3) For uranium enriched below 1 percent in the isotope U-235, its element weight in kilograms multiplied by 0.0001.
(10CFR110.2)

Effective leakage area
The hypothetical area amassed if all the actual cracks and holes in a building shell were collected in one hole with the equivalent infiltration rate.
(ENV RAD)

Effective multiplication constant (k_eff)
Multiplication factor evaluated for a finite medium.
(IEC 50-393-1993)

Effective multiplication factor (or constant)
See multiplication factor.
(USAEC-1974)

Effective range of measurement
Range of values of the quantity to be measured over which the performance of a piece of equipment or assembly meets the requirements of its specifications.
(IEC 50-394-1993)

Effective source height
A mathematical approximation of the height at which the source term is released to the atmosphere, taking into account the initial buoyancy and momentum created by the emission of radioactive gases at high temperature or velocity.
(NUREG/CR 3332)

Effective specific power
The rate of thermal energy emission per unit mass of radioactive material at the time of measurement. It depends on the initial radionuclidic composition and elapsed time.
(ANSI N15.54-1988)

Effective specific power
The rate of energy emission per unit mass of plutonium at the time of measurement. It depends on the initial radionuclidic composition and elapsed time.
(ANSI N15.22-1987)

Efficiency
Describes quantitatively the capability of a given detector to register radiation of a specific type. Several types of efficiency can be defined.
counting (or overall) efficiency: describes the probability for the detection of spontaneous nuclear decay processes of a specific single radionuclide by means of a given detector or detector-system arrangement plus associated instrumentation, and for a specific source geometry. It is the expectation value of the ratio of the number of detected events (recorded pulses) to the number of decay events, and thus relates the activity, A, of a radioactive source and the response of a radiation counting system (mean count rate, corrected for dead-time effects and background).
individual (detection) efficiency: probability for the detection of particles or photons of a specific energy or energy distribution for a given detector arrangement or counting geometry. It is the expectation value of the ratio of the number of detected events (recorded pulses) to the number of emissions.
full-energy peak efficiency: individual efficiency for a given gamma-ray energy related to the full-energy peak area in the pulse-height spectrum associated with energy-dispersive gamma-ray detection.
partial (detection) efficiency: individual efficiency where pulses from only part of the pulse-height spectrum are registered.
intrinsic efficiency: the probability of detecting a particle or photon incident on the detector. It is the expectation value of the ratio of the number of recorded pulses to the number of particles or quanta incident on the detector.
total efficiency: efficiency where any pulse, irrespective of its pulse height, is employed for registration.
(ICRU 52)

Efficiency
The net number of counts registered by the detector system per unit of time divided by the number of photons of interest originating in the radioactive source that is being measured during the same unit of time.
(ANSI N42.12-1980)

Efficiency (counters)
A measure of the probability that a count will be recorded when radiation is incident on a detector. Usage varies considerably, so it is well to ascertain factors (window transmission, sensitive volume, energy dependence, etc.) are included in a given case.
(HPJ 60)

Efficiency (of x ray production)
The fraction of electron power incident on a target that is converted to x-ray power.
(NCRP 51)

Efficiency extrapolation
Extrapolation of the detector count rate (usually of the b-ray detector in a b-g coincidence arrangement) for the counting efficiency tending towards unity in order to obtain the required source activity.
(ICRU 52)

Efficiency, intrinsic (counters)
A measure of the probability that a count will be recorded when a particle or photon of ionizing radiation is incident on a detector.
(ANSI N1.1-1976)

Efficiency-tracer method
Efficiency-extrapolation method applied to pure b-ray emitters by adding a radionuclide emitting coincident b and g rays in order to trace the b-ray detector efficiency by coincidence measurements.
(ICRU 52)

Effluent
Liquid or airborne radioactive materials released to the environs.
(ANSI N320-1979)

Effluent
The liquid or gaseous waste streams released to the environment.
(ANSI N13.10-1974)

Effluent
The liquid or gaseous waste streams released to the environment.
(ANSI N42.18-1974)

Einstein equation
See mass-energy equation.
(USAEC-1974)

Elastic collision
Collision in which the physical content of each colliding system and the total kinetic energy are left unchanged, although the directions of their relative motion will probably be altered.
(IEC 50-393-1993)

Elastic light scattering
A process in which there is no energy exchange between incident photons of light and target particles.
(AM-1993)

Elastic Recoil
The ability to return to the original shape after bouncing off an object.
(NCRP 125)

Elastic scattering
Scattering in which the total kinetic energy is unchanged.
(IEC 50-393-1993)

Elastic scattering
See Compton effect, scattering.
(USAEC-1974)

Elastic scattering
Scattering collision in which the sum of the kinetic energies of neutron and target nucleus remains unchanged after the collision.
(NCRP 38)

Elastic scattering
Collisions in which the kinetic energy of neutron plus nucleus is unchanged by the collision, and the nucleus is left in the same state as before the collision.
(NBS 63)

Elective examination
An examination not requiring immediate execution and therefore able to be planned for the patient's convenience and safety.
(NCRP 102)

Electret ionization chamber
Ionization chamber in which the high voltage electrode is replaced by an electret with a permanent surface potential, the decrease of this potential, caused by the ionization of the filling gas. being used a measure of the radiation dose to be detected.
(IEC 50-394-1993)

Electric dipole
A pair of equal and opposite charges separated by an infinitesimal distance. When the charges are oscillating, the dipole becomes an elementary radiating electric dipole.
(NCRP 67)

Electric dipole moment
A vector, the magnitude of which is equal to the product of the charge of an electric dipole and the separation distance, and the direction of which is from the negative to the positive charge. Electric dipole moment is expressed in units of coulomb meter (C m).
(NCRP 67)

Electric field strength
A field vector quantity, E, that represents the force, F, of an infinitesimal unit positive test charge at a point divided by that charge, q. E = F/q. Electric field strength is expressed in units of volt per meter (V/m).
(NCRP 67)

Electric flux density (displacement)
A vector equal to the product of the electric field strength and the permittivity of the medium. In an anisotropic medium the permittivity is a function of the direction and, hence, the electric flux density is not necessarily in the same direction as the electric field strength. Electric flux density can be considered as a surface charge density expressed in units of coulomb per square meter (C/m²).
(NCRP 67)

Electric penetration assembly (of a nuclear reactor)
Assembly of insulated electric conductors, conductor seals, and opening seals that provides the passage for the electric conductors through a single opening in the nuclear containment structure, while providing a pressure barrier between the inside and the outside of the containment structure.
(IEC 50-394-1993)

Electric polarization
The difference between the electric flux density in a medium and the electric flux density in a vacuum for the same electric field strength. Electric polarization is expressed in units of coulomb per square meter (C/m²).
(NCRP 67)

Electric susceptibility
The ratio of the electric polarization at a point in a medium to the electric flux density that would exist at that point for the same electric field strength if the medium were a vacuum.
(NCRP 67)

Electric utility
Any entity that generates or distributes electricity and which recovers the coat of this electricity, either directly or indirectly, through rates established by the entity itself or by a separate regulatory authority. Investor-owned utilities, including generation or distribution subsidiaries, public utility districts, municipalities, rural electric cooperatives, and State and Federal agencies, including associations of any of the foregoing, are included within the meaning of "electric utility."
(10CFR50.2)

Electrical aerosol analyzer
An aerosol size spectrometer in which the particles are separated by removing those with an electrical mobility greater than a selected value.
(AM-1993)

Electrical aerosol classifier
An aerosol size spectrometer in which the particles are separated by selecting those within a narrow range of electrical mobilities.
(AM-1993)

Electrical length
The ratio of a physical length to that of a wavelength at a given frequency. Electrical length can be expressed in units of fractional or multiple wavelengths, radians, or degrees.
(NCRP 67)

Electrical mobility
An aerosol parameter that indicates a particle's ability to move in an externally applied flow field.
(AM-1993)

Electrical mobility
The ratio of particle terminal velocity to the applied electrical force, assuming one electronic charge on the particle.
(TID-26608)

Electrical mobility (equivalent) diameter
Diameter of a unit-density spherical particle moving at the same velocity in an electric field as the particle in question
(AM-1993)

Electrode
A conductor used to establish electrical contact with a nonmetallic part of a circuit.
(RHH)

Electrodynamic balance
A device which uses superimposed ac and dc fields to levitate particles.
(AM-1993)

Electromagnetic field
The ratio of a physical length to that of a wavelength at a given frequency. Electrical length can be expressed in units of fractional or multiple wavelengths, radians, or degrees.
(NCRP 67)

Electromagnetic interaction
Interaction attributable to an electromagnetic field.
(IEC 50-393-1993)

Electromagnetic radiation
Radiation consisting of associated and interacting electric and magnetic waves that travel at the speed of light. Examples: light, radiowaves, g rays, x rays. All can be transmitted through a vacuum.
(HPJ 60)

Electromagnetic radiation
The propagation of energy in the form of electromagnetic waves through space. (Not intended to describe propagation along waveguides and other transmission lines).
(NCRP 67)

Electromagnetic radiation
Electromagnetic phenomena expressed in scalar or vector functions of space and time.
(NBS 51)

Electromagnetic separation process (isotope separation)
A process for separating isotopes which depends on their behavior in an electromagnetic field.
(ANSI N1.1-1976)

Electromagnetic wave
See wave, electromagnetic.
(NCRP 67)

Electrometer
Apparatus for the measurement of small electrical charges or currents.
(IEC 50-394-1993)

Electrometer
Electrostatic instrument for measuring the difference in potential between two points. Used to measure change in electric potential of charged electrodes resulting from ionization produced by radiation.
(RHH)

Electrometer
An instrument for measuring the difference in electric potential between two points.
(NBS 51)

Electron
Stable elementary particle with one negative elementary electric charge and a rest mass of approximately 9.10939 x l0^-31 kg.
(IEC 50-393-1993)

Electron
Subatomic charged particle. Negatively charged particles are parts of stable atoms. Both negatively and positively charged electrons may be expelled from the radioactive atom when it disintegrates. See beta particle.
(NCRP 111)

Electron
Symbol e^-. An elementary particle with a unit negative charge and a mass 1/1837 that of a proton. Electrons surround the positively charged nucleus and determine the chemical properties of the atom. Positive electrons also exist.
(HPJ 60)

Electron
A stable elementary particle having an electric charge equal to +/- 1.60219 x 10^-19 C. and a rest mass equal to 9.1095 x 10^-31 kg. When used without specification the term means the negatively charged electron, which is also called a negatron or negaton. Its anti-particle, the positively charged electron, is called the positron or positon.
(ANSI N1.1-1976)

Electron
Subatomic charged particle. Negatively charged electrons are parts of stable atoms. Both negatively charged and positively charge electrons may be expelled from the radioactive atom when it disintegrates. See beta rays.
(NCRP 48)

Electron
[Symbol e^-] An elementary particle with a unit negative electrical charge and a mass 1/1837 that of the proton. Electrons surround the positively charged NUCLEUS and determine the chemical properties of the atom. Positive electrons, or positrons, also exist.
(USAEC-1974)

Electron
A stable elementary particle having an electric charge equal to ± 1.60210 x 10^-19 C. and a rest mass equal to 9.1091 x 10^-31 kg.
Secondary Electron: An electron ejected from an atom, molecule or surface as a result of an interaction with a charged particle or photon.
Valence Electron: Electron which is gained, lost or shared in a chemical reaction.
(RHH)

Electron capture
Process in which a proton of a nucleus is transformed into a neutron, by capturing an orbital electron accompanied by neutrino emission, the captured electron being replaced by one of the other shell electrons causing characteristic radiation emission.
(IEC 50-393-1993)

Electron capture
[Abbreviation EC] A mode of radioactive decay of a nuclide in which an orbital electron is captured by and merges with the nucleus, thus forming a new nuclide with the mass number unchanged but the atomic number decreased by 1. (See K-capture.)
(USAEC-1974)

Electron collection pulse chamber
Pulse ionization chamber in which the output signal is due principally to the collection of electrons, taking advantage of their high mobility which is far greater than that of ions.
(IEC 50-394-1993)

Electron collection time
Time interval between the formation of ion pairs at a given point by ionizing radiation and the collection of the corresponding electrons on the collecting electrode.
(IEC 50-394-1993)

Electron multiplier
Group of dynodes subjected to increasing voltages in a vacuum and used to amplify an electron current by a cascade process by means of secondary emission.
(IEC 50-394-1993)

Electron volt
Unit of energy equivalent to the amount of energy gained by an electron passing through a potential difference of on volt (abbreviated: eV; 1 eV = 1.6 x 10^-12 erg). Larger multiple units of the electron volt are frequently used, namely: "keV" for kilo or thousand electron volts, "MeV" for million electron volts, and "BeV" for billion electron volts.
(HPJ 60)

Electron volt
[Abbreviation ev or eV] The amount of kinetic energy gained by an electron when it is accelerated through an electric potential difference of 1 volt. It is equivalent to 1.603 x 10^-12 erg. It is a unit of energy, or work, not of voltage. (See Bev, Mev.)
(USAEC-1974)

Electron volt
A unit of energy equivalent to the energy gained by an electron in passing through a potential difference of one volt. Larger multiple units of the electron volt are frequently used:
keV for thousand or kilo electron volts;
MeV for million or mega-electron volts.
(Abbr. eV, 1 eV = 1.6 x 10^-12 erg.)
(BEIR I)

Electron volt (eV)
A unit of energy equal to the kinetic energy gained in a vacuum by a particle having one electronic charge when it passes through a potential difference of 1 volt; 1eV = 1.6 x 10^-19 joule or 1.6 x 10^-12 erg.
(NCRP 111)

Electron volt (eV)
A unit of energy = 1.6 x 10^-12 ergs = 1.6 x 10^-19 J; 1 eV is equivalent to the energy gained by an electron in passing through a potential difference of 1 V; 1 keV = 1,000 eV; 1 MeV = 1,000,000 eV.
(BEIR V)

Electron volt (eV)
A unit of energy equal to the energy gained by a particle having one electronic charge when it passes in a vacuum through a potential difference of 1 volt; 1 ev = 1.60 x 10^-12 erg.
(NBS 63)

Electron-beam generator
A type of electron accelerator in which the electron beam is brought out into the atmosphere for irradiation purposes.
(NCRP 51)

Electronic equilibrium
See charged particle equilibrium.
(ANSI N1.1-1976)

Electrons
Small negatively charged particles that can be accelerated to high energy and velocity close to the speed of light.
(NCRP 98)

Electrons
Negatively charge particles that orbit around the nucleus of an atom.
(ENV RAD)

Electronvolt (eV)
Special unit of energy equal to the change in energy of an electron in passing through a potential difference of 1 volt in vacuum.1 eV = 1.602 19 x 10^-19 J (approximately).
(IEC 50-393-1993)

Electrophoresis
Charged particle motion induced by an electric field.
(AM-1993)

Electrostatic Attraction (Or Repulsion)
Affinity for attraction (or repulsion) due to electrostatic charges associated with particles.
(NCRP 125)

Electrostatic balance
A device which uses a do field to levitate particles, e.g., the Millikan condenser.
(AM-1993)

Electrostatic collector failed element monitor
Failed element monitor using the measurement of the activity of the fission gas daughters, such as rubidium and cesium, after collecting them on a negative electrode.
(IEC 50-394-1993)

Electrostatic field
The region surrounding an electric charge in which another charge experiences a force.
(RHH)

Electrostatic precipitator
A device in which airborne particles are charged in a unipolar ion field and deposited with a high-voltage electric field.
(AM-1993)

Electrostatic scattering
Mutual repulsion by similarly charged aerosol particles.
(TID-26608)

Electrostatic unit of charge
See Statcoulomb.
(RHH)

Element
Uranium or plutonium.
(10CFR74.4)

Element
One of the 103 known chemical substances that cannot be divided into simpler substances by chemical means. A substance whose atoms all have the same atomic number. Examples: hydrogen, lead, uranium. (Not to be confused with fuel element.) (See atom, matter, nuclide.)
(USAEC-1974)

Element
A category of atoms of all the same atomic number.
(RHH)

Elemental phosphorus plant or plant
Any facility that processes phosphate rock to produce elemental phosphorus. A plant includes all buildings, structures, operations, calciners and nodulizing kilns on one contiguous site.
(40CFR61.121)

Elementary (electric) charge (e)
Absolute value of the electric charge of the electron or the proton, approximately equal to 1.60218 x 10^-19 C.
(IEC 50-393-1993)

Elementary particle
Particle presently considered to be a non-dissociable entity, as distinguished from those which are considered to be assemblies.
(IEC 50-393-1993)

Elutriator
A device used to separate particles by aerodynamic diameter by allowing them to settle in a moving air stream.
(AM-1993)

Emanating power
Under steady-state conditions, the fraction of radon atoms formed in a solid which escape from the solid.
(NCRP 103)

Emanation
In this report, the release of radon from a solid into the surrounding gas or liquid phase.
(NCRP 97)

Emanation
A term used historically to describe what we now know to be the isotopes of radon. It was used by Lord Rutherford, when he was unsure of its nature.
(ENV RAD)

Emanation rate
In this report, the release rate of gas (radon) from a surface in units such as Bq per square meter per second.
(NCRP 103)

Emanation rate
The release rate of radon from a surface in pCi/cm²-sec.
(NCRP 78)

E_max
The maximum beta particle energy emitted by an unattenuated source.
(NCRP 112)

Embolization
Theapeutic introduction of a substance into a vessel in order to occlude it.
(NCRP 107)

Embryo
The human organism in its early stages of development; that is, from fertilization until approximately 8 weeks.
(ICRP 49)

Embryo/fetus
The developing human organism from conception until the time of birth.
(10CFR20.1003)

Embryo/fetus
The developing human organism from conception until the time of birth.
(NCRP 114)

Emergency
A sudden, urgent, usually unforeseen occurrence or occasion requiring immediate action.
(NCRP 111)

Emergency
Any situation which activates the plant's emergency response plan.
(ANSI/ANS-3.8.1-1987)

Emergency
Associated with an accident giving rise, or potentially giving rise, to radiation doses of intakes in excess of those recommended by the Commission for normal operations.
(ICRP 7)

Emergency access
Access to an operating non-Federal or regional low-level radioactive waste disposal facility or facilities for a period not to exceed 180 days, which is granted by NRC to a generator of low-level radioactive waste who has been denied the use of those facilities.
(10CFR62.2)

Emergency action level (EAL)
A parameter or criteria used as a basis for emergency classification.
(ANSI/ANS-3.8.1-1987)

Emergency classes
Four emergency classes have been established. These classes are as follows:
(1) Unusual Event: Events which are in progress or have occurred, which indicate a potential degradation of the level of safety of the plant. Unusual events are nonroutine occurrences which may be of interest to government authorities or to the public. No releases of radioactive material requiring offsite response or monitoring are expected unless further degradation of safety systems occur.
(2) Alert: Events which are in progress or have occurred, which involve actual or potential substantial degradation of the level of safety of the plant. Any radiological releases are expected to be limited to small fractions of the EPA Protective Action Guidelines (Manual of Protective Action Guides and Protective Actions for Nuclear Incidents, EPA-520/1-75-001, September 1975, U.S. Environmental Protection Agency) exposure levels.
(3) Site Area Emergency: Events which are in progress or have occurred, which involve actual or likely major failures or plant functions needed for protection of station personnel and the public. Any radioactive releases are not expected to exceed the EPA Protective Action Guideline exposure levels except near the site boundary.
(4) General Emergency: Events which are in progress or have occurred, which involve actual or imminent substantial core degradation with potential for loss of containment integrity. Radiological releases can be reasonably expected to exceed the EPA Protective Action Guideline exposure levels offsite.
(ANSI/ANS-3.8.1-1987)

Emergency coordinator
The individual within an institution or facility who is assigned the responsibility for developing an emergency plan, and maintaining the plan and its distribution lists.
(NCRP 111)

Emergency director
The individual designated in the emergency plan to exercise command and control over all emergency response personnel for the duration of the emergency.
(NCRP 111)

Emergency measurements
Measurements for persons known or suspected to have been exposed to intakes of radioactive material greater than normally encountered in routine operations. For these situations, rapid analytical procedures giving a timely measurement result may be preferred.
(ANSI N13.30-1989D)

Emergency monitoring programs
Those designed for following an emergency that has the potential to give rise to exposures in excess of the limits recommended for normal operations. Such programs must be able to provide sufficient information quickly enough to aid decisions on the timing and scope of any countermeasures. The distinction between normal and emergency monitoring applies to both source and environmental monitoring programs.
(ICRP 43)

Emergency planning zone (EPZ)
Areas for which planning is needed to assure that prompt and effective actions can be taken to protect the public. (See also Plume EPZ and Ingestion EPZ.)
(ANSI/ANS-3.8.1-1987)

Emergency respirator use
Wearing a respirator when a hazardous atmosphere suddenly occurs that requires immediate use of a respirator either for escape from the hazardous atmosphere or for entry into the hazardous atmosphere to carry out maintenance or some other task.
(ANSI Z88.2-1980)

Emergency response facility
Facility provided to mitigate the consequences of accidents and respond to abnormal operating conditions.
(IEC 50-393-1993)

Emergency response facility (ERF)
An area or collection of areas designated for emergency use.
(1) Technical Support Center (TSC): Onsite facility separate from the Control Room (CR) where technical analysis, direction, communications, and other designated emergency functions are performed.
(2) Emergency Operations Facility (EOF): Facility outside the protected area from which the utility's overall accident management and coordination with offsite response organizations are performed.
(3) Operations Support Center (OSC): Onsite facility separate from the control room where designate operations, health physics, and maintenance support personnel assemble and await specific assignments during an emergency.
(4) Emergency News Center: Facility outside protected area where designated Public Information Officers, utility and government agencies provide media updates and respond to information requests.
(ANSI/ANS-3.8.1-1987)

Emergency response plan
A licensing document which describes the utility's overall emergency response functions, organization, facilities, and equipment as well as appropriate state, county, or local plans. This document is supplemented by specific implementing procedures.
(ANSI/ANS-3.8.1-1987)

Emergency response plan
A plan prepared by a shipper or carrier that addresses activities to be carried out by that shipper or carrier in an accident situation. (In Appendix A, this term refers to a plan prepared by a federal, state, or local governmental agency.)
(ANSI N14.27-1986)

Emergency response team
A group trained and equipped to respond to radiation accidents.
(ANSI N14.27-1986)

Emergency shut-down safety system
Safety system which performs the rapid shut-down of a nuclear reactor by an action which is not necessarily reversible.
(IEC 50-394-1993)

Emergency shutdown
The act of shutting down a reactor suddenly to prevent or minimize a dangerous condition.
(ANSI N1.1-1976)

Emergency shutdown rod
Rod-shaped safety member for immediate reactor shutdown action.
(IEC 50-394-1993)

Emission
Material being discharged into the outdoor atmosphere.
(AM-1993)

Emission band (of a scintillator)
Part of the emission spectrum corresponding to energies, or wavelengths, for which the probability of emission of photons is greatest.
(IEC 50-394-1993)

Emission rate
Of a given radiation source, the number of particles of given type and energy leaving the source per unit time.
(ANSI N1.1-1976)

Emission spectrum (of a scintillator)
Curve representing the distribution of the number of emitted photons as a function of their wavelength or energy.
(IEC 50-394-1993)

Emitting surface of a radiation source
That part of the surface of a source from which the useful radiation is emitted.
(IEC 50-393-1993)

Emphysema
Abnormal dilation of the pulmonary air spaces (alveoli) accompanied by destruction of respiratory tissue.
(NCRP 125)

Empty cylinder
A cylinder containing a residual amount of UF6 and nonvolatile reaction products of uranium (heel) in quantities less than those specified in 8.1.2 of this standard. This definition should not be confused with the category of empty packaging used in 49 CFR 173.427.
(ANSI N14.1-1990)

Emulsion, nuclear
An ionization-sensitive material such as a photographic emulsion used for permanently recording the tracks of charged particles.
(ANSI N1.1-1976)

Emulsion, nuclear
A photographic emulsion specially designed to permit observation of the individual tracks of ionizing particles.
(RHH)

Encapsulated source
A radionuclide sealed in a container such as a tube or needle. See sealed source.
(NCRP 48)

Enclosed filter
A filter that is completely enclosed on all sides and both faces except for reduced end connections or nipples for direct connection into a duct system. Enclosed filters are installed individually because there is a separate run of duct to each filter unit.
(ERDA 76-21)

End effect (of a counter tube)
Effect due to distortion of the electric field near the ends of the collecting electrode of a counter tube and consisting of a counting loss or degradation of the measured spectrum.
(IEC 50-394-1993)

End product
See radioactive series.
(USAEC-1974)

End product
The stable nuclide that is the final member of a radioactive series.
(RHH)

End-point energy
Maximum energy (normally applies to beta emitters)
(NCRP 112)

Endoergic; endothermal
Characterized by the absorption of energy or heat. Endoergic reactions absorb energy as they progress. Endothermal reactions absorb heat as they progress.
(NCRP 51)

Endogeneous
Originating within the body.
(NCRP 94)

Endogeneous
Originating within the body.
(NCRP 45)

Endosteal
Relating to the layer of soft tissue lining bone cavities.
(NCRP 94)

Endosteal
Relating to the layer of soft tissue lining bone cavities.
(NCRP 45)

Endothelial Blood Capillary Cells
Layer of flat cells lining the inside blood vessels and capillaries.
(NCRP 125)

Endotoxin
Toxic cell wall component of gram-negative bacteria.
(AM-1993)

Energy
The capability of doing work. (See kinetic energy, nuclear energy.)
(USAEC-1974)

Energy
Capacity for doing work.
Potential energy: The energy inherent in a mass because of its special relation to other masses.
Kinetic energy: The energy possessed by a mass because of its motion.
Binding energy: The energy represented by the difference in mass between the sum of the component parts and the actual mass of the nucleus.
Excitation energy: The energy required to change a system from its ground state to an excited state. Each different excited state has a different excitation energy.
Ionizing energy: The average Energy lost by ionizing radiation in producing an ion pair in a gas. For air, it is about 33.73 eV.
Radiant energy: The energy of electromagnetic radiation, such as radiowaves, visible light, x and gamma rays.
Reaction energy (nuclear): In the disintegration of a nucleus, it is equal to the sum of the kinetic or radiant energies of the reactants minus the sum of the kinetic or radiant energies of the products. If any product of a specified reaction is in an excited state, the energy of subsequently emitted gamma radiation is not included in the sum. The "ground-state nuclear reaction energy" is the reaction energy when all reactant and product nuclei are in their ground states. (Symbol: Q_o) MKSA units: kg-m²/sec² or joules.
(RHH)

Energy calibration
The relationship between the height of the amplifier output pulse and the energy of the photon originating in the radioactive source.
(ANSI N42.12-1980)

Energy conversion efficiency (of a scintillator)
Ratio of the total energy of the photons emitted by a scintillator to the incident energy absorbed by it.
(IEC 50-394-1993)

Energy density
The total energy contained in an infinitesimal volume of a medium divided by that volume. Energy density is a volume energy density expressed in units of joule per cubic meter (J/m³).
(NCRP 67)

Energy density, dissipated
The electromagnetic energy that is converted to other forms of energy, such as heat, in an infinitesimal volume of a medium divided by the volume. This energy is not directly recoverable in the form of electromagnetic energy. Dissipated energy density is expressed in units of joule per cubic meter (J/m³).
(NCRP 67)

Energy density, stored
The energy stored in the electromagnetic fields in an infinitesimal volume of a medium divided by the volume. This energy is recoverable in the form of electromagnetic energy. Stored energy density is expressed in units of joule per cubic meter (J/m³).
(NCRP 67)

Energy dependence
A change in instrument response with respect to radiation energy for a constant exposure of exposure rate.
(ANSI N42.17C-1989)

Energy dependence
A change in instrument response with respect to radiation energy for a constant dose equivalent or dose-equivalent rate.
(ANSI N42.17A-1989)

Energy dependence
A change in instrument response with respect to radiation energy for a constant exposure or exposure rate.
(ANSI N323-1978)

Energy dependence
The characteristic response of a radiation detector to a given range of radiation energies or wave lengths compared with the response of a standard free-air chamber.
(RHH)

Energy dependent detector
Detector system which has a different response to different energy radiations, all other factors being equal.
(NCRP 112)

Energy deposit
The energy deposit, e_i, is the energy deposited in a single interaction, i:e.

where:
T_in = the energy of the incident ionizing particle (exclusive of rest mass).
T_out = the sum of the energies of all ionizing particles leaving the interaction (exclusive of rest mass).
Q_Dm = the charges of the rest mass energy of the atom and all particles involved in the interaction (Q_Dm > 0: decrease of rest mass; Q_Dm < 0: increase in rest mass).
The unit of e_i is the joule (J); e_i may also be expressed in the unit eV.
(ICRU 36)

Energy deposition event
An event in which energy is imparted to the matter in a specified volume by an ionizing particle of a group of associated ionizing particles.
(ICRU 33)

Energy deposition event
The term "energy deposition event", or briefly "event" denotes the deposition of energy in the mass of interest by correlated, i.e. statistically dependent, ionizing particles.
(ICRU 26)

Energy deposition event
The deposition of energy in the mass of interest by correlated ionizing particles.
(ICRU 19)

Energy fluence
The energy fluence, Y, of particles is the quotient dE_n, by da, where dE_n, is the sum of the energies, exclusive of rest energies, of all the particles which enter a sphere of cross-sectional area da.

(ICRU 26)

Energy fluence
Time integral of energy flux density.
(NCRP 38)

Energy fluence
The sum of the energies, exclusive of rest energies, of all particles passing through a unit cross-sectional area.
(RHH)

Energy fluence (F)
The energy fluence (F) of particles is the quotient of DE_F by Da, where DE_F is the sum of the energies, excluding rest energies of all the particles which enter a sphere of cross sectional area Da.

(NBS 92)

Energy fluence (F)
The energy fluence (F) of particles is the quotient of DE_F by Da, where DE_F is the sum of the energies, exclusive of rest energies, of all the particles which enter a sphere of cross-sectional area Da.

(ICRU 10b)

Energy fluence (Y)
Quotient of dR by da, where dR is the radiant energy incident on a sphere of cross-sectional area da.

(IEC 50-393-1993)

Energy fluence (Y)
The quotient of dR by da, where dR is the radiant energy incident on a sphere of cross-sectional area da.

(ICRP 51)

Energy fluence (Y)
The quotient of dR by da, where dR is the radiant energy incident on a sphere of cross-sectional area da.

(ICRU 33)

Energy fluence (Y)
The energy fluence, Y, of particles is the quotient of dE_fl by da, where dE_fl is the sum of the energies, exclusive of rest energies, of all the particles which enter a sphere of cross sectional area da.

(ICRU 19)

Energy fluence rate
The energy fluence rate, y, is the quotient of dY by dt, where dY is the increment of energy fluence in the time interval dt.

The terms "flux density" and "energy flux density" are occasionally used instead of "fluence rate" or "energy fluence rate."
(ICRU 26)

Energy fluence rate (y)
Quotient of dY by dt, where dY is the increment of energy fluence in the time interval dt.

(IEC 50-393-1993)

Energy fluence rate (y)
The quotient of dY by dt, where Y is the increment of energy fluence in the time interval dt.

(ICRU 33)

Energy flux ()
Quotient of dR by dt, where dR is the increment of radiant energy in the time interval dt.

(IEC 50-393-1993)

Energy flux ()
The quotient of dR by dt, where dR is the increment of radiant energy in the time interval dt.

(ICRU 33)

Energy flux density
The rate of energy transport into a small sphere divided by the cross-sectional area of that sphere. Energy flux density is expressed in units of watt per square meter (W/m²). For ionizing radiation, this quantity is now called energy fluence rate.
(NCRP 67)

Energy flux density
Radiation energy which, per unit time, enters a sphere per unit cross sectional area of that sphere.
(NCRP 38)

Energy flux density (energy fluence rate)
The sum of the energies, exclusive of rest energies, of all particles passing through a unit cross-sectional area per unit of time. (Energy fluence per unit of time).
(RHH)

Energy flux density or energy fluence rate (y)
The quotient of dY by dt, where dY is the increment of energy fluence in the time interval dt.

(ICRU 19)

Energy flux density or intensity (I)
The quotient of DF by Dt where DF is the energy fluence in the time Dt.

(NBS 92)

Energy flux density or intensity (I)
The energy flux density or intensity (I) is the quotient of DF by Dt where DF is the energy fluence in the time Dt. Note: This quantity may also be referred to as energy fluence rate.
(ICRU 10b)

Energy imparted
The stochastic quantity energy imparted, epsilon, by ionizing radiation to the matter in a volume is:

where:
Se_i = the sum of the energies (excluding rest energies) of all those directly and indirectly ionizing particles which have entered the volume,
Se_ex = the sum of the energies (excluding rest energies) of all those directly and indirectly ionizing particles which have left the volume, and
SQ = the sum of all the energies released, minus the sum of all the energies expended, in any transformations of nuclei and elementary particles which have occurred within the volume.
(ICRU 26)

Energy imparted
The stochastic quantity energy imparted, epsilon, by ionizing radiation to the matter in a volume is:

where:
Se_i = the sum of the energies (excluding rest energies) of all those directly and indirectly ionizing particles which have entered the volume,
Se_ex = the sum of the energies (excluding rest energies) of all those directly and indirectly ionizing particles which have left the volume, and
SQ =the sum of all the energies released, minus the sum of all the energies expended, in any transformations of nuclei and elementary particles which have occurred within the volume.
(ICRU 19)

Energy imparted
The energy imparted by ionizing radiation to the matter in a volume is the difference between the sum of the energies of all directly and indirectly ionizing particles which have entered the volume and the sum of the energies of all those which have left it, minus the energy equivalent of any increase in rest mass that took place in nuclear or elementary particle reactions within the volume. Note: The above definition is intended to be exactly equivalent to the previous meaning given by the ICRU to "energy retained by matter and made locally available" or "energy which appears as ionization, excitation or changes of chemical bond energies".
(NBS 92)

Energy imparted
The energy imparted by ionizing radiation in a volume is the difference between the sum of the energies of all the directly and indirectly ionizing particles which have entered the volume and the sum of the energies of all those which have left it, minus the energy equivalent of any increase in rest mass that took place in nuclear or elementary particle reactions within the volume.
(ICRU 10b)

Energy imparted (e)
The energy imparted by ionizing radiation to the matter in a volume is:

where
R_in =the radiant energy incident on the volume, i.e., the sum of the energies (excluding rest energies) of all those charged and uncharged ionizing particles which enter the volume,
R_out = the radiant energy emerging from the volume, i.e., the sum of the energies (excluding rest energies) of all those charged and uncharged ionizing particles which leave the volume, and,
S (Q) =the sum of all changes (decreases: positive sign, increases: negative sign) of the rest mass energy of nuclei and elementary particles in any nuclear transformations which occur in the volume.
(ICRP 51)

Energy imparted (e)
The energy imparted, e, to matter in a volume is

where the summation is performed over all energy deposits, e_i, in that volume. The unit of e is the joule (J).
(ICRU 36)

Energy imparted (e)
The energy imparted by ionizing radiation to the matter in a volume is :

where
R_in =the radiant energy incident on the volume, i.e., the sum of the energies (excluding rest energies) of all those charged and uncharged ionizing particles which enter the volume,
R_out = the radiant energy emerging from the volume, i.e., the sum of the energies (excluding rest energies) of all those charged and uncharged ionizing particles which leave the volume, and,
S(Q) = the sum of all changes (decreases: positive sign, increases: negative sign) of the rest mass energy of nuclei and elementary particles in any nuclear transformations which occur in the volume.
(ICRU 33)

Energy imparted (integral dose)
The total energy absorbed from ionizing radiation in an irradiated region in a phantom or animal. It is frequently obtained by integrating the absorbed dose with respect to mass throughout an irradiated region. It may be stated in joules per kilogram or gray.
(NCRP 68)

Energy imparted (integral dose)
The total energy absorbed from ionizing radiation in an irradiated region in a phantom or patient. It may be stated in joules or kilogram rads. It is frequently obtained by integrating the absorbed dose with respect to mass throughout an irradiated region.
(ICRU 24)

Energy imparted to matter
The difference between the sum of the energies of all the ionizing particles or photons which have entered a volume and the sum of the energies of all those which have left it, minus the energy equivalent of any increase in rest mass that took place in a nuclear or elementary particle reactions within that volume. It is identical with the integral absorbed dose in that volume.
(ANSI N1.1-1976)

Energy imparted (to matter in a volume) (e)
Energy :

where:
R₁ is the radiant energy incident on the volume, i.e. the sum of the energies, excluding rest energies, of all those charged and uncharged ionizing particles which enter the volume,
R₂ is the radiant energy emerging from the volume, i.e. the sum of the energies, excluding rest energies, of all those charged and uncharged ionizing particles which leave the volume, and
SQ is the sum of all changes of the rest mass energy of nuclei and elementary particles in any nuclear transformations which occur in the volume. A positive sign is used when the change is a decrease and a negative sign when the change is an increase.
(IEC 50-393-1993)

Energy loss by radiative process (of a charged particle)
Energy loss due to the emission of radiation when a charged particle is accelerated or decelerated in an electric or magnetic field.
(IEC 50-393-1993)

Energy radiance (r)
The quotient dy by dW, where dy is the energy fluence rate or particles propagating in a specified direction within a solid angle dW.

(ICRU 33)

Energy release (of a nuclear reactor)
Total energy released as a result of a fissile products decay in a nuclear reactor core.
(IEC 50-393-1993)

Energy resolution (of a radiation spectrometer)
Measure, at a given energy, of the smallest difference between the energy of two particles capable of being distinguished by a radiation spectrometer.
(IEC 50-394-1993)

Energy threshold
The minimum energy required to induce a particular nuclear reaction.
(NCRP 94)

Energy threshold
The minimum energy required to induce a particular nuclear reaction.
(NCRP 45)

Energy transfer coefficient
Of a substance for a parallel beam of specified indirectly ionizing particles incident normally on a thin layer of this substance, the sum of the kinetic energies of all charge particles liberated in this layer divided by the layer thickness and by the sum of the kinetic energies of the incident particles. The energy transfer coefficient is a function of the energy of the radiation. According as the layer thickness is expressed in terms of length or mass per unit area, the quantity is called the linear energy transfer coefficient. The mass energy transfer coefficient can also be defined as the kerma divided by the energy fluence.
(ANSI N1.1-1976)

Energy, low or high
In this report, the kinetic energy of particles of photons. Low energy is considered as less than 10 MeV, and high energy is considered as greater than 10 MeV.
(NCRP 51)

Engineered barrier
A manmade structure or device that is intended to improve the land disposal facility's ability to meet the performance objectives in Subpart C.
(10CFR61.2)

Engineered barrier system
The waste packages and the underground facility.
(10CFR60.2)

Engineered containment
A system that has been designed with special features for the purpose of preventing or minimizing the accidental release of radioactive materials.
(NCRP 59)

Engineered safety feature (ESF)
A unit or system that is provided to directly mitigate the consequences of a DBA.
(ERDA 76-21)

Enriched fuel reactor
Reactor fueled with a nuclear fuel obtained from natural uranium, enriched with ²³⁵U, or with any other fissile fuel ²³³U, ²³⁹Pu, etc..., added to it.
(IEC 50-393-1993)

Enriched material
Material in which the concentration of one or more specified isotopes of a constituent is greater than its natural value.
(IEC 50-393-1993)

Enriched material
Material in which the concentration of one or more specified isotopes of a constituent is greater than its natural value.
(ANSI N1.1-1976)

Enriched material
Material in which the percentage of a given isotope present in a material has been artificially increased, so that it is higher than the percentage of that isotope naturally found in the material. Enriched uranium contains more of the fissionable isotope uranium-235 than the naturally occurring percentage (0.7%). (See isotopic enrichment.)
(USAEC-1974)

Enriched material
(1) Material in which the relative amount of one or more isotopes of a constituent has been increased.
(2) Uranium in which the abundance of the ²³⁵U isotope has been increased above normal.
(RHH)

Enriched uranium
Uranium with an increased abundance of ²³⁵U. Enriched uranium varies from the natural ²³⁵U abundance of 0.7% up to almost 100%. Enriched uranium also contains increased abundances of ²³⁴U and might also contain ²³⁶U and ²³³U.
(ANSI/HPS N13.22-1995)

Enriched uranium
Uranium containing more uranium-235 than the naturally occurring distribution of uranium isotopes.
(10CFR71.4)

Enriched uranium
Enriched uranium is a mixture of the isotopes U-234, U-235, and U-238 in which the abundance of the U-235 isotope is increased above 0.71 percent. The specific a activity will increase from about 1.5 x 10³ per mg to 1.4 x 10⁵ dpm per mg, as the enrichment increases from 0.71 percent to about 93 percent. In determining the average specific a activity at any particular enrichment, it should be realized that the U-234 fraction contributes the major portion of the activity above 20 percent enrichment. The term "enriched uranium" as used in this standard may apply to the metal, metallic alloys, or compounds (oxides, carbides, etc.).
(ANSI N7.2-1963)

Enrichment
1 - Process by which the isotopic concentration of one or more specific isotope in a material is increased.
2 - Isotope concentration related to a specified isotope when this concentration exceeds the natural isotope concentration.
(IEC 50-393-1993)

Enrichment
(1) The fraction of atoms of a specified isotope in a mixture of isotopes of the same element when this fraction exceeds that in the naturally occurring mixture.
(2) Any process by which the content of a specified isotope in an element is increased.
NOTE: "Enrichment" has also been taken to mean (a) enrichment factor or (b) enrichment factor minus one (degree of enrichment). These usages are to be avoided.
(ANSI N1.1-1976)

Enrichment
Isotopic enrichment.
(USAEC-1974)

Enrichment factor
Ratio of the fraction of atoms of a particular isotope in a mixture enriched in that isotope, to the fraction of atoms of that isotope in a mixture of natural composition.
(IEC 50-393-1993)

Enrichment factor
The ratio of the fraction of atoms of a particular isotope in a mixture enriched in that isotope to the fraction of atoms of that isotope in a mixture of natural composition.
(ANSI N1.1-1976)

Entrance or access point
Any location through which an individual could gain access to radiation areas or to radioactive materials. This includes entry or exit portals of sufficient size to permit human entry, irrespective of their intended use.
(10CFR20.1003)

Entrance or access point
Any location through which an individual could gain access to areas controlled for the purposes of radiation protection. This includes entry or exit portals of sufficient size to permit human entry, irrespective of their intended use.
(10CFR835.2-1993)

Envelope (equivalent) diameter
Diameter of a sphere composed of the particle bulk material and included voids that has the same mass as the particle in question.
(AM-1993)

Environment
Any area accessible to the public.
(ANSI N545-1975)

Environmental assessment
A concise public document for which the Commission is responsible that serves to:
(1) Briefly provide sufficient evidence and analysis for determining whether to prepare an environmental impact statement or a finding of no significant impact.
(2) Aid the Commission's compliance with NEPA when no environmental impact statement is necessary.
(3) Facilitate preparation of an environmental impact statement when one is necessary.
(10CFR51.14)

Environmental assessment model
A type of model specifically designed to address questions formulated in the context of an environmental assessment. Environmental assessment models are usually less complex mathematically than are models used as tools in research.
(NCRP 123I)

Environmental conditions
Physical conditions such as : ambient temperature, pressure, radiation, humidity, chemical spray expected as a result of normal operating requirements and postulated initiating events.
(IEC 50-393-1993)

Environmental document
An environmental assessment, an environmental impact statement, a finding of no significant impact, an environmental report and any supplements to or comments upon those documents, and a notice of intent.
(10CFR51.14)

Environmental exposure
Exposure to radiation through environmental pathways.
(NCRP 118)

Environmental exposure
Exposure to radiation in nonoccupational situations.
(NCRP 78)

Environmental impact statement
A detailed written statement as required by section 102(2)(C) of NEPA.
(10CFR51.14)

Environmental monitoring
Environmental monitoring is conducted outside the site giving rise to the exposure. It is convenient to draw a distinction between source-related environmental monitoring and person-related environmental monitoring.
(ICRP 43)

Environmental radioactive aerosol monitor
Radioactive aerosol monitor which is used for the continuous measurement of the radioactive emission in a given time interval from aerosols in the environmental air.
(IEC 50-394-1993)

Environmental radiological protection program (ERPP)
The totality of plans, resources, procedures, personnel and equipment used to protect public health and safety and the environment during normal operations from radiological hazards associated with DOE activities and to achieve compliance with the provisions of this part with the goal being to integrate radiological protection of the public and the environment into activities conducted to accomplish the DOE missions.
(10CFR834.2)

Environmental radiological protection program plan (ERPP plan)
A documented description of the Environmental Radiological Protection Program. The ERPP Plan may be a separate plan or part of a site-wide management plan and may contain references to separate documents containing detailed procedures or practices, and/or copies of detailed procedures, schedules, plans, or any other information germane and useful to demonstrating compliance.
(10CFR834.2)

Environmental surveillance
The collection and analysis of samples of air, water, soil, foodstuffs, biota, or other media from DOE sites and their environs and the measurement of external radiation and radioactive materials for purposes of demonstrating compliance with applicable standards, assessing radiation exposures to members of the public, and assessing effects, if any, on the local environment.
(10CFR834.2)

Environs
The uncontrolled area at or near the site boundary.
(ANSI N320-1979)

Enzyme
Numerous complex proteins that are produced by living cells and catalyze specific biochemical reactions at body temperatures.
(HPJ 60)

Enzyme
A biological catalyst of great specificity for a particular substance (substrate) or of a particular group of closely related substances which generally activates or accelerates a biochemical reaction.
(RHH)

Epicadmium
Having energy above the effective cadmium cutoff energy.
(ANSI N1.1-1976)

Epicadmium neutron
Neutron of kinetic energy greater than the effective cadmium cut-off energy.
(IEC 50-393-1993)

Epidemiology
The study of the distribution and determinants of disease in human populations.
(NCRP 114)

Epidemiology
The study of the determinants of the frequency of disease in man. The two main types of epidemiological studies of chronic disease are cohort (or follow-up) studies and case control (or retrospective) studies.
(BEIR V)

Epidemiology
The division of medical science concerned with defining and explaining the interrelationships of the host, agent and environment in causing disease.
(ENV RAD)

Epidemiology
The study of health and illness in human populations.
(NCRP 78)

Epidermis
The outermost layer of cells of the skin.
(RHH)

Epiglottis
Saddle-shaped plate of cartilage, covered with mucous membrane at the root of the tongue, that folds back over the aperture of the larynx, closing it during the act of swallowing.
(NCRP 125)

Epilation
Temporary or permanent removal of hair.
(NBS 63)

Epilation (depilation)
The temporary or permanent removal or loss of hair.
(RHH)

Epiphaniometer
An instrument that measures the surface area of aerosol particles.
(AM-1993)

Epithelial Serous Cell
Found in the trachea and extrapulmonary bronclu of the rat (the function of this cell is unknown although it might contribute to the periciliary liquid layer found beneath the tracheobronchial mucus).
(NCRP 125)

Epithelium
A membranous cellular tissue that covers the surface of some organ or part of the body.
(BEIR IV)

Epithelium
The surface cells that line the airways.
(NCRP 78)

Epithelium
A term applied to cells that line all canals and surfaces having communication with external air; also, cells specialized for secretion in certain glands as the liver, kidneys, etc.
(RHH)

Epithelium
The purely cellular, nonvascular layer covering all the free surfaces of the body, cutaneous, mucous, and serous, including the glands and other structures derived therefrom.
(NBS 63)

Epithermal neutron
Neutron of kinetic energy greater than that of thermal agitation.
(IEC 50-393-1993)

Epithermal neutron
An intermediate neutron.
(USAEC-1974)

Epithermal reactor
Reactor in which the fissions are induced predominantly by epithermal neutrons.
(IEC 50-393-1993)

Epithermal reactor
An intermediate reactor.
(USAEC-1974)

Equilibrium
A state in which the activity of all the progeny within a decay series is equal to the parent activity. For radon progeny, equilibrium is rarely achieved and the progeny activities are usually less than the radon activity.
(NCRP 118)

Equilibrium
Equilibrium, or steady-state, conditions with respect to any quantity Q in a given region of space, are said to have been achieved when the time derivative of Q, dQ/dt, is continuously zero within the noise level of the measuring system.
(ANSI N15.54-1988)

Equilibrium
Equilibrium, or steady-state, conditions, with respect to any quantity Q in a given region of space, that are achieved when the time derivative of Q, dQ/dt, is continuously zero within the noise level of the measuring system.
(ANSI N15.22-1987)

Equilibrium
A state of balance or rest; radioactive equilibrium is the state in which the rate of formation of atoms is equal to the rate of their disintegration by radioactive decay, so that the amount of the element or isotope is constant.
(ENV RAD)

Equilibrium
Equilibrium exists when the activity of all short-lived radon daughters is equal to the parent radon activity. This is rarely achieved and the daughter activities are usually less than the radon activity.
(NCRP 78)

Equilibrium
In a radioactive series, the state which prevails when the ratios between the amounts of successive members of the series remains constant. See also: Secular equilibrium, Transient equilibrium
(RHH)

Equilibrium (secular radioactive)
A steady-state relationship between a parent radionuclide and its daughter product(s) such that their decay rates are equal.
(NCRP 97)

Equilibrium cycle (economics)
For the purpose of calculating economics of a nuclear power plant, an assumed fuel cycle in which feed material and waste materials have constant compositions.
(ANSI N1.1-1976)

Equilibrium equivalent concentration (EC)
The EC of a nonequilibrium mixture of short-lived progeny in air is that activity concentration of the parent gas in radioactive equilibrium with the concentrations of its short-lived progeny that have the same potential alpha energy concentration c_p as the nonequilibrium mixture. Units are Bq/m³.
(ENV RAD)

Equilibrium equivalent concentration (EEC)
The radon concentration, in equilibrium with its short-lived daughters, that has the same potential alpha energy per unit volume as exists in a sample mixture.
(NCRP 97)

Equilibrium equivalent concentration in air
The potential alpha energy concentration of any daughter mixture in air can also be expressed in terms of the so-called equilibrium equivalent concentration (EEC) of their mother nuclide, ²²²Rn (Rn), or ²²⁰Rn (Tn), respectively. The EEC of a non-equilibrium mixture of short-lived radon daughters in air is that activity concentration of ²²²Rn (Rn), or ²²⁰Rn (Tn), in radioactive equilibrium with its short-lived daughters, which has the same potential alpha energy concentration, c_p, as the actual non-equilibrium mixture.
(ICRP 50)

Equilibrium equivalent concentration, c_eq
The activity concentration of radon, in equilibrium with its short-lived progeny which would have the same potential alpha energy concentration as the existing non-equilibrium mixture.
(ICRP 65)

Equilibrium equivalent radon concentration (EC_Rn)
The EC_Rn of a non-equilibrium mixture of short-lived radon decay products in air is that activity concentration of radon in radioactive equilibrium with the concentrations of its short-lived decay products that has the same potential alpha energy concentration C_p as the nonequilibrium mixture to which the EC_Rn refers.
(ICRP 47)

Equilibrium equivalent radon concentration (EC_Rn)
The ECRn of a non-equilibrium mixture of short-lived Rn-daughters in air is that activity concentration of radon in radioactive equilibrium with the concentrations of its short-lived daughters that has the same potential alpha energy concentration c_p as the nonequilibrium mixture to which the EC_Rn refers.
(ICRP 32)

Equilibrium factor
An adjustment used in converting from pCi/L to working level concentration, which takes into account the possible absence of radioactive equilibrium between radon and its progeny.
(ENV RAD)

Equilibrium factor
The "equilibrium factor" F with respect to potential alpha energy is defined as the ratio of the EC_Rn to the actual activity concentration C_Rn of radon in air.
(ICRP 47)

Equilibrium factor
The "equilibrium factor" F with respect to potential a energy is defined as the ratio of the EC_Rn to the actual activity concentration c_Rn of radon in air.
(ICRP 32)

Equilibrium factor in air
The "equilibrium factor" F is defined as the ratio of the EEC to the actual activity concentration C_act of the mother nuclide in air:

(ICRP 50)

Equilibrium factor, f
The ratio of the equilibrium equivalent concentration and the radon gas concentration.
(ICRP 65)

Equilibrium fraction
The simplified factor describing the degree of radioactive equilibrium between radon and its short-lived daughters.
(NCRP 97)

Equilibrium fraction
In equilibrium, the parents and daughters have equal radioactivity, that is as many decay into a specific nuclide as decay out. When fresh radon enters a volume, the daughter products have not yet accumulated, and there is disequilibrium. The working-level definition of radon does not take into account the amount of equilibrium.
(BEIR IV)

Equilibrium or transition thickness
The depth in a sufficiently thick absorber at which a monodirectional X-ray beam, initially electron-free, produces the maximum ionization per unit volume.
(NBS 55)

Equilibrium orbit
The circle of theoretically constant radius on or near which the electrons spend most of their acceleration cycle on a circular electron accelerator.
(NBS 55)

Equilibrium tenth value layer (or half-value layer)
The thickness of a specified material that attenuates a specified radiation by a factor of ten (or two), under broad-beam conditions, in that penetration region where the radiation directional and spectral distributions are practically independent of thickness, so that a single value of the tenth-value (or half-value layer) is valid.
(NCRP 51)

Equilibrium thickness
A thickness of material, impinged upon by primary radiations, sufficient to produce a condition of secondary charged particle equilibrium in the material.
(NCRP 112)

Equilibrium, radiation
The condition in a radiation field where the energy of the radiations entering a volume equals the energy of radiations leaving that volume.
(BEIR IV)

Equilibrium, radioactive
Establishment of a radionuclide parent-daughter relationship whereby the radioactivity of the daughter radionuclide is approximately the same as that of the parent radionuclide.
(HPJ 60)

Equilibrium, radioactive secular
The conditions in which the activities of a parent and progeny in a radioactive decay chain are essentially equal.
(NCRP 103)

Equilibrium, radioactive secular
The condition in which the activities of a parent and daughter in a radioactive decay chain are (very nearly) equal.
(BEIR IV)

Equipment
Associated assemblies intended to achieve a defined final objective.
(IEC 50-394-1993)

Equipment qualification
Generation and maintenance of evidence to ensure that the equipment will operate on demand to meet the system performance and safety requirements.
(IEC 50-393-1993)

Equivalent diameter
Diameter of a sphere having the same value of a specific physical property (activity) as the particle in question.
(AM-1993)

Equivalent dose
A quantity used for radiation-protection purposes that takes into account the different probability of effects which occur with the same absorbed dose delivered by radiations with different radiation weighting factors. It is defined as the product of the average absorbed dose in a specified organ or tissue and the radiation weighting factor. The unit of equivalent dose is joules per kg and its special name is the sievert (Sv).
(NCRP 118)

Equivalent dose
The tissue or organ absorbed dose (Gy or J kg^-1) multiplied by the radiation weighting factor (w_R).
(ICRP 67)

Equivalent dose (H)
The absorbed dose averaged over a tissue or organ, D_T (rather than a point) and weighted for the radiation quality, w_R (radiation weighting factor) of the irradiating radiation, i.e., H_T,R = D_T w_R.
(NCRP 121)

Equivalent dose (H_T)
The equivalent dose, H_T,R, in tissue or organ T due to radiation R, is given by:

where D_T,R is the average absorbed dose from radiation R in tissue T and w_R is the radiation weighting factor. Since w_R is dimensionless, the units are the same as for absorbed dose, J kg^-1, and its special name is sievert (Sv). The total equivalent dose, H_T, is the sum of H_T,R over all radiation types

(ICRP 68)

Equivalent energy
The equivalent energy of radiation comprised of x rays with a range of energies, is the energy of those monoenergetic x rays which in some specified respect have the same property as the radiation.
(ICRU 17)

Equivalent focal spot size
The apparent area at the target, measured perpendicularly to the central ray, from which the x rays emerge.
(NCRP 66)

Equivalent noise charge
In a preamplifier, output noise charge quantity, in energy, corresponding to the input.
(IEC 50-394-1993)

Equivalent quanta per cubic centimeter
A unit of radiation exposure. The number of equivalent quanta per square centimeter in an X-ray beam equals the total X-ray energy crossing a square centimeter measured normally to the direction of flow, divided by the peak-value X-ray photon energy.
(NBS 55)

Equivalent square beam (equivalent field)
A beam having a square field (q.v.) which results in the same values of percentage depth dose, tissue-air ratio, or tissue-phantom ratio as a given rectangular, circular or irregular beam of the same radiation quality.
(ICRU 24)

Equivalent ton
See TNT equivalent.
(USAEC-1974)

Erg
Unit of work done by a force of one dyne acting through a distance of one cm. Unit of energy which can exert a force of one dyne through a distance of on cm. cgs units: dyne-cm or gm-cm²/sec².
(RHH)

Erg
A unit of energy in the cgs system. See kilo-electron-volts.
(NBS 55)

Error
A deviation from correctness.
(ANSI N15.54-1988)

Error
A deviation from correctness.
(ANSI N15.41-1984)

Error
The difference between a measured and a standard, or true, value.
(ANSI N545-1975)

Error of indication
Difference between the indicated value v of a quantity and the conventionally true value vc of that quantity at the point of measurement.

(IEC 50-394-1993)

Error propagation
The translation of input errors into estimates associated with modeling art; in this context, statistical and numerical error propagation techniques are the fundamental methods used to combine parameter uncertainties in an estimate of the overall uncertainty in model predictions. This process is referred to in this report as a "parameter imprecision analysis".
(NCRP 76)

Error propagation
The translation of input errors into estimates associated with assessment modeling; in this context, statistical and numerical error propagation techniques are the fundamental methods used to combine parameter uncertainties into an estimate of the overall uncertainty in model predictions. This process is referred to in this book as 'parameter uncertainty analysis.'
(NUREG/CR 3332)

Error, counting
Statistical fluctuations in results of detection of nuclear events.
(HPJ 60)

Error, random
Indefiniteness of result due to finite precision of experiment. It is a measure of fluctuations in results after repeated experimentation.
(HPJ 60)

Error, statistical
Errors in counting due to the random time-distributions of disintegration.
(RHH)

Error, statistical
Errors in counting due to the random time-distributions of disintegration.
(HPJ 60)

Error, systematic
Reproducible inaccuracy introduced by faulty equipment, calibration, or experimental technique.
(HPJ 60)

Erthyrocyte
Red blood cells.
(HPJ 60)

Erythema
A redness of the skin.
(NCRP 98)

Erythema
An abnormal redness of the skin due to distension of the capillaries with blood. It can be caused by many different agents - heat, drugs, ultraviolet rays, ionizing radiation.
(RHH)

Erythema
Reddening of the skin, primarily due to dilation of small blood vessels and also due to other tissue damage.
(NBS 63)

Erythrocyte
A red blood corpuscle.
(RHH)

Escape peak
1 - Subsidiary peak in a gamma radiation pulse height spectrum present when one or two annihilation quanta escape from the detector while the rest of the g a radiation energy is absorbed in the detector.
2 - Subsidiary peak which appears as a result of an escape of a characteristic X radiation from the detector constituent.
(IEC 50-394-1993)

Esophagus
Portion of the digestive canal between the pharynx and the stomach where it extends from the lower border of the cricoid vertebra to the cardiac orifice of the stomach.
(NCRP 125)

Estimate
A specific numerical value arrived at by the application of an estimator.
(10CFR74.4)

Estimate (noun)
A particular value obtained by applying an estimator (a mathematical function obtained by some method such as least squares or maximum likelihood) to a particular set of sample values.
(ANSI N15.36-1983)

Estimate (verb)
To follow certain statistical principles in determining values of a population's descriptors from information obtained from a sample of that population.
(ANSI N15.36-1983)

Estimated calibration equation
See calibration model.
(ANSI N15.19-1989)

Estimated measurement equation
See measurement model.
(ANSI N15.19-1989)

Estimation
Measurement of a continuous parameter such as the spatial extent or intensity of an image feature.
(ICRU 54)

Estimator
A function of a sample measurement used to estimate a population parameter.
(10CFR74.4)

Estimator
A rule or method, usually expressed as a function of sample values, used to estimate a population parameter.
(ANSI N15.36-1983)

Esu per cm²
One electrostatic unit of electric charge carried by ions of either sign, which are produced by the interaction of radiation in 1 cm³ of air at standard temperature and pressure.
(NBS 55)

ET_seq
Compartment representing prolonged retention in airway tissue of small fraction of particles deposited in the nasal passages.
(ICRP 66)

ET-extrathoracic region
Consists of anterior nose (ET₁) and the posterior nasal passages, larynx, pharynx, and mouth (ET₂).
(ICRP 66)

Eta factor
See neutron yield per absorption.
(ANSI N1.1-1976)

Etch pit
Chemically or electrochemically etched pits or holes, which are observable by the optical microscope, produced originally by the tracks of heavy charged particles on the surface of solids, e.g. plastics.
(IEC 50-393-1993)

Etched track detector
Radiation detector consisting of a material in which local damage, caused by the passage of heavy charged particles, is made visible by etching of the surface, the number of tracks being a measure of the particle fluence.
(IEC 50-394-1993)

Etiology
The science or description of cause(s) of disease.
(BEIR V)

Eugenics
The science which deals with the influences that improve the hereditary qualities of a race or breed.
(RHH)

Euploid
Having uniform exact multiples of the haploid number of chromosomes.
(BEIR IV)

Euploid
Having uniform exact multiples of the haploid number of chromosomes.
(BEIR V)

Euryhaline
Marine organisms capable of withstanding wide variations in osmotic pressure of salinity.
(NCRP 109)

Eutrophic
Bodies of water rich in nutrients and containing a minimal amount of dissolved oxygen, usually a shallow lake, with abundant organic matter.
(NCRP 109)

Eutrophic
Waters with good supply of nutrients and hence a rich organic production.
(NCRP 76)

EVA
Extravehicular activity; any activity undertaken by the crew outside a space vehicle.
(NCRP 98)

Evaluated absorbed dose index, (D'_I)
The absorbed-dose index as evaluated from a dosimeter by the processor.
(ANSI N13.15-1985)

Evaluation
The process of determining whether a particular deviation could create a substantial safety hazard or determining whether a failure to comply is associated with a substantial safety hazard.
(10CFR50.2)

Evaluation
Interpretation of measurements and observations, including determination of compliance with applicable specifications.
(ANSI N42.17C-1989)

Evaluation
Interpretation of measurements and observations, including determination of compliance with applicable specifications.
(ANSI N42.17A-1989)

Evaluation
Interpretation of measurements and observations, including determination of compliance with applicable specifications.
(ANSI N42.17B-1989)

Evaluation level
An activity level in the body or excreta at which the measurement results are examined for validity by a review of workplace monitoring results or additional bioassay monitoring. (The magnitudes of this level differ in ICRP 54 and have different nomenclature in that document.)
(ANSI/HPS N13.22-1995)

Evaporated sample liquid activity meter
Assembly designed to measure the radioactive emission per unit volume in a given time interval in a liquid and utilizing for this purpose residues of evaporated samples.
(IEC 50-394-1993)

Evaporation
Process with more vapor molecules leaving a particle's surface than arriving at the surface, resulting in shrinkage of the particle.
(AM-1993)

Evaporative centrifuge (isotope separation)
A separating device in which a mixture to be separated is introduced into the centrifuge as a liquid. The vapors are removed at a point near the axis of the centrifuge, having been separated by diffusion through the centrifugal field.
(ANSI N1.1-1976)

Excess cases
The difference between the number of cases of thyroid cancer occurring in an irradiated population and the number of thyroid cases occurring in a similar non-irradiated population over the same time period.
(NCRP 80)

Excess reactivity
More reactivity than that needed to achieve criticality. Excess reactivity is built into a reactor (by using extra fuel) in order to compensate for fuel burnup and the accumulation of fission-product Poisons during operation. (See criticality, reactivity.)
(USAEC-1974)

Excitation
Process by which an atom or a nucleus is transferred from one energy level to a higher energy level.
(IEC 50-393-1993)

Excitation
The addition of energy to a system, thereby transferring it from its ground state to an excited state. Excitation of a nucleus, an atom, or a molecule can result from absorption of photons or from inelastic collisions with other particles.
(RHH)

Excited state
The state of a molecule, atom, electron or nucleus when it possesses more than its normal energy. Excess nuclear energy is often released as a gamma ray. Excess molecular energy may appear as fluorescence or heat.
(USAEC-1974)

Exclusion
The removal of counsel representing multiple interests from an interview whenever the NRC official conducting the interview has concrete evidence that the presence of the counsel would obstruct and impede the particular investigation or inspection.
(10CFR19.3)

Exclusion area
That area surrounding the reactor, in which the reactor licensee has the authority to determine all activities including exclusion or removal of personnel and property from the area. This area may be traversed by a highway, railroad, or waterway, provided these are not so close to the facility as to interfere with normal operations of the facility and provided appropriate and effective arrangements are made to control traffic on the highway, railroad, or waterway, in case of emergency, to protect the public health and safety. Residence within the exclusion area shall normally be prohibited. In any event, residents shall be subject to ready removal in case of necessity. Activities unrelated to operation of the reactor may be permitted in an exclusion area under appropriate limitations, provided that no significant hazards to the public health and safety will result.
(10CFR50.2)

Exclusion area
An area defined by a qualified expert to be restricted to all personnel during operation of an accelerator.
(ANSI N43.1-1978)

Exclusion area
An area defined by the radiation protection officer to be forbidden to all personnel during operation of the accelerator.
(NCRP 51)

Exclusion area
The area around a nuclear or radiation facility to which access is controlled.
(ANSI N1.1-1976)

Exclusion area
An area immediately surrounding a nuclear reactor where human habitation is prohibited to assure safety in the event of accident. (See low population zone.)
(USAEC-1974)

Exclusive use
The sole use of a conveyance by a single consignor and for which all initial, intermediate, and final loading and unloading are carried out in accordance with the direction of the consignor or consignee.
(10CFR71.4)

Exclusive use (also referred to in other regulations as sole use or full load)
The sole use of a conveyance by a single consignor and for which all initial, intermediate, and final loading and unloading are carried out in accordance with the direction of the consignor or consignee.
(10CFR71.4)

Exclusive use (sole use or full load)
The sole use of a conveyance by a single consignor and for which all initial, intermediate, and final loading and unloading are carried out in accordance with the direction of the consignor or consignee. Any loading must be performed by personnel having radiological training and resources appropriate for safe handling of the consignment. Specific instructions for maintenance of exclusive use shipment controls must be issued in writing and included with the shipping paper information provided to the carrier by the consignor.
(49CFR173.403)

Exclusive-use
The sole use of a barge by a single consignor and upon which all initial, intermediate, and final loading and unloading operations are carried out in accordance with the direction of the consignor or consignee.
(ANSI N14.24-1985)

Excretion function
A function describing the time dependence of the quantity of material in a compartment, in an organ or in urine or feces per day.
(ICRP 54)

Excursion
A sudden, very rapid rise in the power level of a reactor caused by supercriticality. Excursions are usually quickly suppressed by the negative temperature coefficient of the reactor and/or by automatic control rods. (See safety rod, scram, temperature coefficient of reactivity.)
(USAEC-1974)

Excursion, power
See excursion, reactor.
(ANSI N1.1-1976)

Excursion, reactor
Very rapid increase of reactor power above the normal operating level. This increase may be deliberately caused for experimental purposes or it may be accidental.
(ANSI N1.1-1976)

Executive Branch
The Departments of State, Energy, Defense and Commerce and the Arms Control and Disarmament Agency.
(10CFR110.2)

Exercise
An event that tests the integrated capability and a major portion of the basic elements existing within emergency preparedness plans and organizations.
(ANSI/ANS-3.8.1-1987)

Exhalation
In this report, the transport of radon from the surface of soil or other material into the atmosphere.
(NCRP 97)

Exhalation rate
The rate at which radon is released from a solid surface into the adjacent air, in Bq/m²/s. It is a function of the radon production rate and the diffusion coefficient of the solid.
(ENV RAD)

Exhalation valve
A device which allows exhaled air to leave a respirator and prevent outside air from entering through the valve.
(ANSI Z88.2-1969)

Exhalation valve
A device which allows exhaled air to leave a respirator and prevent outside air from entering through the valve.
(ANSI Z88.2-1980)

Exhaust hood
A structure to enclose or partially enclose a contaminant-producing operation or process, or to guide air flow in an advantageous manner to capture a contaminant, which is connected to a duct, pipe, or channel which removes the contaminant from the hood.
(ANSI Z9.2-1971)

Exhaust rates
Volume rate of flow to be exhausted from specific contaminant-producing operations in order to prevent exceeding of the safe level of contaminant concentration.
(ANSI Z9.2-1971)

Exhaust system
A system for removing contaminated air from a space, comprising one or more of the elements of exhaust hoods, duct work, air-cleaning equipment, exhauster, and stack. An exhaust system operates as a functional entity, and the performance of all parts is affected by the design and performance of all other parts.
(ANSI Z9.2-1971)

Existing impoundment
Any uranium mill tailings impoundment which is licensed to accept additional tailings and is in existence as of December 15, 1989.
(40CFR61.251)

Existing source
Any stationary source which is not a new source.
(40CFR61.02)

Exit dose
The absorbed dose delivered by a single fixed beam of radiation to the surface of the animal through which the beam re-emerges.
(ICRU 30)

Exit dose
The absorbed dose delivered by a single fixed beam of radiation to the surface of the animal through which the beam re-emerges.
(ICRU 24)

Exit dose
Dose of radiation at the surface of the body opposite to that on which the beam is incident.
(RHH)

Exoelectron
Electron having energy of approximately 1 eV, emitted by thermal or optical stimulations from solid metal surfaces, semiconductors or insulators, excited by irradiation with gamma radiation, X radiation or ultraviolet radiation or charged particles.
(IEC 50-393-1993)

Exoergic
That which liberates energy.
(RHH)

Exoergic, exothermal
Characterized by the production of energy or heat.
(NCRP 51)

Expanded and aligned radiation field
A uniform, unidirectional field with fluence and its energy distribution equal to that of the actual field at the point of reference.
(ICRU 43)

Expanded field
In the expanded field, the fluence and energy distribution have the same values used throughout the volume of interest as in the actual field at the point of reference.
(ICRP 51)

Experimental hole
See channel, irradiation.
(ANSI N1.1-1976)

Experimental reactor
Reactor operated primarily to obtain reactor physics or engineering data for the design or development of a reactor or reactor type.
(IEC 50-393-1993)

Experimental reactor
A reactor to test the design of new reactors.
(USAEC-1974)

Expiratory Reserve Volume
Largest amount of air that can be forced out of the lungs after a normal breath has been let out; includes the tidal volume expired down to the residual volume
(NCRP 125)

Explosive material
Any chemical compound, mixture, or device, which produces a substantial instantaneous release of gas and heat spontaneously or by contact with sparks or flame.
(10CFR61.2)

Exponential absorption
Absorption of a beam of particles according to the relation

where I is the radiation quantity being considered, I_o is the initial value of the quantity, x is the amount of material traversed (length, mass per unit area, moles per unit area, or atoms per unit area), and µ is the corresponding absorption coefficient.
(ANSI N1.1-1976)

Exponential assembly
Subcritical assembly used for an exponential experiment.
(IEC 50-393-1993)

Exponential assembly
A subcritical assembly used for an exponential experiment.
(ANSI N1.1-1976)

Exponential decay
The decrease in the radioactivity of a sample in accordance with the equation

where A and A_o are the activities present at times t and zero, respectively, and l is the characteristic decay constant.
(ANSI N1.1-1976)

Exponential experiment
Experiment, performed with a subcritical assembly of reactor materials, and an independent neutron source, used to determine the neutron characteristics of a configuration of these materials.
(IEC 50-393-1993)

Exponential experiment
An experiment, performed with a subcritical assembly of reactor materials. and an independent neutron source, used to determine the neutron characteristics of a configuration of these materials. With the usual placement of the neutron source (i.e., thermal neutrons introduced through one face of a cube or cylinder) the neutron flux in the assembly decreases exponentially with distance from the boundary adjacent to the source.
(ANSI N1.1-1976)

Exponential pile
See exponential assembly.
(ANSI N1.1-1976)

Exponential survival curve
A survival curve without a shoulder which appears as a straight line when plotted in semi-log coordinates.
(ICRU 30)

Export
Export from the United States.
(10CFR110.2)

Exposure
Being exposed to ionizing radiation or to radioactive material.
(10CFR20.1003)

Exposure
In this Report, exposure is often used in its more general sense and not as the specifically defined radiation quantity. In the formal sense, a measure of the quantity of x or gamma radiation based on its ability to ionize air through which it passes.
(NCRP 118)

Exposure
In this Report, exposure is used in its more general sense of "the condition of being subject to radiation" and not as the specifically defined radiation quantity for x rays.
(NCRP 114)

Exposure
A quantitative measure of x or gamma radiation at a certain place, based on its ability to produce ionization in air. The former special unit of exposure was the roentgen (R). 1R = 2.58 x 10^-4 C/kg. In the international system (SI), the special unit is coulomb per kilogram. ("Exposure" also is frequently used as a synonym for irradiation).
(NCRP 111)

Exposure
A measure of the ionization produced in air by x- or gamma-radiation. It is the sum of the electrical charges on all of the ions of one sign produced in air when all electrons liberated by photons in a volume element of air are completely stopped in the air, divided by the mass of the air in the volume element. The special unit of exposure is the roentgen.
(HPJ 60)

Exposure
In this report, exposure is used most often in its more general sense and not as the specifically defined radiation quantity. In certain instances "exposure" is used in a formal sense as a measure of the quantity of x or gamma radiation based upon its ability to ionize air through which it passes. The SI unit of exposure is coulomb per kilogram.
(NCRP 107)

Exposure
A measure of the ionization produced in air by x- or gamma-radiation. Exposure is the sum of electric charges on all ions of one sign produced in air when all electrons liberated by photons in a volume of air are completely stopped, divided by the mass of the air in the volume. The unit of exposure in air is the roentgen (R) or in SI units, coulombs per kg (C kg^-1).
Acute exposure: Radiation exposure of short duration.
Chronic exposure: Radiation exposure of long duration, because of fractionation or protraction.
(NCRP 98)

Exposure
The incidence of ionizing radiation on living or inanimate material. Also, the measure of the ionization produced in a specified mas of air by x or gamma radiation, which may be used as a measure of the ionizing radiation to which one is exposed. When using SI units, air kerma is often used in place of exposure. Air kerma has the units of J kg^-1 (gray). In conventional units, the special unit of exposure is the roentgen, R. An exposure of 1 R corresponds to an air kerma of 8.7 mGy. (See kerma, gray, roentgen).
(NCRP 105)

Exposure
In this report, exposure is used in its more general sense and not as the specifically defined radiation quantity. It is not specifically limited to exposure to x-rays.
(NCRP 101)

Exposure
(1)The act or instance of exposing, or
(2) The condition or being or having been exposed. It is used in ANSI N13.15 to describe beta or neutron irradiations as well as photon irradiations.
(ANSI N13.15-1985)

Exposure
A quantitative measure of the radiation experienced by a film dosimeter that, for ionizing radiation, is usually reported in terms of the dose equivalent in the body immediately beneath the dosimeter.
(ANSI N13.7-1983)

Exposure
Exposure, X, is a dosimetric quantity for ionizing electromagnetic radiation, based on the ability of the radiation to produce ionization in air. The exposure is the absolute value of the total charge of the ions of one sign produced in air when all the electrons liberated by photons per unit mass of air are completely stopped in air. The SI unit of exposure is coulomb per kilogram (C kg^-1). The former special unit of exposure was roentgen (R), with
1 R = 2.58 x 10^-4 C kg^-1 (exactly).
(ICRP 33)

Exposure
The exposure is defined as X = DQ/Dm, where DQ is the sum of the electrical charges on all the ions of one sign produced in air when all the electrons liberated by photons in a volume element of air whose mass is Dm are completely stopped in air (See also "roentgen").
(NCRP 69)

Exposure
A measure of the ionization produced in air by x or gamma radiation; the sum of electric charges on all ions of one sign produced in air when all electrons liberated by photons in a volume of air are completely stopped in air, divided by the mass of the air in the volume; a unit of exposure in air is the roentgen (abbr., R).
Acute exposure - Radiation exposure of short duration.
Chronic exposure - Radiation exposure of long duration, because of fractionation or protraction.
(BEIR III)

Exposure
A measure of x or gamma radiation based upon the ionization produced in air by x or gamma rays. The special unit of exposure is the roentgen. (For radiation protection purposes of NCRP 49, the number of roentgens may be considered to be numerically equivalent to the number of rads or rems.)
(NCRP 51)

Exposure
(1) For x or gamma radiation in air, the sum of the electrical charges of all of the ions of one sign produced in air when all electrons liberated by photons in a suitably small element of volume of air are completely stopped in air, divided by the mass of the air in the volume element. It is commonly expressed in roentgens.
(2) The incidence of radiation on living or inanimate material, by accident or intent.
(ANSI N1.1-1976)

Exposure
A measure of x or gamma radiation at a certain place, based on its ability to produce ionization in air. The unit of exposure is the roentgen (R).
(NCRP 48)

Exposure
The quotient of dQ by dm, where dQ is the absolute value of the total charge of ions of one sign produced in air when all the electrons (negatrons and positrons) liberated by photons in a volume element of air having mass dm are completely stopped in air. The special unit of exposure in the roentgen (R). 1 R = 2.58 x 10^-4 C kg^-1.
(ANSI N545-1975)

Exposure
A measure of the ionization produced in air by x or gamma radiation. It is the sum of the electrical charges on all ions of one sign produced in air when all electrons liberated by photons in a volume element of air are completely stopped in air, divided by the mass of the air in the volume element. The special unit of exposure is the roentgen.
(BEIR I)

Exposure
The exposure of x or gamma rays is the total charge produced due to ionization in air by electrons that are ejected per unit mass of air. The special unit of exposure is the roentgen.
(NCRP 38)

Exposure
Exposure (X) is the term reserved for the quantitative assessment of ionizing electromagnetic radiation fields. The exposure at a given place is a measure of the radiation based upon its potential ability to produce ionization in air. The special unit of exposure is the roentgen (R). One roentgen is the exposure of x- or g-radiation such that the associated corpuscular emission per kilogram of air produces, in air, ions carrying 2.58 x 10^-4 coulombs of electric charge of either sign. For a wide range of energies one roentgen will result in an absorbed dose in soft tissue of approximately one rad under conditions of charged particle equilibrium.
(ICRP 15)

Exposure
See exposure dose.
(NBS 73)

Exposure
See dose (measured in air, without backscatter).
(NBS 54)

Exposure
The total quantity of radiation at a given point, measured in air. The measurement of exposure is made at a given point in the radiation field without the presence of a scattering body.
(NBS 51)

Exposure (internal)
The situation leading to intake of a radionuclide, and/or the situation existing after a radionuclide has been deposited in an organ or tissue.
(FGR 11)

Exposure (X)
Quotient of dQ by dm, where the value of dQ is the absolute value of the total charge of the ions of one sign produced in air when all the electrons, negatrons and positrons, liberated by photons in air of mass dm are completely stopped in air.

(IEC 50-393-1993)

Exposure (X)
A measure of the quantity of x or gamma radiation based upon its ability to ionize air through which it passes. The SI unit of exposure is coulomb per kilogram. The previously used special unit of exposure, roentgen (R), is being phased out. 1R = 2.58 x 10^-4 C kg^-1 (exactly). The physical quantity exposure is being replaced by the quantity air kerma in air.
(NCRP 102)

Exposure (X)
The quotient dQ by dm, where dQ is the absolute value of the total charge of the ions of one sign produced in air when all the electrons (negatrons and positrons) liberated by photons in air of mass dm are completely stopped in air.

(ICRP 51)

Exposure (X)
The measure of the radiation impinging on the site of interest as measured in air,

where dQ is the absolute value of the total charge of ions of one sign produced in air when all the electrons (negatrons and positrons) liberated by photons in air of mass dm are completely stopped in air. The traditional unit of exposure is the roentgen (R). The SI unit of exposure is C kg^-1, where C stands for coulomb.
(NCRP 83)

Exposure (X)
The exposure, X, is the quotient dQ by dm, where dQ is the absolute value of the total charge of the ions of one sign produced in air when all the electrons liberated by photons in a volume element of air of mass dm are completely stopped in air.

(ICRU 30)

Exposure (X)
The exposure, X, is the quotient dQ by dm, where dQ is the absolute value of the total charge of the ions of one sign produced in air when all the electrons (negatrons and positrons) liberated by photons in a volume element of air of mass dm are completely stopped in air.

The special unit of exposure is the roentgen (R). 1 R = 2.58 x 10^-4 C kg^-1 (exactly).
(ICRU 19)

Exposure (X)
A measure of the ability of a particular field of electromagnetic radiation, i.e., x rays or gamma rays, to ionize air. These radiations interact with the molecules in the air to produce electrons which in turn ionize the air. The special unit of exposure is the roentgen, symbol R, this being 2.58 x 10^-4 coulombs per kilogram of air.
(ICRU 20)

Exposure (X)
The quotient DQ by Dm, where DQ is the sum of the electrical charges on all the ions of one sign produced in air when all the electrons (negatrons and positrons), liberated by photons in a volume element of air whose mass is Dm, are completely stopped in air.

The special unit of exposure is the roentgen (R).
1 R = 2.58 x 10^-4 C/kg.
(NBS 92)

Exposure cycle
The period between the preexposure annealing and the readout of the phosphor.
(ANSI N545-1975)

Exposure device
A shield in the form of a package designed to contain and allow the controlled use of one or more sources for the purpose of making radiographic exposures.
(ANSI N432-1980)

Exposure dose
The exposure dose of X- or gamma radiation at a certain place is a measure of the radiation that is based upon its ability to produce ionization in air. The unit of exposure dose is the roentgen. (When the meaning is clear, this term may be shortened to "exposure").
(NBS 73)

Exposure dose
Exposure dose of X- or gamma radiation at a certain place is a measure of the radiation which is based upon its ability to produce ionization.
(NBS 63)

Exposure dose rate (exposure rate)
Exposure dose per unit time.
(NBS 73)

Exposure head
A device that locates the gamma radiography sealed source in the selected working position. (An exposure head is also known as a source stop.)
(10CFR34.3)

Exposure head
A device which locates the sealed source at the desired focal position. It may be a separable unit or an integral part of a source guide tube.
(ANSI N432-1980)

Exposure limits
The maximum radiation dose equivalent permitted under specified conditions.
(ANSI N13.6-1966)

Exposure Pathway
Mode of intake (e.g., inhalation, ingestion, absorption).
(HPS N13.42-1997)

Exposure rate
The exposure per unit time.
(NCRP 69)

Exposure rate
The exposure per unit time.
(ANSI N43.2-1977)

Exposure rate
The exposure per unit time.
(NCRP 49)

Exposure rate
The exposure per unit time.
(ANSI N1.1-1976)

Exposure rate
The exposure per unit time.
(NCRP 48)

Exposure rate
The quotient of DX by Dt, where DX is the increment of exposure in time Dt.

(NBS 92)

Exposure rate
The amount of radiation (exposure) delivered at a given point per unit time.
(NBS 51)

Exposure rate ()
Quotient of dX by dt, where dX is the increment of exposure in the time interval dt.

(IEC 50-393-1993)

Exposure rate ()
The quotient of dX by dt, where dX is the increment of exposure in the time interval dt.

(ICRU 33)

Exposure rate ()
The quotient of dX by dt, where dX is the increment of exposure in the time interval dt.

A special unit of exposure rate is any quotient of the roentgen or its multiple or submultiple by a suitable unit of time (R s^-1, R min^-1, mR h^-1, etc.).
(ICRU 19)

Exposure rate constant (G_d)
The exposure rate constant, G_d, of a radioactive nuclide emitting photons is the quotient of l²(dX/dt)_d by A, where (dX/dt)_d is the exposure rate due to photons of energy greater than d, at a distance l from a point source of this nuclide having an acitivity A.

The special units of exposure rate constant are Rm²h^-1Ci^-1 or any convenient multiple of these.
(ICRU 19)

Exposure route
A pathway by which radiation reaches, or radioactive material enters, the body. The main internal exposure routes are inhalation, ingestion, absorption through the skin and entry through a cut or wound in the skin.
(NCRP 114)

Exposure route
A pathway by which a radionuclide or other toxic material can enter the body. The main exposure routes are inhalation, ingestion, absorption through the skin, and entry through a cut or wound in the skin.
(HPJ 60)

Exposure time
The time interval in a radiological examination within which x rays are incident upon the body part under examination.
(NCRP 66)

Extended source
A source of particles or photons which cannot be considered a point source, e.g., whose linear dimensions are greater than 1/10 the distance between source and observation point.
(NCRP 51)

Extended-medium filter
A filter having a pleated medium or a medium in the form of bags, socks, or other shape to increase the surface area relative to the frontal area of the filter.
(ERDA 76-21)

Extension link
A load-bearing member that provides for a desired change in spacing between the container aid the crane hook.
(ANSI N14.6-1986)

Extension of emergency access
An extension of the access that had been previously granted by NRC to an operating non-Federal or regional low-level radioactive waste disposal facility or facilities for a period not to exceed 180 days.
(10CFR62.2)

External audit
An audit of those portions of another organization's quality assurance program not under the direct control or within the organizational structure of the auditing organization.
(ANSI N46.2-1978)

External cathode counter tube
Counter tube, the envelope of which is generally of glass and the cathode of which is a carbon or metal coating on the external surface of this envelope.
(IEC 50-394-1993)

External dose
That portion of the dose equivalent received from radiation sources outside the body.
(10CFR20.1003)

External dose or exposure
That portion of the dose equivalent received from radiation sources outside the body (i.e., "external sources").
(10CFR835.2-1998)

External dose or exposure
That portion of the dose equivalent received from radiation sources (e.g., "external sources") outside the body.
(10CFR835.2-1993)

External dose rate conversion factor
A factor which when multiplied by the radionuclide concentration in air or on a contaminated surface gives the dose rate from external sources to a specific organ in the body.
(NUREG/CR 3332)

External dosimetry
Deals with the calculation of absorbed dose from radiation that originates outside the body.
(NUREG/CR 3332)

External irradiation
Exposure of the body to ionizing radiation from outside.
(ICRP 36)

External radiation
See radiation.
(HPJ 60)

External radiation
Radiation from a source outside the body.
(BEIR I)

Extinction
The removal of light by absorption and scattering.
(TID-26608)

Extinction coefficient
A measured parameter given by the amount of light scattered and absorbed by a particle divided by the amount incident upon it.
(AM-1993)

Extracarmeral
Pertaining to that portion of the instrument exclusive of the detector.
(ANSI N42.17A-1989)

Extracarmeral
Pertaining to that portion of the instrument exclusive of the detector.
(ANSI N42.17C-1989)

Extracarmeral
Pertaining to that portion of the instrument exclusive of the detector.
(ANSI N320-1979)

Extracarmeral
Pertaining to that portion of the instrument exclusive of the detector.
(ANSI N323-1978)

Extracarmeral effect
Apparent response of an instrument by radiation on any other portion of the system than the detector.
(ANSI N42.18-1974)

Extracarmeral effect
Apparent response of an instrument by radiation on any other portion of the system than the detector.
(ANSI N13.10-1974)

Extracarmeral response
An instrument response arising from the action of the radiation field on parts of the instrument other than the intended radiosensitive element.
(ANSI N317-1980)

Extraction cycle
A series of steps involving solvent extraction, stripping, and in some cases scrubbing.
(ANSI N1.1-1976)

Extrapolated boundary
Hypothetical surface outside an assembly on which the neutron fluence rate would be zero if extrapolated from the flux distribution neglecting the distribution within a few mean free paths of the physical surface.
(IEC 50-393-1993)

Extrapolated boundary
A hypothetical surface outside an assembly on which the neutron flux density would be zero if extrapolated from the flux distribution neglecting the distribution within a few mean free paths of the physical surface.
(ANSI N1.1-1976)

Extrapolated range
The distance from a radiation source given by extrapolation to zero flux density of a tangent to the flux density-versus-distance curve taken at that point where the flux density has decreased to one-half its initial value.
(ANSI N1.1-1976)

Extrapolation
The projection of model calculations to situations outside the realm of past experience or known data. Model calculations performed within the realm of experience and pertinent data are considered to be interpolations unless verified by measurement.
(NCRP 123I)

Extrapolation distance
In the one group theory of neutron transport: the distance beyond the boundary of a medium to a point at which the asymptotic neutron flux density would go to zero if it were represented by the same function as within the boundary. NOTE: The asymptotic flux density is the flux density far from boundaries, localized sources, and localized absorbers.
(ANSI N1.1-1976)

Extrapolation distance, linear
In the one-group theory of neutron transport, the distance beyond the boundary of a medium to a point at which the tangent to the asymptotic neutron flux density at the boundary goes to zero. NOTE: The asymptotic flux density is the flux density far from boundaries, localized sources, and localized absorbers.
(ANSI N1.1-1976)

Extrapolation ionization chamber
Ionization chamber in which one of the characteristics can be varied, normally the spacing between electrodes, in order to extrapolate the chamber response to zero sensitive mass.
(IEC 50-394-1993)

Extrathoracic
Region of the respiratory system above the larynx, containing the nose and the mouth.
(AM-1993)

Extrathoracic (ET) airways
Consists of anterior nose (ET₁) and the posterior nasal passages, larynx, pharynx and mouth (ET₂).
(ICRP 68)

Extreme environment
An environment likely to occur in health physics practice but beyond the scope of routine conditions with regard to the physical or radiation environment exposure.
(ANSI N42.17C-1989)

Extreme environment
One in which ambient temperature or humidity or both outside a specified range of values.
(ANSI N42.17B-1989)

Extremity
Hand, elbow, arm below the elbow, foot, knee, or leg below the knee.
(10CFR20.1003)

Extremity
The hand, the elbow, the arm below the elbow, the knee, the leg below the knee, and the foot.
(HPS N13.41-1997)

Extremity
Hands and arms below the elbow or feet and legs below the knee.
(10CFR835.2-1993)

Extrinsic semiconductor
A semiconductor having impurities or other imperfections and in which the charge carrier densities of each sign are different.
(IEC 50-394-1993)

Eye dose equivalent
Applies to the external exposure to the lens of the eye and is taken as the dose equivalent at a tissue depth of 0.3 centimeter (300 mg/cm²).
(10CFR20.1003)

Eyepiece
A gas-tight transparent window(s) in a full facepiece, helmet, hood or suit, through which the wearer may see.
(ANSI Z88.2-1980)

Eyepiece
A gas-tight transparent window(s) in a full facepiece through which the wearer may see.
(ANSI Z88.2-1969)

Note: References shown in ()