Borders' Dictionary of Health Physics

I/g
Roentgens per millicurie-hour at 1 cm from an unshielded point source of any particular gamma-emitting radioisotope.
(NBS 54)

I₀
Activity of particles present in the volume of ambient air to be inspired = C_AtB.
(ICRP 66)

IAEA
The International Atomic Energy Agency.
(10CFR110.2)

IAEA
The International Atomic Energy Agency or its duly authorized representatives.
(10CFR75.4)

IAEA material balance area
An area established for IAEA accounting purposes, such that:
(1) The quantity of nuclear material in each transfer into or out of each material balance area can be determined; and
(2) The physical inventory of nuclear material in each material balance area can be determined when necessary in accordance with specified procedures.
(10CFR75.4)

Iamina Propria
Connective tissue layer of the mucous membrane in humans.
(NCRP 125)

ICDA
The International Classification of Diseases Adapted for use in the U.S. The ICDA is periodically revised by the World Health Organization; the 8th ICDA is adapted from the 8th ICD and was issued in 1972.
(BEIR V)

ICRP
An abbreviation for the name of the International Commission on Radiological Protection, an international organization formed by the International Congress of Radiology in 1928 to develop recommendations for protection against ionizing radiation. Reports of the ICRP that are pertinent to this standard have been referred to by report number; these reports are listed in the references presented in the last appendix to this standard.
(ANSI/HPS N13.22-1995)

ICRP (International Commission on Radiological Protection)
An international organization whose primary function is to prepare recommendations to deal with the basic principles of radiation protection. The ICRP's policy is to "leave to the various national protection committees the responsibility of introducing the detailed technical regulations, recommendations, or codes of practice best suited to the needs of the individual countries."
(HPJ 60)

ICRU sphere
A 30-cm diameter tissue-equivalent sphere with a density of 1 g cm^-3 and a mass composition of 76.2% oxygen, 11.1% carbon, 10.1% hydrogen and 2.6% nitrogen.
(ICRU 39)

Ideal fluid
A hypothetical fluid having no viscosity.
(AM-1993)

Ideal observer
The ideal observer is the Bayesian decision maker who minimizes the "cost" or "risk" when determining a decision strategy for a given task.
(ICRU 54)

Identification under the agreement
Identification by the IAEA pursuant to Article 39(b) of the principal text of the Agreement of Article 2(a) of the Protocol.
(10CFR75.4)

Igneous rock
Rock formed by the cooling of liquid material; for example, basalt and granite.
(ENV RAD)

Image intensifier
An x-ray image receptor which increases the brightness of a fluorosopic image by electronic amplification and image minification.
(NCRP 107)

Image intensifier
An x-ray image receptor which increases the brightness of a fluorosopic image by electronic amplification and image minification.
(NCRP 102)

Image quality
An inexact and indefinable term relating to the fidelity with which all the characteristic of an image (not only its shape) approach an agreed conventional representation of the object producing it.
(NCRP 68)

Image receptor
A system for deriving a diagnostically usable image from the x rays transmitted through the patient. Examples: screen-film system; stimulable phosphor; solid state detector.
(NCRP 107)

Image receptor assembly
An image receptor in a specialized contained necessary for proper operation of the receptor.
(NCRP 102)

Immediately dangerous to life or health
Included are conditions that pose an immediate threat to life or health and conditions that pose an immediate threat of severe exposure to contaminants such as radioactive materials which are likely to have adverse delayed effects on health.
(ANSI Z88.2-1969)

Immediately Dangerous to Life or Health (IDLH)
Any atmosphere that poses an immediate hazard to life or produces immediate irreversible debilitating effects on health.
(ANSI Z88.2-1980)

Immune system
The lymphatic system, including spleen, thymus, and bone marrow.
(HPJ 60)

Immunity
The power which a living organism possesses to resist and overcome infection.
(RHH)

Immunoglobulin
A protein (as an antibody) made up of light chains and heavy chains usually linked by disulfide bonds. Human Immunoglobulin Classes:
IgA: Biologic Function - Secretory Antibody
IgG: Biologic Function - Fix Complement
IgM: Biologic Function - Fix Complement; efficient agglutination
(HPJ 60)

Impact parameter
In elastic scattering, the minimum distance at which two interacting particles would pass each other if there were no scattering.
(ANSI N1.1-1976)

Impaction
As air is taken into the lung, it follows a tortuous path, changing direction many times. At each change of direction, the momentum of the particles carried in the air stream causes them to impact on the bifurcations of the lung. The force on the particle causing it to move and impact on the lung surface is the Stokes force, which is proportional to the velocity of the air moving with respect to the particle. Impaction is important for particles with large aerodynamic diameters.
(BEIR IV)

Impaction
A particle collision with a collection surface caused by the interaction of inertial and hydrodynamic forces.
(TID-26608)

Impaction
A process by which a particle or droplet is removed from an airstream by striking an object held in the airstream. When a particle grazes an object and is thus retained, the term "interception" applies.
(ANSI N13.1-1969)

Impaction parameter
The ratio of particle stopping distance to the characteristic dimension of the flow field or obstacle.
(TID-26608)

Impactor
A device in which aerosol particles with sufficiently high inertia in a deflected air stream are impacted onto a surface.
(AM-1993)

Impedance, characteristic
The ratio of voltage to current at a point along a uniform section of a two or more conductor transmission line that is free of standing wave components, i.e., for a wave traveling in one direction. Characteristic impedance is expressed in units of ohm (W).
(NCRP 67)

Impedance, intrinsic
The wave impedance for a plane wave in an unbounded medium. Its value depends only on the properties of the medium. Intrinsic impedance is expressed in units of ohm (W).
(NCRP 67)

Impedance, wave
The ratio of the electric field strength to the corresponding magnetic field strength of a propagating wave at a point. For a plane wave, the wave impedance is the same as the intrinsic impedance. In a waveguide, there is a wave impedance associated with each mode of propagation supported by the structure. Wave impedance is expressed in units of ohm (2).
(NCRP 67)

Impinger
A device in which particles are removed by impacting the aerosol particles into a liquid.
(AM-1993)

Implant
Encapsulated radioactive material embedded in a tissue for therapy. It may be permanent (seed) or temporary (needle).
(RHH)

Implanted junction detector
Semiconductor detector in which the junction is produced by implantation of donor (N) or acceptor (P) impurities.
(IEC 50-394-1993)

Implementation level (or "program implementation level")
A level of potential exposure as estimated from air monitoring, or a quantity of material in process, above which a bioassay program is to be implemented.
(ANSI/HPS N13.22-1995)

Implosion weapon
A weapon in which a quantity of fissionable material, less than a critical mass at ordinary pressure, has its volume suddenly reduced by compression (a step accomplished by using chemical explosives) so that it becomes supercritical, producing a nuclear explosion. (See supercritical mass.)
(USAEC-1974)

Import
Import into the United States.
(10CFR110.2)

Importance function
In a critical system, the average asymptotic number of neutrons in the system descended from a neutron of a given position and velocity.
(IEC 50-393-1993)

Importance function
In a critical system, the average asymptotic number of neutrons in the system descended from a neutron of a given position and velocity. It is proportional to the adjoint of the neutron flux density.
(ANSI N1.1-1976)

Importance, relative
For neutrons of type A relative of neutrons of type B, the average number of neutrons with the velocity and position of type B which must be added to a critical system to keep the chain reaction rate constant after removal of a neutron with the velocity and position of type A.
(ANSI N1.1-1976)

Important to safety
With reference to structures, systems, and components means those engineered structures, systems, and components essential to the prevention or mitigation of an accident that could result in a radiation dose to the whole body, or any organ, of 0.5 rem or greater at or beyond the nearest boundary of the unrestricted area at any time until the completion of permanent closure.
(10CFR60.2)

In growth, radioactive
Increase in number of daughter atoms present as a result of radioactive decay of the parent.
(HPJ 60)

In line
A system where the detector assembly is adjacent to or immersed in the total effluent stream.
(ANSI N42.18-1974)

In line
A system where the detector assembly is adjacent to or immersed in the total effluent stream.
(ANSI N13.10-1974)

In utero
In the womb, i.e., before birth.
(BEIR V)

In utero
In the womb, i.e., before birth.
(NCRP 98)

In utero
In the uterus; refers to a fetus or embryo.
(NCRP 105)

In vitro
(Literally, in glass), in culture or in the test-tube (as opposed to in vivo, in the living individual.
(BEIR V)

In vitro
Refers to a procedure carried out in a test tube or other vessel, e.g., tissue culture study: See in vivo.
(NCRP 105)

In Vitro Measurement
Synonymous with indirect bioassay.
(HPS N13.30-1996)

In vivo
In the living organism.
(BEIR V)

In vivo
Refers to a procedure carried out in the living body: See in vitro.
(NCRP 105)

In vivo
Pertains to within the body.
(NCRP 101)

In Vivo Measurement
Synonymous with direct bioassay.
(HPS N13.30-1996)

In-box
Refers to an item within a glovebox that can be handled or manipulated only by means of the box gloves or tools within the box.
(ERDA 76-21)

In-cell
Refers to an item located within a cell or enclosure that can be handled or manipulated only by means of manipulators and/or a crane and other tools within the cell.
(ERDA 76-21)

In-channel and out-of-channel events
When a singlechannel pulse-height analyzer is used in the g channel, those g pulses which do (do not) fall into the pulse-height range selected are referred to as in-channel (out-of-channel) events.
(ICRU 52)

In-core neutron fluence rate mapping system
Assembly designed to map the neutron fluence rate of a nuclear reactor core.
(IEC 50-394-1993)

In-core temperature measuring sensor
Device, fixed or movable, designed to provide a signal for the measurement of temperature at a defined point in the region of a reactor core or primary envelope.
(IEC 50-394-1993)

In-core temperature measuring system
System, using in-core temperature measuring sensors, which is designed for the measurement of primary coolant, fuel and reactor structure temperatures.
(IEC 50-394-1993)

In-duct filter
Refers to a single-filter arrangement in which the filter unit is clamped between two sections of duct or taped into a space between two sections of duct.
(ERDA 76-21)

In-pile
A term used to designate experiments or equipment inside a reactor. (See Pile.)
(USAEC-1974)

In-pile loop
See loop.
(USAEC-1974)

In-pile test
In-core test; that is, an irradiation test conducted within the core of a reactor.
(ANSI N1.1-1976)

In-place test
Penetration test of filter units or charcoal adsorbers made after they are installed.
(ERDA 76-21)

In-vitro measurement
Synonymous with indirect bioassay.
(ANSI N13.30-1989D)

In-vitro methods
Detection of radiations emitted by radioactive materials excreted or removed from the body, using radiochemical and/or radioanalytical techniques.
(HPJ 60)

In-vitro methods
Detection of radiations emitted by radioactive materials excreted or removed from the body, using radiochemical and/or radioanalytical techniques.
(NCRP 87)

In-vivo counting
The measurement of the amount of radioactivity in the human body through counting of the number of gammas which emerge from the body.
(ENV RAD)

In-vivo measurement
Synonymous with direct bioassay.
(ANSI N13.30-1989D)

In-vivo measurement
The measurement of radioactivity in the human body utilizing instrumentation which detects radiation emitted from radionuclides in the body; identical to direct bioassay.
(ANSI N343-1978)

In-vivo methods
Detection of radiation emitted by radioactive materials deposited in the body, usually by whole body (or critical organ) counting techniques.
(HPJ 60)

In-vivo methods
Detection of radiation emitted by radioactive materials deposited in the body, usually by whole body (or critical organ) counting techniques.
(NCRP 87)

Inactive stack
A stack to which no further routine additions of phosphogypsum will be made and which is no longer used for water management associated with the production of phosphogypsum. If a stack has not been used for either purpose for two years it is presumed to be inactive.
(40CFR61.201)

Inadvertent intruder
A person who might occupy the disposal site after closure and engage in normal activities, such as agriculture, dwelling construction, or other pursuits in which the person might be unknowingly exposed to radiation from the waste.
(10CFR61.2)

Incendiary device
Any self-contained device intended to create an intense fire that can damage normally flame-resistant or retardant materials.
(10CFR73.2)

Inches of water
A unit of pressure or pressure differential (1 in.wg = 0.036 psi).
(ERDA 76-21)

Incidence
The rate of occurrence of a disease; usually expressed in number of cases per million.
(NCRP 98)

Incidence
The rate at which new cases of a disease develop during some specified time period. The number of new cases of disease found in the population measured over a period of time.
(NCRP 80)

Incidence
The rate of occurrence of a disease within a specified period of time; usually expressed in number of cases per million (10⁶) per year.
(BEIR I)

Incidence (or incidence rate)
The rate of occurrence of a disease within a specified period; usually expressed in number of cases per 100,000 persons per year.
(BEIR V)

Incidence (or incidence rate)
The rate of occurrence of a disease within a specified period; usually expressed in number of cases per 100,000 persons per year.
(BEIR IV)

Incidence (or incidence rate)
The rate of occurrence of a disease within a specified period; usually expressed in number of cases per 100,000 persons per year.
(BEIR III)

Incidence rate
The rate of occurrence of a disease within a specified period of time, often expressed as number of cases per 100,000 individuals per year. In this report it is expressed as cumulative lifetime incidence per 1,000 individuals.
(NCRP 98)

Incident
An occurrence or situation of seemingly minor importance.
(NCRP 111)

Incident wave
See wave, incident.
(NCRP 67)

Incidental Radioactive Material
Any radioactive material not otherwise subject to specific licensing under this part that is contained in or a contaminant of any non-radioactive material that:
(1) For purposes unrelated to the regulations in this part, is exported or imported for recycling or resource recovery of the non-radioactive component; and
(2) Will not be processed for separation of the radioactive component before the recycling or resource recovery occurs or as part of the resource recovery process.
The term does not include material that contains or is contaminated with "hazardous waste" as defined in section 1004(5) of the Solid Waste Disposal Act, 42 U.S.C. 6903(5).
(10CFR110.2)

Inclination of orbit
This is the acute angle that the trajectory of the orbit makes with the earth's equator.
(NCRP 98)

Incoherent scattering
Scattering in which no definite relation exists between the phases of the scattered and incident waves.
(IEC 50-393-1993)

Increment (incremental addition)
See calibration increment.
(ANSI N15.19-1989)

Incremental slope plot
A plot of incremental changes in liquid height versus volume, ideally computed from a set of standardized calibration data.
(ANSI N15.19-1989)

Independent action
A dose-effect dependence for radiation X, not influenced by an exposure to radiation Y.
(ICRU 30)

Independent assay
A measurement that has a demonstrated statement of accuracy and that utilizes basic principles that are different from the NDA measurement under consideration. (This requirement for different basic principles is based on the rationale that the likelihood of two independent methods being biased by the same amount and in the same direction is small.)
(ANSI N15.35-1983)

Independent certifying organization
An independent organization that meets all of the criteria of Appendix A to this part.
(10CFR34.3)

Independent Spent Fuel Storage Installation or ISFSI
A complex designed and constructed for the interim storage of spent nuclear fuel and other radioactive materials associated with spent fuel storage. An ISFSI which is located on the site of another facility may share common utilities and services with such a facility and be physically connected with such other facility and still be considered independent: Provided, that such sharing of utilities and services or physical connections does not:
(1) Increase the probability or consequences of an accident or malfunction of components, structures, or systems that are important to safety; or
(2) reduce the margin of safety as defined in the basis for any technical specification of either facility.
(10CFR72.3)

Indian organization
Any commercial group, association, partnership, or corporation wholly owned or controlled by an Indian tribe.
(10CFR170.3)

Indian tribe
An Indian tribe as defined in the Indian Self-Determination and Education Assistance Act (25 U.S.C. 450).
(10CFR61.2)

Indian tribe
Any Indian tribe, band, nation, or other organized group or community of Indians recognized as eligible for the services provided by the Secretary of the Interior because of their status as Indians.
(10CFR170.3)

Indian tribe
An Indian tribe as defined in the Indian Self Determination and Education Assistance Act (Pub. L. 93-638).
(10CFR72.3)

Indicated value
A scale reading or displayed value.
(ANSI N42.17B-1989)

Indicated value
A scale or decade reading or displayed value.
(ANSI N42.17A-1989)

Indicated value
A scale reading or displayed value.
(ANSI N42.17C-1989)

Indirect Bioassay
The in vitro measurement of radioactive material in excreta or other biological materials removed from the body.
(HPS N13.42-1997)

Indirect bioassay
The assessment of radioactive material deposited in the body by detection of radioactivity in material excreted or removed from the body (in vitro measurement).
(NCRP 118)

Indirect bioassay
The assessment of radioactive material deposited in the body by detection of radioactivity in material excreted or removed from the body (See in-vitro methods).
(HPJ 60)

Indirect bioassay
Measurements to determine the presence of or to estimate the amount of radioactive material in the excreta of in other biological materials removed from the body. (Synonymous with in-vitro measurement.)
(ANSI N13.30-1989D)

Indirect bioassay
The assessment of radioactive material deposited in the body by detection of radioactivity in material excreted or removed from the body (See in-vitro methods).
(NCRP 87)

Indirect bioassay
The estimation of radioactivity in the human body based
(1) on measurements of radioactivity in excreta or other materials taken from the body and
(2) on a biological model for the radionuclide movement in body tissues and organs.
(ANSI N343-1978)

Indirect Radiobioassay
Measurements to determine the presence of or to estimate the amount of radioactive material in the excreta or in other biological materials removed from the body. (Synonymous with in vitro measurement.)
(HPS N13.30-1996)

Indirect reading pocket dosimeter
An indirect reading pocket dosimeter is basically a capacitor which is charged to a predetermined voltage. When exposed to X- or gamma radiation, or both, ionization occurs in the chamber containing the electrodes, causing a decrease in the charging voltage. The change in voltage is proportional to the exposure. The indirect reading dosimeter utilizes an external electrometer system to read the dosimeter.
(ANSI N13.5-1972)

Indirect recoil fraction
Those atoms which terminate their recoil path in a solid grain but diffuse out of the solid through the recoil path, while the solid is still molten.
(ENV RAD)

Indirect-cycle reactor system
A reactor system in which a heat exchanger transfers heat from the reactor coolant to a second fluid which then drives a turbine.
(USAEC-1974)

Indirectly ionizing particle
Uncharged particle such as, neutron, photon, which can liberate directly ionizing particles or can initiate a nuclear transformation.
(IEC 50-393-1993)

Indirectly ionizing particles
Uncharged particles (neutrons, photons, etc.) which can liberate directly ionizing particles or can initiate nuclear transformations.
(ICRU 19)

Indirectly ionizing particles
Uncharged particles (neutrons, photons, etc.) which can liberate directly ionizing particles or can initiate nuclear transformations.
(NBS 92)

Indirectly ionizing particles
Uncharged particles (neutrons, photons, etc.) which can liberate directly ionizing particles or can initiate nuclear transformations.
(ICRU 10f)

Indirectly ionizing particles
Uncharged particles (neutrons, photons, etc.) which can liberate directly ionizing particles or can initiate nuclear transformations.
(ICRU 10b)

Indirectly ionizing radiation
Uncharged particle (neutrons, photons, etc.) which can liberate directly ionizing particles or can cause nuclear transformations.
(NCRP 51)

Indirectly ionizing radiation
Radiation composed on uncharged particles which are capable of releasing charged particles when interacting with matter.
(NCRP 38)

Individual
Any human being.
(10CFR20.1003)

Individual
Any human being.
(10CFR835.2-1993)

Individual
Any human being.
(10CFR20.3)

Individual dose equivalent, penetrating H_p(d)
The individual dose equivalent, penetrating, H_p(d), is the dose equivalent in soft tissue, defined as in the ICRU sphere below a specified point on the body at a depth, d, that is appropriate for strongly penetrating radiation.
(ICRP 60)

Individual dose equivalent, penetrating, H_p(d)
The dose equivalent in soft tissue (defined as in the ICRU sphere) below a specified point on the body at depth, d, that is appropriate for strongly penetrating radiation. The recommended depth, d, for monitoring in terms of H_p(d) is 10 mm, and H_p(d) may be written as H_p(10).
(ICRP 51)

Individual dose equivalent, penetrating, H_p(d)
The individual dose equivalent, penetrating, H_p(d), is the dose equivalent in soft tissue (defined as in the ICRU sphere) below a specified point on the body at a depth, d, that is appropriate for strongly penetrating radiation.
(ICRU 39)

Individual dose equivalent, superficial H_s(d)
The individual dose equivalent, superficial, H_s(d), is the dose equivalent in soft tissue below a specified point on the body at a depth, d, that is appropriate for weakly penetrating radiation.
(ICRP 60)

Individual dose equivalent, superficial, H_s(d)
The dose equivalent in soft tissue (defined as in the ICRU sphere) below a specified point on the body at depth, d, that is appropriate for weakly penetrating radiation. The recommended depth, d, for monitoring in terms of H_s(d) is 0.07 mm, and H_s(d) may be written as H_s(0.07).
(ICRP 51)

Individual dose equivalent, superficial, H_s(d)
The individual dose equivalent, superficial, H_s(d), is the dose equivalent in soft tissue (defined as in the ICRU sphere) below a specified point on the body at a depth, d, that is appropriate for weakly penetrating radiation.
(ICRU 39)

Individual monitoring
(1) The assessment of dose equivalent by the use of devices designed to be worn by the individual;
(2) The assessment of committed effective dose equivalent by bioassay or by determination of the time-weighted air concentrations to which an individual has been exposed, i.e., DAC-hours; or
(3) The assessment of dose equivalent by the use of survey data.
(10CFR20.1003)

Individual monitoring
Individual monitoring is concerned with measurements carried out directly on people. Its use in routine monitoring programs is likely to be rare but it could be employed in circumstances where a few individuals may be exposed at a substantial fraction of the dose limit due to a single source or a multiplicity of sources. It may be of use following an accident to assess actual dose equivalents to individuals and to provide information to the public.
(ICRP 43)

Individual monitoring devices (individual monitoring equipment)
Devices designed to be worn by a single individual for the assessment of doe equivalent such as film badges, thermoluminescent dosimeters (TLDs), pocket ionization chambers, and personal ("lapel") air sampling devices.
(10CFR20.1003)

Individual reference range (IRR)
The range of individual dose equivalent values that, if exceeded, automatically triggers optimization activity.
(NCRP 107)

Individual Shipment
A shipment consisting of one lot of freight tendered to a carrier by one consignor at one place at one time for delivery to one consignee on one bill of lading. This lot may consist of:
(1) Only one item or
(2) A number of containers all listed on the same set of shipping documents. This one lot of freight or "distinct" shipment can be transported on the same carrier with other distinct shipments containing the same items as long as each shipment is covered by separate sets of shipping documents.
(10CFR110.2)

Indoor radon concentration
Concentration of radon or radon decay products in a house. Concentration is dependent on the geologic formation under the house and the structural conditions of the house, as well as other factors.
(RRM)

Induced radioactivity
Radioactivity resulting from a nuclear reaction.
(IEC 50-393-1993)

Induced radioactivity
See radioactivity.
(HPJ 60)

Induced radioactivity
Radioactivity that is created when substances are bombarded with neutrons, as from a nuclear explosion or in a reactor, or with charged particles produced by accelerators. (See activation.)
(USAEC-1974)

Industrial irradiator
An industrial irradiator is comprised of an array of sealed sources, often of extended dimensions, together with shielding and suitable product conveying equipment, designed to irradiated a large quantity of material to a specified absorbed dose within specified limits of uniformity during passage through the irradiator.
(ICRU 18)

Industrial radiography (radiography)
An examination of the structure of materials by nondestructive methods, utilizing ionizing radiation to make radiographic images.
(10CFR34.3)

Inelastic collision
Collision in which at least one system gains internal excitation energy at the expense of the total kinetic energy.
(IEC 50-393-1993)

Inelastic scattering
Scattering in which the total kinetic energy changes.
(IEC 50-393-1993)

Inelastic scattering
See scattering.
(USAEC-1974)

Inelastic scattering
Scattering collision on neutron with attendant loss of kinetic energy which is expended in excitation of the target nucleus.
(NCRP 38)

Inelastic scattering
Scattering collision of neutron with attendant loss of kinetic energy which causes excitation of the target nucleus, and subsequent release of gamma rays.
(NBS 63)

Inert
Substances that do not react with other substances under most conditions and create a respiratory hazard by displacing air and producing oxygen deficiency (for example, helium, neon, argon).
(ANSI Z88.2-1980)

Inertial Impaction of Particles
Fraction of particles that may contact airway walls because of their inertia (particles do not follow the curvature of the airstream exactly)
(NCRP 125)

Infinite multiplication factor (k_¥)
Multiplication factor evaluated for an infinite medium or for an infinite repeating lattice.
(IEC 50-393-1993)

Infinity dose (D_¥)
The integral of dose rate from the time of administration to infinity,

(NCRP 83)

Influence quantity
A radiation field, electromechanical condition, or environmental condition that may produce a response.
(ANSI N42.17A-1989)

Influence quantity
A radiation field, electromechanical condition, or environmental condition that may provoke a response.
(ANSI N42.17B-1989)

Influence quantity
A radiation field, electromechanical condition, or environmental condition that may provoke a response.
(ANSI N42.17C-1989)

Information
Generally, the property of one or more observations (e.g., data) that allows the precision and/or accuracy of subsequent estimates or decisions to be increased. Expressed mathematically by Shannon as a reduction in entropy.
(ICRU 54)

Ingestion EPZ
An area of approximately 50 miles radius surrounding a nuclear power plant where actions could be necessary to protect the public from the ingestion of contaminated water or foods.
(ANSI/ANS-3.8.1-1987)

Inhalability (Inspirable Particulate Mass)
Fraction of the suspended material in ambient air that enters the nose or mouth with the volume of air inhaled.
(NCRP 125)

Inhalable
Fraction of an aerosol that can enter the human respiratory system.
(AM-1993)

Inhalation valve
A device that allows respirable air to enter the facepiece and prevents exhaled air from leaving the respirator through the valve.
(ANSI Z88.2-1980)

Inhalation valve
A device that allows respirable air to enter the facepiece and prevents exhaled air from leaving the facepiece through the intake opening.
(ANSI Z88.2-1969)

Inherent filtration
See filter.
(NCRP 102)

Inhour
A unit of reactivity equal to the increase in reactivity of a critical reactor which produces a reactor time constant of one hour (short for inverse hour).
(ANSI N1.1-1976)

Inhour equation
The equation which relates the reactivity of a reactor to its time constant.
(ANSI N1.1-1976)

Injection tool
A device used for controlled subsurface injection of radioactive tracer material.
(10CFR39.2)

Inland service
All navigable rivers, lakes, and canals, except the Great Lakes, and man-made water routes within the continental boundary of the United States and within the innermost lines of demarcation for coastwise service.
(ANSI N14.24-1985)

Inlet efficiency
Fraction of ambient particles that is delivered to the aerosol transport section of a sampling system by the inlet; it is the product of the aspiration and transmission efficiencies.
(AM-1993)

Insoluble material
A term loosely used to describe the relative degree of solubility of a material in body fluids. Recognizing that no material is absolutely insoluble, the terms low solubility or poorly soluble are preferable.
(HPJ 60)

Inspection
Examination or measurement to verify whether an item or activity conforms to specified requirements.
(ANSI N46.2-1978)

Inspections
(1) Routine inspections designed to evaluate the licensee's activities within the context of the licensee having primary responsibility for protection of the public and environment.
(2) Non-routine inspections in response or reaction to an incident, allegation, followup to inspection deficiencies or inspections to determine implementation of safety issues. A non-routine or reactive inspection has the same purpose as the routine inspection.
(10CFR170.3)

Inspector
A qualified individual who performs inspections for the fabricator or purchaser.
(ANSI N14.6-1986)

Inspector
A person who performs inspection activities to verify conformance to specific requirements.
(ANSI N46.2-1978)

Inspirable
Same as inhalable; inhalable is the currently preferred term.
(AM-1993)

Inspiratory Capacity
Index of the maximum volume of air breathed in during inhalation; includes the tidal volume and inspiratory reserve volume.
(NCRP 125)

Installation
(1) A production facility or utilization facility as defined in Sec. 50.2 of this chapter;
(2) A uranium hexafluoride production plant;
(3) A fuel fabrication plant;
(4) An independent spent fuel storage installation (ISFSI) or a monitored retrievable storage installation (MRS) as defined in Sec. 72.3 of this chapter; or
(5) Any location where the possession of more than one effective kilogram of nuclear material is licensed pursuant to parts 40 or 70 of this chapter, or pursuant to an Agreement State license.
(6) Any facility used for separating the isotopes of uranium or enriching uranium in the isotope 235, except laboratory scale facilities designed or used for experimental or analytical purposes only; or any equipment or device, or important component part especially designed for such equipment or device, capable of separating the isotopes of uranium or enrichment uranium in the isotope 235.
(10CFR75.4)

Installation
(1) A production facility or utilization facility as defined in §50.2 of this chapter;
(2) A uranium hexafluoride production plant;
(3) A fuel fabrication plant;
(4) An independent spent fuel storage installation (ISFSI) or a monitored retrievable storage installation (MRS) as defined in §72.3 of this chapter; or
(5) Any location where the possession of more than one effective kilogram of nuclear material is licensed pursuant to Parts 40 or 70 of this chapter, or pursuant to an Agreement State license.
(6) Any facility used for separating the isotopes of uranium or enriching uranium in the isotope 235, except laboratory scale facilities designed or used for experimental or analytical purposes only; or any equipment or device, capable of separating the isotopes or uranium or enrichment uranium in the isotope 235.
(10CFR75.4)

Installation
A radiation source with associated equipment, and the space in which it is located.
(NCRP 102)

Installation
Radiation sources with associated equipment, and the space in which they are located.
(NCRP 49)

Installation
A radiation source, with its associated equipment, and the space in which it is located.
(NBS 73)

Installation enclosure
That portion of an x-ray installation which clearly defines the transition form a noncontrolled to a controlled area, and provides such shielding as may be required to limit the dose rate in the noncontrolled areas during normal operation.
(ANSI N43.2-1977)

Installed life (of equipment)
Interval of time from installation to permanent removal from operation, during which the equipment shall meet all design requirements for the specified operational conditions.
(IEC 50-393-1993)

Instant working level meter
An instrument designed to give rapid if not instantaneous, direct readings of the working level in an atmosphere.
(NCRP 97)

Instrument
A complete system designed to quantify one or more characteristics of ionizing radiation or radioactive material.
(ANSI N42.17C-1989)

Instrument
A complete system designed to quantify one or more characteristics of ionizing radiation or radioactive material.
(ANSI N42.17A-1989)

Instrument
A complete system designed to quantify one or more characteristics of ionizing radiation or radioactive material.
(ANSI N42.17B-1989)

Instrument
A complete system designed to quantify a particular type of ionizing radiation.
(ANSI N317-1980)

Instrument
A complete system designed to quantify one or more particular ionizing radiation or radiations.
(ANSI N323-1978)

Instrument efficiency (for a source)
Ratio between the number of particles per unit time, detected by an instrument and the surface emission rate of a source in a specified geometry relative to the source.
(IEC 50-394-1993)

Instrument precision
A qualitative term used to describe the dispersion of the measurement results obtained from an instrument for a given sample or item.
(ANSI N15.36-1983)

Instrument range
The region between the limits within which a quantity is measured, received, or transmitted, expressed by stating the lower and upper range values. In a nuclear reactor, the range of operating power levels in which the power is too low to manifest itself in terms of measurable temperature changes and must be measured by nuclear instruments, such as ionization chambers; usually considered to involve power levels representing a multiplication of the startup source by a factor of 100 or more and thereby distinguished from the lower "source range". (See counter range, power range, source range and period range.)
(ANSI N1.1-1976)

Insula
A triangular area of the cerebral cortex which forms the floor of the lateral cerebral fossa, which is, in turn, a depression on the floor of the cranial cavity.
(ICRP 49)

Insulating core transformer (ICT)
A high voltage power supply consisting of a transformer, the core of which is separated into insulated segments, each having a secondary winding which drives its own rectifier. The rectifier outputs are connected in series to produce the high voltage. An accelerating column may be directly attached to the high voltage terminal, or it may be physically separated from the unit and connected to it by a high-voltage shielded cable.
(RHH)

Intake
The amount of radioactive material taken into the body by inhalation, absorption through the skin, injection, ingestion, or through wounds.
(HPS N13.42-1997)

Intake
(1) The ingestion or inhalation of a radioactive material.
(2) The amount of radioactive material taken into the body by inhalation, ingestion, absorption through the skin, injection, or via a wound.
(ANSI/HPS N13.22-1995)

Intake
The amount of radioactive material taken into the body by inhalation, absorption through the skin, ingestion or through wounds.
(NCRP 118)

Intake
The amount of radioactive material taken into the body by inhalation, absorption through the skin, injection, ingestion or through wounds.
(HPJ 60)

Intake
The amount of radioactive material taken into the body by inhalation, absorption through the skin, injection, ingestion or through wounds.
(NCRP 87)

Intake
The amount of radioactive material taken into the body.
(NCRP 87)

Intake Retention Fraction (IRF)
The fraction of a single acute intake of a radionuclide that is expected to be present at a specific time, in an in vivo or in vitro bioassay compartment of interest.
(HPS N13.42-1997)

Integral dose
The number obtained by integrating the radiation dose over a volume of interest. This is an extensive function and is analogous to heat. The traditional unit of integral exposure dose is the gram roentgen; of integral absorbed dose, the gram rad.
(NCRP 83)

Integral dose
See energy imparted.
(NCRP 66)

Integral dose
See energy imparted.
(ICRU 30)

Integral dose
See energy imparted.
(ICRU 24)

Integral dose (volume dose)
A measure of the total energy absorbed by a patient or object during exposure to radiation.
(RHH)

Integral experiment
An experiment giving information about the total (integral) effect of several parameters or processes in a system rather than about their separate (differential) effects.
(ANSI N1.1-1976)

Integral non-linearity (of a measuring assembly)
1 - Departure from linear response expressed as a percentage of the maximum rated output pulse amplitude.
2 - Departure from linear relationship between pulse height and channel expressed as a percentage of the maximum channel in a multichannel pulse height analyzer.
(IEC 50-394-1993)

Integrated neutron flux
Flux multiplied by time, usually expressed as nvt, when n = the number of neutrons per cubic centimeter, v = their velocity in centimeters per second, and t = time in seconds. (See flux.)
(USAEC-1974)

Integrated Plant Assessment (IPA)
A licensee assessment that demonstrates that a nuclear power plant facility's structures and components requiring aging management review in accordance with Sec. 54.21(a) for license renewal have been identified and that the effects of aging on the functionality of such structures and components will be managed to maintain the CLB such that there is an acceptable level of safety during the period of extended operation.
(10CFR54.3)

Integrated Plant Assessment (IPA)
A licensee assessment that demonstrates that a nuclear power plant facility's systems, structures, and components important to license renewal have been identified and that age-related degradation unique to license renewal will be managed to ensure that the facility's licensing basis will be maintained during the renewal term.
(10CFR54.3)

Integrating exposure pathway
A pathway in which the radionuclide concentration increases with continuing release of materials into the environment and may persist beyond the cessation of these releases.
(NUREG/CR 3332)

Integrating ionization chamber
Ionization chamber intended to measure the accumulated charge caused by individual ionizing events occurring during a determined interval of time.
(IEC 50-394-1993)

Integrating monitor
An instrument designed to estimate the cumulative exposure to radon or radon daughter products in an atmosphere.
(NCRP 97)

Intensifying screen
Sheet of cardboard or other substance coated with fluorescent material, placed in contact with the film in radiography. The x or gamma rays excite the fluorescent substance. The light thus emitted adds to the radiation effect on the film and produces an image of greater density for a given exposure. Sheets of thin lead may be used in industrial radiography with very high energy radiation. In this case, the increased effect is due largely to secondary electrons and x rays emitted by the lead.
(RHH)

Intensity
The energy or the number of photons or particles of any radiation incident upon a unit area or flowing through a unit of solid material per unit of time. In connection with radioactivity, the number of atoms disintegrating per unit of time. (See flux.)
(USAEC-1974)

Intensity
Amount of energy per unit time passing through a unit area perpendicular to the line of propagation at the point in question.
(RHH)

Intensity
See radiation intensity.
(NBS 55)

Intensity (of radiation field)
For purposes of this report, field intensity is defined as radiation fluence (rate), radiation energy fluence (rate) or quantities derived from these, such as absorbed dose (rate) and dose equivalent (rate).
(NCRP 112)

Interaction
Mutual forces between particles in atoms, or nuclei. or between particles that collide.
(IEC 50-393-1993)

Intercalibration
The process, procedures, and activities used to ensure that the several laboratories engaged in a monitoring program can produce compatible data. When compatible data outputs are achieved and this situation is maintained, the laboratories can be said to be intercalibrated.
(HPJ 60)

Interception
Process by which the physical size of an inhaled particle (equal to the particle radius) brings it into direct contact with the airway wall.
(NCRP 125)

Interception
Collision with and deposition of a particle on an object when the particle passes within one particle radius of the object.
(AM-1993)

Interception
A particle collision with a collection surface that takes place when the distance between the streamline passing through the center of the particle and the collection surface is less than the particle radius.
(TID-26608)

Interference (in shielding material)
Discontinuity or void in a shielding barrier, e.g., aperture, piping, ductwork, maze, which tends to reduce the effective thickness of the barrier.
(NCRP 51)

Interferon
A meat-stable soluble basic antiviral protein of low molecular weight produced by cells exposed to the action of a virus, sometimes to that of another intracellular parasite (as a brucella), or experimentally to that of certain chemicals.
(HPJ 60)

Interleukin-1 (IL-1)
A polypeptide that acts as a local chemical mediator and induces T cells to secrete interleukin-2 a growth factor for T cells.
(ICRP 59)

Interleukin-3 (IL-3)
A polypeptide that is produced by some helper T cells that stimulates proliferation of various hematopoietic cells.
(ICRP 59)

Interleukin-6 (IL-6)
A polypeptide that promotes maturation of B cells to Ig-secreting cells and helps activate T cells.
(ICRP 59)

Interlock
A device used to assure proper and safe use of a radiation installation by monitoring (usually by electrical devices) the status, presence or position of various associated devices such as source position, collimator opening, beam direction, door closure, filter presence and preventing the production or emission or radiation if the potential for an unsafe condition is detected.
(NCRP 102)

Interlock
A device that automatically causes a reduction of the exposure rate upon entry by personnel into a high radiation area.
(NCRP 59)

Interlock
A device which automatically shuts down the accelerator under certain conditions of system malfunction and where there is penetration of barriers containing such devices.
(ANSI N43.1-1978)

Interlock
Device which automatically shuts off or reduces the radiation emission rate from an accelerator to acceptable levels, e.g., by the opening of a door into a radiation area. In certain applications, an interlock can be used to prevent entry into a radiation area.
(NCRP 51)

Interlock
A device which automatically causes a reduction of the exposure rate upon entry by personnel into a high radiation area. Alternatively, an interlock may prevent entry into a high radiation area.
(NCRP 49)

Interlock
A device, usually electrical and/or mechanical, to prevent activation of a control until a preliminary condition has been met, or prevent hazardous operations. Its purpose is usually safety.
(RHH)

Interlock
A device for precluding access to an area of radiation hazard either by preventing entry or by automatically removing the hazard.
(NBS 73)

Intermediate (epithermal) neutron
A neutron having energy greater than that of a thermal neutron but less than that of a fast neutron. The range is generally considered to be between about 0.5 and 100,000 electron volts.
(USAEC-1974)

Intermediate (epithermal) reactor
A reactor in which the chain reaction is sustained mainly by intermediate neutrons.
(USAEC-1974)

Intermediate neutron
Neutron of kinetic energy between the energies of slow and fast neutrons.
(IEC 50-393-1993)

Intermediate neutrons
Neutrons of energies of about 1 eV to 10 keV.
(NCRP 38)

Intermediate neutrons
Neutrons of energies between 0.5 eV and 10 keV.
(NBS 63)

Intermediate neutrons slow neutrons
Neutrons with energies of about 1 eV to a few hundred keV.
(NCRP 51)

Intermediate reactor, intermediate spectrum reactor
Reactor in which fissions are induced predominantly by intermediate neutrons.
(IEC 50-393-1993)

Intermediate zone
This zone is the third to form, its early cellular occupants are immature neurons that are destined never to divide again and have migrated to it from the ventricular zone. In the cerebrum, cells migrate through this intermediate layer to form a cortical plate at the junction of the intermediate and marginal zones.
(ICRP 49)

Intermodal
Between modes of transportation, such as water-to-rail or water-to-truck. This term is usually used in describing a cargo transfer from one mode to another.
(ANSI N14.24-1985)

Internal audit
An audit of those portion of an organization's quality assurance program retained under its direct control and within its organizational structure.
(ANSI N46.2-1978)

Internal conversion
Emission of an electron from an atom due to the liberation of energy from its excited nucleus.
(IEC 50-393-1993)

Internal conversion
One of the possible mechanisms of decay from the metastable state (isometric transition) in which transition energy is transferred to an orbital electron, causing its ejection from the atom. The ratio of the number of internal conversion electrons to the number of gamma quanta emitted in the de-excitation of the nucleus is called the "conversion ratio."
(RHH)

Internal conversion coefficient
Quotient of the number of internal conversion electrons emitted by that of unconverted gamma quanta from a specified excited state.
(IEC 50-393-1993)

Internal dose
That portion of the dose equivalent received from radioactive material taken into the body.
(10CFR20.1003)

Internal Dose Assessment
An assessment of the intake and associated internal radiation dose to workers based on measurements taken in the work environment or from individual bioassay measurements.
(HPS N13.42-1997)

Internal dose or exposure
That portion of the dose equivalent received from radioactive material taken into the body (e.g., "internal sources").
(10CFR835.2-1993)

Internal dose rate conversion factor
A factor which when multiplied by the quantity of radionuclide ingested, inhaled, or injected gives the steady-state, or maximum internal dose rate to a specific organ of the body.
(NUREG/CR 3332)

Internal dosimetry
A process of measurement and calculation that results in an estimate of dose equivalent from a radionuclide in the body.
(ANSI N13.14-1983)

Internal dosimetry
A process of measurement and calculation which results in an estimate of internal dose or dose commitment.
(ANSI N343-1978)

Internal emitter
A term used for a radionuclide deposited in the body.
(HPJ 60)

Internal emitter
A term used for a radionuclide deposited in the body.
(NCRP 87)

Internal gas detector
Ionization detector designed to measure the activity of the gas which is used wholly or partly as the filling gas.
(IEC 50-394-1993)

Internal irradiation
Exposure of the body to ionizing radiation from inside.
(ICRP 36)

Internal radiation
Radiation emitted from radionuclides distributed within the body.
(FGR 11)

Internal radiation
Radiation from a source within the body (as a result of deposition of radionuclides in body tissue).
(BEIR I)

International system (SI)
System of units commonly used in most of the world outside of the United States.
(ENV RAD)

Interstate commerce commission (ICC)
The ICC regulates the economic aspects of interstate waterborne (and other) transport and has statutory authority to approve or deny rate setting tariffs for such activities.
(ANSI N14.24-1985)

Interstitial implants
Solid or encapsulated radiation sources, made in the form of seeds, wires or other shapes to be inserted directly into tissue that is to be irradiated. (See brachytherapy.)
(USAEC-1974)

Interstitial treatment
Radiation treatment in which needles or "seeds" are introduced directly into tissues. See brachytherapy.
(NCRP 48)

Interventional radiology
Diagnostic and therapeutic radiologic thechniques that entail manipulation within the body after introduction of a catheter or other instrument through a natural opening or through the skin.
(NCRP 107)

Intracavitary treatment
Radiation treatment in which encapsulated sources are introduced into body cavities. See brachytherapy.
(NCRP 48)

Intrauterine applicator
A container for encapsulated sources to be introduced into the uterus. See brachytherapy.
(NCRP 48)

Intrinsic background
The contribution to the instrument reading from the instrument itself, independent of any external radiation.
(NCRP 112)

Intrinsic background level
Readings of a measuring instrument when there is no radiation present.
(IEC 50-394-1993)

Intrinsic impedance
See impedance, intrinsic.
(NCRP 67)

Intrinsic permeability
The measure of the ability of a rock or soil to transmit fluid under a fluid potential gradient (See hydraulic conductivity).
(NCRP 76)

Intrinsic permeability
The measure of the ability of a rock or soil to transmit fluid under a fluid potential gradient (See hydraulic conductivity).
(NUREG/CR 3332)

Intrinsic safety
Concept of a system, equipment or assembly, such that the most probable errors will cause a reaction improving the safety of the system, equipment or assembly.
(IEC 50-393-1993)

Intrinsic semiconductor, I-type semiconductor
An effectively pure semiconductor in which, under conditions of thermal equilibrium, the charge carrier densities of each sign are practically equal.
(IEC 50-394-1993)

Intrinsic tracer
An isotope, present naturally in a given sample, that may be used to trace a given element through chemical and physical processes.
(ANSI N1.1-1976)

Introduced into a hearing
The introduction or incorporation of testimony or documentary matter into the record of a hearing.
(10CFR110.2)

Intruder barrier
A sufficient depth of cover over the waste that inhibits contact with waste and helps to ensure that radiation exposures to an inadvertent intruder will meet the performance objectives set forth in this part, or engineered structures that provide equivalent protection to the inadvertent intruder.
(10CFR61.2)

Intrusion alarm
A tamper indicating electrical, electromechanical, electrooptical, electronic or similar device which will detect intrusion by an individual into a building, protected area, vital area, or material access area, and alert guards or watchmen by means of actuated visible and audible signals.
(10CFR73.2)

Invariant imbedding
In transport theory, a mathematical technique which allows integral parameters of a structure (e.g., reflection coefficients) to be obtained without giving a detailed description of the neutron flux density in the structure.
(ANSI N1.1-1976)

Inventory change
An increase or decrease, established in accordance with the procedures required by this part, in terms of batches of nuclear material in an IAEA material balance area.
(10CFR75.4)

Inventory difference (ID)
The quantity obtained by subtracting ending inventory (EI) and removals (R) from beginning inventory (BI) and additions to inventory (A). Mathematically, ID=BI+A-EI-R. ID is sometimes also referred to as "material unaccounted for" (MUF) in this chapter.
(10CFR74.4)

Inverse square law
A physical law stating that the intensity of x or gamma radiation from a point source emitting uniformly in all directions is inversely proportional to the square of the distance from the source. Example: A point source that produces 10 Gy/h at 1 m will produce 2.5 Gy/h at 2m.
(NCRP 105)

Inverse square relation
That rule which states that the intensity of radiation from a point source decreases as 1/d² from the source in a non-absorbing medium, where d is the distance from the source.
(NCRP 51)

Inversion
A stable atmospheric condition near the earth's surface by which the temperature increases with altitude.
(NCRP 97)

Inversion condition
A meteorologic condition in which temperature increases with altitude, generally caused by a warm air mass overlying a colder one.
(RRM)

Inversion layer
For a given type of semiconductor, surface layer of the opposite type.
(IEC 50-394-1993)

Inversions
An atmospheric condition near the earth's surface by which the temperature increases with altitude.
(NCRP 94)

Inversions
An atmospheric condition near the earth's surface by which the temperature increases with altitude.
(NCRP 45)

Investigation level
An activity level in the body or excreta at which the measurement results are examined for validity and investigation is made to see whether exposures can be reduced ALARA, as used in ICRP 54.
(ANSI/HPS N13.22-1995)

Investigation level
A value of dose equivalent or radionuclide intake above which the result is sufficiently important to justify further investigation.
(HPJ 60)

Investigation level
A value of dose equivalent or radionuclide intake above which the result is sufficiently important to justify further investigation.
(NCRP 87)

Investigation level
Values of dose equivalent or radionuclide intake above which the result is sufficiently important to justify further investigations or enquiries, such as a review of the circumstances causing it or an assessment of the consequences.
(ICRP 51)

Investigation level (for intake of radionuclides)
Level of committed dose equivalent or intake above which the result is regarded as sufficiently important to justify further investigation. Investigation levels are defined for routine monitoring, IL_R and for special or operational monitoring, IL_S. Derived investigation levels, DIL_R and DIL_S, are values of body or organ content or elimination rate that correspond to investigation levels, IL_R and IL_S. These values are calculated by means of defined models of intake, deposition, uptake, retention and elimination.
(ICRP 54)

Investigation Level (IL)
An intake (I) of a single radionuclide equal to 0.02 of the stochastic ALI, or for a mixture of radionuclides a value of 0.02 for the sum of the individual intakes (Ii) relative to the stochastic ALI_i values. In this standard, an investigation level corresponds to a committed effective dose equivalent of 1 mSv (100 mrem).
(HPS N13.42-1997)

Investigative program
A listing of activities that the auditor intends to follow in order to make an assessment about the activities to be audited, including the scope, depth, and frequency of these activities.
(ANSI N15.38-1982)

Ion
Atom or group of bound atoms with a non-zero total electric charge.
(IEC 50-393-1993)

Ion
Atomic particle, atom, or chemical radical bearing an electric charge, either negative or positive.
(BEIR III)

Ion
An atom that is electrically charged because of gain or loss of electrons.
(NCRP 48)

Ion
An atom or molecule that has lost or gained one or more electrons. By this ionization it becomes electrically charged. Examples: an alpha particle, which is a helium atom minus two electrons; a proton, which is a hydrogen atom minus its electron.
(USAEC-1974)

Ion
Atomic particle, atom, or chemical radical bearing an electrical charge, either negative or positive.
(BEIR I)

Ion
Atomic particle, atom, or chemical radical bearing an electric charge, either negative or positive.
(RHH)

Ion collection pulse chamber
Pulse ionization chamber in which the output signal is due principally to the total collection of ions and electrons.
(IEC 50-394-1993)

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

Ion engine
An engine which provides thrust by expelling accelerated or high velocity ions. Ion engines using energy provided by nuclear reactors are proposed for space vehicles.
(USAEC-1974)

Ion exchange
A chemical process involving reversible interchange of ions between a solution and a particular solid material, such as an ion-exchange resin consisting of a matrix of insoluble material interspersed with fixed ions of a charge opposite to that in solution.
(BEIR III)

Ion exchange
A chemical process involving the reversible interchange of various ions between a solution and a solid material, usually a plastic or a resin. It is used to separate and purify chemicals, such as fission products, rare earths, etc., in solutions.
(USAEC-1974)

Ion exchange
A chemical process involving reversible interchange of ions between a solution and a particular solid material such as an ion exchange resin consisting of a matrix of insoluble material interspersed with fixed ions of opposite charge.
(BEIR I)

Ion generating tube
Devices designed for ionization of air which contain, as a sealed source or sources, byproduct material consisting of a total of not more than 500 microcuries or polonium-210 per device or of a total of not more than 50 millicuries of hydrogen-3 (tritium) per device.
(10CFR31.3)

Ion pair
A closely associated positive ion and negative ion (usually an electron) having charges of the same magnitude and formed from a neutral atom or molecule by radiation. (Compare pair production.)
(USAEC-1974)

Ion pair
Two particles of opposite charge, usually referring to the electron and positive atomic or molecular residue resulting after the interaction of ionizing radiation with the orbital electrons of atoms.
(RHH)

Ionization
Formation of ions by the addition or removal of electrons to or from atoms or molecules, or by the splitting of molecules.
(IEC 50-393-1993)

Ionization
The process of adding one or more electrons to, or removing one or more electrons from, atoms or molecules, thereby creating ions. High temperatures, electrical discharges, or nuclear radiations can cause ionization.
(HPJ 60)

Ionization
The process by which a neutral atom or molecule acquires a positive or negative charge.
Primary ionization:
1. In collision theory: the ionization produced by the primary particles as contrasted to the "total ionization" which includes the secondary ionization" produced by delta rays.
2. In counter tubes: The total ionization produced by incident radiation without gas amplification.
Secondary ionization: Ionization produced by delta rays.
Specific ionization: Number of ion pairs per unit length of path of ionizing radiation in a medium; e.g.; per cm of air or per micron of tissue.
Total ionization: The total electric charge of one sign on the ions produced by radiation in the process of losing its kinetic energy. For a given gas, the total ionization is closely proportional to the initial ionization and is nearly independent of the nature of the ionizing radiation. It is frequently used as a measure of radiation energy.
(BEIR IV)

Ionization
A process in which one or more electrons are liberated from a parent atom or molecule or other bound state.
(ICRU 33)

Ionization
The production of ions in material, usually by exposure to x rays or radiations from radioactive material.
(NCRP 48)

Ionization
Any process by which an atom, molecule, or ion gains or loses electrons.
(ANSI N1.1-1976)

Ionization
The process whereby a neutral atom or molecule is split into positive and negative ions.
(NBS 51)

Ionization by collision
Ionization produced when ions already formed are accelerated as by an electric field to velocities high enough to produce more ions by collisions with neutral atoms or molecules.
(NBS 51)

Ionization chamber
A radiation sensing instrument which relies on the detection of free electron-ion pairs.
(AM-1993)

Ionization chamber
Ionization detector consisting of a chamber filled with a suitable gas, or gaseous mixture, in which an electric field, insufficient to induce gas multiplication, is provided for the total collection at the electrodes of charges associated with the ions and the electrons produced in the sensitive volume of the detector by the ionizing radiation.
(IEC 50-394-1993)

Ionization chamber
An instrument that detects and measures ionizing radiation by measuring the electrical current that flows when radiation ionizes gas in a chamber, making the gas a conductor of electricity.
(HPJ 60)

Ionization chamber
A device for detection of ionizing radiation or for measurement of radiation dose or dose rate.
(NCRP 105)

Ionization chamber
A gas-filled enclosure for measuring radiation by means of ions produced therein.
(ANSI N1.1-1976)

Ionization chamber
A container with electrodes on which suitable voltages are impressed for collecting only ions formed in the gas in the chamber by the ionizing event.
(NBS 51)

Ionization chamber (alpha)
An instrument designed to estimate the quantity of radon, within its fixed volume, either by alpha pulse counting or by total ionization measurement.
(NCRP 97)

Ionization chamber with internal gas source
Ionization chamber in which the filling gas consists in all or in part of the radioactive gas whose activity is to be measured.
(IEC 50-394-1993)

Ionization chamber, air wall
An ionization chamber in which the walls and electrodes produce ionization equivalent to that in a free-air ionization chamber.
(ANSI N1.1-1976)

Ionization chamber, extrapolation
An ionization chamber of adjustable volume which permits the estimation of the limiting value of the ionization current per unit volume as the volume becomes vanishingly small.
(ANSI N1.1-1976)

Ionization chamber, free-air
An ionization chamber so designed that the observed ionization current is wholly due to ions and electrons arising from the absorption or radiation in air.
(ANSI N1.1-1976)

Ionization chamber, integrating
An ionization chamber which indicates total ionization over a period of time.
(ANSI N1.1-1976)

Ionization chamber, pocket
A type of personnel monitor activated by radiation producing ions within it. See monitor.
(NCRP 48)

Ionization chamber, tissue equivalent
An ionization chamber in which materials of the walls, electrodes, and gas are so selected as to produce ionization essentially equivalent to that characteristic of the tissue being simulated.
(ANSI N1.1-1976)

Ionization counter instrumentation
An ionization chamber which has no internal amplification by gas multiplication and which is used for counting ionizing particles.
(ANSI N1.1-1976)

Ionization current
Electric current resulting from the motion under the influence of an electric field and collection of ions and electrons produced in an ionized medium.
(IEC 50-394-1993)

Ionization density
Number of ion pairs per unit volume.
(BEIR IV)

Ionization density
Number of ion pairs per unit volume.
(BEIR III)

Ionization density
Number of ion pairs per unit volume.
(BEIR I)

Ionization density
Number of ion pairs per unit volume.
(RHH)

Ionization detector
Radiation detector whose signal is due to ionization in the sensitive volume of the detector.
(IEC 50-394-1993)

Ionization path (track)
The trails of ion pairs produced by an ionizing particle or photon in its passage through matter.
(HPJ 60)

Ionization path (track)
The trail of ion pairs produced by ionizing radiation in its passage through matter.
(BEIR IV)

Ionization path (track)
The trail of ion pairs produced by ionizing radiation in its passage through matter.
(BEIR III)

Ionization path (track)
The trail of ion pairs produced by ionizing radiation in its passage through matter.
(BEIR I)

Ionization path (track)
The trail of ion pairs produced by ionizing radiation in its passage through matter.
(RHH)

Ionization track
Part of the path of an ionizing particle which is visible in a track chamber, a nuclear emulsion, etc.
(IEC 50-394-1993)

Ionization, linear
The total number of ion pairs, including those created by secondary ionizing processes, produce by a directly ionizing particle.
(ANSI N1.1-1976)

Ionization, total
The total number of ion pairs produced in any way by a directly ionizing particle.
(ANSI N1.1-1976)

Ionizing event
Production of an ion or a group of ions by interaction of a single particle with matter.
(IEC 50-393-1993)

Ionizing event
Any occurrence in which an ion or group of ions is Produced; for example, by passage of a charged particle through matter.
(USAEC-1974)

Ionizing event
Any occurrence of a process in which an ion or group of ions is produced.
(RHH)

Ionizing radiation
Radiation consisting of directly or indirectly ionizing particles or a mixture of both.
(IEC 50-393-1993)

Ionizing radiation
See radiation.
(HPJ 60)

Ionizing radiation
Radiation sufficiently energetic to dislodge electrons from an atom. Ionizing radiation includes x and gamma radiation, electrons (beta radiation), alpha particles (helium nuclei), and heavier charge atomic nuclei. Neutrons ionize indirectly by colliding with atomic nuclei.
(BEIR V)

Ionizing radiation
Electromagnetic radiation ( x or gamma rays) or particulate radiation (alpha particles, beta particles, electrons, positrons, protons, neutrons, and heavy particles) capable of producing ions by direct or secondary processes in passage through matter.
(NCRP 105)

Ionizing radiation
Any electromagnetic or particulate radiation capable of producing ions, directly or indirectly, in its passage through matter.
(NCRP 98)

Ionizing radiation
Any radiation capable of displacing electrons from atoms or molecules, thereby producing ions.
(FGR 11)

Ionizing radiation
For the purposes of this report, radiation having a sufficiently large photon energy to directly ionize atomic or molecular systems with a single quantum event. It is to be distinguished form non-ionizing radiation that may lead to ionization of these systems through multiple quantum events.
(NCRP 67)

Ionizing radiation
Any radiation displacing electrons from atoms or molecules, thereby producing ions.
(NCRP 65)

Ionizing radiation
Charged particles (for example, positive or negative electrons, protons or other heavy ions) and/or uncharged particles (for example, photons or neutrons) capable of causing ionization by primary or secondary processes.
(ICRU 33)

Ionizing radiation
Any radiation consisting of directly or indirectly ionizing particles or a mixture of both.
(NCRP 51)

Ionizing radiation
Electromagnetic or particulate radiation that directly or indirectly produces ionization when interacting with matter.
(ANSI N319-1976)

Ionizing radiation
Radiation capable of ionizing neutral atoms.
(NCRP 48)

Ionizing radiation
Any radiation (alpha, beta, or gamma) that directly or indirectly displaces electrons from the outer domains of atoms.
(ERDA 76-21)

Ionizing radiation
Any radiation displacing electrons from atoms or molecules, thereby producing ions. Examples: alpha, beta, gamma radiation, short-wave ultraviolet light. Ionizing radiation may produce severe skin or tissue damage. (See radiation, radiation burn, radiation illness.)
(USAEC-1974)

Ionizing radiation
Any electromagnetic or particulate radiation capable of producing ions, directly or indirectly, in its passage through matter.
(BEIR I)

Ionizing radiation
Any radiation consisting of directly or indirectly ionizing particles or a mixture of both.
(ICRU 19)

Ionizing radiation
Any radiation consisting of directly or indirectly ionizing particles or a mixture of both.
(NBS 92)

Ionizing radiation
Any radiation consisting of directly or indirectly ionizing particles or a mixture of both.
(ICRU 10b)

Ionizing radiation
Any radiation consisting of directly or indirectly ionizing particles or a mixture of both.
(ICRU 10f)

Iris
The circular pigmented membrane behind the cornea perforated by the pupil. Its circular muscle fibers allow the size of the pupil to be varied.
(NCRP 98)

Irradiance
The energy flux density of an electromagnetic wave incident upon a surface. Irradiance is expressed in units of watt per square meter (W/m²).
(NCRP 67)

Irradiated fuel shipping cask
A packaging system for the transport of irradiated fuel.
(ANSI N14.19-1986)

Irradiated volume
That tissue volume which receives a dose that is considered significant in relation to normal tissue tolerance.
(ICRU 50)

Irradiated volume
The irradiated volume is that volume, larger than the treatment volume, which receives an absorbed dose considered to be significant in relation to tissue tolerance.
(ICRU 38)

Irradiated volume
The irradiated volume is that volume, larger than the treatment volume, which receives an absorbed dose which is considered significant in relation to tissue tolerance. The significant absorbed dose level can be expressed as absorbed dose in percentage (e.g. 50%) of the specified target absorbed dose. The irradiated volume, as well as the treatment volume, will depend on the treatment technique used.
(ICRU 29)

Irradiation
Incidence of ionizing radiation on living or inanimate material.
(IEC 50-393-1993)

Irradiation
Exposure to ionizing radiation.
(NCRP 51)

Irradiation
Exposure to ionizing radiation.
(ANSI N1.1-1976)

Irradiation
Exposure to radiation.
(NCRP 48)

Irradiation
Exposure to radiation, as in a nuclear reactor. (See spent fuel.)
(USAEC-1974)

Irradiation
Exposure to radiation.
(RHH)

Irradiation channel, experimental hole
Hole through a reactor biological shield into the interior of the reactor in which irradiations are carried out.
(IEC 50-393-1993)

Irradiation field
Cross-sectional area of a restricted radiation beam.
(IEC 50-393-1993)

Irradiation rig
An assembly, for insertion in a reactor, which contains materials for experimental irradiation together with instruments for the measurement (and sometimes control) of the conditions under which the irradiation is carried out.
(ANSI N1.1-1976)

Irradiator
A facility that uses radioactive sealed sources for the irradiation of objects or materials and in which radiation dose rates exceeding 5 grays (500 rads) per hour exist at 1 meter from the sealed radioactive sources in air or water, as applicable for the irradiator type, but does not include irradiators in which both the sealed source and the area subject to irradiation are contained within a device and are not accessible to personnel.
(10CFR36.2)

Irradiator operator
An individual who has successfully completed the training and testing described in Sec. 36.51 and is authorized by the terms of the license to operate the irradiator without a supervisor present.
(10CFR36.2)

Irrespirable
Unfit for breathing.
(ANSI Z88.2-1980)

Irrespirable
Unfit for breathing.
(ANSI Z88.2-1969)

Irretrievable well logging source
Any sealed source containing licensed material that is pulled off or not connected to the wireline that suspends the source in the well and for which all reasonable effort at recovery has been expended.
(10CFR39.2)

Isoaxial sampling
Sampling condition in which the air flowing into an inlet has the same direction as the ambient air flow.
(AM-1993)

Isobar
One of a set of nuclides having the same mass number but different atomic numbers.
(IEC 50-393-1993)

Isobar
One of two or more nuclides having about the same atomic mass but different atomic numbers, hence different chemical properties. Example: ¹²C, ¹²N, and ¹²O are isobars.
(USAEC-1974)

Isobars
Nuclides having the same mass number but different atomic numbers.
(RHH)

Isobars, nuclear
Nuclides having the same mass number but different atomic numbers.
(ANSI N1.1-1976)

Isocenter
The point of intersection of the center of the primary beam of a rotating beam of radiation and the axis of rotation of the beam.
(NCRP 101)

Isocenter
Many radiation machines are constructed so that the source of radiation can rotate about a horizontal axis, the beam axis being restricted to a vertical plane. In such cases, the isocenter is a fixed point in space located at the intersection of the beam axis and the horizontal axis of rotation.
(NCRP 69)

Isocenter
Many radiation machines are constructed so that the source of radiation can rotate about a horizontal axis, the collimator axis (q.v.) moving in a vertical plane. The isocenter is the intersection of the collimator axis and the axis of rotation.
(ICRU 24)

Isochronous cyclotron
A cyclotron which uses a constant accelerating frequency and focuses the particles by means of wedge-shaped sectors on the magnet poles.
(RHH)

Isocortex
The laminated, phylogenetically younger part of the cerebral cortex which reaches its highest development in the human.
(ICRP 49)

Isodose
Descriptive of a locus at every point of which the absorbed dose is the same.
(ANSI N1.1-1976)

Isodose chart
A set of isodose curves, usually drawn for regular intervals of percentage depth dose, which represent the absorbed dose distribution in a particular plane within the phantom.
(NCRP 69)

Isodose chart
A family of isodose curves, usually drawn for equal increments of percentage depth dose, representing the distribution of absorbed dose in a specified plane for a specified beam.
(ICRU 24)

Isodose chart
Chart showing the distribution of radiation in a medium by means of lines or surfaces drawn through points receiving equal doses. Isodose charts have been determined for beams of x rays traversing the body, for radium applicators used for intracavitary or interstitial therapy, and for working areas where x rays or radioactive nuclides are employed.
(RHH)

Isodose curve
The locus, on a flat section of an irradiated medium, of all points having the same dose or dose rate values.
(IEC 50-393-1993)

Isodose curve
A line (usually in a plane) along which the absorbed dose is constant.
(NCRP 69)

Isodose curve
A line (usually in a plane) along which the absorbed dose is constant.
(ICRU 30)

Isodose curve
A line (usually in a plane) along which the absorbed dose is constant.
(ICRU 24)

Isodose curve
A line (usually in a plane) along which the absorbed dose is constant.
(ICRU 23)

Isodose curve
A curve depicting loci of identical radiation doses in a structure.
(RHH)

Isodose curves
Curves or lines drawn to connect points where identical amounts of radiant energy reach a certain depth in tissue.
(USAEC-1974)

Isodose surface
The locus, in an irradiated medium, of all points having the same dose or dose rate values.
(IEC 50-393-1993)

Isodose surface
A surface on which the absorbed dose is constant.
(NCRP 69)

Isodose surface
A curved surface, along which the absorbed dose is constant.
(ICRU 30)

Isodose surface
A curved surface, along which the absorbed dose is constant.
(ICRU 24)

Isodose surface
A surface on which the absorbed dose is constant.
(ICRU 23)

Isointensity contours
Imaginary lines on the surface of the ground or water, or lines drawn on a map, joining points in a radiation field which have the same radiation intensity at a given time.
(USAEC-1974)

Isokinetic
The condition in which the flow into a sampling probe matches the direction and velocity of the fluid being sampled.
(TID-26608)

Isokinetic
A condition which prevails when the velocity of air entering a sampling probe or the collector when held in the airstream is identical to the velocity of the airstream being sampled at the point.
(ANSI N13.1-1969)

Isokinetic sampling
Sampling condition in which the air flowing into an inlet has the same velocity and direction as the ambient air flow.
(AM-1993)

Isolation
Inhibiting the transport of radioactive material so that amounts and concentrations of this material entering the accessible environment will be kept within prescribed limits.
(10CFR60.2)

Isolation zone
Any area adjacent to a physical barrier, clear of all objects which could conceal or shield an individual.
(10CFR73.2)

Isomer
One of two or more nuclides with the same numbers of neutrons and protons in their nuclei, but with different energies; a nuclide in the excited state and a similar nuclide in the ground state are isomers.
(USAEC-1974)

Isomeric state
An excited state having a mean life long enough to be observed.
(ANSI N1.1-1976)

Isomers
Nuclides having the same number of neutrons and protons but capable of existing, for a measurable time, in different quantum states with different energies and radioactive properties. Commonly, the isomer of higher energy decays to one of lower energy by the process of isomeric transition.
(RHH)

Isomers, nuclear
Nuclides having the same mass number and atomic number, but occupying different nuclear energy states.
(ANSI N1.1-1976)

Isosmotic
Equal tension or equal osmotic pressure.
(NCRP 109)

Isotone
One of a set of nuclides having the same number of neutrons in their atomic nuclei.
(IEC 50-393-1993)

Isotone
One of several nuclides having the same number of neutrons but a different number of protons in their nuclei. Example: potassium-39 (K²⁰) and calcium-40 (Ca²⁰) are isotones.
(USAEC-1974)

Isotones
Two or more nuclides having the same neutron number.
(ANSI N1.1-1976)

Isotones
Nuclides having the same number of neutrons in the nuclei.
(RHH)

Isotope
One of a set of nuclides having the same atomic number but different mass numbers.
(IEC 50-393-1993)

Isotope
One of several nuclides having the same number of protons in their nuclei, and hence having the same atomic number, but differing in the number of neutrons, and therefore, in the mass number. Almost identical chemical properties exist between isotopes of a particular element. The use of this term as a synonym for nuclide is to be discouraged.
(HPJ 60)

Isotope
In the strict sense, any of two or more species of a chemical element with the same atomic number but different atomic weight; often incorrectly applied to radionuclide or radiopharmaceutical.
(NCRP 105)

Isotope
One of several forms or nuclides of the same chemical element that have the same number of protons in the nucleus and therefore have the same chemical properties, but have differing numbers of neutrons and differing nuclear properties.
(ERDA 76-21)

Isotope
One of several nuclides of the same element, having the same nuclear charge but different nuclear mass.
(NCRP 48)

Isotope
One of two or more atoms with the same atomic number (the same chemical element) but with different atomic weights. An equivalent statement is that the nuclei of isotopes have the same number of protons but different numbers of neutrons. Thus, ¹²C, ¹³C, and ¹⁴C are isotopes of the element carbon, the subscripts denoting their common atomic numbers, the superscripts denoting the differing mass numbers, or approximate atomic weights. Isotopes usually have very nearly the same chemical properties, but somewhat different physical properties. (See radioisotope.)
(USAEC-1974)

Isotope
One of several different atoms of a particular element, having the same number of protons in their nuclei, and hence having the same atomic number, but differing in the number of neutrons and hence in the mass number.
(NBS 73)

Isotope
One of several nuclides having the same number of protons in their nuclei, and hence belonging to the same element, but differing in the number of neutrons, and therefore differing in mass. for example, strontium-88 and strontium-90 are isotopes.
(NBS 66)

Isotope effect
The effect of difference of mass between isotopes of the same element on non-nuclear physical and chemical properties, such as the rate of reaction or position of equilibrium of chemical reactions involving the isotopes.
(NCRP 62)

Isotope effect
The effect on the atomic properties of isotopes due to their differing masses.
(ANSI N1.1-1976)

Isotope farm
A carbon-14 growth chamber, or greenhouse, arranged as a closed system in which plants can be grown in a carbon-14 dioxide (¹⁴CO₂) atmosphere and thus become labeled with ¹⁴C. Isotope farms also can be used with other labeled materials, such as heavy water (D₂O), phosphorus-35 (³⁵P), etc., to produce biochemically labeled compounds. (See tracer, isotopic.)
(USAEC-1974)

Isotope separation
The process of separating isotopes from one another, or changing their relative abundances, as by gaseous diffusion or electromagnetic separation. All systems are based on the mass differences of the isotopes. Isotope separation is a step in the isotopic enrichment process. (See mass spectrometer.)
(USAEC-1974)

Isotope, radioactive
Any isotope that is unstable, thus undergoing decay with the emission of a characteristic radiation.
(HPJ 60)

Isotope, stable
A nonradioactive isotope of an element.
(HPJ 60)

Isotopes
Nuclides that have the same number of protons in their nuclei, and hence the same atomic number, but that differ in the number of neutrons, and therefore in the mass number; chemical properties of isotopes of a particular element are almost identical. The term should not be used as a synonym for nuclide.
Stable isotope: A non-radioactive isotope of an element.
Isotope effect (chemistry): The effect of the difference in the mass between isotopes of an element on the rate and/or equilibria of chemical transformations.
Isotope separation: Process in which a mixture of isotopes of an element is separated into its component isotopes, or in which the abundance of isotopes is such a mixture is changed.
(BEIR IV)

Isotopes
One of two or more atoms with the same atomic number (the same chemical element) but with different atomic weights. An equivalent statement is that the nuclei of isotopes have the same number of protons but different numbers of neutrons. Isotopes usually have very nearly the same chemical properties, but somewhat different physical properties.
(NCRP 65)

Isotopes
Nuclides having the same atomic number but different mass numbers.
(ANSI N1.1-1976)

Isotopes
uclides having the same number of protons in their nuclei, and hence the same atomic number, but differing in the number of neutrons, and therefore in the mass number. Almost identical chemical properties exist between isotopes of a particular element. The term should not be used as a synonym for nuclide.
(BEIR I)

Isotopic enrichment
A process by which the relative abundances of the isotopes of a given element are altered, thus producing a form of the element which has been enriched in one particular isotope. Example: enriching natural uranium in the uranium-235 isotope. (See enriched material, gaseous diffusion.)
(USAEC-1974)

Isotopic power generator
A device for generating power from the heat produced by the radioactive decay of a radionuclide. The heat is usually converted to electricity by thermoelectric or thermionic devices.
(ANSI N1.1-1976)

Isotropic
Having the same properties in all directions.
(NCRP 67)

Isotropic
A condition in which properties are the same in whatever direction they are measured. With reference to radiation emission, this term indicates equal emission in all directions from a point source or each differential size element of any extended source. See also anisotropic.
(NCRP 51)

Isotropic antenna
A hypothetical antenna radiating or receiving equally in all directions, representing a convenient reference for expressing directional properties of actual antennas.
(NCRP 67)

Isotropy
As applied to ground water, referring to the character of a groundwater medium in which the properties at any point within the medium are the same in all directions.
(NCRP 76)

Issuance
Issuance of a part 70 permit will occur, if the State is the permitting authority, in accordance with the requirements of part 70 of this chapter and the applicable, approved state permit program. When the EPA is the permitting authority, issuance of a Title V permit occurs immediately after the EPA takes final action on the final permit.
(10CFR61.2)

Item
Any discrete quantity or container of special nuclear material or source material, not undergoing processing, having an unique identity and also having an assigned element and isotope quantity.
(10CFR74.4)

Item
An object or quantity of material on which a set of observations can be made.
(ANSI N15.54-1988)

Item
An all inclusive term used in place of any of the following: appurtenance, assembly, component, equipment, material, module, part, structure, subassembly, subsystem, system, or unit.
(ANSI N46.2-1978)

Items important to safety
Items which are defined by the rules related to nuclear safety and items which if they were to fail to act, or act when not required to act, may result in the need for action to prevent undue radiation exposure of the plant personnel or members of the public.
(IEC 50-393-1993)

Iterated fission expectation
In a critical reactor, the average value, after many generations, of the number of fissions per generation arising from the daughter neutrons of a given neutron.
(IEC 50-393-1993)

Iterated fission expectation
In a critical reactor, their average value after many generations of the number of fissions per generation arising from the neutrons descended from a given neutron. (Frequently called iterated fission probability.)
(ANSI N1.1-1976)

Note: References shown in ()