Radiation Safety Terms and Definition

Accident, global
– A community-wide radiological accident affecting a significant fraction (or all) of a country and its inhabitants.

Accident, community-wide
– A radiological accident whose impact is not limited to the site or facility itself, but extends to adjacent residential areas which may realistically or potentially be exposed to radiation.

Accident, localized
– A community-wide radiological accident in which the total number of affected inhabitants is ten thousand or less.

Emergency exposure
– An unplanned exposure which exceeds dose limits for personnel or the public.

Emergency plan
– An action plan describing the actions to be taken in the event of an accident at a facility where ongoing activities involving radiological or radiological/nuclear technologies are performed.

Accident, facility
– A radiological incident whose effects do not extend beyond the site or facility, and in which only personnel receive an emergency exposure.

Accident, radiological
– Any unplanned event at any facility with radiological or nuclear/radiological technology, provided two necessary and sufficient conditions are met:

– Loss of control over a source;

– People have been (or might be) exposed as a result of the loss of control over the source.

Accident, radiological/nuclear
– Any unplanned event at a facility with radiological/nuclear technology, involving a loss of control over a nuclear chain reaction simultaneously coupled with actual or potential danger of a self sustaining fission reaction.

Accident, regional
– A community-wide radiological accident which turns out to affect several population centers, one or more administrative regions, or even one or more oblasts, with a total affected population greater than ten thousand.

Accident, transboundary
– A global radiological accident in which the affected region extends beyond the boundaries of the country in which the accident occurred.

– The number of spontaneous nuclear transformations occurring within a time interval. The unit of measure is the becquerel (Bq).

Alpha-radiation (radiation)
– Corpuscular ionizing radiation consisting of alpha particles (helium nuclei) emitted during nuclear decay, nuclear reactions, or nuclear transformations.

Nuclear power plant (NPP)
– A nuclear plant intended for the production of electrical power.

Nuclear plant (NP)
– An enterprise that uses a nuclear reactor (or reactors) for the production of energy.

Nuclear heating plant (NHP)
– A nuclear plant for production of hot water.

Nuclear heat and power plant (NHPP)
– A nuclear plant intended for the production of heat and electrical power.

Directly ionizing radiation
– Ionizing radiation consisting of charged particles (electrons, protons, alpha particles, etc.) with sufficient kinetic energy to ionize atoms and molecules within materials.

Beta radiation (radiation)
– Corpuscular ionizing radiation, consisting of electrons or positrons with a continuous energy spectrum, generated in transformations of nuclei or unstable particles (such as electrons). Characterized in terms of the cutoff energy E? or the mean spectral energy.

Averted dose
– Dose averted through application of a specific countermeasure; calculated as the difference between the dose in the absence of the countermeasure and the dose once the countermeasure has been fully implemented.

Internal deposition
– The processes by which aerosol particles initially penetrate into various morphological features of the respiratory system, thereby determining the amount of aerosol remaining in the respiratory system. The impurities are later redistributed by the muco ciliary mechanism, physical and chemical transformations, transport in body fluids, etc.

Internal exposure
– Exposure of the human body, individual organs, and tissue from sources of ionizing radiation located within the body itself.

Intervention, automatically justified acute
– An intervention for which the dose averted through implementation of the intervention is large enough to cause acute clinical symptoms of radiation injury: Radiation sickness, radiation burns on skin, radiation thyroidites, etc.

Intervention, justified
– An intervention for which the health benefit from the averted dose is greater than the total loss incurred through implementation of the intervention.

Intervention, unjustified
– An intervention for which the averted dose is below a minimum value called the justification level. The justification level corresponds to the averted dose at which the (health) benefit of the intervention turns out to be smaller than the loss produced by the intervention.

Gas/aerosol release (release)
– Release of radioactive material into the atmosphere from process piping and ventilation systems associated with an enterprise.

Gamma-radiation (radiation)
– Short-wavelength (wavelength < 0.1 nm) electromagnetic radiation generated during radioactive nuclear decay, nuclear transitions from an excited state to the ground state, interactions between high-velocity charged particles and matter (see brehmsstrahlung), annihilation of electron positron pairs, etc.

Source of ionizing radiation (radiation source)
– An object containing radioactive material or a device which produces ionizing radiation (or is or is capable of producing ionizing radiation under certain conditions).

– Individuals not categorized as personnel who voluntarily and knowingly assist patients during performance of X-ray or radiological procedures or participate in medical/biological research.

Collective effective dose
– Sum of the individual effective doses received by a specific population subgroup over a specific period of time.

Dose per unit ingestion/inhalation (e)
– Annual effective dose of internal radiation for one of six reference ages for unit (1 Bq) ingestion/inhalation.

Deterministic (nonstochastic) effects
– Radiation effects which appear to have a specific dose threshold, and whose severity depends on the amount of radiation received (acute radiation sickness, radiation burns, etc.).

Stochastic effects
– Radiation effects which do not have a [dose] threshold (i.e., the probability of occurrence is non-zero at any dose of ionizing radiation) and whose probability of occurrence increases with increasing dose (while the relative severity [of the effects] is independent of dose). Stochastic effects include malignant neoplasmas (somatic stochastic effects) and hereditarily-transmitted genetic mutations (hereditary effects).

– A general measure of all detrimental effects resulting from the exposure of a group of individuals (loss of health due to stochastic and deterministic effects, concern and alarm among individuals for their health and their family’s health, and all effects having an adverse impact on the comfort of such individuals as a result of the exposure to radiation itself and any countermeasures implemented).

External exposure
– Exposure of an object (for example, the human body) to a source of ionizing radiation located outside the object.

Affected region
– Region requiring planning and implementation of various measures due to an accident. This region will depend on the size of the accident. The boundaries of the affected region in any particular case are determined by [the appropriate] governmental regulatory authorities (in this case, various executive agencies of the Ukrainian Government).

Restricted zone
– Zone of potential excess individual exposure (i.e., exposure in excess of the dose limit) immediately surrounding a radiation-generating/nuclear facility. Within this zone, residence of Category-B individuals is forbidden, limits are imposed on economic activity unrelated to the radiation-generating or nuclear facility, and radiation monitoring is performed.

Observation zone
– Zone potentially affected by radioactive releases or discharges from a radiation-generating/nuclear facility and subject to monitoring of processes to ensure radiation safety of the radiation-generating or nuclear facility.

Radioactive isotopes
– Radioactive isotopes with identical numbers of protons in the nucleus, e.g., the following radioactive isotopes of iodine: Iodine-125, -127, -129, -131, -132, -133, etc.

Commercial source
– A source of ionizing radiation (of either natural or artificial origin) used for a specific purpose in industry, science, medicine, or other field, with the aim of receiving a material or other benefit during all phases of the source life cycle from mining (fabrication) to burial (disposition).

Incorporated radionuclide
– A radionuclide incorporated into the body.

Ionizing radiation
– Radiation (in either particle form or electromagnetic form) which directly or indirectly ionizes or excites atoms or molecules as it interacts with matter.

Dose limit quota
– The fraction of the Category C dose limit (DL) allocated to normal operating mode for a specific commercial source.

– Any action leading to: A reduction in individual or collective dose, a reduction in the probability of exposure resulting from an accident or chronic exposure situation, or a reduction in the health damage due to the accident or chronic exposure situation itself.

Countermeasure, high priority
– A countermeasure to prevent the acute or chronic exposure of members of the public from reaching dose levels that might cause acute radiation related clinical symptoms.

Countermeasure, emergency
– A countermeasure aimed at prevention of threshold deterministic effects.

Countermeasure, indirect
– A countermeasure which will not reduce the individual or collective doses to the public, but will reduce (or compensate for) health losses due to accidental exposure.

Countermeasure, direct
– Countermeasures which will lead to the reduction of accident-related individual or collective doses to the public.

Monitoring, dosimetric (radiation/dosimetric)
– A system of measurements and calculations oriented towards the evaluation of exposure doses for individuals or groups of individuals, as well as the measurement of radiation in the industrial and natural environments.

Monitoring, personnel dosimetric
– A monitoring system for monitoring the individual doses of internal and external radiation received by Category A and Category B individuals.

Critical group
– The portion of the population which receives or may receive the highest exposure to a given source based on age, gender, social/professional indicators, location of residence, or other indicators.

Dose limit (DL)
– The primary operational radiation/health standard intended to protect individuals in Category A, Category B, and Category C from all commercial sources of ionizing radiation.

Medical exposure
– Exposure of individuals (patients) for medical examination or treatment (or exposure of volunteers).

Monitoring, emergency (radiation)
– Determination of the radionuclide content in the environment, food products, and water; determination of doses received by the public; and prediction of doses received by the public in support of decision-making to determine the need for intervention (in addition to the form, scale, and duration of intervention).

Monoenergetic ionizing radiation
– Ionizing radiation which consists of identical monoenergetic particles or photons.

– Intake of radioactive substances via the respiratory tract, digestive tract, or skin.

– Intake of radioactive substances via the respiratory tract.

– Intake of radioactive substances into the digestive system via the oral cavity.

Lower limit of justifiability (justifiability limit)
– The averted dose for which the health benefit of a countermeasure (upon implementation) will be virtually identical to the detriment of the intervention.

Indirectly ionizing radiation
– Ionizing radiation consisting of photons or neutral particles that are produced by ionizing radiation as it interacts with matter.

Limited exemption
– Exemption of a practice or a source of ionizing radiation (within the framework of an overall practice) from certain types of regulatory oversight by a regulatory authority.

– Effect of ionizing radiation from sources located outside the body (external exposure) or from sources located inside the body (internal exposure).

– An individual who has been prescribed a radiological or X ray procedure for diagnostic or therapeutic purposes.

Half life
– A characteristic of a radionuclide – the time in which the number of nuclei of a given radionuclide decreases by a factor of two (due to spontaneous nuclear transformations).

Iodine phase of an accident
– The early phase in an accident in which significant releases of iodine radionuclides occur; during this phase, there is a serious danger that these radionuclides will be inhaled or ingested with food, thereby exposing the thyroid gland in members of the public (especially children) to radiation.

Relocation (to new areas of residence)
– Relocation of the public from areas contaminated with radiation due to a community-wide accident to areas with low (zero) individual accident-related doses.

Emergency personnel
– Individuals working on the facility which was involved in the accident. Includes both primary personnel and personnel on loan from other organizations.

Personnel, primary
– Personnel from the facility involved in the accident, as well as personnel in previously arranged emergency teams (rapid reaction medical teams, emergency dosimetry groups, fire fighting teams especially trained for fighting fires during radiological accidents, repair teams, and the like).

Personnel on loan
– Individuals obtained on loan for emergency operations; must be trained and provided information on the radiation environment in the areas where the work is to be performed.

Full exemption
– Full exemption (without additional oversight) of a practice or a source of ionizing radiation from NRBU 97 requirements by a regulatory authority.

Potential alpha particle energy
– Total alpha-particle energy released in the complete decay of radon daughter products (polonium 218, lead 214, bismuth 214, and polonium 214) to lead 210.

Absorbed dose rate (in air) (ADR)
– Dose rate absorbed per unit volume of air.

Justification principle
– A principle of radiological protection under which the benefit from a given human activity is required to exceed the total detriment to society or the individual.

Dose-limit principle
– A principle of radiological protection under which the exposure values associated with a given human activity are required to remain within (not to exceed) established levels.

Optimization principle
– A principle of radiological protection under which the benefit from a given human activity is required not only to exceed the associated detriment, but also to be as large as possible.

Natural radiation background
– Exposure from cosmic sources and terrestrial radionuclides naturally present on Earth, not including technologically amplified sources of natural origin. Exposure from such sources cannot feasibly be reduced.

Device for generating ionizing radiation (non radionuclide source)
– A device (X ray tube, accelerator, oscillator, etc.) which generates ionizing radiation through changes in the velocity of charged particles, annihilation of charged particles, or nuclear reactions.

Radiological protection
– All legal, regulatory, design, medical, engineering, and management measures used to support radiation safety.

Radiation safety
– A condition under which radiation generating/nuclear facilities and the environment remain within primary dose limits, unjustified exposures do not occur, and exposures to personnel and the public are reduced as far below established dose limits as may be achievable and economically justified.

Radiation risk
– Probability that an individual will experience a given stochastic effect as a result of exposure.

Radiation factor (effect)
– Any type of radiation effect which will (or might) cause human exposure or radioactive contamination of the environment.

Radiation producing/nuclear facility
– Any materials, devices, or structures which contain or might contain nuclear materials or sources of ionizing radiation (power-plant reactors, industrial reactors, research reactors, experimental reactors, devices, installations, test facilities, equipment, tools, storage facilities, warehouses, and vehicles, as well as electrical power plants, manufacturing facilities, and materials processing facilities where such materials and sources are used; including facilities involved in research, development, production, testing, transportation, and storage of nuclear explosive devices).

– A property of radionuclides that undergo spontaneous transformation into atoms of different elements (nuclides or radionuclides) as the nucleus transitions from one energy state to another, accompanied by the emission of ionizing radiation.

Radioactive contamination
– Presence or dispersal of radioactive materials in excess of their natural content in the environment and/or human body.

– Radioactive atoms with a given mass number and atomic number. Radionuclides of the same chemical element are called isotopes.

Removable surface radioactive contamination (non fixed)
– That portion of surface contamination with radionuclides (or radioactive materials) which is spontaneously transferred (or transferred through use and operation) from a contaminated surface into the environment or can be removed using decontaminating agents.

Radiation/health procedures
– All approved regulations, conditions, decision making criteria (including numerical values of standards, reference levels, etc.), measurement methods, or measurement tools used to ensure uniformity and harmonization of radiation safety requirements and radiation monitoring tools and methods.

Reference man
– A series of age-dependent mathematical models of the human body (mathematical phantoms) used for radiation/health regulation of radiation.

Reference value (of a quantity, parameter, etc.)
– A value used to standardize various factors, both for man (professional, age, and gender structure of the population, its living conditions, and its activities), and for the environment and exposure conditions.

Reference commercial source
– A standard source not explicitly specified, but used in radiation health regulations. The reference commercial source produces a dose that is equivalent to the reference dose quota.

Reference age (RA)
– One of six fixed ages used in the regulatory system for radiation. The scale of reference ages is listed in Table II.2.3.

– Quantitative measure (probability) of the detriment incurred as the result of certain specific events, including exposure to radiation. Determined from the number of cases in a given population.

Justification level
– Averted dose level at which the health benefit of a countermeasure to be implemented will be less than the detriment of the intervention.

Intervention level
– Averted dose level above which a specific countermeasure must be implemented in the event of accidental or chronic exposure.

Action level
– A derived quantity obtained from the intervention levels, expressed in terms of such measurable indicators of the radiation environment as: Absorbed dose rate in air in an open area, activity concentration of radionuclides in air, concentration of radionuclides in foodstuffs, radionuclide fallout density, etc.

Residual (non preventable) dose level
– The portion of a dose from a given accident related source that remains despite implementation of a countermeasure.

Acceptable radiation level
– Residual dose level considered acceptable from the point of view of human health.

Liquid discharge (discharge)
– Discharge of radioactive materials generated or used at an enterprise into the environment with waste water.

Annual effective dose
– Total effective dose from external radiation within a one year period, plus the expected effective dose of internal radiation accumulated as the result of radionuclide incorporation over a one-year period.

Annual radionuclide intake
– Radionuclide activity incorporated during a one-year period.

Work area
– Area (room) continuously or temporarily occupied by personnel while working with sources of ionizing radiation. If the work with sources of ionizing radiation is performed at various locations within a room, the entire room shall be considered the work area.

Mean annual equivalent equilibrium radon activity
– Mean annual radon activity per unit volume (in equilibrium with its decay products) that would have the same potential alpha particle energy per unit volume as the actual mixture.

Thermodynamic diameter – Diameter of a spherical particle having the same diffusion coefficient in air as the aerosol particle under consideration.
Technologically amplified sources of natural origin
– Sources of ionizing radiation of natural origin that become concentrated or more accessible as a result of human commercial or economic activities, thereby causing enhancement of the natural radiation background.

Tissue equivalent
– A material whose electron density, effective atomic number, and elemental composition are similar to those of human tissue.

Accident phase, early (acute)
– One of the phases of a community wide accident, with a duration ranging from a few hours to one or two months after occurrence of the accident. Includes the following events:

a)  -  Releases of gas, aerosols, and liquids containing radioactive materials from the source of the accident;

b)  -  Air transport of radionuclides and intense groundward migration of radionuclides;

c)  -  Radioactive fallout and formation of a radioactive trail.

Accident phase, intermediate (stabilization phase)
– One of the phases of a community wide accident, beginning one to two months post-accident and extending to 1–2 years post accident, during which (because of radioactive decay) there are no radioactive isotopes of tellurium, iodine, 140Ba, or 140La, but 95Zr, 95Nb, ruthenium isotopes, cerium isotopes, 134Cs, 136Cs, and 137Cs begin to play an important role in formation of the gamma ray field. Radioactive isotopes of cesium (134Cs, 136Cs, and 137Cs) and strontium (89Sr, 90Sr) ingested with foodstuffs produced in areas contaminated with radiation are the main sources of internal radiation during the intermediate phase of the accident.

Accident phase, late (recovery phase)
– One of the phases of a community wide accident, beginning 1–2 years post accident, when 137Cs in fallout is the main source of external radiation and 137Cs and 90Sr ingested with foodstuffs produced in areas contaminated with these radionuclides are the main sources of internal radiation.

Background exposure
– Exposure to sources of natural background radiation.

Fixed (non removable) surface radioactive contamination
– That portion of surface contamination with radionuclides (or radioactive materials) which does not spontaneously transfer (or transfer through use and operation) from a contaminated surface into the environment and cannot be removed using decontamination agents (without destroying the integrity of the surface).

Chronic exposure
– Exposure over a long period of time (generally more than a year).

Characteristic radiation
– Photon radiation with a discrete energy spectrum, resulting from a change in the state of the electrons in the atom.

– A term used to refer to all unfavorable clinically observed effects on human health – both the stochastic and deterministic effects of exposure.

Nuclear material
– A material produced (or especially created) which is capable of fission via a chain reaction under special conditions (e.g., plutonium-239, uranium 235- and uranium 238-enriched uranium, etc.).


Radiation Safety Standards of Ukraine (NRBU-97)