Borders' Dictionary of Health Physics

Objective evidence
Any documented statement of fact, other information, or record, either quantitative or qualitative, pertaining to the quality of an item or service based on observations, measurements, or test which can be verified.
(ANSI N46.2-1978)

Observed ratio
The ratio of the radionuclide stable-element-concentration in one medium to the radionuclide stable-element-concentration in a precursor pathway.
(NUREG/CR 3332)

Occupancy factor (T)
The factor by which the workload should be multiplied to correct for the degree of occupancy (by any one person) of the area in question while the source is in the "ON" condition and emitting radiation. The multiplication is carried out for radiation protection purposes to determine compliance with the dose equivalent limits.
(NCRP 102)

Occupancy factor (T)
The factor by which the workload should be multiplied to correct for the degree of occupancy of the area in question while the source is "ON".
(NCRP 49)

Occupancy factor (T)
The factor by which the workload should be multiplied to correct for the degree or type of occupancy of the area in question.
(NBS 73)

Occupancy factor (T)
The factor by which the workload should be multiplied to correct for the degree or type of occupancy of the area in question.
(NBS 59)

Occupational dose
An individual's ionizing radiation dose (external and internal) as a result of that individual's work assignment. Occupational dose does not include doses received as a medical patient or doses resulting from background radiation or participation as a subject in medical research programs.
(10CFR835.2-1998)

Occupational dose
The dose received by an individual in the course of employment in which the individual's assigned duties involve exposure to radiation or to radioactive material from licensed and unlicensed sources of radiation, whether in the possession of the licensee or other person. Occupational dose does not include dose received from background radiation, from any medical administration the individual has received, from exposure to individuals administered radioactive materials and released in accordance with Sec. 35.75, from voluntary participation in medical research programs, or as a member of the public.
(10CFR20.1003)

Occupational dose
Exposure of an individual to radiation (i) in a restricted area; or (ii) in the course of employment in which the individual's duties involve exposure to radiation, provided that "occupational dose" shall not be deemed to include any exposure of an individual to radiation for the purpose of medical diagnosis or medical therapy of such individual.
(10CFR20.3)

Occupational exposure
An individual's exposure to ionizing radiation (external and internal) as a result of that individual's work assignment. Occupational exposure does not include planned special exposures, exposure received as a medical patient, background radiation, or voluntary participation in medical research programs.
(10CFR834.2)

Occupational exposure
Exposure of the worker that is directly attributable to the worker's occupation.
(NCRP 118)

Occupational exposure
The exposure of an individual to ionizing radiation in the course of employment in which the individuals normal duties or authorized activities necessarily involve the likelihood of exposure to ionizing radiation.
(NCRP 107)

Occupational exposure
In this report, exposure to people from external, penetrating, ionizing radiation fields and irradiation by internally deposited radionuclides that are directly attributable to one's occupation.
(NCRP 101)

Occupational exposure
Exposure of the worker during a period of work.
(NCRP 78)

Occupational exposure
The exposure of an individual to ionizing radiation in a controlled area or in the course of employment in which the individual's normal duties or authorized activities necessarily involve the likelihood of exposure to ionizing radiation.
(NCRP 51)

Occupational radiation exposure
Radiation exposure resulting from, and received in, the course or an individual's employment.
(ANSI N13.6-1966)

Occupationally exposed
Exposed to radiation as a direct result of occupational duties.
(NCRP 105)

Occupiable area
Any room or other space, indoors or outdoors, that is likely to be occupied by any person, either regularly or periodically during the course of his work, habitation, or recreation and in which an ionizing radiation field exists because of radiation sources in the vicinity.
(NCRP 49)

Occupied area
An area that may be occupied by persons or radiation-sensitive materials.
(NBS 73)

Occupied space
Space that may be occupied by persons, or radiation-sensitive materials and devices, during the time that radioactive materials are in the vicinity.
(NBS 54)

Occupied space
The space neighboring an electron accelerator that is occupied or may be occupied by persons during times when the accelerator is producing radiation.
(NBS 55)

Ocean service
All navigable waters of any ocean or the Gulf of Mexico more than 20 nautical miles offshore.
(ANSI N14.24-1985)

Odor threshold limit
The lowest concentration of a contaminant in air that can be detected by the olfactory sense.
(ANSI Z88.2-1980)

Off-line
Mode of operation of the computer system in which the input data used by the program being performed is independent of the current state of the process plant.
(IEC 50-394-1993)

Off line
A system where an aliquot is withdrawn from the effluent stream and conveyed to the detector assembly.
(ANSI N42.18-1974)

Off line
A system where an aliquot is withdrawn from the effluent stream and conveyed to the detector assembly.
(ANSI N13.10-1974)

Off-gas
The gaseous effluent from a process or operation.
(ERDA 76-21)

Off-Gas Treatment
A generic term describing the removal of various materials from the air stream associated with incineration.
(ANSI/HPS N13.45-1998)

Off-line system
One that is not operating or is normally held in standby.
(ERDA 76-21)

Offgas
The normal gasborne discharge from any process vessel or other process equipment. The flow rate is normally much less than the ventilation exhaust or recirculation rate.
(ANSI N303-1978)

Offgas system
The system comprised of air-and-gas treatment equipment, transfer equipment, ducts, stacks, and other components required to collect, treat, and dispose of gasborne materials from process vessels and from equipment that is usually within cells or glove boxes.
(ANSI N303-1978)

Offshore platform radiography
Industrial radiography conducted from a platform over a body of water.
(10CFR34.3)

Offshore waters
That area of land and water, beyond Agreement States' Submerged Lands Act jurisdiction, on or above the U.S. Outer Continental Shelf.
(10CFR150.2)

Offsite
All areas not onsite.
(ANSI/ANS-3.8.1-1987)

Old bone
As used in ICRP 20-1972: All bone existing at time zero, the time of injection.
(ICRP 20)

Olfactory Region
Membranes in the upper part of the nasal cavities that contain the olfactory receptors for the sense of smell.
(NCRP 125)

Oligotrophic
Water deficient in nutrients.
(NCRP 76)

Omnivorous
Feeding on both plants and animals.
(NCRP 76)

On site
Location within a facility that is controlled with respect to access by the general public.
(ANSI N13.10-1974)

On site
Location within a facility that is controlled with respect to access by the general public.
(ANSI N42.18-1974)

On-line
Mode of operation of the computer system in which the input data used by the program being performed is acquired automatically from the process plant to represent its current state.
(IEC 50-394-1993)

On-line system
One that is operating or is normally in operation, as opposed to an off-line system.
(ERDA 76-21)

On-the-job training
A systematic, structured method using a qualified person to provide the required job-related knowledge and skills to a trainee, usually in the actual work place, with proficiency documented.
(ANSI/ANS-15.4-1988)

Oncogenes
Genes that carry the potential for cancer.
(BEIR V)

Oncogenes
Genes that carry the potential for cancer.
(BEIR IV)

One group theory
A theory of neutron behavior in which all neutrons are assumed to belong to a single energy group. In this theory, all neutrons born in fission are considered to be injected into this group, all absorptions are removals from the group, and reaction probabilities are taken as identical for all neutrons in the system.
(ANSI N1.1-1976)

One-group model
A model in which the neutron population is assigned a single effective energy.
(ANSI N1.1-1976)

Onsite
That area surrounding the reactor in which the utility has the authority to control all activities including the exclusion or removal of personnel and property.
(ANSI/ANS-3.8.1-1987)

Opacity
Degree to which an aerosol obscures an observer's view.
(AM-1993)

Open-cycle reactor system
A reactor system in which the coolant passes through the reactor core only once and is then discarded.
(USAEC-1974)

Open-face filter
A filter with no restrictions over the ends or faces of the unit, as opposed to the enclosed filter with reduced-size end connections.
(ERDA 76-21)

Open-face sampler
A filter cassette sampler with the inlet approximately the same size as the filter.
(AM-1993)

Operating license
Having a license issued pursuant to Sec. 50.57 of this chapter. It does not include licenses that only authorize possession of special nuclear material after the Commission has received a request from the licensee to amend its licensee to permanently withdraw its authority to operate or the Commission has permanently revoked such authority.
(10CFR171.5)

Operating pressure
The desired pressure corresponding to any single condition of operation.
(ERDA 76-21)

Operating range
Range of reactor power level within which a reactor is designed to operate in a steady-state condition.
(IEC 50-393-1993)

Operating range
The region between the limits within which a quantity is measured.
(ANSI N317-1980)

Operation
An impoundment is being used for the continued placement of new tailings or is in standby status for such placement. An impoundment is in operation from the day that tailings are first placed in the impoundment until the day that final closure begins.
(40CFR61.251)

Operational
A uranium mill tailings pile that is licensed to accept additional tailings, and those tailings can be added without violating subpart W or any other Federal, state or local rule or law. A pile cannot be considered operational if it is filled to capacity or the mill it accepts tailings from has been dismantled or otherwise decommissioned.
(40CFR61.221)

Operational bypass
Approved action or device which renders inoperable certain protective actions when they are not necessary in a particular mode of plant operation.
(IEC 50-393-1993)

Operational conditions (of equipment)
Influence quantities expected as a result of normal operating requirements, expected extremes in normal operating requirements and postulated conditions appropriate for the postulated initiating events of the station.
(IEC 50-393-1993)

Operational crew
The body of people in charge of a plant operation, including the supervisory operator, the shift leader and those staff members and experts who are authorized to be present in the control room.
(IEC 50-393-1993)

Operational quantities
Quantities used in radiation protection practice that are measurable and provide a sufficiently conservative assessment of limiting quantities to ensure the absence of underestimates.
(ANSI/HPS N13.11-1993)

Operator
Any individual licensed under this part to manipulate a control of a facility.
(10CFR55.4)

Operator
Any individual who personally utilizes or manipulates a source of radiation.
(NCRP 102)

Oppenheimer-phillips process
A nuclear reaction in which low energy deuteron approaches sufficiently close to a nucleus for the nucleus to strip the neutron from the deuteron but still repel the remaining proton.
(ANSI N1.1-1976)

Optical (equivalent) diameter
Diameter of a calibration particle that scatters as much light in a specific instrument as the particle being measured.
(AM-1993)

Optical (single) particle counter
An aerosol size spectrometer that differentiates particles by the amount of light scattered by each particle.
(AM-1993)

Optical density
A quantitative measure of the darkening of the developed photographic emulsion.
(ANSI N13.7-1983)

Optical transfer function (OTF)
The two-dimensional Fourier transform of the point spread function. The values of the OTF on a line in a specified direction through the origin of the spatial frequency domain are given by the one-dimensional Fourier transform of the corresponding line spread function. The OTF is generally a complex function and can be separated into the MTF and the phase transfer function.
(ICRU 54)

Optically coupled
A process of matching the refractive index of optical media; the space between the window of a scintillation detector and the window of a photomultiplier tube coupled to the detector is filled with a transparent material such as high viscosity silicon fluid with a refractive index close to those of the two windows.
(HPJ 60)

Optimal radiation protection
In this report, that level of radiation protection that, when either increased or decreased, results in decreased net benefit. hence optimal radiation protection yields the greatest net benefit to society.
(NCRP 107)

Optimization
This has the same meaning as ALARA.
(NCRP 91)

Optimization
A process that is applied prior to the release of radioactive material into the environment which optimizes radiation protection on the basis of a differential benefit/cost analysis aimed at keeping the exposures as los as reasonably achievable, economic and social factors being taken into account.
(ICRP 29)

Optimization of radiation protection
The process of determining and providing optimal radiation protection. This has the same meaning as ALARA.
(NCRP 107)

Optimum interspersed hydrogenous moderation
The presence of hydrogenous material between packages to such an extent that the maximum nuclear reactivity results.
(10CFR71.4)

Orange oxide
Uranium trioxide.
(USAEC-1974)

Orbit
The region occupied by an electron as it moves about the nucleus of an atom. (See shell.)
(USAEC-1974)

Orbital electron capture
A radioactive transformation in which the nucleus captures an orbital electron.
(ANSI N1.1-1976)

Ordinary concrete
There are many different types of ordinary concrete. The differences are due to a variation in the mix proportions and elemental composition of the cement, sand, coarse aggregate and water. In the context of ANSI/ANS-6.4, ordinary concrete means Type 04 having a theoretical density of 2.35 g/cm³.
(ANSI/ANS-6.4-1985)

Ordinary concrete
A Portland-cement concrete whose constituents are those usually used in construction. Thus, ordinary concrete excludes those mixtures where special materials (iron, etc.) have been added to enhance the radiation-shielding properties. For example, the term excludes "heavy concrete".
(NCRP 51)

Ore content meter
Assembly for determining the concentration of a specific metal, such as uranium, beryllium, thorium, in an ore.
(IEC 50-394-1993)

Ore processing
Uranium milling and other procedures for producing U₃O₈ from uranium ore or from uranium concentrates produced as a byproduct from phosphate or other non-nuclear chemical production plants.
(10CFR75.4)

Ore sorting equipment
Equipment using natural or artificially induced radioactivity for the removal of sterile ore and the classification of ores in categories to relevant element contents.
(IEC 50-394-1993)

Organ
An organized group of tissues having one or more definite functions to perform in an animal body.
(HPJ 60)

Organ
Group of tissues which together perform one or more definite functions in a living body.
(RHH)

Organ (dose) weighting factor
Factor indicating the relative risk of cancer induction or heredity defects from irradiation of a given tissue or organ; used in calculation of effective dose equivalent and committed effective dose equivalent, and denoted w_T by the ICRP.
(FGR 11)

Organ burden
The quantity of a radionuclide present in an organ at a particular point in time.
(HPJ 60)

Organ burden
The quantity of a radionuclide present in an organ at a particular point in time.
(NCRP 87)

Organ burden
The quantity of a radionuclide present in an organ of the body.
(ANSI N13.14-1983)

Organ burden
The quantity of a radionuclide present in an organ of the human body at a specified time.
(ANSI N343-1978)

Organ weighting factor (w_T)
A factor that indicates the ratio of the risk of stochastic effects attributable to irradiation of a given organ or tissue (T) to the total risk when the whole body is uniformly irradiated.
(NCRP 107)

Organ weighting factors
Factors indicating the proportion of the total risk to the body of cancer and heredity defects attributable to a given organ or group or organs (i.e., organ dose weighting factors).
(NCRP 84)

Organic
The compounds of carbon. Examples are saturated hydrocarbons (methane, ethane, butane), unsaturated hydrocarbons (ethylene, acetylene), alcohols(methyl alcohol, propyl alcohol), ethers (methyl ether, ethyl ether), aldehydes (formaldehyde), ketones (dimethyl ketone), organic acids (formic acid, acetic acid), halides (chloroform, carbon tetrachloride), amides (formanide, diisocyanate), amines (methylamine), epoxies (epoxyethane, propylene oxide, and aromatics (benzene, toluene, xylene).
(ANSI Z88.2-1980)

Organic scintillator solute material
An organic compound which can absorb radiant energy and immediately (typically within 10^-9 second) re-emit this energy as photons in the ultraviolet range.
(ANSI N42.15-1980)

Organic tritium
The tritium associated with organic molecules.
(NCRP 62)

Organic-cooled reactor
A reactor that uses organic chemicals, such as mixtures of polyphenyls (diphenyls and terphenyls), as coolant.
(USAEC-1974)

Organometallic
Compounds in which metal are chemically bonded to organic groups (for example, ethyl silicate, tetraethyl lead, and organic phosphates).
(ANSI Z88.2-1980)

Organometallic
Compounds in which metal are chemically bonded to organic groups (for example, ethyl silicate, tetraethyl lead, and organic phosphates).
(ANSI Z88.2-1969)

Organs at risk
Organs at risk are those radiosensitive organs in or near the target volume which would influence treatment planning and/or the prescribed dose. For example, in an intracavitary application for cervix carcinoma, the main organs at risk are rectum, bladder, ureters and possibly sigmoid colon.
(ICRU 38)

Organs at risk
Organs at risk are specially radiosensitive organs in or near the target volume whose presence influence treatment planning and/or prescribed dose.
(ICRU 29)

Orifice meter
A device used to measure flow rate in a duct by measuring the pressure drop across a calibrated constriction.
(AM-1993)

Origen
The ORNL Isotope Generation and Depletion Code - a computer code that solves equations of radioactive growth and decay for large numbers of isotopes. The code is used to compute compositions, inventories, and radiation levels of fission products, cladding material, and fuel elements in LWRs, LMFBRs, MSBRs, and HTGRs.
(NCRP 62)

Oronasal Breathing
Respiratory intake of air either by nose and/ or mouth.
(NCRP 125)

Oropharynx
Central portion of the pharynx lying between the soft palate and upper portion of the epiglottis.
(NCRP 125)

Osmosis
The passage of pure solvent from the lesser to the greater concentration when two solutions are separated by a membrane which selectively prevents the passage of solute molecules, but is permeable to the solvent.
(RHH)

Osmotic
Pertaining to osmosis.
(RHH)

Osomoregulation
Regulation of the osmotic pressure of body fluids by controlling the amount of water and/or salt in the body.
(NCRP 109)

Osteocytes
Bone cells within the mineralized bone.
(NCRP 94)

Osteocytes
Bone cells within the mineralized bone.
(NCRP 45)

Osteogenic potential
Potential to produce bone cancer, osteosarcoma.
(NCRP 84)

Osteosarcoma
Malignant tumor of the connective tissue of the bone.
(NCRP 125)

Other production or utilization facility
A facility other than a nuclear reactor licensed by the Commission under the authority of section 103 or 104 of the Atomic Energy Act of 1954, as amended (the Act), and pursuant to the provisions of part 50 of this chapter.
(10CFR170.3)

Other professionals
Qualified persons, including nurses, industrial hygienists, and safety engineers who by the nature of their training or experience can function effectively with the guidance of a physician, in accordance with applicable federal and state regulations.
(ANSI Z88.6-1984)

Outliers
Data points or data sets that are anomalous relative to the accumulated body of calibration data.
(ANSI N15.19-1989)

Output
The exposure rate, dose rate, or a quantity related in a known manner to these rates from a teletherapy unit for a specified set of exposure conditions.
(10CFR35.2)

Output
A measure of the radiation beam produced by a radiation source. It is usually stated as the exposure rate or absorbed dose rate at an approximate calibration point under a closely defined set of conditions.
(NCRP 68)

Output
The exposure rate or absorbed dose rate at a specified point under specified conditions.
(NCRP 69)

Output
The measure of a radiation beam produced by a radiotherapy treatment unit. It is usually stated as the exposure rate or absorbed dose rate at a calibration point (q.v.) under a closely defined set of conditions. For x rays generated at potentials below 150 kV the measurement is usually carried out free in air at the spatial position of the calibration point and the result converted to absorbed dose rate at the phantom surface as recommended in ICRU Report 23. For all other photon energies the measurement is carried out in a phantom at a specified depth. For a given generator potential-filter combination, or a given gamma ray energy, the output of a treatment unit may conveniently refer to a single beam measured under conditions which can be readily reproduced, the exposure (or absorbed dose) rate under other conditions of interest being related to this single measurement by predetermined multiplication factors. However, this method should not be used to relate x-ray beams with different generator potential-filter conditions since, in this case, the continued constancy of the multiplying factors cannot be assumed.
(ICRU 24)

Outside an installation
Used with an implied limitation to the region in which the installation may significantly affect the radiation dose to members of the public. This region could include areas geographically remote from the installation.
(ICRP 7)

Overhead and General and Administrative costs
(1) The Government benefits for each employee such as leave and holidays, retirement and disability benefits, health and life insurance costs, and social security costs;
(2) Travel costs;
(3) Direct overhead, e.g., supervision and support staff that directly support the NRC safety mission areas (administrative support costs, e.g., rental of space, equipment, telecommunications and supplies); and
(4) Indirect costs that would include, but not be limited to, NRC central policy direction, legal and executive management services for the Commission and special and independent reviews, investigations, and enforcement and appraisal of NRC programs and operations.
(10CFR171.5)

Overload
Response of less than full scale (that is, maximum scale reading) when exposed to quantify one or more particular ionizing radiation or radiations.
(ANSI N323-1978)

Overload response
The behavior of the instrument where the response is less than full scale or decade (i.e., maximum scale or decade reading) when exposed to radiation intensities greater than the upper limit.
(ANSI N42.17A-1989)

Overmoderated
Of a multiplying system, having a moderator-to-fuel volume ratio greater than that which makes for some specified reactor parameter an optimum value.
(ANSI N1.1-1976)

Overpressure
Pressure in excess of the design of operating pressure.
(ERDA 76-21)

Overpressure
The transient pressure over and above atmospheric pressure caused by a shock wave from a nuclear explosion. (See shock wave.)
(USAEC-1974)

Overvoltage (of a Geiger-Muller counter tube)
Difference between the operating voltage and the Geiger-Muller threshold.
(IEC 50-394-1993)

Owl
A device used to measure diameter of monodisperse aerosol particles by illumination with white light and detection of higher-order Tyndall spectra.
(AM-1993)

Owner
The individual, agency, contractor, company, or corporation that carries title to or will carry title to the packaging during its use.
(ANSI N14.1-1990)

Owner
The person, group, company, agency, or corporation who has or will have title to the nuclear facility.
(ANSI N46.2-1978)

Owner
A person, organization, or institution having title to or administrative control over one or more installations or sources of radiation.
(NCRP 49)

Owner or operator
Any person who owns, leases, operates, controls, or supervises a stationary source.
(40CFR61.02)

Oxygen deficiency - not immediately dangerous to life or health
An atmosphere having an oxygen concentration below the minimum legal requirement but above that which is immediately dangerous to life or health.
(ANSI Z88.2-1980)

Oxygen effect
The observation that oxygen enhances the radiation response has been demonstrated for a wide variety of biological endpoints. Although the term "oxygen effect" implies that hypoxia is the reference condition, it is common practice to use air as the reference base (100 percent O₂ is frequently equally sensitizing); neither condition reflects necessarily the oxygen concentration in the tissue of interest.
(ICRU 30)

Oxygen enhancement ratio (OER)
The ratio of the doses to achieve the same biological effect under hypoxic and aerated conditions. The ratio is the same at all survival levels and therefore oxygen is considered to be a dose-modifying factor.
(NCRP 98)

Oxygen enhancement ratio (OER)
The ratio of the dose required under conditions of hypoxia to that under conditions in air to produce the same level of effect.
(ICRU 30)

Note: References shown in ()