Borders' Dictionary of Health Physics

t
Duration of exposure (h).
(ICRP 66)

T cells
Lymphocytes that develop in the thymus and are responsible for cell-mediated immunity.
(HPJ 60)

t_a
Time constant (in S) for residence of air in the alveolar-interstitial airways = {V_T - V_D(ET) V_D(BB) + V_D(bb)](1 + V_T/FRC}/V
(ICRP 66)

t_b
Time constant (in S) for conduction of air through the bronchioles = V_D(bb) (1 + 0.5 V_T/FRC)/V
(ICRP 66)

t_b
Time constant (in S) for conduction of air through the trachea and bronchi = V_D(BB) (1 + 0.5 V_T/FRC)/V
(ICRP 66)

T-target tissue
Tissue or organ in which radiation is absorbed.
(ICRP 66)

T65 dosimetry
A system of gamma ray and neutron exposure assigned to each individual survivor of the atomic bombings of Hiroshima and Nagasaki based upon the stated distance from the hypocenter and shielding.
(ICRP 49)

Tactical Response Team
The primary response force for each shift which can be identified by a distinctive item of uniform, armed with specified weapons, and whose other duties permit immediate response.
(10CFR73.2)

Tag
See tracer, isotopic.
(USAEC-1974)

Tailings
Tailings shall have the same meaning as in section 101(8) of the Uranium Mill Tailings Radiation Control Act of 1978, 42 U.S.C. 7911(8).
(40CFR61.221)

Tailings
Waste or refuse left in various processes of milling or mining. Tailings often contain a major portion of the radioactive materials present in the undisturbed ore.
(NCRP 118)

Tails
See depleted uranium.
(USAEC-1974)

Tamper-Safing
The use of devices on containers or vaults in a manner and at a time that ensures a clear indication of any violation of the integrity of previously made measurements of special nuclear material within the container or vault.
(10CFR74.4)

Tank
Any vessel used for retaining solutions that is equipped with a system for measuring its liquid content. In this standard, the term "tank" refers to the vessel being calibrated, and not to the prover vessel.
(ANSI N15.19-1989)

Tank reactor
A reactor in which the core is suspended in a closed tank, as distinct from an open pool reactor. These are commonly used as research and test reactors.
(USAEC-1974)

Target
Material subjected to irradiation in an accelerator or nuclear reactor to induce a reaction or produce nuclear material.
(10CFR110.2)

Target
The part of an x-ray tube anode assembly impacted by the electron beam to produce the useful x-ray beam.
(NCRP 102)

Target
That part of the anode which is bombarded by electrons from the cathode resulting in the production of x rays.
(NCRP 66)

Target
Any object or surface bombarded by particles or photons.
(NCRP 51)

Target
An object bombarded by particles or photons.
(ANSI N1.1-1976)

Target
Material subjected to particle bombardment (as in an accelerator) or irradiation (as in a research reactor) in order to induce a nuclear reaction; also a nuclide that has been bombarded or irradiated. (See cross section, X ray.)
(USAEC-1974)

Target organ or target, (k)
An organ for which the radiation absorbed dose is calculated.
(MIRD)

Target theory (hit theory)
A theory explaining some biological effects of radiation on the basis that ionization, occurring in a discrete volume (the target) within the cell, directly causes a lesion which subsequently results in a physiological response to the damage at that location. One, two, or more "hits" (ionizing events within the target) may be necessary to elicit the response.
(BEIR IV)

Target tissue
Tissue or organ in which radiation is absorbed.
(ICRP 68)

Target tissue
Tissue or organ in which radiation is absorbed.
(ICRP 67)

Target tissue (T)
Tissue (which may be a body organ) in which radiation is absorbed.
(ICRP 56)

Target tissue (T)
Any tissue or organ of the body in which radiation is absorbed.
(FGR 11)

Target tissue (T)
Tissue (which may be a body organ) in which radiation is absorbed.
(ICRP 30)

Target volume
The target volume contains those tissues that are to be irradiated to a specified absorbed dose according to a specified time-dose pattern. For curative treatment the target volume consists of the demonstrated tumor(s), if present, and any other tissue with presumed tumor.
(ICRU 38)

Target volume (biological)
The volume of discrete biological entities (i.e., chromosome strand, bacterium, gene, virus, etc.) primarily responsible for a given radiation effect.
(ANSI N1.1-1976)

Target volume (volume of interest)
The region in the specimen to which it is desired to deliver a specified dose.
(ICRU 30)

Target volume (volume of interest)
The region in the specimen to which it is desired to deliver a specified dose.
(ICRU 24)

Target volume (volume of interest)
The region in the specimen to which it is desired to deliver a specified dose.
(ICRU 23)

Task group lung model
The model for behavior of particles in the respiratory tract of man developed by the Task Group on Lung Dynamics of the ICRP.
(NCRP 84)

Task Group On Lung Dynamics (TOLD)
An ICRP task group that promulgated revised models for deposition and retention of inhaled materials in the human respiratory tract in 1966.
(NCRP 125)

Taurine
A colorless crystalline compound C₂H₇NO₃S of neutral reaction found in the juices of muscle, especially in invertebrates, and obtained as a cleavage product of taurocholic acid.
(HPJ 60)

TB-tracheobronchiolar
Combined regions consisting of airway generations 0 through 15.
(ICRP 66)

Teaching exercise
Demonstration by a teacher or experiment by a pupil.
(ICRP 36)

Teaching reactor
A research reactor or subcritical assembly.
(USAEC-1974)

Technical specifications
Those specific criteria, limiting conditions, and surveillance requirements contained in a facility operating license, proposed by the applicant and approved by the Nuclear Regulatory Commission (NRC).
(ANSI N303-1978)

Technician
An individual skilled in the application of radiation monitoring and radiation survey techniques to the extent that he is capable of assuming responsibility for routine monitoring and survey operations once the radiation protection aspects of the operation have been programmed under the guidance of a qualified expert.
(USAS N13.2-1969)

Techniques of therapy
Fixed Beam Therapy (stationary beam therapy): The target volume is irradiated at different times by one or more beams at definite angles relative to the patient. There are two different techniques used for this purpose.
(1) Fixed SSD Technique: The source-surface distance is fixed a priori. The source-tumor distance depends on the location of the tumor and the direction of the beam.
(2) Isocentric Technique (Fixed SAD Technique): A chosen point in the target volume is placed at the isocenter (q.v.). The source surface distance will depend on the depth of the tumor and the direction of the beam.
Moving Beam Therapy: Treatment by one or more radiation beams, which move in relation to the patient during irradiation. Most commonly, the motion of the source describes a circle or circular arc with the patient located on the axis of this rotation. The former is former is called rotation therapy, the latter is called arc therapy or pendulum therapy. Most commonly also, the axis of the radiation beam lies in the plane (plane of rotation) in which the motion takes place. This is called planar rotation therapy. On some occasions, the motion of the source describes a straight line, usually parallel to the long axis of the patient.
(ICRU 24)

Telangiectasia
Dilation of the capillary vessels and very small arteries.
(ICRP 59)

Telangiectasia
Dilation of the capillary vessels and very small arteries.
(NCRP 98)

Telencephalon
The endbrain, i.e., the terminal part of the prosencephalon. It gives rise to the right and left cerebral vesicles, i.e., the future cerebral hemispheres.
(ICRP 49)

Teletherapy
Treatment in which the source of radiation is at a distance from the body, as contrasted to brachytherapy.
(NCRP 107)

Teletherapy
Therapeutic irradiation with collimated x rays or gamma rays, the source being at 50 cm or more from the body. Contrast with the definition of brachytherapy.
(NCRP 48)

Teletherapy
See gammma-ray beam therapy.
(NCRP 49)

Teletherapy
Radiation treatment administered by using a source that is at a distance from the body, usually employing gamma-ray beams from radioisotope sources. (See radiation therapy.)
(USAEC-1974)

Teletherapy
Therapeutic irradiation with collimated gamma rays.
(NBS 73)

Teletherapy
Therapeutic irradiation with collimated gamma rays.
(NBS 54)

Teletherapy physicist
The individual identified as the teletherapy physicist on a Commission license.
(10CFR35.2)

Teletherapy source
A sealed source of small dimensions designed for use in teletherapy.
(ICRU 18)

Temperature coefficient of reactivity
The partial derivative of reactivity with respect to temperature. (The temperature may be that of some specified location or component.)
(ANSI N1.1-1976)

Temperature coefficient of reactivity
The change in reactor reactivity (per degree of temperature) occurring when the operating temperature changes. The coefficient is said to be positive when an increase in temperature increases the reactivity, negative when an increase in temperature decreases reactivity. Negative temperature coefficients are desirable because they help to prevent power excursions. (See excursion, reactivity.)
(USAEC-1974)

Temperature shock
A rapid and large temperature change.
(ANSI N42.17C-1989)

Temporary emergency access
Access that is granted at NRC's discretion under §62.23 of this part upon determining that access is necessary to eliminate an immediate and serious threat to the public health and safety or the common defense and security. Such access expires 45 days after the granting and cannot be extended.
(10CFR62.2)

Temporary jobsite
A place where licensed materials are present for the purpose of performing well logging or subsurface tracer studies.
(10CFR39.2)

Temporary jobsite
A location where radiographic operations are conducted and where licensed material may be stored other than those location(s) of use authorized on the license.
(10CFR34.3)

Tenth value layer (TVL)
Thickness of a specified substance which, when introduced into the path of a given beam of radiation, reduces the kerma rate to one-tenth of its original rate.
(NCRP 102)

Tenth-value layer (or thickness)
Thickness of a specified substance which, when introduced into the path of a given beam of radiation, reduces the absorbed dose index or dose-equivalent index to one-tenth. The magnitude of the tenth-value layer may be different for absorbed dose index and dose equivalent index.
(NCRP 51)

Tenth-value layer (TVL)
Thickness of a specified substance which, when introduced into the path of a given beam of radiation, reduces the exposure rate to one-tenth.
(NCRP 49)

Tenth-value layer (TVL)
Thickness of an absorber required to attenuate a beam of radiation by a factor of ten.
(ANSI N1.1-1976)

Tenth-value layer (TVL)
Thickness of an absorber required to attenuate a beam of radiation to one-tenth.
(NBS 73)

Teratogenic
Capable of causing a malformation of the fetus.
(ICRU 30)

Teratogenic effects
Effects occurring in offspring as a result of insults sustained in-utero.
(FGR 11)

Teratogenic effects
Effects occurring in offspring as a result of insults sustained in-utero.
(NCRP 91)

Terminal settling velocity
Equilibrium velocity of a particle, approached when falling under the opposing influences of gravity and fluid drag.
(AM-1993)

Terminal velocity
The velocity at which the fluid resistance to the motion of a body equals the force causing the motion, usually the force of gravity.
(TID-26608)

Termination
The end of employment with the licensee or, on the case of individuals not employed by the licensee, the end of a work assignment in the licensee's restricted area in a given calendar quarter, without expectation or specific scheduling or reentry into the licensee's restricted areas during the remainder of that calendar quarter.
(10CFR20.3)

Ternary fission
A fission in which two normal-range fission products and a high-energy light nuclide, most frequently an alpha particle, are given off. In ²³⁵U this occurs in about 1 out of 300 events.
(NCRP 62)

Test
Procedure with the following sequence:
(1) Submission of dosimeters from a processor's current stock to a testing laboratory over a period of several months, in numbers sufficient for the specified irradiations in any one test category or subcategory covered by a processor's service.
(2) Irradiation of the dosimeters by personnel of the testing laboratory using the type(s) of radiation specified for this test category or subcategory.
(3) Evaluation by the processor of the response of the returned dosimeters in terms of shallow and deep dose equivalent for tests of protection monitoring, or in terms of deep absorbed dose for tests of accident monitoring.
(4) Submission of these evaluations to the testing laboratory.
(5) Analysis of the submitted evaluations by the testing laboratory.
(6) Reporting of the results of this analysis (also referred to as "test results") to the processor.
(ANSI/HPS N13.11-1993)

Test
A procedure whereby the instrument, component, or circuit is evaluated for satisfactory operation.
(ANSI N42.17C-1989)

Test
A procedure whereby the instrument, component, or circuit is evaluated for satisfactory operation.
(ANSI N42.17A-1989)

Test
A procedure whereby the instrument, component, or circuit is evaluated for performance or satisfactory operation.
(ANSI N42.17B-1989)

Test
Procedure with the following sequence:
(1) Submission of dosimeters of a processor's current stock to a testing laboratory over a period of several months, in number sufficient for the specified irradiations in any one test category covered by a processor's service.
(2) Irradiation of the dosimeters by personnel of the testing laboratory using the type(s) or radiation specified for this test category.
(3) Evaluation by the processor of the response of the returned dosimeters in terms of shallow and deep dose equivalent for tests of protection monitoring, or in terms of deep absorbed dose for tests of accident dosimetry.
(4) Submission of these evaluations by the testing laboratory.
(5) Analysis of the submitted evaluations by the testing laboratory.
(6) Reporting the results of this analysis (also referred to as "test results") to the processor.
(ANSI N13.11-1983)

Test
A procedure whereby the instrument, component, or circuit is evaluated for satisfactory operation.
(ANSI N323-1978)

Test category
Each type of radiation (or of radiation mixtures) and range of irradiation level for which separate tests are performed.
(ANSI/HPS N13.11-1993)

Test category
Each type, range of irradiation levels, and energy of radiation (or of radiation mixtures) for which separate tests are performed.
(ANSI N13.11-1983)

Test duration
Elapsed time between the test initiation and the test termination.
(IEC 50-394-1993)

Test initiation (in nuclear instrumentation)
Application of a test input.
(IEC 50-394-1993)

Test input
Real or simulated, but deliberate, perturbation of a measured variable or signal which is imposed upon all or part of a safety monitoring assembly, a safety logic assembly, or a final assembly for the purpose of testing.
(IEC 50-394-1993)

Test interval
Elapsed time between the initiation of identical tests on the same sensor, measuring and safety monitoring assembly, safety logic assembly, or final assembly.
(IEC 50-394-1993)

Test object
Objects having established value and associated uncertainty that are used for testing weighing instruments, mass measurement processes, and other test objects. Synonyms: checkweight, working standard, secondary standard, in-house standard (IHS). Test objects may be constructed as physical replicas or artifacts of production objects to minimize weighing errors due to factors such as buoyancy and balance loading.
(ANSI N15.18-1988)

Test program
A formalized schedule of tests which specifies the sequence of tests, the procedures to be employed, and the acceptance criteria.
(ERDA 76-21)

Test reactor
A reactor specially designed to test the behavior of materials and components under the neutron and gamma fluxes and temperature conditions of an operating reactor.
(USAEC-1974)

Test subcategory
A subset of a test category which includes only a limited portion of the energy range of the full category. A processor may opt to take one or more of the subcategories in a given category (See footnotes on Table 1).
(ANSI/HPS N13.11-1993)

Test termination (in nuclear instrumentation)
Removal of a test input with the results of the test being known.
(IEC 50-394-1993)

Testing
An element of verification for the determination of the capability of an item to meet specified requirements by subjecting the item to a set of physical, chemical, environmental, or operating conditions.
(ANSI N46.2-1978)

Testing Facility
A nuclear reactor licensed by the Commission under the authority of subsection 104c of the Act and pursuant to the provisions of Sec. 50.21(c) of this chapter for operation at:
(1) A thermal power level in excess of 10 megawatts; or
(2) A thermal power level in excess of 1 megawatt, if the reactor is to contain:
(i) A circulating loop through the core in which the applicant proposes to conduct fuel experiments; or
(ii) A liquid fuel loading; or
(iii) An experimental facility in the core in excess of 16 square inches in cross-section.
(10CFR171.5)

Testing facility
A nuclear reactor licensed by the Commission under the authority of subsection 104c of the Act and pursuant to the provisions of §50.21(c) of this chapter for operation at:
(1) A thermal power level in excess of 10 megawatts; or
(2) A thermal power level in excess of 1 megawatt, if the reactor is to contain: (i) A circulating loop through the core in which the applicant proposes to conduct fuel experiments; or (ii) A liquid fuel loading; or (iii) An experimental facility in the core in excess of 16 square inches in cross-section
(10CFR170.3)

Testing facility
A nuclear reactor which is of a type described in § 50.21(c) of this part and for which an application has been filed for a license authorizing operation at:
(1) A thermal power level in excess of 10 megawatts; or
(2) A thermal power level in excess of 1 megawatt, if the reactor is to contain: (i) A circulating loop through the core in which the applicant proposes to conduct fuel experiments; or (ii) A liquid fuel loading; or (iii) An experimental facility in the core in excess of 16 square inches in cross-section
(10CFR50.2)

Testing Laboratory
A laboratory authorized to prepare bioassay specimens (excreta samples and phantoms) with known amounts of radioactive material for distribution to service laboratories. The testing laboratory is responsible for evaluating the performance of the service laboratories in meeting the performance specifications of this standard.
(HPS N13.30-1996)

Testing laboratory
The external laboratory that provides standards or spiked samples with known amounts of uranium for the external quality control program of the service laboratory.
(ANSI/HPS N13.22-1995)

Testing laboratory
A group, independent of the processor's operation, that is carrying out the procedures outlined in this standard.
(ANSI/HPS N13.11-1993)

Testing laboratory
A laboratory authorized to prepare bioassay specimens (excreta samples and phantoms) by adding known amounts of radioactive material for distribution to service laboratories. The testing laboratory is responsible for evaluating the performance of the service laboratories in meeting the performance specification of this standard.
(ANSI N13.30-1989D)

Testing laboratory
A group independent of the processor's operation that is carrying out the procedures outlined in ANSI N13.11.
(ANSI N13.11-1983)

Testing reactor
A "testing facility" as defined in § 50.2 of this chapter.
(10CFR100.3)

TG-57
Test Group-57 of Operation Plumbbob, NTS
(RAH)

TGLD
Task Group on Lung Dynamics (ICRP), sometimes TGLM for Task Group on Lung Model
(RAH)

TGLM
Task Group on Lung Model (ICRP), sometimes TGLD for Task Group on Lung Dynamics
(RAH)

TH-thoracic region
Combined bronchial, bronchiolar, and alveolar-interstitial regions.
(ICRP 66)

Thalamus
A large ovoid mass of gray substance, with a flattened inner or medial surface, which serves as a relay station for sensory stimuli to the cerebral cortex; it also has important integrative and nonspecific functions.
(ICRP 49)

Therapeutic source assembly
A therapeutic source housing assembly for x-ray and electron beam production with a therapeutic beam limiting device attached.
(NCRP 102)

Therapeutic-type protective tube housing
(a) For x ray therapy equipment not capable of peak tube potentials of 500 kV or above, the following definition applies: An x-ray tube housing so constructed that the leakage radiation at a distance of one meter from the source dose not exceed one roentgen in an hour when the tube is operated at its maximum rated continuous current for the maximum rated tube potential.
(b) For x ray therapy equipment capable of peak tube potentials of 500 kV or above, the following definition applies: An x-ray tube housing so constructed that the leakage radiation at a distance of one meter from the source dose not exceed one roentgen in an hour or 0.1 percent of the useful beam exposure rate at one meter from the source, whichever is greater, when the tube is operated at its maximum rated continuous current for the maximum rated accelerating potential.
(NCRP 49)

Therapy
Medical treatment of a disease.
Brachytherapy: (Therapy at a short distances)
The treatment of disease with sealed radioactive sources placed near, or inserted directly into, the diseased area.
Contact radiation therapy: X-ray therapy with specially constructed tubes in which the target-skin distance is very short (less than 2 cm). The voltage is usually 40 to 60 kV.
Radiation therapy: Treatment of disease with any type of radiation.
Rotation therapy: Radiation therapy during which either the patient is rotated before the source of radiation or the source is revolved around the patient. In this way, a larger dose is built up at the center of rotation within the patient's body than on any area of the skin.
Teletherapy: (Therapy at long distance). The treatment of disease with gamma radiation from a source located at a distance from the patient.
(RHH)

Thermal (slow) neutron
A neutron in thermal equilibrium with its surrounding medium. Thermal neutrons are those that have been slowed down by a moderator to an average speed of about 2200 meters per second (at room temperature) from the much higher initial speeds they had when expelled by fission. This velocity is similar to that of gas molecules at ordinary temperatures. (See fission.)
(USAEC-1974)

Thermal breeder reactor
A breeder reactor in which the fission chain reaction is sustained by thermal neutrons.
(USAEC-1974)

Thermal burn
A burn of the skin or other organic material due to radiant heat, such as that produced by the detonation of a nuclear explosive. (See flash burn, radiation burn, radiation illness.)
(USAEC-1974)

Thermal bypass
An opening (usually vertical) from which warm air can leave a building.
(ENV RAD)

Thermal column
A large body of moderator, adjacent to or inside a reactor to provide thermal neutrons for experiments.
(ANSI N1.1-1976)

Thermal column
A channel built into some research reactors to supply thermal neutrons for experimental purposes. It consists of a large body of moderator located adjacent to the core or reflector. Neutrons escaping from the reactor enter the thermal column where they are slowed down to thermal energies with velocities of about 2200 meters per second. (See thermal neutron.)
(USAEC-1974)

Thermal diffusion
The diffusion which takes place in a multicomponent fluid as a result of a temperature gradient.
(ANSI N1.1-1976)

Thermal effect
A change in a medium or system that is directly associated with heat production when electromagnetic energy is absorbed.
(NCRP 67)

Thermal efficiency
The ratio of the electric power produced by a power plant to the amount of heat produced by the fuel; a measure of the efficiency with which the plant converts thermal to electrical energy.
(USAEC-1974)

Thermal fission
Fission caused by thermal neutrons.
(IEC 50-393-1993)

Thermal inelastic scattering
Inelastic scattering in which a particle exchanges energy with a molecule or lattice.
(IEC 50-393-1993)

Thermal instability (reactor theory)
The lack of regulation in response to temperature changes.
(ANSI N1.1-1976)

Thermal leakage factor
The fraction of neutrons in a chain-reacting system which leak out of the system after having been thermalized and before they are absorbed by the system.
(ANSI N1.1-1976)

Thermal neutrons
Neutrons in thermal equilibrium with the medium in which they exist.
(IEC 50-393-1993)

Thermal neutrons
Strictly, neutrons in thermal equilibrium with their surroundings, In this report, all neutrons with energies of less than about 1 eV are termed "thermal".
(NCRP 51)

Thermal neutrons
Strictly, neutrons in thermal equilibrium with their surroundings, In this report, all neutrons with energies of less than about 1 eV are termed "thermal".
(NCRP 38)

Thermal neutrons
Strictly, neutrons in thermal equilibrium with their surroundings. In this Handbook, all neutrons with energies of less than 0.5 ev are included in this category.
(NBS 63)

Thermal power measuring assembly
Assembly including sub-assemblies for measuring the temperature and the flow-rates of the cooling fluids, associated to a computer, and designed to determine the thermal power of a nuclear reactor.
(IEC 50-394-1993)

Thermal precipitator
A device that deposits particles using a temperature gradient.
(AM-1993)

Thermal radiation
Electromagnetic radiation emitted from the fireball produced by a nuclear explosion. Thirty-five percent of the total energy of a nuclear explosion is emitted in the form of thermal radiation, as light, ultraviolet and infrared radiation.
(USAEC-1974)

Thermal reactor
Reactor in which fissions are induced predominantly by thermal neutrons.
(IEC 50-393-1993)

Thermal reactor
A reactor in which the fission chain reaction is sustained primarily by thermal neutrons. Most reactors are thermal reactors. (See thermal neutron.)
(USAEC-1974)

Thermal shield
Shield intended to reduce heat generation by ionizing radiation in, and heat transfer to, exterior regions.
(IEC 50-393-1993)

Thermal shield
A layer or layers of high density material located within a reactor pressure vessel or between the vessel and the biological shield to reduce radiation heating in the vessel and the biological shield. (See biological shield, shield.)
(USAEC-1974)

Thermal spike
The momentary zone of high temperature produced in a solid or liquid along the track of a fission fragment or other high energy particle.
(ANSI N1.1-1976)

Thermal utilization
The probability in an infinite medium that a thermal neutron be absorbed in the fissile material.
(ANSI N1.1-1976)

Thermal utilization factor
In an infinite medium, the ratio of the number of thermal neutrons absorbed in a fissionable nuclide or in nuclear fuel, as specified, to the total number of thermal neutrons absorbed.
(ANSI N1.1-1976)

Thermalization
Establishment of thermal equilibrium between neutrons and their surroundings.
(ANSI N1.1-1976)

Thermalization
Establishment of thermal equilibrium between neutrons and their surroundings.
(RHH)

Thermel
The THERMal ELement of the calorimeter, including the sample chamber and temperature sensor.
(ANSI N15.22-1987)

Thermionic conversion
The conversion of heat into electricity by evaporating electrons from a hot metal surface and condensing them on a cooler surface. No moving parts are required.
(USAEC-1974)

Thermionic emission
Electron emission due to thermal agitation.
(IEC 50-393-1993)

Thermocouple
A device consisting essentially of two conductors made of different metals, joined at both ends, producing a loop in which an electric current will flow when there is a difference in temperature between the two junctions. (See Seebeck effect, thermoelectric conversion.)
(USAEC-1974)

Thermodynamic diameter (D_th)
Diameter (µm) of a spherical particle that has the same diffusion coefficient in air as the particle of interest.
(ICRP 68)

Thermoelectric conversion
The conversion of heat into electricity by the use of thermocouples. (See thermocouple.)
(USAEC-1974)

Thermogram
A spacial representation of the temperature distribution within a medium.
(NCRP 67)

Thermography
A noninvasive diagnostic radiologic imaging technique that uses infrared radiation to picture the heat emitted by the surface, which characterizes the temperature distribution in the various underlying organs and tissue of the body.
(BEIR III)

Thermoluminescence
The release of light in a crystalline material as it is heated at a constant rate. The light emitted is proportional to the previous radiation dosage that the material has received.
(NCRP 101)

Thermoluminescence (TL)
A process of releasing radiation-induced energy as light in response to heating.
(ANSI N13.15-1985)

Thermoluminescence (TL) phosphor
A material capable of absorbing energy imparted by ionizing radiation, stroing that energy, and reemitting a fraction therof in the form of ultraviolet, visible, and infrared photons as a result of thermal stimulation.
(ANSI N545-1975)

Thermoluminescence dosemeter
Dosemeter, consisting of one or more thermoluminescent detectors, which may be mounted in an appropriate holder, intended to be worn on a person's body or placed in an environment, for the purpose of assessing the appropriate dose equivalent at or near the position where it is placed.
(IEC 50-394-1993)

Thermoluminescence dosimeter (TLD)
The thermoluminescence phosphor(s) packaged for field use.
(ANSI N545-1975)

Thermoluminescence dosimetry (TLD) system
The TLD, all equipment used for the preparation and readout of the TLD, and all other associated supporting facilities and procedures.
(ANSI N545-1975)

Thermoluminescence dosimetry system
Thermoluminescence dosemeter, the reader and all associated equipment.
(IEC 50-394-1993)

Thermoluminescence dosimetry system
The detecting device or dosimeters plus the related data collecting and data processing instruments and techniques required to estimate from the measurement the absorbed-dose index or dose-equivalent index for a person who wears the dosimeter.
(ANSI N13.15-1985)

Thermoluminescent detector, TLD
Radiation detector using a thermoluminescent material which, by thermal stimulation, emits a luminescent radiation, the intensity of which is a function of the energy stored in the detector during its irradiation.
(IEC 50-394-1993)

Thermoluminescent dosimeter
A solid sate radiation dosimeter that can absorb energy which may be released later, in the form of light, by heating the material. Examples of material utilized as TLDs include LiF, CaF₂, CaSO₄:Mn, CaF₂:Mn, etc.
(NCRP 66)

Thermoluminescent dosimeter (TLD)
A dosimeter using a material which upon heating emits light in direct proportion to the amount of radiation to which the material was exposed.
(NCRP 118)

Thermoluminescent dosimeter (TLD)
An integrating detector where radiation energy is absorbed (trapped) and can be read out later by thermal excitation of the detector.
(NCRP 97)

Thermoluminescent material
Substance exhibiting the property of thermoluminescence.
(IEC 50-394-1993)

Thermonuclear bomb (device)
A hydrogen bomb (device).
(USAEC-1974)

Thermonuclear reaction
A nuclear reaction in which the participating particles obtain their required kinetic energy from thermal agitation. The term usually applies to nuclear fusion reaction.
(ANSI N1.1-1976)

Thermonuclear reaction
A reaction in which very high temperatures bring about the fusion of two light nuclei to form the nucleus of a heavier atom, releasing a large amount of energy. In a hydrogen bomb, the high temperature to initiate the thermonuclear reaction is produced by a preliminary fission reaction. (See fusion, Sherwood.)
(USAEC-1974)

Thermophoresis
Particles motion in a temperature gradient, i.e., from a hotter to a colder region.
(AM-1993)

Thick shield
Shield which effects a substantial reduction of a radiation field as a result of its presence. For the purposes of this report, the term usually implies a shielding transmission ration of 10^-6 or less.
(NCRP 51)

Thick target
Target whose dimension in the direction of incident particulate radiation is equal to or greater than the range of the incident particles.
(NCRP 51)

Thickness meter
Measuring assembly, including an ionizing radiation source and a radiation meter, intended for non-destructive measurement of the thickness of a material by means of ionizing radiation.
(IEC 50-394-1993)

Thimble ionization chamber
Ionization chamber in which the outer electrode has shape and dimension similar to those of a thimble.
(IEC 50-394-1993)

Thin wall counter tube
Counter tube with an envelope of such low absorption as to permit the detection of low penetrating power radiation.
(IEC 50-394-1993)

Thomas method
A modification of the Tsivoglou method for estimating the concentrations of individual short-lived daughter products of ²²²Rn, involving a change in the counting protocol.
(NCRP 97)

Thoracic
Region of the respiratory tract from the larynx down.
(AM-1993)

Thoracic (TH) airways
Combined Bronchial, Bronchiolar and Alveolar Interstitial regions.
(ICRP 68)

Thoracic Lymphatic System
Structures involved in the lymph system which include lymph capillaries, lacteals, lymph nodes, lymph vessels and main lymph ducts.
(NCRP 125)

Thorium
A naturally radioactive element. Thorium-232 is the parent of one radioactive series, and specific thorium nuclides are members of the three radionuclide series (See Appendix A).
(NCRP 118)

Thorium
[Symbol Th] A naturally radioactive element with atomic number 90 and, as found in nature, an atomic weight of approximately 232. The fertile thorium-232 isotope is abundant and can be transmuted to fissionable uranium-233 by neutron irradiation. (See fertile material, transmutation.)
(USAEC-1974)

Thorium series
The naturally radioactive series that starts with ²³²Th.
(ENV RAD)

Thorium series (sequence)
The series of nuclides resulting from the radioactive decay of thorium-232. Many man-made nuclides decay into this sequence. The end product of this sequence in nature is lead-208. (See decay, radioactive; radioactive series.)
(USAEC-1974)

Thoron
The isotope of radon in the thorium series (²²⁰Rn).
(ENV RAD)

Threshold dose
The amount of radiation that is required to cause a particular effect in at least 1-5 per cent of the exposed individuals.
(ICRP 41)

Threshold dose
The minimum dose of radiation that will produce a detectable biological effect. (See absorbed dose, biological dose.)
(USAEC-1974)

Threshold dose
The minimum absorbed dose that will produce a detectable degree of any given effect.
(BEIR I)

Threshold dose
The minimum absorbed dose that will produce a detectable degree of any given effect.
(RHH)

Threshold energy
The limiting kinetic energy (expressed in the laboratory system) of an incident particle, below which a specified process cannot occur.
(ANSI N1.1-1976)

Threshold hypothesis
The assumption that no radiation injury occurs below a specified dose.
(BEIR IV)

Threshold hypothesis
The assumption that no radiation injury occurs below a specified dose.
(BEIR III)

Threshold hypothesis
The assumption that no radiation injury occurs below a specified dose level.
(BEIR I)

Threshold limit value (TLV)
The TLV as defined by the American Conference of Governmental Industrial Hygienist refers to airborne concentration of substances and represents conditions under which it is believed that nearly all workers may be repeatedly exposed day to day with an acceptable low probability of occupational illness.
(ANSI N43.1-1978)

Threshold of response (to pulses)
Minimum amplitude of a pulse required for a given circuit to perform its function in response to that pulse.
(IEC 50-394-1993)

Threshold type survival curve
A survival curve with a shoulder which may be fitted by a multi-target or multi-hit or other mathematical expression depending upon the exact shape of the curve.
(ICRU 30)

Threshold, nuclear-reaction
The minimum particle or photon energy required to initiate a specific endothermal (endoergic) nuclear reaction.
(NCRP 51)

Threshold, photoelectric
The quantum of energy hno that is just enough to release an electron from a given system in the photoelectric effect. The corresponding frequency, no, and wavelength, lo, are the threshold frequency and wavelength respectively. For example, in the surface photoelectric effect, the threshold hno for a particular surface is the energy of a photon which, when incident on the surface, causes the electron to emerge with zero kinetic energy.
(RHH)

Threshold, radiation-effect
The minimum absorbed dose (or dose equivalent) of radiation that will produce a specified effect or a specified type of damage to the irradiated material.
(NCRP 51)

Thrombocytopenia
Decreased number of platelets per cubic millimeter of circulating blood.
(NBS 63)

Thymidine
A nucleoside C₁₀H₁₄N₂O that is composed of thymidine and deoxyribose and occurs as a structural part of DNA.
(HPJ 60)

Thyroid uptake
The thyroid uptake (TU), expressed as a percentage; that is,

where:
P = counts per unit time from the patient
P_B = counts per unit time from the patient with the "B" filter in place
S = counts per unit time from the reference activity in the neck phantom
S_B = counts per unit time from the reference activity in the neck phantom with the "B" filter in place
K = ratio of reference activity to the activity administered to the patient
(ANSI N44.3-1973)

Tidal air volume
Volume of the air inhaled per breath.
(NCRP 78)

Tidal Volume
Volume of air that enters and leaves the lung during normal breathing.
(NCRP 125)

Tidal volume
Volume of gases inhaled or exhaled during each breath.
(AM-1993)

Tidal volume
The volume of air breathed in and out under any condition.
(NCRP 76)

Time constant range
Range of power level within which the reactor time constant rather than reactor power is of primary importance for reactor control.
(IEC 50-393-1993)

Time constant, reactor
The time require for the neutron flux density in a reactor to change by a factor of e (2.718...) when the flux density is rising or falling exponentially. (Also called period, reactor.)
Note the term "reactor time constant" is preferred to "reactor period."
(ANSI N1.1-1976)

Time jitter (j), walk
The variation in arrival time of pulses, in particular of b and g events which constitute a genuine coincidence at the coincidence mixer. The variation is caused by changes in the behavior of detection and electronic equipment as a function of the energy and interactions of the originating beta and gamma rays.
(ICRU 52)

Time-Limiting Aging Analysis
Those licensee calculations and analyses that:
(1) Involve systems, structures, and components within the scope of license renewal, as delineated in Sec. 54.4(a);
(2) Consider the effects of aging;
(3) Involve time-limited assumptions defined by the current operating term, for example, 40 years;
(4) Were determined to be relevant by the licensee in making a safety determination;
(5) Involve conclusions or provide the basis for conclusions related to the capability of the system, structure, and component to perform its intended functions, as delineated in Sec. 54.4(b); and
(6) Are contained or incorporated by reference in the CLB.
(10CFR54.3)

Time-of-flight (of a particle)
Time taken by a particle to move between two specified points.
(IEC 50-394-1993)

Time-of-flight spectrometer
A device for separating and sorting neutrons (or other particles) into categories of similar energy, measured by the time it takes the particles to travel a known distance.
(USAEC-1974)

Time-since-exposure (TSE) model
A model in which the relative risk is not constant but varies with the time after exposure.
(BEIR IV)

Time-to-amplitude converter
Assembly or sub-assembly intended to provide an output signal whose amplitude is proportional either to the time interval between two input signals or to the duration of the input signal.
(IEC 50-394-1993)

Time-to-digital converter
Assembly or sub-assembly intended to provide an output signal which is a digital representation of the time interval between two input pulses, start and stop pulses, or of the duration of the input signal.
(IEC 50-394-1993)

Time-weighted average (TWA)
The average concentration of a contaminant in air during a specific time period.
(ANSI Z88.2-1980)

Timer
A time-measuring device designed to automatically make or break electrical connections at the end of a preset time interval.
(ANSI N537-1976)

Tissue activity meter
Assembly designed to locate, by means of appropriate probes, fixed radionuclides within tissues.
(IEC 50-394-1993)

Tissue Depth
Depth of tissues lining the respiratory tract including the mucus and cells lining the trachea, main bronchus or bronchial airway.
(NCRP 125)

Tissue dose
Absorbed dose received by tissue in the region of interest, expressed in rads.
(RHH)

Tissue dose
The dose imparted to tissue by ionizing radiation.
(NBS 55)

Tissue dose equivalent conversion factor (H_T,50)
The committed dose equivalent per unit intake of radionuclide to the tissue or organ T.
(FGR 11)

Tissue equivalence
1 - For X, gamma and neutron radiation, the property possessed by a material when the mass energy absorption coefficient of the material is equal to the mass energy absorption coefficient of tissue.
2 - For beta radiation, the property possessed by a material when the collision mass stopping power of the material is equal to the collision mass stopping power of tissue.
(IEC 50-393-1993)

Tissue equivalent material
Material having interaction properties under irradiation similar to those of soft tissue, the composition of which is taken as :
(IEC 50-393-1993)

Tissue equivalent material
Material made up of the same elements in the same proportions as they occur in a particular biological tissue. In some cases, the equivalence may be approximated with sufficient accuracy on the basis of effective atomic number.
(HPJ 60)

Tissue equivalent material
Material that absorbs and scatters ionizing radiation to the same degree as a particular biological tissue.
(ANSI N1.1-1976)

Tissue equivalent material
A liquid or solid whose absorbing and scattering properties for a given radiation simulate as closely as possible those of a given biological material, such as fat, bone or muscle. For muscle or soft tissue, water is usually the best tissue equivalent material.
(ICRU 23)

Tissue equivalent material (bolus)
A material, the absorption and scattering properties of which, for a given irradiation, simulate as nearly as possible those of a given biological material, such as soft tissue, muscle, bone or fat. Water is usually the best soft tissue-equivalent material for x and gamma radiation.
(ICRU 30)

Tissue maximum ratio (TMR)
See tissue phantom ratio.
(ICRU 24)

Tissue phantom ratio (TPR)
The ratio of the absorbed dose rate at a given point in a phantom to the absorbed dose rate at the same point in space at a standard depth in a phantom, all the conditions of irradiation (e.g., field size) being the same. When the depth is taken to be that of the peak dose, this quantity is called the tissue-maximum ratio.
(ICRU 24)

Tissue substitute
Any material used to simulate a particular body tissue with respect to a set of physical characteristics is called a tissue substitute.
(ICRU 44)

Tissue tolerance
The capacity of a tissue to withstand irradiation without developing a nonstochastic effect.
(ICRP 41)

Tissue weighting factor
The relationship between the probability of stochastic effects and equivalent dose is found also to vary with the organ or tissue irradiated. It is, therefore, appropriate to define a further quantity, derived from equivalent doe, to indicate the combination of different doses to several different tissues in a way which is likely to correlate well with the total of the stochastic effects. The factor by which the equivalent dose in tissue or organ T is weighted is called the tissue weighting factor, w_T. The values of w_T are chosen so that a uniform equivalent dose over the whole body gives an effective dose numerically equal to the uniform equivalent dose. The sum of the tissue weighting factors is then unity. The recommended values for tissue weighting factors are:

Tissue or Organ Tissue weighting factor, w_T
Gonads 0.20
Bone Marrow (red) 0.12
Colon 0.12
Lung 0.12
Stomach 0.12
Bladder 0.05
Breast 0.05
Liver 0.05
Oespophagus 0.05
Thyroid 0.05
Skin 0.01
Bone Surface 0.01
Remainder 0.05

Tissue or Organ	Tissue weighting factor, w_T
Gonads	0.20
Bone Marrow (red)	0.12
Colon	0.12
Lung	0.12
Stomach	0.12
Bladder	0.05
Breast	0.05
Liver	0.05
Oespophagus	0.05
Thyroid	0.05
Skin	0.01
Bone Surface	0.01
Remainder	0.05

(ICRP 60)

Tissue weighting factor (w_T)
A factor that indicates the ratio of the risk of effects attributable to irradiation of a given organ or tissue, T, to the total risk when the whole body is uniformly irradiated.
(NCRP 121)

Tissue weighting factor (w_T)
The factor by which the equivalent dose in a tissue or organ is weighted to represent the relative contributions of that tissue or organ to the total detriment resulting from uniform irradiation of the body.
(ICRP 68)

Tissue weighting factor (w_T)
The tissue weighting factors are dimensionless factors to derive the effective dose from the equivalent dose. They are based on the different sensitivities of tissues to radiation.
(ICRP 67)

Tissue- or organ-average absorbed dose
For radiation protection purposes, is useful to define tissue- or organ average absorbed dose, D_T, i.e.,

where e_T is the total energy imparted in a tissue or organ and m_T is the mass of that tissue or organ. For example, m_T may range from less than 10g for the ovaries to over 70 kg for the whole body.
(ICRP 60)

Tissue-air ratio (TAR)
The ratio of the absorbed dose at a given point in a phantom to the absorbed dose at the same point in air within a volume of phantom material just large enough to provide the maximum electronic buildup.
(NCRP 69)

Tissue-air-ratio
The ratio of the absorbed dose at a given point in a phantom to the absorbed dose at the same point in free air within a volume of phantom material just large enough to provide the maximum electronic build-up at the point of reference.
(ICRU 23)

Tissue-air-ratio (TAR)
The ratio of the absorbed dose rate at a given point in a phantom to the absorbed dose rate at the same point is space, but at the center of a small amount of phantom material of mass just large enough to provide electronic equilibrium at the point of measurement.
(ICRU 30)

Tissue-equivalent ionization chamber
Ionization chamber, intended to determine the absorbed dose in tissue, and in which the materials of the walls, the electrodes and the gas filling have the same effective atomic number as soft tissue.
(IEC 50-394-1993)

Tissue-equivalent material
A material, the absorption and scattering properties of which, for a given irradiation, simulate as nearly as possible those of a given biological material, such as soft tissue, muscle, bone or fat. Water is usually the best soft tissue-equivalent material for x and gamma radiation.
(NCRP 66)

Tissue-equivalent scintillation detector
Radiation scintillation detector made from a material whose effective atomic number is nearly equal to that of soft tissue
(IEC 50-394-1993)

Tissue-maximum ratio
The ratio of the absorbed dose at a given point in a phantom to the absorbed dose at the same point with the amount of medium above limited to only that thickness required to achieve maximum electron buildup (with extended medium to the sides and below).
(NCRP 69)

Tissues At Risk
Cells endangered from exposure to radionuclides in the air.
(NCRP 125)

Title V permit
Any permit issued, renewed, or revised pursuant to Federal or State regulations established to implement title V permit issued by a State permitting authority is call a part 70 permit in this part.
(40CFR61.02)

TLC
Total lung capacity (L)
(ICRP 66)

TLD (thermoluminescent dosimeter)
A crystalline material used for dosimetry by the thermoluminescent method. TLDs are usually LiF but are also available as CaF₂, BeO, and CaSO₄. They are available as ribbons, rods, chips, powder, or extrusions.
(NCRP 101)

TLD (thermoluminescent dosimeter)
A crystalline material used for dosimetry by the thermoluminescent method. TLD's are usually LiF but are also available as CaF₂, Li₂, B₄O₇ and CaSO₄. They are available as ribbons, rods, chips, powder or extrusions.
(NCRP 83)

TLD calibration
Establishing the relationship between TL response and exposure in roentgens and all procedures associated therewith.
(ANSI N545-1975)

TLD field batch
TLD's having similar TL response and similar thermal and exposure histories.
(ANSI N545-1975)

TLV
Threshold Limit Value. A table of these values and accompanying precautions is published annually by the American Conference of Governmental Industrial Hygienists.
(ANSI Z88.2-1969)

TNT equivalent
A measure of the energy released in the detonation of a nuclear explosive expressed in terms of the weight of TNT (the chemical explosive, trinitrotoluene) which would release the same amount of energy when exploded. It is usually expressed in kilotons or megatons. The TNT equivalence relationship is based on the fact that 1 ton of TNT releases one billion (10⁹) calories of energy. (See kiloton energy, megaton energy, yield.)
(USAEC-1974)

Tolerance dose
The maximum amount of radiation that a tissue can withstand without developing a clinically detrimental nonstochastic effect.
(ICRP 41)

Tolerance dose
An early standard for radiation protection based upon the dose that could be 'tolerated' without serious harm to humans.
(NUREG/CR 3332)

Toll enrichment
A proposed arrangement whereby privately owned uranium could be enriched in uranium-235 content in government facilities upon payment of a service charge by the owners. (See isotopic enrichment, uranium.)
(USAEC-1974)

Tomography
X-Ray technique designed to show detailed images of structures in a selected plane of tissue by blurring images of structures in all other planes.
(NCRP 125)

Tomography
A special technique to show in detail images of structures lying in a predetermined plane of tissue, while blurring or eliminating detail in images of structures in other planes.
(NCRP 107)

Total absorption detection efficiency
For a given detection assembly and photon energy, ratio of the number of photons detected in the total absorption peak to the total number of photons emitted by the radiation source in the same time interval.
(IEC 50-394-1993)

Total absorption detector efficiency
For a given photon energy, ratio of the number of photons detected in the total absorption peak to the number of photons which are incident on the detector in the same time interval.
(IEC 50-394-1993)

Total absorption peak
In X or gamma radiation, the peak of the spectral response curve corresponding to the total absorption in a detecting material of the photon energy.
(IEC 50-394-1993)

Total depletion voltage (of a semiconductor detector)
Reverse voltage at which the depletion layer extends over essentially the whole thickness of the semiconductor.
(IEC 50-394-1993)

Total detection efficiency
The ratio of the total (peak plus Compton) counting rate to the gamma-ray emission rate.
(ANSI N42.14-1978)

Total effective dose equivalent (TEDE)
The sum of the effective dose equivalent (for external exposures) and the committed effective dose equivalent (for internal exposures).
(10CFR835.2-1998)

Total effective dose equivalent (TEDE)
The sum of deep-dose equivalent (for external exposures) and committed effective dose equivalent (for internal exposures).
(10CFR20.1003)

Total effective dose equivalent (TEDE)
The sum of the deep-dose equivalent (for external exposures) and the committed effective dose equivalent (for internal exposures).
(10CFR50.2)

Total Effective Dose Equivalent (TEDE)
The sum of the deep dose equivalent due to external irradiation of the whole body and the committed effective dose equivalent.
(HPS N13.42-1997)

Total effective dose equivalent (TEDE)
The sum of the effective dose equivalent (for external exposures) and the committed effective dose equivalent (for internal exposures). Unless otherwise stated, the term "dose" means TEDE.
(10CFR834.2)

Total effective dose equivalent (TEDE)
The sum of the effective dose equivalent (for external exposures) and the committed effective dose equivalent (for internal exposures). For purposes of compliance with this part, deep dose equivalent to the whole body may be used as effective dose equivalent for external exposures.
(10CFR835.2-1993)

Total equivalent dose
When the radiation field is composed of types and energies with different values of w_R, the absorbed dose must be subdivided in blocks, multiplied by its own value of w_R, and summed to determine the total equivalent dose, i.e.

where D_T,R is the average absorbed dose from radiation R in tissue T. Alternatively, the absorbed dose resulting from increments of energy between E and E + dE can be multiplied by the w_R values and integrated over the energy spectrum to determine the total equivalent dose.
(ICRP 60)

Total linear attenuation coefficient (µ)
Quotient of the fraction of uncharged ionizing particles which interact when traversing a material by the total number of particles, dN/N, and by the distance dl traversed in the material.

(IEC 50-393-1993)

Total linear stopping power (S)
For a material and for charged particles, quotient of dE by dl, where dE is the energy lost by a charged particle in traversing a distance dl in the material.
(IEC 50-393-1993)

Total lung capacity
Volume of air contained in the lung at maximum inspiration.
(AM-1993)

Total mass stopping power
The total mass stopping power, S/r, of a material for charged particles is the quotient of dE by rdl, where dE is the energy lost by a charged particle in traversing a distance of dl in the material of density r,

Unit: J m² kg^-1. S/r may also be expressed in eV m² kg^-1.
(ICRU 44)

Total mass stopping power (S/r)
For a material and for charged particles, quotient of total linear stopping power S by density r.

For energies at which nuclear interactions can be neglected, the total mass stopping power is:

(IEC 50-393-1993)

Total mass stopping power (S/r)
The total mass stopping power of a material for charged particles is the quotient dE by rdl, where dE is the energy lost by a charged particle in traversing a distance dl in the material of density r.

Note: S = total linear stopping power.
(ICRP 51)

Total reference air kerma
The total reference air kerma is the sum of the products of the reference air kerma rate and the duration of the application for each source.
(ICRU 38)

Totally depleted semiconductor detector
Semiconductor detector in which the thickness of the depletion layer is essentially equal to the thickness of the semiconductor material.
(IEC 50-394-1993)

Towing vessel
The vessel used to propel a barge (either by pushing or towing).
(ANSI N14.24-1985)

Townsend avalanche
Gas multiplication chain process in which a charged particle rapidly gives rise by collision to a large number of charged particles.
(IEC 50-394-1993)

Toxic dust
Dust that may be harmful to the respiratory system or to other parts of the body through passing from the respiratory tract into the blood stream.
(ANSI Z88.2-1969)

Toxic material area
Any area in which toxic materials exist such that the toxicity concentrations exceed the threshold limit values (TLV).
(ANSI N43.1-1978)

Trabecular bone
Equivalent to "Cancellous Bone" in ICRP Publication 20, i.e. any bone with a surface/volume ratio greater than 60 cm² cm^-3; in Reference Man it has a mass of 1000 g.
(ICRP 68)

Trabecular bone
Equivalent to "Cancellous Bone" in ICRP Publication 20, i.e. any bone with a surface/volume ratio greater than 60 cm² cm^-3; in Reference Man it has a mass of 1000 g.
(ICRP 67)

Trabecular bone
Equivalent to "Cancellous Bone" in ICRP Publication 20, i.e., any bone with a surface/volume ratio grater than 60 cm² cm^-3. In Reference Man trabecular bone has a mass of 1000 g.
(FGR 11)

Trabecular bone
Spongy or cancellate bone usually found internal to compact bone and containing a meshwork of intercommunicating spaces that are filled with bone marrow.
(NCRP 83)

Trabecular bone
Equivalent to "Cancellous Bone" in ICRP Publication 20, i.e. any bone with a surface/volume ratio greater than 60 cm² cm^-3; in Reference Man it has a mass of 1000 g.
(NCRP 84)

Trabecular bone
Equivalent to "Cancellous Bone" in ICRP Publication 20, i.e. any bone with a surface/volume ratio greater than 60 cm² cm^-3; in Reference Man it has a mass of 1000 g.
(ICRP 30)

Trabeculated bone, or trabecular bone
Bone containing marrow cavities.
(NCRP 94)

Trabeculated bone, or trabecular bone
Bone containing marrow cavities.
(NCRP 45)

Trace dose
A dose of radionuclide administered to find out something about an organ, its shape, or its function. The administered dose must be so small as not to produce any radiation effect that might alter the status quo of the patient.
(NCRP 48)

Traceability
The ability to relate individual measurement results to national standards or nationally accepted measurement systems through an unbroken chain of comparisons.
(10CFR74.4)

Traceability
The consistency of any measurement system with national standards, based on the documented record of a program of intercomparative measurements. The ability to relate an analytical result to a standard reference material.
(ANSI N15.54-1988)

Traceability
The consistency of any measurement system with national standards, based on the documented record of a program of intercomparative measurement.
(ANSI N15.22-1987)

Traceability
The ability to trace the history, application or location of an item and like items or activities by means of record identification.
(ANSI N46.2-1978)

Traceable to national standards
The calibration factor of a field instrument is said to be directly traceable to national radiation standards if it has been calibrated in a radiation beam by comparison with a national standard, or with a secondary standard that has been calibrated against a national standard. A calibration factor is applicable to the instrument calibrated at the specified quality of radiation.
(NCRP 69)

Tracer
The isotope or non-natural mixture of isotopes of an element that may be incorporated into a sample to make possible observation of the course of that element, alone or in combination, through a chemical, biological, or physical process. The observations may be made by measurement or radioactivity or of isotopic abundance.
(HPJ 60)

Tracer
A nuclide introduced into a system in order to follow the behavior of some component of that system.
(ANSI N1.1-1976)

Tracer fluid
The gas or liquid that is used to detect leakage or measure leakage rates.
(ANSI N14.5-1987)

Tracer, isotopic
An isotope of an element, a small amount of which may be incorporated into a sample of material (the carrier) in order to follow (trace) the course of that element through a chemical, biological or physical process, and thus also follow the larger sample. The tracer may be radioactive, in which case observations are made by measuring the radioactivity. If the tracer is stable, mass spectrometers, density measurement, or neutron activation analysis may be employed to determine isotopic composition. Tracers also are called labels or tags, and materials are said to be labeled or tagged when radioactive tracers are incorporated in them. (See carrier, radioactive tracer.)
(USAEC-1974)

Tracer, isotopic
The isotope or non-natural mixture of isotopes of an element which may be incorporated into a sample to permit observation of the course of that element, alone or in combination, through a chemical, biological, or physical process. The observations may be made by measurement or radioactivity or of isotopic abundance.
(RHH)

Trachea
Air tube extending from the larynx to the major bronchi whose membranous wall contains cartilage and muscular fibers.
(NCRP 125)

Trachea
The windpipe. The duct by which air passes from the larynx (in the throat) to the bronchi in the lungs.
(RRM)

Tracheobronchial (TB) Region
Area of the trachea and bronchi down to the terminal bronchioles which functions in gas transport.
(NCRP 125)

Tracheobronchial compartment
Region of the respiratory tract from the larynx to the terminal bronchioles.
(AM-1993)

Tracheobronchial tree
The portion of the respiratory system which conducts air to the alveoli.
(NCRP 78)

Track
Visual manifestation of the path of an ionizing particle in a chamber or photographic emulsion.
(RHH)

Track chamber
Chamber which makes visible the paths of ionizing particles passing through it or formed in it.
(IEC 50-394-1993)

Track-etch
The trade name for a specific brand of solid state nuclear track detector.
(NCRP 97)

Train
A set of components arranged in series. In a filter system this may be as simple as a damper, HEPA filter, fan, and damper or as complex as a damper, condenser, moisture separator, heater, prefilter, HEPA filter, charcoal adsorber, another charcoal adsorber, HEPA filter, fan, and damper.
(ERDA 76-21)

Trajectory model
Atmospheric transport model which is driven by an observed or predicted wind field, generally for distances beyond 10 km. Diffusion is accounted for using a moving-box, growing puff or small air-particle elements.
(NCRP 76)

Transfer
The transfer of possession from one person to another person.
(10CFR110.2)

Transfer
The movement of a radionuclide form one environmental medium to another, e.g., from air to grass.
(ICRP 29)

Transfer coefficient to milk
The fraction of an element ingested daily by a cow that is secreted in milk at steady state or equilibrium.
(NUREG/CR 3332)

Transfer coefficient to milk (F_im)
The fraction of element (i) ingested daily by a cow that is secreted in milk at steady-state or equilibrium.
(NCRP 76)

Transfer coefficient to milk (F_m)
The fraction of element i ingested daily by a cow that is secreted in milk at a steady-state of equilibrium.
(NCRP 123I)

Transfer coefficient to other animal product (e.g., meat, eggs)
The fraction of element (i) ingested daily by a herbivore that can be measured in 1 kg of animal product at steady-state or equilibrium.
(NCRP 76)

Transfer coefficient to other animal product (eg., meat, eggs) (F_f)
The fraction of element i ingested daily by an herbivore that can be measured in 1 kg of animal product at a steady-state or equilibrium.
(NCRP 123I)

Transfer coefficient to other animal products
The fraction of an element ingested daily by a herbivore that can be measured per unit mass of animal product at steady state or equilibrium.
(NUREG/CR 3332)

Transfer compartment
The compartment introduced (for mathematical convenience) into most of the biokinetic models used in this report to account for the translocation of the radioactive material through the body fluids from where they are deposited in tissues.
(ICRP 68)

Transfer compartment
The compartment introduced (for mathematical convenience) into most of the metabolic models used in this report to account for the delay between radioactive material entering body fluids and its deposition in particular tissues.
(ICRP 30)

Transfer function meter
Assembly for determining the transfer function of a nuclear reactor by measuring the variation of the neutron fluence rate caused by a modulation of the reactivity.
(IEC 50-394-1993)

Transfer instrument
Instrument or dosimeter exhibiting high precision which has been standardized against a national or derived standardized source.
(ANSI N323-1978)

Transfer Reference Standard (TRS)
A material that contains radionuclides of interest in chemical and physical forms similar to bioassay specimens and is used to certify the amount of activity present in a person or sample measured. The radionuclides used for the preparation of the TRS are directly related to standard reference materials (SRMs).
(HPS N13.42-1997)

Transfer Reference Standard (TRS)
A material that contains radionuclide components of interest in chemical and physical forms similar to bioassay specimens, and is used to certify the amount of activity present in a person or sample measured. The radionuclides used for the preparation of the TRS are, when possible, related to SRMs. The preparation procedures are verified and documented.
(HPS N13.30-1996)

Transfer reference standard (TRS)
A material that contains radionuclidic components of interest in chemical and physical forms similar to bioassay specimens, and is used to certify the amount of activity present in a person or sample measured. The radionuclides used for the preparation of the TRS are, when possible, related to SRM's. The preparation procedures are verified and documented.
(ANSI N13.30-1989D)

Transfer standard
An instrument or radioactive source which has been standardized (calibrated) in terms of response (for an instrument) or radioactivity content, radiation emission rate or dose rate (for a source) by measurements made against a national (NIST) standard or a standard maintained by a secondary calibration laboratory.
(NCRP 112)

Transformation
The process of radioactive decay in which one radionuclide is transformed into another.
(NCRP 84)

Transformation, nuclear
Transmutation.
(USAEC-1974)

Transformed cells
Tissue culture cells changed in vitro from growing in an orderly pattern and exhibiting contact inhibition to growing in a pattern more like that of cancer cells, resulting in the loss of contact inhibition.
(BEIR IV)

Transient equilibrium
Relatively short-term equilibrium within a portion of a radioactive series where the parent has a long half-life only relative to successive series members. An example is the radon progeny series.
(ENV RAD)

Transient shipment
A shipment of nuclear material, originating and terminating in foreign countries, on a vessel or aircraft that stops at a United States port.
(10CFR70.4)

Transient shipment
A shipment of nuclear material, originating and terminating in foreign countries, on a vessel or aircraft that stops at a United States port.
(10CFR40.4)

Transit measurements (transit dose)
A measure or the primary radiation transmitted through the patient by a single stationary beam. It is normally measured at a point on the central ray some distance beyond the patient, using a technique which eliminates scattered radiation at the point of measurement as far as possible.
(ICRU 24)

Transit time (in a photomultiplier tube)
Time between the arrival at the photocathode of a light pulse having a finite flux and infinitesimal duration, and the occurrence of a stated point, peak amplitude for instance, on the output current pulse.
(IEC 50-394-1993)

Transit time jitter (in a photomultiplier tube)
Variation in the transit times corresponding to different light pulses having a finite flux and infinitesimal duration, each giving rise to not more than a single photoelectron.
(IEC 50-394-1993)

Transition
A nuclear change from one energy state to another accompanied by the emission of particles. Often called decay, of a disintegration.
(MIRD)

Transition region
A region of a tank in which cross-sectional area changes abruptly with height, usually because of such internal structures as coils, agitators, and the like.
(ANSI N15.19-1989)

Transition, isomeric
The process by which a nuclide decays to an isomeric nuclide (i.e., one of the same mass number and atomic number) of lower quantum energy. Isomeric transitions, often abbreviated I.T., proceed by gamma ray and/or internal conversion electron emission.
(RHH)

Transitional facility attachment
That portion of the Transitional Subsidiary Arrangements to the Protocol to the Agreement that pertains to a particular installation that has been identified pursuant to Article 2(a) thereof.
(10CFR75.4)

Transitory exposure pathways
A pathway in which the radionuclide concentration is directly proportional to the rate of release of the radionuclide into the environment.
(NUREG/CR 3332)

Translocation
The transfer of material absorbed from the respiratory tract to other tissues in the body.
(ICRP 66)

Translocation
A chromosome aberration resulting from chromosome breakage and subsequent rearrangement of the parts between the same or different chromosomes.
(BEIR IV)

Translocation
An inclusive term denoting movement of a radionuclide by either transfer or transport mechanisms and by man's industrial or agricultural activities.
(ICRP 29)

Transmission coefficient
The ratio of the electric or magnetic field strength phasors associated with a transmitted wave to that associated with an incident wave.
(NCRP 67)

Transmission density meter
Density meter for measurement of the radiation transmitted through the material.
(IEC 50-394-1993)

Transmission efficiency
Fraction of aspirated particles that is transmitted through an inlet to the rest of the sampling system.
(AM-1993)

Transmission line
A physical structure for guiding electromagnetic energy. Common examples are: wire pairs, coaxial lines, strip lines, and waveguides.
(NCRP 67)

Transmission ratio
See shielding transmission ratio.
(NCRP 51)

Transmission semiconductor detector
Semiconductor detector whose thickness, including its entrance and exit windows, is sufficiently small to permit particles to pass completely through the detector.
(IEC 50-394-1993)

Transmission soil density meter
Portable radiation density meter intended to determine soil density by measurement of the radiation transmitted through the soil.
(IEC 50-394-1993)

Transmission thickness meter
Thickness meter intended to determine thickness by measurement of the radiation transmitted through the material
(IEC 50-394-1993)

Transmissivity
The rate at which water is transmitted through a unit width of the aquifer under a unit hydraulic gradient.
(NCRP 76)

Transmutation
Transformation of a nuclide of one element to a nuclide of another element, by means of a nuclear reaction.
(IEC 50-393-1993)

Transmutation
Any process in which a nuclide is transformed into a different nuclide, or more specifically, when transformed into a different element by a nuclear reaction.
(RHH)

Transplutonium element
An element above plutonium in the periodic table, that is, one with an atomic number greater than 94. (See transuranic element.)
(USAEC-1974)

Transport
Any land, sea, or air conveyance or modules for these conveyances such as rail cars or standardized cargo containers.
(10CFR73.2)

Transport
The physical movement of material from one location to another.
(10CFR110.2)

Transport
The movement of a material within a single environmental medium, e.g., dispersion in the atmosphere.
(NCRP 123I)

Transport
The movement of a material within a single environmental medium, e.g., dispersion in the atmosphere.
(NCRP 76)

Transport
The movement of a radionuclide within a single environmental medium, e.g., dispersion in the atmosphere.
(ICRP 29)

Transport index
The dimensionless number (rounded up to the first decimal place) placed on the label of a package to designate the degree of control to be exercised by the carrier during transportation. The transport index is determined as follows:
(1) The number expressing the maximum radiation level in millirem per hour at 1 meter from the external surface of the package; or
(2) For Fissile Class II packages, the number expressing the maximum radiation level in millirem per hour at 1 meter from the external surface of the package, or the number obtained by dividing 50 by the allowable number of the packages which may be transported together as determined under §71.59, whichever number is larger.
(10CFR71.4)

Transport index
The dimensionless number (rounded up to the first decimal place) placed on the label of a package to designate the degree of control to be exercised by the carrier during transportation. The transport index is determined as follows:
(1) The number expressing the maximum radiation level in millirem per hour at one meter (3.3 feet) from the external surface of the package; or
(2) For Fissile Class II packages or packages in a Fissile Class III shipment, the number expressing the maximum radiation level at one meter (3.3 feet) from the external surface of the package, or the number obtained by dividing 50 by the allowable number of packages, which may be transported together, whichever is larger.
(49CFR173.403)

Transport index
The number placed on a package to designate the degree of control to be exercised by the carrier during transportation. The transport index to be assigned to a package of radioactive materials shall be determined by either (1) or (2) whichever is larger:
(1) The highest radiation dose rate, in millirem per hour at 1 meter (3.3 feet) from any external surface of the package; or
(2) For Fissile-Class-Il packages only, the transport index number calculated by dividing the number 50 by the number of similar packages that may be transported together. The number expressing the transport index shall be rounded up to the next highest tenth.
(ANSI N14.1-1990)

Transport index
A number on a label on a shipping container that indicates the exposure rate, in milliroentgens per hour, at one meter from the surface of the box, at the time of shipment.
(NCRP 48)

Transport mean free path
The reciprocal of the macroscopic transport cross section.
(ANSI N1.1-1976)

Transport theory (reactor technology)
A theory, for the treatment of the diffusion in a medium of neutrons or gamma rays, based on the Boltzmann transport equation.
(ANSI N1.1-1976)

Transuranic element (isotope)
An element above uranium in the Periodic Table, that is, with an atomic number greater than 92. All 11 transuranic elements are produced artificially and are radioactive. They are neptunium, plutonium, americium, curium, berkelium, californium, einsteinium, fermium, mendelevium, nobelium, and lawrencium.
(HPJ 60)

Transuranics
Elements with atomic number greater than 92.
(ANSI/HPS N13.45-1998)

Transuranium element
A transuranic element.
(USAEC-1974)

Treated volume
The volume enclosed by an isodose surface, selected and specified by the radiation oncologist as being appropriate to achieve the purpose of treatment (e.g., tumor eradication, palliation).
(ICRU 50)

Treatment
A process to change the physical, chemical, or biological characteristics of radioactive waste (e.g., incineration).
(ANSI/HPS N13.45-1998)

Treatment
Any method, technique, or process, including storage for radioactive decay, designed to change the physical, chemical or biological characteristics or composition of any radioactive material.
(10CFR110.2)

Treatment
A system used to remove all or part of one or more radionuclides or noxious chemicals from a gasborne-effluent stream.
(ANSI N303-1978)

Treatment
The process of removing all or a part of one or more chemical components, particulate components, or radionuclides from an off-gas stream.
(ERDA 76-21)

Treatment volume
The treatment volume is defined as the volume enclosed by a relevant isodose surface selected by the radiotherapist, and encompasses at least the target volume.
(ICRU 38)

Treatment volume
The treatment volume is the volume enclosed by an isodose surface, the value of which is the minimum target absorbed dose. In some cases the treatment volume may be considerably larger than the target volume.
(ICRU 29)

Triage
The process of determining which casualties (from a large number of persons exposed to heavy radiation) need urgent treatment, which ones are well enough to go untreated, and which ones are beyond hope of benefit from treatment. Used in medical aspects of civil defense.
(USAEC-1974)

Tribal governing body
A Tribal organization as defined in the Indian Self-Determination and Education Assistance Act (25 U.S.C. 450).
(10CFR61.2)

Trilinear chart, nuclear
A trilinear coordinate grid on which the nuclides have been plotted according to their mass, atomic, and neutron numbers.
(ANSI N1.1-1976)

Trip
Switching of a device with two defined states from one to the other.
(IEC 50-393-1993)

Tripartite conferences
The first of what became known as the Tripartite Conferences was held at Chalk River, Canada in September 1949, attended by representatives of the United States, Canada and the United Kingdom. The first meeting led to agreement about the permissible dose for workers that had been put forward by NCRP. It took two more meetings, one at Harwell, England and the last at Harriman, New York in 1953, before agreement was reached about complete new protection standards.
(ICRP 59)

Triple point
The temperature and pressure at which all three phases (Solid, liquid, or gas) of a compound coexist at equilibrium.
(NCRP 62)

Tritium
Not only tritium but also includes compounds and mixtures containing tritium in which the ratio of tritium to hydrogen by atoms exceeds one part in 1,000.
(10CFR110.2)

Tritium
A radioactive isotope of hydrogen with two neutrons and one proton in the nucleus. It is man-made and is heavier than deuterium (heavy hydrogen). Tritium is used in industrial thickness gauges, and as a label in experiments in chemistry and biology. Its nucleus is a triton. (See hydrogen.)
(USAEC-1974)

Tritium
The hydrogen isotope with one proton and two neutrons in the nucleus (Symbol: ¹H³ or T).
(RHH)

Triton
Nucleus of the isotope of mass number 3 of hydrogen. called tritium.
(IEC 50-393-1993)

Triton
The nucleus of tritium as a product of a nuclear reaction.
(NCRP 62)

Triton
The nucleus of a tritium (³H) atom. (See hydrogen, tritium.)
(USAEC-1974)

Triton
The nucleus of tritium, the hydrogen isotope of mass number 3, used as a nuclear projectile or as a product of a nuclear reaction.
(RHH)

Tropopause
The boundary between the thermal atmosphere region (troposphere) characterized by decreasing temperature with height and the region of fairly constant temperature with height (stratosphere).
(NCRP 94)

Tropopause
The boundary between the thermal atmospheric region (troposphere) characterized by decreasing temperature with height and the region of fairly constant temperature with height (stratosphere).
(NCRP 62)

Tropopause gap
The region where exchange of air takes place between the stratosphere and troposphere, usually in the latitudes of the jet stream, 30-50^o N and S.
(NCRP 94)

Tropopause gap
The region where exchange of air takes place between the stratosphere and troposphere, usually in the latitudes of the jet stream, 30-50^o N. and 30-50^o S.
(NCRP 62)

Tropopause gap
The region where exchange of air takes place between the stratosphere and troposphere, usually in the latitudes of the jet stream, 30-50^o N and S.
(NCRP 45)

True coincidence
Coincidence due to pulses originating from a single event.
(IEC 50-394-1993)

True count rate (r_b, r_g or r_bg)
Is the count rate that would be observed in the absence of all dead-time losses and fortuitous coincidences.
(ICRU 52)

True positive fraction (TPF)
The conditional probability of deciding that an observed data set (e.g., image) was generated by a specified state (e.g., that a specified disease was present) when, in fact, that state was present. True positive fraction (TPF) is equivalent to the "sensitivity" index often used in the medical literature to indicate the ability of a diagnostic test to detect disease when it is present.
(ICRU 54)

Tryptamine
A crystalline amine C₁₀H₁₂N₂ derived from tryptophan; also, any of various substituted derivatives of this amine of which some are significantly hallucinogenic or neurotoxic.
(HPJ 60)

Tsivoglou method
The original method of estimating the concentrations of the individual short-lived daughter products of ²²²Rn by making three sequential measurements of alpha activity of a filtered air sample.
(NCRP 97)

Tube
See photomultiplier.
(HPJ 60)

Tube current
The electron current that flows from the cathode to the anode in an x-ray tube.
(NCRP 66)

Tube, boron counter
A counter tube filled with boron trifluoride (BF₃) and/or having electrodes coated with boron or boron compounds used for detecting slow neutrons by the (n, a ) reaction of ¹⁰B.
(RHH)

Tube, electron multiplier
A tube in which small electron currents are amplified by a cascade process employing secondary emission.
(RHH)

Tube, photomultiplier
An electron multiplier tube in which the electrons initiating the cascade originate by photoelectric emission.
(RHH)

Tumor
In its general sense, a swelling. The term is often synonymous with neoplasm. A malignant tumor is capable of metastasizing.
(RHH)

Tumorigenicity
Ability of cells to proliferate into tumors when inoculated in a specified host organism under specified conditions.
(BEIR IV)

Turbulent deposition
The process by which air streams fail to follow the contour ridgeways and, hence, transport particles to the walls.
(ENV RAD)

Turbulent flow
Chaotic flow with streamlines looping back on themselves; less "well-behaved" than laminar flow.
(AM-1993)

Two-filter method
A method for estimating radon concentration based on removing the radon daughters form an air sample with a input filter, allowing decay in a chamber and measuring the freshly formed radon decay products on a second filter.
(NCRP 97)

Two-group model
A multigroup model in which the neutrons are divided into two energy groups, usually a thermal group, and a fast or epithermal group containing all neutrons having energies above thermal.
(ANSI N1.1-1976)

Type A package
A packaging designed to retain the integrity of containment and shielding required by this part under normal conditions of transport as demonstrated by the tests set forth in §173.465 or §173.466, as appropriate.
(49CFR173.403)

Type A packaging
A packaging designed to retain the integrity of containment and shielding required by this part under normal conditions of transport as demonstrated by the tests set forth in §173.465 or §173.466, as appropriate.
(49CFR173.403)

Type A quantity
A quantity of radioactive material, the aggregate radioactivity of which does not exceed A₁ for special form radioactive material or A₂ for normal form radioactive material, where A1 and A2 are given in Appendix A of this part or may be determined by procedures described in Appendix A of this part.
(10CFR71.4)

Type A specific license of broad scope
A specific license authorizing receipt, acquisition, ownership, possession, use, and transfer of any chemical or physical form of the byproduct material specified in the license, but not exceeding quantities specified in the license, for purposes authorized by the Act. The quantities specified are usually in the multicurie range.
(10CFR33.11)

Type B package
A Type B packaging together with its radioactive contents.
(49CFR173.403)

Type B package
A Type B package together with its radioactive contents. On approval, a Type B package design is designated by NRC as B(U) unless the package has a maximum normal operating pressure of more than 700 kilopascal (100 lb/in²) gauge or a pressure relief device which would allow the release of radioactive material to the environment under the tests specified in Section 71.73 (hypothetical accident conditions), in which case it will receive a designation B(M). B(U) refers to the need for unilateral approval of international shipments; B(M) refers to the need for multilateral approval. There is no distinction made in how packages with these designations may be used in domestic transportation. To determine their distinction for international transportation, see DOT regulations in 49 CFR Part 173. A Type B package approved prior to September 6, 1983, was designated only as Type B. Limitations on its use are specified in Section 71.13.
(10CFR71.4)

Type B package
A package that contains a quantity of radioactive material greater than the A₁ or A₂ values tabulated in 10 CFR 71 or 49 CFR 173.435.
(ANSI N14.24-1985)

Type B packaging
A Type B packaging together with its radioactive contents.
(49CFR173.403)

Type B packaging
A packaging that is designed to meet the criteria given in the applicable documents in 2.2.1 and 2.2.5 of this standard.
(ANSI N14.5-1987)

Type B quantity
A quantity of radioactive material greater than a Type A quantity.
(10CFR71.4)

Type B specific license of broad scope
A specific license authorizing receipt, acquisition, ownership, possession, use, and transfer of any chemical or physical form of by product material specified in Section 33.100, Schedule A, of this part for purposes authorized by the Act. The possession limit for a Type B broad license, if only one radionuclide is possessed thereunder, is the quantity specified for that radionuclide in §Sec. 33.100, Schedule A, Column I. If two or more radionuclides are possessed thereunder, the possession limit for each is determined as follows: For each radionuclide, determine the ratio of the quantity possessed to the applicable quantity specified in § 33.100, Schedule A, Column I, for that radionuclide. The sum of the ratios for all radionuclides possessed under the license shall not exceed unity.
(10CFR33.11)

Type B(m) package
A Type B packaging together with its radioactive contents, that for international shipments requires multilateral approval of the package design, and may require approval of the conditions of shipment. Type B(M) packages are those Type B package designs which have a maximum normal operating pressure of more than 7 kilograms per square centimeter (100 pounds per square inch) gauge or a relief device which would allow the release of radioactive material to the environment under the hypothetical accident conditions specified in 10 CFR part 71.
(49CFR173.403)

Type B(u) package
A Type B packaging, together with its radioactive contents, that for international shipments, requires unilateral approval only of the package design and of any stowage provisions that may be necessary for heat dissipation.
(49CFR173.403)

Type C specific license of broad scope
A specific license authorizing receipt, acquisition, owner ship, possession, use, and transfer of any chemical or physical form of by product material specified in § 33.100, Schedule A, for purposes authorized by the Act. The possession limit for a Type C broad license, if only one radionuclide is possessed thereunder, is the quantity specified for that radionuclide in § 33.100, Schedule A, Column II. If two or more radionuclides are possessed thereunder, the possession limit is determined for each as follows: For each radionuclide determine the ratio of the quantity possessed to the applicable quantity specified in Section 33.100, Schedule A, Column II, for that radionuclide. The sum of the ratios for all radionuclides possessed under the license shall not exceed unity.
(10CFR33.11)

Type F materials
Deposited materials that are readily absorbed into blood from the respiratory tract. (Fast rate of absorption.)
(ICRP 68)

Type F materials
Deposited materials that are readily absorbed into blood from the respiratory tract. (Fast solubilization.)
(ICRP 66)

Type I Cells
Large, flattened cells that line the alveoli covering about 97 percent of the surface; they maintain the barrier between the air and blood of the lung.
(NCRP 125)

Type II Cells
Cuboidal cells of the alveoli that synthesize, secrete and recycle components of pulmonary surfactant.
(NCRP 125)

Type M materials
Deposited materials that have intermediate rates of absorption into blood from the respiratory tract. (Moderate rate of absorption.)
(ICRP 68)

Type M materials
Deposited materials that have intermediate rates of absorption into blood from the respiratory tract. (Moderate rate of solubilization.)
(ICRP 66)

Type S materials
Deposited materials that are relatively insoluble in the respiratory tract. (Slow rate of absorption.)
(ICRP 68)

Type S materials
Deposited materials that are relatively insoluble in the respiratory tract. (Slow solubilization.)
(ICRP 66)

Type testing
Evaluation or measurement of all identified performance characteristics of a representative sample of production model instruments.
(ANSI N42.17C-1989)

Type testing
Evaluation or measurement of all identified performance characteristics of a representative sample of production model instruments.
(ANSI N42.17B-1989)

Type testing
Evaluation or measurement of all identified performance characteristics of a representative sample of production model instruments.
(ANSI N42.17A-1989)

Type-A quantity of radioactive material
A quantity of UF₆ that does not exceed the limits of a type-A package as specified in 49 CFR 173.431.
(ANSI N14.1-1990)

Type-B quantity of radioactive material
A quantity of UF₆ greater than that of a type-A quantity.
(ANSI N14.1-1990)

Typical Path Lung Model (TPLM)
Lung model using a single unique pathway to represent either the total lung or a portion of the lung.
(NCRP 125)

Note: References shown in ()