Borders' Dictionary of Health Physics

H_T(t)-committed equivalent dose
The time integral of the equivalent dose rate in a particular tissue that will be received by an individual following an intake of radioactive material into the body. The integration time is 50 y for adults. and from intake to 70 y of age for children.
(ICRP 66)

H_T-equivalent dose
The absorbed dose averaged over a tissue or organ and weighted for the radiation quality that is of interest.
(ICRP 66)

H-bomb
A hydrogen bomb.
(USAEC-1974)

Ha-ras
An oncogene originally found in two rodent sarcoma viruses (strains Harvey and BALB). Its product is an enzyme catalysing guanosine triphosphate (GTP). It is a member of multigene family (Ki-ras, N-ras, q.v.), members of which are often in mutated forms in tumours.
(ICRP 59)

Habitable
Capable of providing for continued occupancy during emergency conditions within pre-established radiological and occupational limits set by the Code of Federal Regulations, Title 10, "Energy," Part 50, "Domestic Licensing of Production and Utilization Facilities," General Design Criteria 19, "Control Room."
(ANSI/ANS-3.8.1-1987)

Half life, radioactive
Time for the activity of any particular radioisotope to be reduced to half its initial value.
(NBS 73)

Half life, radioactive
Time for the activity of any particular radioisotope to be reduced to half its initial value.
(NBS 54)

Half value depth (HVD)
The depth in water at which the exposure rate of a beam of radiation is half that at the water surface.
(ICRU 17)

Half value layer
The thickness of a specified material which attenuates the beam of radiation so that the exposure rate or absorbed dose rate at a point is reduced by half. The contribution of all scattered radiation, other than that which might be present in the beam initially, is deemed to be excluded.
(ICRU 30)

Half value layer (energy fluence) (HVL_Y)
As for HVL_X but with energy fluence substituted for exposure.
(ICRU 17)

Half value layer (exposure) (HVL or HVL_x)
The thickness of a specified material which attenuates the beam of radiation so that the exposure rate is reduced to one half of its original value. In this definition the contribution of all scattered radiation, other than that which might be present initially in the beam concerned, is deemed to be excluded.
(NCRP 69)

Half value layer (fluence) (HVL_F)
As for HVL_X but with fluence substituted for exposure.
(ICRU 17)

Half value layer (half thickness)
The thickness of any particular material necessary to reduce the intensity of an x-ray or g-ray beam to one-half it original value.
(HPJ 60)

Half-life
Time interval required to reduce the rate of emission of a radioisotope by a factor of two.
(AM-1993)

Half-life
The time interval during which one-half of the initial number of atoms of a radioactive nuclide undergo radioactive decay. After two half-lives, one-fourth of the initial atoms remain undecayed, after three half-lives, one-eighth remain, and so on.
(NCRP 118)

Half-life
The time required to reduce the amount of a radionuclide to one half the amount originally present. Physical or radioactive half-life refers to reduction of activity by radioactive decay; biological half-life refers to biological elimination from the body; and effective half-life refers to the combined action of radioactive decay and biological elimination.
(NCRP 105)

Half-life
The time in which half the atoms of a particular radioactive substance disintegrate to another nuclear form. Measured half -lives vary from millionths of a second to billions of years. (See decay, radioactive.)
(USAEC-1974)

Half-life
The time in which the curiage of a particular radioactive nuclide has decayed to half its initial value.
(NBS 66)

Half-life (physical, biological, or effective)
The time for a quantity of a radionuclide, i.e., it activity, to diminish by a factor of a half (because of nuclear decay events, biological elimination of the material, or both, respectively).
(FGR 11)

Half-life, biological
The time required for the body to eliminate one-half of an administered dose of any substance by regular processes of elimination. This time is usually the same for both stable and radioactive isotopes of a particular element.
(HPJ 60)

Half-life, biological
Time required for the body to eliminate half of an administered dose of any substance by regular processes of elimination; it is approximately the same for both stable and radioactive isotopes of a particular element.
(BEIR V)

Half-life, biological
The time required for the amount of a particular substance in a biological system to be reduced to one half of its value by biological processes when the rate of removal is approximately exponential.
(ANSI N1.1-1976)

Half-life, biological
See biological half-life.
(USAEC-1974)

Half-life, biological
The time required for the body to eliminate one-half of an administered dosage of any substance by regular processes of elimination. Approximately the same for both stable and radioactive isotopes of a particular element.
(BEIR I)

Half-life, effective
Time required for a radioactive element fixed in the tissue of an animal body to be diminished 50% as a result of the combined action of radioactive decay and biologic elimination.

(HPJ 60)

Half-life, effective
Time required for a radioactive element in an animal body to be diminished by 50% as a result of the combined action of radioactive decay and biological elimination.

(BEIR III)

Half-life, effective
The time required for the amount of a particular radionuclide in a system to be reduced to one half of its value as a consequence of both radioactive decay and other processes such as biological elimination and burnup when the rate of removal is approximately exponential.
(ANSI N1.1-1976)

Half-life, effective
The time required for a radionuclide contained in a biological system, such as a man or an animal, to reduce its activity by half as a combined result of radioactive decay and biological elimination.
(USAEC-1974)

Half-life, effective
Time required for a radioactive element in an animal body to be diminished by 50% as a result of the combined action of radioactive decay and biological elimination.

(RHH)

Half-life, radioactive
The time required for a radioactive substance to lose 50% of its activity by decay. Each radionuclide has a unique half-life. Also called "physical half-life."
(HPJ 60)

Half-life, radioactive
Time required for the radioactive substance to lose 50% of its activity by decay. Each radionuclide has a unique half-life.
(BEIR V)

Half-life, radioactive
Time required for a radioactive substance to lose 50 percent of its activity by decay.
(NCRP 103)

Half-life, radioactive
Time required for the radioactive substance to lose 50% of its activity by decay. Each radionuclide has a unique half-life.
(BEIR IV)

Half-life, radioactive
Time required for the radioactive substance to lose 50% of its activity by decay. Each radionuclide has a unique half-life.
(BEIR III)

Half-life, radioactive
For a single radioactive decay process, the time required for the activity to decrease to half its value by that process.
(ANSI N1.1-1976)

Half-life, radioactive
The time for the activity of any particular radioactive nuclide to be reduced to one-half its initial value.
(NCRP 48)

Half-life, radioactive
The time for the activity of any particular radioactive nuclide to be reduced to one-half its initial value.
(NCRP 49)

Half-life, radioactive
Time required for the radioactive substance to lose 50% of its activity by decay. Each radionuclide has a unique half-life.
(BEIR I)

Half-life, radioactive
The time for the activity of any particular radioactive nuclide to be reduced to one-half its initial value.
(NCRP 51)

Half-life, radioactive
Time required for the radioactive substance to lose 50% of its activity by decay. Each radionuclide has a unique half-life.
(RHH)

Half-Life/Biological
The time for one half of a radioactive material to be eliminated from the body by natural, biological means. Biological half-lives may range from a few hours to many decades.
(ANSI/HPS N13.45-1998)

Half-Life/Effective
The time for one half of a radioactive material in the body to be removed by the combined effects of biological elimination and radioactive decay.
(ANSI/HPS N13.45-1998)

Half-Life/Radioactive (or physical)
The time for a radionuclide to lose half of its radioactivity by radioactive decay. Radioactive half-lives may range from millionths of a second to millions of years depending on the radionuclide.
(ANSI/HPS N13.45-1998)

Half-mask facepiece
See facepiece.
(ANSI Z88.2-1980)

Half-mask facepiece
See facepiece.
(ANSI Z88.2-1969)

Half-space
A standard idealized geometry in practical radiation measurements, where the source medium is considered to be uniformly distributed throughout all space on one side of an infinite plane boundary, e.g., the air-ground interface.
(NCRP 94)

Half-thickness
The thickness of any given absorber that will reduce the intensity of a beam of radiation to one-half its initial value.
(USAEC-1974)

Half-time
See residence time.
(USAEC-1974)

Half-time, biological (T_b)
The time in which half the quantity of a material in a compartment, in an organ or in the whole body is eliminated by biological processes.
(ICRP 54)

Half-time, effective (T_e)
The time taken for the activity of a radioactive material in a compartment, in an organ or in the whole body to be reduced to half its value by a combination of biological elimination and radioactive decay.

(ICRP 54)

Half-time, physical (T_R)
The time taken for the activity of a radionuclide to lose its value by radioactive decay.
(ICRP 54)

Half-value layer
The thickness of a specified substance which, when introduced into the path of a given beam of radiation, reduces the value of a specified radiation quantity by one-half. It is sometimes expressed in terms of mass per unit area. (Also called half-value thickness.)
(ANSI N1.1-1976)

Half-value layer
The thickness of any particular material necessary to reduce the dose rate of an X-ray beam to one-half its original value.
(USAEC-1974)

Half-value layer
Thickness of an absorber required to attenuate a beam of radiation to one-half.
(NBS 73)

Half-value layer (half thickness) (HVL)
The thickness of a specified substance which, when introduced into the path of a given beam of radiation, reduces the exposure rate by one-half.
(NCRP 49)

Half-value layer (half thickness) (HVL)
The thickness of a specified substance which, when introduced into the path of a given beam of radiation, reduces the exposure rate by one-half.
(RHH)

Half-value layer (HVL)
Thickness of a specified substance which, when introduced into the path of a given beam of radiation, reduces the kerma rate by one-half.
(NCRP 102)

Half-value layer (HVL)
Thickness of an absorber required to reduce a beam of radiation to one-half its incident dose rate.
(NBS 54)

Half-value layer (HVL)
The thickness of absorbing material necessary to reduce the dose rate produced at a point by an X-ray beam to one-half its original value. A statement of half-value layer at high X-ray energies should always be accompanied by a statement on the amount of previous filtration. The concept of a half-value layer, especially at high energies, must be applied with caution since the rate of change of dose rate with thickness or depth is not always a unique characteristic of the primary radiation.
(NBS 55)

Half-value layer (or thickness)
The 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 by one-half. The magnitude of the half-value layer may be different for absorbed dose index and dose equivalent index.
(NCRP 51)

Half-value thickness
The thickness of a given material required to reduce the radiation intensity by a factor of two.
(NCRP 112)

Hand and foot counter
A monitoring device arranged to give a rapid radiation survey of hands and feet of persons working with radioactive materials, to detect radioactive contamination. (See counter, monitor, personnel monitoring, radioactive contamination.)
(USAEC-1974)

Hand or foot contamination warning assembly
Assembly which gives warning signals when the radioactive emission rate from hands or feet exceeds some predetermined value.
(IEC 50-394-1993)

Hand-foot-clothing radioactive contamination monitor
Radiation monitor which measures the radioactive emission in a given time interval from hands, feet and clothing.
(IEC 50-394-1993)

Hands-on experience
Experience in all of those areas considered to be directly involved in the radiography process.
(10CFR34.3)

Hard radiation
Ionizing radiation of high energy which has high penetrating ability.
(ANSI N1.1-1976)

Hardening
See spectral hardening.
(ANSI N1.1-1976)

Hardness
A relative specification of the quality or penetrating power of x-rays. In general, the shorter the wavelength the harder the radiation.
(RHH)

Hatch-Choate equations
Expressions that, given a characteristic diameter and geometric standard deviation of a distribution, allow the calculation of any other characteristic diameter of the distribution.
(AM-1993)

Haversian canals
Cavities within mineralized bone in which run the blood vessels, lymph vessels and nerves. The canals are lined with connective tissue, the endosteum.
(NCRP 45)

Haversian system
The freely anastomosing nutrient channels of compact bone, containing blood vessels, lymph nodes and nerves.
(NCRP 83)

Haversian system (osteon)
An Haversian system or Osteon is the roughly cylindrical volume of bone which surrounds a blood vessel and which is formed by osteoblasts in the cylindrical space excavated by osteoclastic resorption of bone. The process of resorption and subsequent apposition at the same site in compact bone is referred to as haversian remodeling. Haversian canals in man range from 45-65 mm in diameter. Osteons average 240 mm in diameter. They are found in compact but almost never in cancellous bone.
(ICRP 20)

Hazard, radiation
See radiation hazard.
(NBS 73)

Hazard, radiation
See radiation hazard.
(NBS 54)

Hazardous atmosphere
Any atmosphere, either immediately or not immediately dangerous to life or health, which is oxygen deficient or which contains a toxic or disease producing contaminant exceeding the legally established permissible exposure limit (PEL) or, where applicable, the Threshold Limit Value (TLV) as established by the American Conference of Governmental Industrial Hygienists (ACGIH).
(ANSI Z88.2-1980)

Hazardous waste
Those wastes designated as hazardous by Environmental Protection Agency regulations in 40 CFR Part 261.
(10CFR61.2)

Head end (fuel reprocessing)
One of several possible sets of steps in a given fuel-reprocessing scheme intended to bring nuclear fuels or different forms into a given physical and chemical state suitable for a common subsequent treatment.
(ANSI N1.1-1976)

Head harness
That part of a facepiece assembly which secures the facepiece to the wearer.
(ANSI Z88.2-1980)

Head harness
A device for holding the facepiece securely in place on the wearer's head.
(ANSI Z88.2-1969)

Health physicist
A person qualified by training and experience to be professionally engaged in the practice of health physics.
(NCRP 111)

Health physicist
The person responsible for the radiation protection program within a facility.
(ANSI N343-1978)

Health physics
The science concerned with the recognition, evaluation and control of health hazards from ionizing radiation.
(HPJ 60)

Health physics
The profession devoted to the protection of humans and their environment from potential radiation hazards, identifying potential beneficial effects of radiation and assisting in the development of beneficial effects of ionizing and nonionizing radiation thus providing for the utilization of radiation for the benefit of mankind.
(NCRP 111)

Health physics
The science concerned with the recognition, evaluation and control of health hazards from ionizing radiation.
(NCRP 65)

Health physics
The science of radiation protection.
(ANSI N1.1-1976)

Health physics
The science concerned with the recognition, evaluation and control of health hazards from ionizing radiation.
(USAEC-1974)

Health physics technician
An individual trained in the principles of health physics and equipped with, and knowledgeable in the operation of, appropriate radiation detection instruments.
(ANSI N14.24-1985)

Health, radiological
The art and science of protecting human beings from injury by radiation, as well as promoting better health through beneficial applications of radiation.
(HPJ 60)

Health, radiological
The art and science of protecting human beings from injury by radiation, and promoting better health through beneficial application of radiation.
(RHH)

Healthy worker effect
Lower mortality rate among workers than among the general population if their health has not been adversely affected by work.
(ENV RAD)

Heap-leach extraction
The application of chemical agents to ore stockpiles or mine walls for the extraction of the mineral content.
(NCRP 118)

Heat exchanger
Any device that transfers heat from one fluid (liquid or gas) to another or to the environment.
(USAEC-1974)

Heat sink
Anything that absorbs heat; usually part of the environment, such as the air, a river, or outer space.
(USAEC-1974)

Heat-flow calorimeter
A calorimeter so constructed that the heat generated in the calorimeter flows at equilibrium through a thermal resistance. The average temperature rise thus established across this resistance is related to the rate of heat generation by means of a separate calibration experiment using a calibrated source of thermal power.
(ANSI N15.22-1987)

Heater replacement
The method by which the thermal power of a sample is determined by placing the sample in the chamber that is separated from a constant-temperature environment (heat sink) by a known thermal resistance, and measuring the rate of heat flow from the sample chamber into the heat sink when the system has attained thermal equilibrium. Under these conditions, the temperature difference between the sample chamber and the heat sink is proportional to the thermal power of the sample.
(ANSI N15.54-1988)

Heavily populated area
Urban areas within the United States that have total populations of 100000 persons or more are designated as heavily populated areas by the Nuclear Regulatory Commission (NRC) for purposes of regulation of spent nuclear fuel shipments. (For a listing of these areas, see NUREG-0561, Rev. 1.)
(ANSI N14.24-1985)

Heavy hydrogen
Deuterium.
(USAEC-1974)

Heavy ions
Nuclei of elements such as nitrogen, carbon, boron, neon, argon, or iron which are positively charged due to some or all of the planetary electrons having been stripped from them.
(NCRP 98)

Heavy ions
The term is frequently used to refer to energetic accelerated stripped nuclei of elements of Z > 2.
(ICRU 30)

Heavy particle
Any particle having a rest mass greater than that of the electron.
(NCRP 38)

Heavy particles
Includes heavy ions and neutrons and protons.
(ICRU 30)

Heavy water
[Symbol D₂O] Water containing significantly more than the natural proportion (one in 6500) of heavy hydrogen (deuterium) atoms to ordinary hydrogen atoms. Heavy water is used as a moderator in some reactors because it slows down neutrons effectively and also has a low cross section for absorption of neutrons.
(USAEC-1974)

Heavy water content meter
Content meter designed for continuously or discontinuously determining the heavy water content of a heavy water-light water mixture in a nuclear reactor.
(IEC 50-394-1993)

Heavy water reactor (HWR)
A nuclear reactor in which heavy water serves as a moderator and sometimes also as a coolant.
(NCRP 81)

Heavy water reactor (HWR)
A nuclear reactor in which heavy water serves as a moderator and sometimes also as a coolant.
(NCRP 62)

Heavy-light water heat exchanger leak monitor
Monitor designed to detect leakages between the primary heavy water coolant circuit and secondary light water coolant circuit of a nuclear reactor, by detecting radioactivity in the secondary circuit.
(IEC 50-394-1993)

Heavy-water-moderated reactor
A reactor that uses heavy water as its moderator. Heavy water is an excellent moderator and thus permits the use of inexpensive natural (unenriched) uranium as a fuel.
(USAEC-1974)

Heel
A residual amount of UF₆ and nonvolatile reaction products of uranium.
(ANSI N14.1-1990)

Heel
Any liquid that remains in the tank as a result of some operation; in particular, the uncalibrated liquid in the tank at the start of a calibration run.
(ANSI N15.19-1989)

Heel effect
Non-uniform intensity observed because a small fraction of the x-ray beam emitted in a direction nearly parallel to the angled target surface must pass through more target material before escaping from the target than does the major portion of the beam which is emitted more perpendicularly.
(Note: In addition to the non-uniform intensity the angled target also produces non-uniform image resolution due to variations in apparent focal spot size as viewed from various positions on the film).
(NCRP 102)

Heel effect
The unequal intensity across the x-ray beam, the intensity being greatest on the cathode side of the beam and least intense on the anode side of the beam. Some of this variation is reduced by the use of lead apertures and shutters which limit the periphery of the primary x-ray beam.
(NCRP 66)

Helium counter tube
Proportional counter tube containing helium 3 to detect neutrons.
(IEC 50-394-1993)

Helmet
That portion of a respirator which shields the eyes, face, neck, and other parts of the head.
(ANSI Z88.2-1980)

Helmet
A device that shields the eyes, face, neck, and other parts of the head.
(ANSI Z88.2-1969)

Hemangiosarcoma
Malignant neoplasm originating from blood vessels and involving endothelial and fibroblastic tissue.
(NCRP 125)

Hematopoietic system
The blood-forming organs, principally the bone marrow and lymph nodes.
(HPJ 60)

Henry's constant
The ratio of the air concentration to the water concentration of a gas or volatile compound.
(ENV RAD)

Henry's law
The mass of a slightly soluble, inert gas that dissolves in a definite mass of a liquid at a given temperature is very nearly directly proportional to the partial pressure of that gas.
(NCRP 45)

Henrys Law
The solubility of a gas in a liquid is proportional to the partial pressure ofthe gas, i.e., by doubling the pressure, twice as much gas passes into solution.
(NCRP 125)

HEPA filter
High-efficiency particulate air filter-also obsoletely known as AEC, CWS, superinterception, absolute, and super high efficiency filter. A throwaway extended-pleated-medium dry-type filter with (1) a rigid casing enclosing the full depth of the pleats, (2) a minimum particle removal efficiency of 99.97% for thermally generated monodisperse DOP smoke particles with a diameter of 0.3 mm, and (3) a maximum pressure drop of 1.0 in. wg when clean and operated at its rated airflow capacity.
(ERDA 76-21)

Heredity
Transmission of characters and traits from parent to offspring.
(RHH)

Heritage
A term collectively referring to the influence of species, genetic background, ethnic group, and environment on susceptibility to thyroid carcinoma.
(NCRP 80)

Hertz
Unit of frequency equal to one cycle per second.
(RHH)

Heterogeneous
Consisting of individual components that may differ from each other in size, shape, and chemical composition.
(AM-1993)

Heterogeneous nucleation
Formation of droplets on condensation nuclei (existing submicrometer particles).
(AM-1993)

Heterogeneous reactor
Reactor in which the core materials are segregated to such an extent that its neutron characteristics cannot be accurately described by the assumption of homogeneous distribution of the materials throughout the core.
(IEC 50-393-1993)

Heterogeneous reactor
A reactor in which the fuel is separate from the moderator and is arranged in discrete bodies, such as fuel elements. Most reactors are heterogeneous.
(USAEC-1974)

Heterozygous
Having the two genes at corresponding loci on homologous chromosomes different for one or more loci.
(HPJ 60)

High contamination area
Any area, accessible to individuals, where removable surface contamination levels exceed or are likely to exceed 100 times the removable surface contamination values specified in appendix D of this part.
(10CFR835.2-1998)

High contamination area
Any area where contamination levels are greater than 100 times the values specified in appendix D of this part.
(10CFR835.2-1993)

High dose rate
In this Report, the term high dose rate refers to any dose rate higher than 0.2 gray per minute (12 grays per hour), although it usually refers to dose rates as high as 2 to 5 grays per minute, i.e., treatment sessions of a few minutes duration.
(ICRU 38)

High efficiency filter
A filter which removes from air 99.97% or more of monodisperse dioctyl phthalate (DOP) particles having a mean particle diameter of 0.3 micrometer.
(ANSI Z88.2-1980)

High efficiency particulate air (HEPA) filter
A gas filter having a fibrous medium that produces a particle-removal efficiency of at least 99.97% for 0.3-micron-diameter monodisperse dioctylphthalate (DOP) particles, on a count basis, in accordance with American Association for Contamination control Standard for HEPA Filters, AACC CS-1.
(ANSI N303-1978)

High enriched uranium
Uranium enriched to 20 percent or greater in the isotope uranium-235.
(10CFR110.2)

High enriched uranium
Uranium enriched to 20 percent or greater in the isotope uranium-235.
(10CFR170.3)

High enriched uranium
Uranium enriched to 20 percent or greater in the isotope uranium-235.
(10CFR74.4)

High Enriched Uranium Fuel
Uranium enriched to 20 percent or greater in the isotope uranium-235.
(10CFR171.5)

High LET
Radiation having a high linear energy transfer, for example, alpha particles, heavy ions and interaction productions of fast neutrons. The ionization density along the radiation track is high.
(ICRP 59)

High LET
Radiation having a high linear energy transfer, for example, protons, alpha particles, heavy ions and interaction products of fast neutrons.
(NCRP 98)

High purity semiconductor detector
Semiconductor detector in which the high purity of the material employed avoids the need for compensation.
(IEC 50-394-1993)

High radiation area
An area accessible to individuals, in which radiation levels could result in an individual receiving a dose equivalent in excess of 0.1 rem (1 mSv) in 1 hour at 30 centimeters from the radiation source or from any surface that the radiation penetrates.
(10CFR20.1003)

High radiation area
Any area, accessible to individuals, in which radiation levels could result in an individual receiving a deep dose equivalent in excess of 0.1 rem (0.001 sievert) in 1 hour at 30 centimeters from the radiation source or from any surface that the radiation penetrates.
(10CFR835.2-1993)

High radiation area
Any area, accessible to personnel, in which there exists radiation, originating in whole or in part within licensed material, at such levels that a major portion of the whole body could receive in any one hour a dose in excess of 100 millirem.
(10CFR20.202)

High radiation area
Any area, accessible to personnel, in which there exists radiation at such levels that a major portion of the body (whole body, head and trunk, active blood forming organs, gonads, or eye lenses) could receive in any 1 hour a dose equivalent, H, in excess of 100 mrem.
(ANSI N43.1-1978)

High radiation area
Any area, accessible to personnel, in which there exists radiation at such levels that a major portion of the body could receive in any 1 hour a dose equivalent, H, in excess of 100 mrem.
(NCRP 51)

High temperature gas cooled reactor (HTGR)
A prototype gas cooled reactor in which the coolant is pressurized helium gas; the fuel consists of fully enriched uranium and thorium.
(NCRP 62)

High temperature gas reactor (HTGR)
A reactor in which the coolant is pressurized helium gas; the fuel consists of fully enriched uranium and thorium.
(NCRP 81)

High-Level Radioactive Waste
Irradiated reactor fuel, liquid wastes resulting from the operation of the first cycle solvent extraction system or equivalent, concentrated wastes from subsequent extractions in the reprocessing of irradiated reactor fuel, and solids into which such liquid wastes have been converted.
(ANSI/HPS N13.45-1998)

High-level radioactive waste or HLW
(1) Irradiated reactor fuel,
(2) liquid wastes resulting from the operation of the first cycle solvent extraction system, or equivalent, and the concentrated wastes from subsequent extraction cycles, or equivalent, in a facility for reprocessing irradiated reactor fuel, and
(3) solids into which such liquid wastes have been converted.
(10CFR60.2)

High-level radioactive waste or HLW
(1) The highly radioactive material resulting from the reprocessing of spent nuclear fuel, including liquid waste produced directly in reprocessing and any solid material derived from such liquid waste that contains fission products in sufficient concentrations; and
(2) other highly radioactive material that the Commission, consistent with existing law, determines by rule requires permanent isolation.
(10CFR72.3)

High-level waste
High-level radioactive waste is defined by 10 CFR 60 (May 1983) as
(1) irradiated reactor fuel,
(2) liquid waste resulting from the operation of the first cycle solvent extraction system, or equivalent, and the concentrated waste from subsequent extraction cycles, or equivalent, in a facility for reprocessing irradiated reactor fuel, and
(3) solids into which such liquids have been converted.
(NCRP 76)

Highly enriched uranium (HEU) fuel
Fuel in which the weight percent of U-235 in the uranium is 20% or greater. Target material, special instrumentation, or experimental devices using HEU are not included.
(10CFR50.2)

Highway route controlled quantities
Quantities of radioactive materials as defined in Department of Transportation (DOT) regulations 49 CFR 173.403(1), to which specified highway routing and notification requirements apply.
(ANSI N14.24-1985)

Highway route controlled quantity
A quantity of a single package which exceeds:
(1) 3000 times the A₁ value of the radionuclides as specified in §173.433 for special form radioactive material;
(2) 3000 times the A₂ value of the radionuclides as specified in §173.433 for normal form radioactive material;
(3) 30,000 curies whichever is least.
(49CFR173.403)

Hilar Area Or Nodes
Depression or recess at entrance or exit of vessels to an organ; the root of the lung and its lymph nodes.
(NCRP 125)

Historical data
A compilation of the available published and unpublished information concerning a particular type of event.
(10CFR72.3)

HLW facility
A facility subject to the licensing and related regulatory authority of the Commission pursuant to Sections 202(3) and 202(4) of the Energy Reorganization Act of 1974 (88 Stat 1244). These are DOE "facilities used primarily for the receipt and storage of high-level radioactive wastes resulting from activities licensed under such Act [the Atomic Energy Act]" and "Retrievable Surface Storage Facilities and other facilities authorized for the express purpose of subsequent long-term storage of high-level radioactive wastes generated by [DOE], which are not used for, or are part of, research and development activities."
(10CFR60.2)

Hole
Vacancy appearing in an energy band normally filled, behaving like a carrier of one positive elementary charge.
(IEC 50-394-1993)

Homeostatic control
Maintenance of a relatively stable state of equilibrium between interdependent elements in an organism.
(NCRP 94)

Homeostatic control
Maintenance of a relatively stable state of equilibrium between interdependent elements in an organism.
(NCRP 45)

Homogeneity
The properties, or conditions of isotropy or anisotropy are constant from point to point in the ground water medium.
(NCRP 123I)

Homogeneity
The properties, or conditions of isotropy or anisotropy are constant from point to point in the ground water medium.
(NCRP 76)

Homogeneity coefficient
The ratio of the first to second half-value layers; usually applied to a heterogeneous X-ray beam.
(ANSI N42.17A-1989)

Homogeneity coefficient
The ratio of the first to second half-value layers; usually applied to a heterogeneous X-ray beam.
(ANSI N42.17C-1989)

Homogeneous nucleation
Formation of droplets in the absence of condensation nuclei; also called self-nucleation.
(AM-1993)

Homogeneous phantom
A homogeneous phantom is a phantom made of one material only.
(ICRU 44)

Homogeneous reactor
Reactor in which the core materials are distributed in such a manner that its neutron characteristics can be accurately described by the assumption of homogeneous distribution of the materials throughout the core.
(IEC 50-393-1993)

Homogeneous reactor
A reactor in which the fuel is mixed with or dissolved in the moderator or coolant. Example: a fused-salt reactor.
(USAEC-1974)

Hood
That portion of a respirator which completely covers the head, neck, and portion of the shoulders.
(ANSI Z88.2-1980)

Hood
A protective device, usually providing special ventilation to carry away gases, in which dangerous chemical, biological, or radioactive materials can be safely handled.
(USAEC-1974)

Hood
A device that completely covers the head, neck, and portion of the shoulders.
(ANSI Z88.2-1969)

Horizontal elutriator
A horizontal channel through which aerosol flows and particles above a given size or size range are removed by gravitational settling.
(AM-1993)

Hose mask
See respirator.
(ANSI Z88.2-1980)

Hose mask
See respirator.
(ANSI Z88.2-1969)

Host rock
The geologic medium in which the waste is emplaced.
(10CFR60.2)

Hot
Very radioactive.
(IEC 50-393-1993)

Hot
Highly radioactive.
(ERDA 76-21)

Hot
An expression commonly used to mean "highly radioactive" (See hot atom.)
(ANSI N1.1-1976)

Hot
Highly radioactive.
(USAEC-1974)

Hot atom
An atom in an excited energy state or having kinetic energy above the thermal level of the surroundings, usually as a result of nuclear processes.
(ANSI N1.1-1976)

Hot cell
A heavily shielded enclosure in which radioactive materials can be handled remotely with manipulators and viewed through shielding windows to limit danger to operating personnel.
(ERDA 76-21)

Hot cell
A heavily shielded enclosure in which radioactive materials can be handled by persons using remote manipulators and viewing the materials through shielded windows or periscopes. (See shield.)
(USAEC-1974)

Hot cell
A heavily shielded enclosure for handling and processing (by remote means or automatically) or storing highly radioactive materials.
(RHH)

Hot channel factor
The ratio of the change in the enthalpy of the coolant over that fuel channel in which the change is greatest to the average change over the reactor core.
(ANSI N1.1-1976)

Hot channel safety factor
The safety factor corresponding to the ratio of the maximum change of enthalpy in case of an incident to the nominal variation of enthalpy in the channel in which the temperature is the highest (hot channel).
(ANSI N1.1-1976)

Hot laboratory
A laboratory designed for the safe handling of radioactive materials, and usually containing one or more hot cells.
(USAEC-1974)

Hot particle
A discrete radioactive fragment that is insoluble in water and is no larger than approximately 1 mm in any dimension.
(NCRP 106)

Hot particle
An aggregation of radionuclide atoms.
(NCRP 84)

Hot radiochemical laboratory
Radiochemical laboratory designed for chemical and technological operations associated with the treatment and study of highly radioactive preparations.
(IEC 50-393-1993)

Hot spot
An area of unusually high concentration of a radionuclide in an organ or tissue, frequently on a microscopic scale.
(NCRP 84)

Hot spot
A surface area of higher-than-average radioactivity. Also a part of a fuel element surface that has become overheated.
(USAEC-1974)

Hot spot factor
Ratio of the maximum heat flux to the average flux in a nuclear reactor.
(ANSI N1.1-1976)

Hot spot safety factor
The safety factor by which the nominal temperature difference between the can and the coolant at a given point is multiplied to obtain the value of that difference resulting from heat transfer parameters taking their maximum permissible values in case of an incident. The point chosen is that at which the highest temperature increase would occur (hot spot).
(ANSI N1.1-1976)

Hot spots
In many situations tissues outside the target area will receive a relatively high absorbed dose. A hot spot is an area which receives an absorbed dose higher than 100% of the specified target absorbed dose. However, as in the case of the maximum target absorbed dose,a hot spot is considered clinically meaningful only if the corresponding isodose curve encloses an area of at least 2 cm² in a section.
(ICRU 29)

Hot testing
Testing of method, process, apparatus, or instrumentation under normal working conditions and at expected activity levels.
(ANSI N1.1-1976)

Hot-wire anemometer
A device used to measure air velocity by measuring the change in resistance of a heated wire.
(AM-1993)

Hotelling observer
The Hotelling observer demonstrates maximum discrimination ability, in terms of the SNR figure of merit (Equation C.5), among all observers that are limited to performing only linear operations on the data. When the data is normally distributed, including the unequal variance case, this observer also demonstrates maximum discrimination as specified by the area under the ROC curve. When the data is not normally distributed, the SNR figure of merit may no longer be predictive of the area under the ROC curve. It will then be necessary to obtain that area to test for optimality of observers. This observer is also referred to as the Hotelling/Fisher observer and the Fisher discriminant because of the convergence of the work of Hotelling (1931) and Fisher (1936).
(ICRU 54)

Hounsfield units
See CT number.
(NCRP 102)

House-dust mites
Common insects living in mattresses and carpets; excreta are common allergens.
(AM-1993)

HTGR
High Temperature Gas Cooled Reactor
(RAH)

HTGR
High Temperature Gas Cooled Reactor
(NCRP 62)

Human use
The internal or external administration of byproduct, source, or special nuclear material, or the radiation therefrom, to human beings.
(10CFR170.3)

Humic acids
Organic acids obtained from or present in humus, the organic portion of soil.
(NCRP 94)

Humic acids
Organic acids obtained from or present in humus, the organic portion of soil.
(NCRP 45)

Hydraulic conductivity (permeability)
The volume of water that will move per unit time in the aquifer under a unit gradient through a unit cross sectional area perpendicular to the direction of flow.
(NCRP 123I)

Hydraulic conductivity (permeability)
The volume of water that will move per unit time under a unit gradient through a unit cross-sectional area perpendicular to the direction of flow.
(NUREG/CR 3332)

Hydraulic diameter
Hypothetical diameter of an object equal to four times the object's cross-sectional area divided by the perimeter of that area.
(AM-1993)

Hydrides
Compounds in which hydrogen is chemically bonded to metals and certain other elements (for example, diborance and lithium hydride.)
(ANSI Z88.2-1980)

Hydrides
Compounds in which hydrogen is chemically bonded to metals and certain other elements (for example, diborance and lithium hydride.)
(ANSI Z88.2-1969)

Hydrogen
[Symbol H] The lightest element, No. 1 in the atomic series. It has two natural isotopes of atomic weights 1 and 2. The first is ordinary hydrogen, or light hydrogen; the second is deuterium, or heavy hydrogen. A third isotope, tritium, atomic weight 3, is a radioactive form produced in reactors by bombarding lithium-6 with neutrons.
(USAEC-1974)

Hydrogen bomb
A nuclear weapon that derives its energy largely from fusion. (See thermonuclear reaction.)
(USAEC-1974)

Hydrogeologic unit
Any soil or rock unit or zone which by virtue of its porosity or permeability, or lack thereof, has a distinct influence on the storage or movement of groundwater.
(10CFR61.2)

Hydrophilic Molecule
Molecule that readily absorbs moisture; bibulous.
(NCRP 125)

Hydrosol
Suspension of particles in a liquid.
(AM-1993)

Hygroscopicity
Degree of absorption and retention of moisture.
(NCRP 125)

Hygroscopicity
Property of a chemical that indicates its tendency to absorb water from the air.
(AM-1993)

Hyperon
General term applied to various very short-lived particles, with or without charge, of spin 1/2 or 3/2, and of rest mass greater than that of the neutron.
(IEC 50-393-1993)

Hyperon
One of a class of short-lived elementary particles with a mass greater than that of a proton and less than that of a deuteron. All hyperons are unstable and yield a nucleon as a decay product. (See baryon.)
(USAEC-1974)

Hyperthyroidism (thyrotoxicosis)
Functional, metabolic state caused by excessive thyroid hormone.
(NCRP 80)

Hyphae
A chain of fungal cells.
(AM-1993)

Hypopharyus
Lowermost portion of the pharynx that leads to the larynx and esophagus.
(NCRP 125)

Hypothyroidism
Functional, metabolic state caused by inadequate amounts of thyroid hormone.
(NCRP 80)

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