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A symbol for hydrogen.

A symbol for committed dose equivalent.

A symbol for hahnium.

A chemical element with atomic number 72. Hafnium was discovered in 1932 by Dirk Coster and Georg de Hevesy who identified x-rays consistent with element 72 during x-ray spectroscopy studies on the mineral zircon. The name hafnium is derived from Hafnia, the Latin name for Copenhagen.

Symbol: Hf.
Related to transition metals.

(obsolete term)

A synonym for dubnium.

Symbol: Ha.

The time required for one half of a radioactive sample to decay.

Symbol: T1/2.
Synonym: half period.
Synonym: half value time.
Synonym: radioactive half-life.
Related to biological half-life.
Related to effective half-life.

half period
A synonym for half-life.

That absorber thickness required to attenuate the intensity of a radiation beam by one half.

half-value layer
A synonym for half-value thickness.

half-value thickness
That amount of an absorber which is required to reduce the intensity of a radiation by one half.

Symbol: D.
Synonym: half-value layer.

half value time
A synonym for half-life.

Of or pertaining to two or more halogens that have an oxidation state of -1.

Related to astatine.
Related to bromine.
Related to chlorine.
Related to fluorine.
Related to halogens.
Related to iodine.

The set of chemical elements that form group VIIA in the periodic chart. Halogen is derived from the Greek term for salt former as the elements will react with metals to form salts. The elements making up the halogens include fluorine (F, Z=9), chlorine (Cl, Z=17), bromine (Br, Z=35), iodine (I, Z=53), and astatine (At, Z=85).

Related to astatine.
Related to bromine.
Related to chlorine.
Related to fluorine.
Related to halides.
Related to iodine.

A chemical element with atomic number 108.

Symbol: Hs.
Synonym: (obsolete) unniloctium.
Related to transition metals.

A symbol for deep-dose equivalent.

A symbol for helium.

A symbol for effective dose equivalent.
Reference: 10CFR20.1003; 10CFR30.4; 10CFR70.4; 10CFR76.4; USACHPPM TG 204.

A symbol for committed effective dose equivalent.

health physics
The study of the effects of radiation on humans, the monitoring of radiation exposure and the reduction of health risks associated with radiation exposure.

Acronym: HP.

heat exchanger
Any device that transfers heat from one system to another. In a nuclear reactor, the heat exchanger transfers heat from the reactor cooling system to water that passes through the turbo generators to produce electricity.

Symbol: HX.

heat of formation
A synonym for binding energy.

The increase in temperature of a fuel rod due to an increased rate of fission in the reactor core.

Acronym: H/U.

heavy hydrogen
A synonym for deuterium.

heavy water
(1) Water in which the hydrogen atoms are the nuclide 2H.

(2) A sample of water whose hydrogen consists primarily of the nuclide 2H.

Acronym: HW.
Symbol: D2O.
Synonym: deuterium oxide.
Related to light water.

heavy-water-moderated reactor
A reactor that uses heavy water as its moderator.

A chemical element with atomic number 2. Helium was first observed in 1868 by Pierre-Jules-César Janssen who identified a new spectral line in a solar spectrum during a solar eclipse. Later that year Jospeh Norman Lockyer concluded that Janssen had discovered a new element, one that had yet to be found on earth. The name helium is derived from helios, Latin for sun.

Symbol: He.
Related to noble gases.

A synonym for highly-enriched uranium.

A symbol for hafnium.

A symbol for mercury.

high enriched uranium
A synonym for highly-enriched uranium.

high-level radioactive waste
(1) Radioactive waste that produces enough decay heat to require continuous cooling.

(2) Irradiated reactor fuel  Nuclear Fuel Reprocessing (1) 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. Solids into which the liquid wastes have been converted are included. (2) 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. Other Highly radioactive material that the Nuclear Regulatory Commission, consistent with existing law, determines by rule requires permanent isolation.

(3) The highly radioactive waste material that results from the reprocessing of spent nuclear fuel, including liquid waste produced directly in reprocessing and any solid waste derived from the liquid, that contains a combination of transuranic waste and fission products in concentrations requiring permanent isolation.

Acronym: HLRW.
Synonym: high-level waste.

high-level waste
A synonym for high-level radioactive waste.

Acronym: HLW. Related to radioactive waste.

highly-enriched uranium
general  Uranium enriched to at least 20% 235U.
weapons  Uranium enriched to about 90% 235U.

Acronym: HEU.
Synonym: high-enriched uranium.

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.

Reference: 10CFR20.
Related to radiation area.
Related to very high radiation area.

high temperature gas-cooled reactor
A synonym for gas-cooled reactor.

An acronym for high-level radioactive waste.

An acronym for high-level waste.

A symbol for holmium.

A chemical element with atomic number 67. Holmium was first observed in 1878 by Jacques Soret and Marc Delafonatine who named it Element X. Swedish chemist, Per Teodor Cleve was credited for the discovery when he obtained a sample of holmium from the mineral erbia. The name holmium is derived from Holmia, Latin for Stockholm.

Symbol: Ho.
Synonym: (obsolete) element X.
Related to lanthanides.
Related to rare earths.
Related to yttrium earths.


Related to cold.

hot cell
A synonym for cave.

hot spot
Location where the radioactivity or radiation is higher than expected. Part of a fuel element surface that has become overheated.

An acronym for health physics.

A symbol for hassium.

A symbol for shallow-dose equivalent.

A synonym for equivalent dose.
Reference: NUREG-0544, Rev. 4.

A symbol for committed dose equivalent.
Reference: 10CFR20.1003; DOE G 440.1-3; USACHPPM TG 204.

An acronym for heatup.

An acronym for heavy water.

An acronym for heat exchanger.

A chemical element with atomic number 1. Hydrogen was discovered in 1766 by Henry Cavendish. In his experiments, Cavendish demonstrated that hydrogen would explode in air and so the element was referred to as fire air. Further experiments proved that hydrogen, when combined with oxygen, made up water. The name hydrogen is derived from hydros-gen, Greek for water producing.

Symbol: H.
Synonym: (obsolete) hyplogen.
Synonym: (obsolete) protium.

(obsolete term) A name Rutherford proposed in 1932 for the nuclide 1H, hydrogen.

A synonym for hydrogen.
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