Planck's constant, h , divided by 2p. Planck's constant, h , divided by 2p.
HALF LIFE, BIOLOGICAL For a substance, the time required for the amount of that 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. IUPAC94.
HALF LIFE, EFFECTIVE For a radioactive substance, the time required for the amount of that substance in a biological system to be reduced to one half of its value by both radioactive decay and biological processes, when the rate of removal is approximately exponential. IUPAC94.
HALF LIFE, PARTIAL In nuclei undergoing branching decay , the half-life that would be evident if a particular branch were the sole means of decay. The partial half-life of a nucleus by a specific mode of decay is the (total) half-life divided by the branching fraction for that specific decay path.
HALF LIFE, RADIOACTIVE For a single radioactive decay process, the time required for the number of atoms or the activity to decrease to half its value by that process.
HALF THICKNESS 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. CAN
HALF-VALUE LAYER See half thickness .
HALF-VALUE THICKNESS See half thickness .
HALO A luminous or colored circle seen in the light around an object; frequently applied to radioactive inclusions in minerals.
HAP Hydrated antimony pentoxide, an inorganic ion-exchanger.
HAPTEN A substance, particularly of low molecular weight, which cannot to induce antibody formation by itself, but which when combined with larger molecules such as proteins can do so. This combination is called an immunogen .
HARD RADIATION Radiation whose particles or photons have a high energy and, as a result, penetrate materials relatively easily. M.
HARDENING (NEUTRONS) The increase in the fraction of higher energy neutrons in a reactor beam flux due to preferential absorption of low-energy neutrons by a sample.
HD VALUE In autoradiography , a measure of resolution corresponding to the distance from a straight radiographic line that accounts for 50% of the grains. J.
HEALTH PHYSICS A division of occupational health dealing particularly with protection of personnel from the harmful effects of ionizing radiation . NM.
HEAVY ELEMENTS A term often used with reference to the actinides and still heavier elements.
HEAVY ION A nucleus consisting of more than one nucleon. Frequently, the term is further restricted to nuclei with atomic numbers greater than two.
HEAVY ION ACCELERATOR An accelerator in which the beam consists of heavy ions .
HEAVY ION REACTION A nuclear reaction in which the interacting nuclei are heavy ions .
HEAVY WATER Water containing a significant fraction (up to 100%) of deuterium in the form of D2O or HDO. IUPAC82..
HETEROGENEOUS COUNTING A technique in solid state scintillation counting of radiochromatograms in which the scintillant is solid bead material with which a flow cell is packed and that does not chemically interact with the eluting medium. J.
HIAA Heavy-ion activation analysis
HIGH FLUX REACTOR A nuclear reactor designed to produce neutron flux densities several orders of magnitude greater than in conventional reactors.
HMD Hydrated manganese dioxide, an inorganic ion-exchanger.
HOLD-BACK CARRIER See carrier, hold back
HOMOGENEOUS COUNTING A technique for counting radiochromatograms in a flow cell by injecting liquid scintillant into the eluting medium. Jones.
HOT ATOM An atom in an excited energy state or having kinetic energy above the ambient thermal level, usually as a result of nuclear processes. IUPAC82..
HOT CELL A heavily shielded enclosure for highly radioactive materials. It may be used for their handling or processing by remote means or for their storage. IUPAC82..
HOT LABORATORY A heavily shielded, specially equipped laboratory to protect personnel working with large amounts of substances emitting gamma radiation and to protect the environment from contamination.
HPGe See germanium detector, high purity . Also known as intrinsic germanium.
HPLC High performance liquid chromatography.
HWR Heavy water reactor, that is, one moderated and cooled with heavy water .
HYDROLYSIS Reaction with water as a solvent involving the rupture of one or more bonds in the reacting solute. For weak electrolytes, this can alter the acidity and subsequent chemical behavior of the aqueous solvent.
HYPERFINE STRUCTURE Small differences in energy states of atoms or molecules that have different orientations between nuclear spin and electron angular momentum owing to the interaction between the nuclear and electron magnetic moments. FKMM.