Biological half-life(Tb).The time by which one half of an administered
dosage of a substance is eliminated by biological processes such as
urinary and fecal excretions.
Bremsstrahlung.g-Ray photons produced by deceleration of charged par-
ticles near the nucleus of an absorber atom.
Carrier.A stable element that is added in detectable quantities to a radio-
nuclide of the same element, usually to facilitate chemical processing of
the radionuclide.
Carrier-free.A term used to indicate the absence of any stable atoms in a
radionuclide sample.
Collimator.A device to confine a beam of radiation within a specific field
of view. Collimators may be converging, pinhole, diverging, and parallel-
hole types.
Collimator efficiency.The number of photons passing through the collima-
tor for each unit of activity present in a source.
Collimator resolution.A component of spatial resolution of an imaging
system contributed by the collimator. It is also called geometric
resolution.
Committed dose equivalent(HT,50).The dose equivalent to organs or tissues
of reference (T) that will be received from an intake of radioactive mate-
rial by an individual during the 50-year period following intake.
Compton scattering.In this process, a g-ray transfers only a partial amount
of energy to an outer orbital electron of an absorber, and the photon itself
is deflected with less energy.
Conversion electron (e−). SeeInternal conversion.
Critical organ. SeeOrgan, critical.
Cross section (s).The probability of occurrence of a nuclear reaction or the
formation of a radionuclide in a nuclear reaction. It is expressed in a unit
termed barn; 1 barn = 10 −^24 cm^2.
Curie (Ci).A unit of activity. A curie is defined as 3.7 × 1010 disintegrations
per second.
Dead time.The period of time that a counter remains insensitive to count
the next after an event.
Decay constant (l).The fraction of atoms of a radioactive element
decaying per unit time. It is expressed as l=0.693/ , where is the
half-life of the radionuclide.
Deep-dose equivalent (Hd).Dose equivalent at a tissue depth of 1 cm
(1000 mg/cm^2 ) resulting from external whole-body exposure.
Dose.The energy of radiation absorbed by any matter.
Dosimeter.An instrument to measure the cumulative dose of radiation
received during a period of radiation exposure.
Dosimetry.The calculation or measurement of radiation absorbed doses.
Effective half-life (Te).Time required for an initial administered dose to be
reduced to one half as a result of both physical decay and biological elim-
ination of a radionuclide. It is given by Te=(Tp×Tb)/(Tp+Tb), where Te
t^12 t^12Appendix B. Terms Used in Text 303