is the effective half-life, and Tpand Tbare the physical and biological half-
lives, respectively.
Electron (e−).A negatively charged particle rotating around the atomic
nucleus. It has a charge of 4.8 × 10 −^10 electrostatic units and a mass of
9.1 × 10 −^28 g, equivalent to 0.511 MeV, or equal to 1/1836 of the mass
of a proton.
Electron capture (EC).A mode of decay of a proton-rich radionuclide in
which an orbital electron is captured by the nucleus, accompanied by
emission of a neutrino and characteristic x-rays or Auger electrons.
Electron volt (eV).The kinetic energy gained by an electron when acceler-
ated through a potential difference of 1 V.
Energy resolution.Capability of a detecting system to separate two g-ray
peaks of different energies. It is given by the full width at half maximum
(FWHM) of a given photopeak.
Erg.The unit of energy or work done by a force of 1 dyne through a dis-
tance of 1 cm.
Fission (f). A nuclear process by which a nucleus divides into two
nearly equal smaller nuclei, along with the emission of two to three
neutrons.
Free radical.A highly reactive chemical species that has one or more
unpaired electrons.
Generator, radionuclide.A device in which a short-lived daughter is sepa-
rated chemically and periodically from a long-lived parent adsorbed on
adsorbent material. For example,99mTc is separated from^99 Mo from the
Moly generator with saline.
Gray (Gy).The unit of absorbed radiation dose in SI units. One gray is
equal to 100 rad.
Half-life ().A unique characteristic of a radionuclide, defined by the time
during which an initial activity of a radionuclide is reduced to one half.
It is related to the decay constant lby =0.693/l.
Half-value layer(HVL). The thickness of an absorbing material required to
reduce the intensity or exposure of a radiation beam to one half of the
initial value when placed in the path of the beam.
Internal conversion.An alternative mode to g-ray decay in which nuclear
excitation energy is transferred to an orbital electron, which is then
ejected from the orbit.
Intrinsic efficiency.The number of radiations detected divided by the
number of radiations striking the detector.
Intrinsic resolution.A component of the spatial resolution of an imaging
system that is contributed by the detector and associated electronics and
depends on the photon energy, detector thickness, and the number of PM
tubes.
Ion.An atom or group of atoms with a positive charge (cation) or a nega-
tive charge (anion).
Isobars.Nuclides having the same mass number, that is, the same total
number of neutrons and protons. Examples are^5726 Fe and^5727 Co.
t^12t^12304 Appendix B. Terms Used in Text