Precision.A term used to indicate the reproducibility of the measurement
of a quantity when measurements are made repeatedly.
Quality factor (QF).A factor dependent on linear energy transfer that is
multiplied by absorbed doses to calculate the dose equivalents in rem. It
is used in radiation protection to take into account the relative radiation
damage caused by different radiations. It is 1 for x-,g-, and b-rays and 10
for neutrons and protons.
Rad.The unit of radiation-absorbed dose. One rad is equal to 100 ergs of
radiation energy deposited per gram of any matter, or 10−^2 J/kg of any
matter.
Radiation weighting factor(Wr).A factor that depends on the types of radi-
ation and is used to convert rad to rem in radiation protection. Rem =
rad ×Wr.
Range.The straight line distance traversed by a charged particle in an
absorber.
Relative biologic effectiveness (RBE).A factor used to calculate the dose
equivalent in rem from rad. It is defined as the ratio of the amount of a
standard radiation that causes certain biological damage to the amount
of radiation in question that causes the same biological damage.
Roentgen.The quantity of x- or g-radiations that produces one electrosta-
tic unit of positive or negative charge in 1 cm^3 of air at 0°C and 760-
mm Hg pressure (standard temperature and pressure, STP). It is equal to
2.58 × 10 −^4 C/kg air.
Roentgen equivalent man (rem).A dose equivalent defined by the absorbed
dose (rad) times the relative biological effectiveness or quality factor of
the radiation in question.
Sensitivity.The number of counts per unit time detected by an imaging device
for each unit of activity present in a source. It is expressed in cps/mCi.
Shallow-dose equivalent (Hs).Dose equivalent at a tissue depth of 0.007 cm
(7 mg/cm^2 ) averaged over an area of 1 cm^2 from external exposure to the
skin.
Sievert (Sv).The SI unit of dose equivalent and equal to 100 rem.
Spatial resolution.A measure of the ability of an imaging device to faith-
fully reproduce the image of an object. It is given by the modulation
transfer function (MTF) and is determined by the Fourier transform of
the line spread function.
Specific activity.The amount of radioactivity per unit mass of a radionuclide
or labeled compound.
Specific ionization.The number of primary and secondary ion pairs pro-
duced by an incident radiation per unit path length in an absorber.
Thermal neutron.Neutrons of thermal energy 0.025 eV.
Tissue weighting factor (WT).The weighting factor of an organ or tissue is
the proportion of risk of stochastic effects resulting from irradiation of
that organ or tissue to the total risk of stochastic effects when the total
body is irradiated uniformly.
306 Appendix B. Terms Used in Text