Introduction to Health Physics: Fourth Edition - Ruang Baca FMIPA UB

INTERACTION OF RADIATION WITH M ATTER 181
where the three right-hand terms are the attenuation coefficients for the photoelectric
effect, for Compton scattering, and for pair production, respectively. In computing
attenuation of radiation for purposes of shielding design, the total attenuation
coefficient as defined in Eq. (5.46) is used.
Equation (5.46) gives the fraction of the energy in a beam that is removed, per
unit absorber thickness. The fraction of the beam’s energy that is deposited in the
absorber considers only the energy transferred to the absorber by the photoelectron,
by the Compton electron, and by the electron pair. Energy carried away by
the scattered photon in a Compton interaction and the energy carried off by the
annihilation radiation after pair production is not included. The energy absorption
coefficient, which is also called the true absorption coefficient, is given by
hf − 1.02
μe = μpe + μCe + μpp
(5.47)
hf
and is used in the calculation of radiation dose. The total attenuation and true
absorption coefficients for air are shown in Figure 5-20, and the energy absorption
coefficients for water, air, compact bone, and muscle are listed in Table 5-4.
NEUTRONS
Production
The most prolific source of neutrons is the nuclear reactor. The splitting of a uranium
or a plutonium nucleus in a nuclear reactor is accompanied by the emission of several
Figure 5-20. Linear attenuation coefficients and absorption coefficients of air for gamma rays as a
function of energy.