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

226 CHAPTER 6
If we divide Eq. (6.16b) by 34 Sv per C/kg, we obtain the specific gamma ray emission
in exposure units:
1.24 × 10−7 ( Sv air kerma) - m
Ɣ = fi × E i
Sv air kerma
34 i
C/kg
2
MBq-h
2
−9 C/kg −m
= 3.65 × 10 fi × Ei
.
i
MBq-h
(6.17)
When exposure is measured in roentgens and activity in curies, the specific gammaray
emission is closely approximated by
Ɣ = 0.5
i
fi × Ei
R-m 2
Ci-h
(6.18)
Table 6-3 lists the specific gamma ray emission of some isotopes that are frequently
encountered by health physicists.
Beta Radiation
Examination of a beta-particle absorption curve, such as the one in Figure 5-2, shows
it to be approximately linear when plotted on semilog paper. This means that the
decrease in beta intensity with increasing depth into an absorbing medium, for
depths less than the beta range, can be approximated by
ϕ = ϕ0e −μβ t , (6.19)
TABLE 6-3. Specific Gamma-Ray Emission Constant of Some Radioisotopes
ISOTOPE
R-m 2
Ci-h
Ɣ
2 Sv-m
Air kerma
MBq-h
Antimony-122 0.24 5.68E−08
Cesium-137 0.33 7.82E−08
Chromium-51 0.016 3.77E−09
Cobalt-60 1.32 3.13E−07
Gold-198 0.23 5.44E−08
Iodine-125 0.07 1.66E−08
Iodine-131 0.22 5.20E−08
Indium-192 0.48 1.14E−07
Iron-59 0.64 1.52E−07
Mercury-203 0.13 3.08E−08
Potassium-42 0.14 4.73E−08
Radium-226 0.825 1.96E−07
Sodium-22 1.20 2.84E−07
Sodium-24 1.84 4.35E−07
Zinc-65 0.27 6.39E−08
From Radiological Health Handbook. Rev ed. Rockville, MD: US Public Health Service, Bureau of Radiological Health;
1970.