A factor of 2170/10 =217 or more would be needed to reduce the exposure
to less than 10 mR/hr. In terms of HVL, 2^8 =256, that is, 8 HVLs would be
needed. Since 1 HVL =3 mm of lead, 8 HVLs would be equal to 24 mm.
Therefore, 8 HVLs or 24 mm of lead would be necessary.
Obviously, shielding is an important means of protection from radiation.
Radionuclides should be stored in a shielded area. The radiopharmaceuti-
cal dosages for patients should be carried in shielded syringes. Radionu-
clides emitting b-particles should be stored in containers of low-Zmaterial
such as aluminum and plastic because in high-Zmaterial, such as lead, they
produce highly penetrating bremsstrahlung radiations. For example,^32 P is
a b−emitter and should be stored in plastic containers instead of lead
containers.
Activity
It should be obvious that the radiation exposure increases with the inten-
sity of the radioactive source. The greater the source strength, the more the
radiation exposure. Therefore, one should not work unnecessarily with large
quantities of radioactivity.
Personnel Monitoring
According to 10CFR20, personnel monitoring is required under the fol-
lowing conditions:
- Occupational workers including minors and pregnant women likely to
receive in 1 year a dose in excess of 10% of the annual limit of exposure
from the external radiation source - Individuals entering high or very high radiation areas
Monitoring for occupational intake of radioactive material is also
required if the annual intake by an individual is likely to exceed 10% of the
ALIs in 10CFR20, Table 1, Appendix B, and if minors and pregnant women
are likely to receive a committed effective dose equivalent in excess of
0.05 rem (0.5 mSv) in 1 year.
Three devices are used to measure the exposure of ionizing radiations
received by an individual: the pocket dosimeter, the film badge, and the
thermoluminescent dosimeter. The pocket dosimeter has been described in
Chapter 7.
Film Badge
The film badge is most popular and cost-effective for personnel monitor-
ing and gives reasonably accurate readings of exposures from b-,g- and x-
radiations. The film badge consists of a radiation-sensitive film held in a
plastic holder (Fig. 16.2). Filters of different metals (aluminum, copper, and
cadmium) are attached to the holder in front of the film to differentiate
Radiation Protection 277