Biomedical Engineering Reference
In-Depth Information
Fig. 15.9
Attenuation in lead of X rays produced with (peak)
potential differences from 50 kVp to 200 kVp. (
National Bureau
of Standards Handbook 76
, 1961, Washington, DC.)
4. The occupancy factor,
T
, which takes into account the
fraction of the time that an area outside the barrier is likely
to be occupied by a given individual. (Average weekly
exposure rates may be greater than
P
in areas not occupied
full time by anyone.) In the absence of more specific
information, the occupancy factors given in Table 15.2 may
be used as guides for shielding design. The allowed average
kerma rate in the area is
P
/
T
mGy wk
-1
.
5. The distance,
d
, in meters from the target of the tube to the
location under consideration. The curves in Figs. 15.9 and
