Calculate the radiation field intensity at 12 inches
from the surface of the vessel shown in Figure 3.
Total distance = 12 + 2 + 10 = 24 inches
Dose rate for unshielded source:
Percent transmission of gamma radiation through
two-inch steel (vessel wall), 0.25-inch source well
wall = .18 X .83 = 0.517. Resultant field intensity =
8.6 X 0.517 = 4.45 mr/hr.
To estimate the dosage received by personnel
working in the vicinity of the source, the occupancy
must be known. Suppose that a man worked 24
hours per week within 12 inches of the vessel. He
would receive a dose in excess of 100 mr. He
would then require a monitoring device.
11.2 NRC Regulations
A current copy of the Title 10 Code of Federal
Regulations, Parts 19, 20 and 30 should be
obtained. These should be read thoroughly to
become familiar with the laws governing the use of
radioactive materials.
a) The “Individual User” listed on the “Application
for By-product Material License” (Form NRC-313) is
responsible for the source. If this person is
transferred or is changed to a position where he is
no longer responsible for the source, the license
must be amended prior to the assignment of the
new user. [30.32, 30.33, 30.34, 30.38]
b) Use of the source is usually licensed for a
particular plant site. If the source is transferred to a
different plant site the license must be amended
prior to the transfer. [30.34 and 30.38]
c) A record of the initial radiation survey must be
kept for reference. [20.40 1 b]
d) Records of the periodic leakage test must be
maintained.
e) A label must be attached to the source holder,
or source well, stating the type and quantity of
radioactive material and the date of manufacture.
The label must bear the conventional radiation
symbol. An NRC-approved label is attached to the
source holder by Ronan Engineering prior to
shipment. For sources in source wells, and NRC-
approved tag is placed on the source shipping and
storage contained. [20.203]
mr/hr 8.6 1000 X
476
5
1000 X
2
(24)
10 X 0.5
rate Dose ===
SOURCE HOLDER
SOURCE WELL
1/4” WALL
THICKNESS
SOURCE ROD
SOURCE CS-137
10 MILLICURIE
304 SS
2” WALL
THICKNESS
DETECTOR
10.00” 12.00”
Figure 3:
Dosage
(68 pages)
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