10
012208
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) 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
