[ RadSafe ] NCRP-147: does it really works?
dsimpkin at wi.rr.com
Fri Jun 9 12:27:59 CDT 2006
Alessandro Tofani wrote:
>I've recently checked the algorithms proposed by NCRP-147 Report
for primary radiation shielding to the following >test case: rad room
(chest bucky), 120 patients/week, 2.3 mGy/patient @ 1 m, dp=2 m, U=1,
T=1/5(corridor), P=0.02 >mGy/week. Equation 4.7 gives a barrier
transmission of 1.449E-03, which can be obtained with approximately
1.5 >mm of lead or 120 mm of concrete (from figures B2 and B3,
respectively). However, if we apply equation 4.8 to the >same case,
the barrier thickness is approximately 0.22 mm of lead and 2996 (!)
mm of concrete. My suspicion is >that fitting parameters of table B.1
are wrong .....
Putting Alessandro's parameters into NCRP-147 eqn 4.8 with the
fitting parameters from Table B.1 (alpha, beta, and gamma = 2.264
mm-1, 1.308E+01 mm-1, 5.600E-01 for Pb and 3.552E-02 mm-1, 1.177E-01
mm-1, 6.007E-01 for concrete) yields barriers of 1.49 mm Pb and 107
mm concrete, quite consistent with calculating the transmission per
eqn 4.7 and reading Figures B.2 and B.3.
If I might be so bold, PLEASE note that the fitting parameters in the
tables in NCRP-147 have both positive and negative exponents. A
number of folks have contacted me stating that they've been unable to
reproduce the examples in the report. The problems were traced back
to them copying all exponents from the fitting tables as negative
values (which must say something about our psyche as scientists/engineers).
ps. Question: "NCRP-147: does it really works?" Answer: "Ya damn betcha."
pps: A little Excel is a dangerous thing....
More information about the RadSafe