[ RadSafe ] NCRP-147: does it really works?

Douglas Simpkin 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).

Best regards,

Doug Simpkin
ps. Question: "NCRP-147: does it really works?"  Answer: "Ya damn betcha."
pps: A little Excel is a dangerous thing....

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