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

[Alessandro Tofani]

Dear Colleagues,
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 (the "classical" method of HVL, with an average peak votage of 88 kV, gives 2 mm of lead and 150 mm of concrete). Did anybody find similar discrepancies?
Regards

Alessandro Tofani
Medical Physicist
Livorno Hospital
Phone  +39-0586-223266
Fax +39-0586-223653