Iridium-192 HVL

["Feldman, Gerald" <gfeldman@MSX.NDC.MC.UCI.EDU>]

Dear Radsafe Group,



While doing some shielding design, I found two published values for the HVL

(in lead) for the emissions from Iridium-192.  Several references (including

NCRP Report #49 and the Health Physics and Radiological Health Handbook)

state that the HVL is 0.6 cm Pb, while others (including NCRP Report #40 and

the Radionuclide and Radiation Protection Data Handbook 1998, Delacroix,

et.al.) state that the value is 0.3 cm Pb.  There is quite a disparity

between 0.6 cm and 0.3 cm, and although I'm inclined to use the more

conservative number, I would like some justification for this.  I understand

_why_ there might be different values (encapsulated source vs. bare, good

vs. poor geometry, actual measurement vs. calculated, large attenuation vs.

small ["beam-hardening" effects], etc.), but I would like to know the origin

of these values so I can have some confidence in my calculations.  



Does anyone have additional information about the origin of these two

values?



Thanks,



Gerald Feldman, M.S.

RSO

UCI Medical Center

Orange, CA

gfeldman@uci.edu

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