RE: Cs-137 gamma ray constants discrepancy

["Dale Boyce" <dboyce@intiso.com>]

There have been a couple of long threads in the history of radsafe on the
discrepancies among gamma constants.  The main answer is what gamma constant
are you interested in?  Tables exist that list, to name a few:

Deep dose equivalent (1 cm tissue depth)
Peak deep dose at depth (regardless of depth of peak dose depth)
Whole body dose equivalent
Exposure in air
Entrance dose equivalent

there are probably (several) more

The old and withdrawn ANSI standard which the previous version of the RHH
listed gave peak dose at depth and the ANSI/ANS report clearly stated that
it was intended for shielding calculation (and by ommission not dose
calculation).

The Current ANSI/ANS standard uses whole body dose equivalent calculated by
monte carlo and depends on the geometry of the irradiation.

For a quick gut check on the constant you want to use take the expected
photon energy emission per decay in KeV from the Table of Radioactive
Isotopes (if the majority of the photons are above 70 KeV) and divide that
number by 2.  This will give you to a very good approximation the entrance
dose equivalent in mrad/hr/Ci at one meter.  The entrance dose equivalent is
not a bad estimate of the whole body dose equivalent for energetic gamma's.

Dale Boyce
dboyce@intiso.com



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