Reason for Gamma constant differences

["Boyce, Dale" <DBoyce@intiso.com>]

One has to pay close attention to the question asked when it comes to gamma
dose constants.  It depends on the exposure or dose equivalent in which you
are interested.

Bruce's answer calculated from muen/rho and a conversion factor to R is
probably the best answer given so far to the specific question. 

In the second edition of the RHH they use a withdrawn ANSI/ANS standard that
calulates peak dose at depth (buildup can makes the peak dose appear at a
depth dependent on energy).  This standard was intended as a conservative
model for shielding calculations.

I believe the current ANSI/ANS standard calculates whole body dose
equivalent as a function of exposure geometry,  a whole different animal.
Probably the one you want if you are worried about health effects and high
dose.

Another one that is useful is the entrance dose equivalent calculated in
tissue from muen/rho in tissue.  This one is easily estimated by  dividing
the energy in MeV by 2 and multiplying by the branching ratio. Sum over all
of the emitted gammas and you have to a good approximation of the entrance
dose equivalent in Rads/hr/Ci at one meter.  Below 70 kev this method breaks
down, and you have to lookup muen/rho.

If you are a regulator/the regulated you'll be interested in the dose at a
depth of 1 g/cm^2. Some absorption. Some buildup.

I'm not sure what third edition of RHH tabulates.

The range of values you get for these different critters is substantial.

Dale E. Boyce
International Isotopes Inc.
dboyce@intiso.com

A dose is not a dose equivalent is not a different dose equivalent is not an
exposure.
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