Re: Mass Energy Absorption Coefficient

["Dale E. Boyce" <dale@radpro.uchicago.edu>]

Good catch Alan.  Not too picky at all since any energy escaping from
the volume under consideration should probably be included and Compton
scattered photons are probably the dominant mode for energy escape.
Having said that, at least one reference, Tsoulfanidis "Measurement
and Detection of Radiation", ignores the flourescence correction to
the photoelectric effect and the pair production correction for the
escaping anihilation photons.  The flourescence is probably ignored
because the low energy photons are locally absorbed, there is no
comment on it in the book.  Tsoulfanidis comments that the correction
for the 511 photons is sometimes made and gives a reference, Hubbell,
J.H., NSRDS-NBS 29 August 1969, that makes this correction.  Since
Hubbell is one of the most common sources of Mass Energy Absorption
Coefficients, it seems to me to be questionable why anyone would
leave that correction out of their definition for the coefficient.

For very high photon energies, such as around teletherapy accelerators,
one might also need to consider photonuclear production of neutrons as
an energy escape mechanism.

Dale Boyce
dale@radpro.uchicago.edu