Re: Mass Energy Absorption Coefficient -Reply

[aenns@unixg.ubc.ca (Alan Enns)]

On Thursday, Paul Frame said (in part):
>My poor understanding would have me believe that the mass energy
>absorption coefficient and the mass energy transfer coefficient
>usually apply to an infinitimally small region. As such the 511 keV
>annihilation photons from pair production should not be considered to
>be absorbed...

For tissue yes, but wouldn't this depend on the absorption coef. of the 
material?

>Why might Tsoulfanidis assume the 511 stuff (along with the
>photoelectric effect x rays) were absorbed? Because his "volume under
>consideration" is large. It could be said he is interested in the
>real world rather than an infinitesimal point and is not  cocerned
>with what Hubbell does.  Evans comments "For larger absorbers it has
>been a common approximation to ignore this correction term for
>annihilation radiation." In other words, how many 511 photons
>produced in someones body by pair production would escape? Not many.
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Alan Enns
Radiation Safety Assistant,
Department of Health, Safety and Environment
University of British Columbia,
Canada.
aenns@unixg.ubc.ca
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