RE: attenuation coefficients in air

["Fulmer, Philip" <FulmerP@ttnus.com>]

Andy,

Indeed, the pair production cross section becomes the dominant
interaction at the higher energies.  Not only does the pair production
cross section increase with energy, but a few additional photon
interactions enter the fray beyond what we're used to seeing at the
lower energies.  For instance, photoneutron production requires a
minimum photon energy that exceeds the binding energy of the last
nucleon in the nucleus.  Once that threshold is exceeded, the shield
around a high energy photon source becomes a source of neutrons as well.
All the accelerator folks on Radsafe can probably add a lot more info
(and probably a few interesting stories); so I will defer to them.

Philip



________________________
Philip C. Fulmer, PhD, CHP
TetraTech NUS
900 Trail Ridge Road
Aiken, SC 29803
(803) 649-7963
fulmerp@ttnus.com

________________

Are these mass attenuation coefficients accurate?

If so, what causes this increased shielding effectiveness for very
high-energy gammas?  This seems to contradict what I would intuitively
expect, but my intuition's been wrong before.  Does the pair production
cross-section start to rise above about 50 MeV?
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