Gamma backscatter peak

Fig. 5.12. Energy of Compton edge and backscattered peak for gammas of energy <0.7 MeV.

The steep decline up to 2000 keV, the normal spectrometry range, is due to Compton events, backscatter and bremsstrahlung resulting from the decay of muons into high-energy electrons and positrons. On this are superimposed the 511 keV annihilation radiation and all the gamma-ray peaks from the background nuclides and the peaks from activations described below. 

Backscattering is minimal for alpha particles because they are mostly stopped in the backing material (NCRP 1985b). A typical factor is 1.03. Backscattered gamma rays add to the Compton continuum a broad peak at an energy of about 0.2 MeV. 

All of the peaks due to the nuclides mentioned above will be sat on a continuum due to Compton scattering of the gamma-rays and backscattering and bremmstrahlung due to direct interaction of cosmic particles. This will be discussed further in Section 13.4.6. 

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