Where do the peaks in gamma spectroscopy originate from?

[feynmanism]

Hello. Where do the peaks observed in gamma spectroscopy come from? May some specific angles for diffraction be a reason?

 

[Astronuc]

Radionuclides emit gamma rays at fairly speicific energy corresponding to particular transitions in the nucleus. The peaks, assuming one means the large peaks, are from those characteristic gamma rays.

For some radionuclides which have energies greater than 1.12 MeV, the gamma ray may interact with a nucleus (nuclear field) and a positron-electron pair may be formed. In this case, one will see smaller peaks at 0.511 and 1.022 MeV lower energy if one or both annihilation photons escape from the detection system.

Compton scattering, in which a photon looses part of its energy to an atomic electron produces the broad plateau of energy at the lower energy ranges of the gamma spectrum.