Search for the triple-escape peak in HPGe detectors

Triple-escape peaks can be generated when either the electron or the positron created by the pair-formation interaction inside the active volume generates a Bremsstrahlung γ-ray with enough energy to produce another pair; however, they were never observed. MCNP5 and MCNPX simulations differ greatly in the triple-escape peak intensity for photon energies around 6 MeV but agree for 14 MeV incoming photons. An empirical model was developed to check the order of magnitude of the simulated results. An experiment performed to observe the triple-escape peak yielded negative result; the upper limit for the intensity ratio between the triple- and double-escape peaks for 6.13 MeV photons in a 240 cm3 HPGe detector is 9×10−4.