Dead-layer thickness effect for gamma spectra measured in an HPGe p-type detector

The present work studies the influence of the dead-layer thickness effect on the gamma spectra of a high purity germanium (HPGe) p-type detector at two different points in time. The study was conducted with the Canberra GC1518 detector, which had a dead-layer thickness of 1.15 mm in 2005 and 1.46 mm in 2009. The measurement of gamma spectra for the reference point-like sources, 137Cs, 60Co and 22Na, indicated that the spectra in the energy region of 50–170 keV measured in 2009 were higher than those measured in 2005. This result implies that, in this energy interval, the dead-layer thickness effect is observed, which can be explained by the contribution of the delayed signals. Furthermore, the measured spectra in this energy region were higher than those calculated by MCNP5 code. These findings make it possible to evaluate the contribution of delayed signals, which are proportional to the thickness of the dead layer.