The role of secondary defects in the loss of energy resolution of fast neutron irradiated HPGe gamma ray detectors

The resolution characteristics of two (p and n-type) high purity germanium gamma ray detectors, irradiated with fast neutrons, are studied in detail. The influence of the neutron dose on the energy resolution as well as the annealing temperature of irradiated detectors are investigated. Similarities are observed between the annealing behaviour of the defects created by fast neutron irradiation in high purity germanium and the changes in the energy resolution of the detectors when they are annealed. The energy resolution of the detectors, measured by the means of a resolution factor which takes into account tailing effects, has been investigated. Its behaviour has been illustratively explained by the differences between the respective role of the stable defects at low temperature (<100 K) and those formed by a thermal treatment up to room temperature