Effects of 33-MeV Proton Bombardent on the Performance of CdTe Gamma-Ray Detectors

A measurement program to investigate the performance of CdTe gamma-ray detectors after bombardment with 33-MeV protons has been undertaken in order to evaluate the effects of energetic protons encountered on earth-orbiting satellites. The pulse heights and energy resolutions of the 59.6 keV line from Am241 and the 122 keV line from Co57 and the leakage currents of the detectors were monitored as a function of proton fluence. Of the two types of CdTe detectors tested, far greater radiation effects were observed in those obtained from Tyco (chlorine doped) than in the sensor obtained from Hughes (indium doped). In the former detectors the relative pulse heights appeared to decrease slowly with increasing fluence up to about (5-9) × 109 protons/cm2 beyond which the gain degraded at a faster rate. The energy resolution and leakage currents were observed to improve at moderate fluence levels near (1-3) × 109 protons/cm2. In one of the two chlorine doped sensors tested, the intrinsic detector resolution at 59.6 keV improved from 4.3 keV to 2.6 keV at a fluence of 2 × 109 protons/cm2 and subsequently degraded beyond its original performance level after 5 × 109 protons/cm2.