Changes in detection characteristics of CdTe X-ray sensors by proton irradiation

Abstract

This paper reports on the performance changes in CdTe:Cl semiconductor X-ray detectors seen after irradiation with 50 MeV protons up to a fluence of 1.6 ṡ10¹¹cm^-2. The rationale for the irradiation parameters is described. Performance was quantified before and after irradiations by obtaining X-ray spectra with a barium-133 radioactive source and detectors cooled to -20°C. Energy resolutions, electron and hole drift lengths, and energy calibration parameters were extracted by fitting model spectra to the data. Ten crystals of dimension 10 ×10 ×1 mm³ were used, with two each being irradiated to 20%, 40%, 60%, 80%, and 100% of the maximum fluence. Each crystal is pixelized and the eight large pixels of area 9.6 mm² are analysed separately to allow estimation of uncertainties.

The main observations are a strong decrease of the electron drift length and an increase of the electronic noise with fluence. The hole drift length shows a tendency to increase with fluence. A basic interpretation of some observations in terms of an increasing density of acceptor trap levels with fluence is given.