Gallium arsenide resistive photoconductors are widely used for the characterisation of picosecond radiation pulses. They are used to measure both the intensity and the temporal shape of the pulse. We have investigated the influence of the physical and electrical properties of high resistivity GaAs crystals (LEC, VGF) supplied by various manufacturers on the detector response to fast visible and gamma-ray pulses. The detector characteristics: response time and sensitivity, were tested both before and after pre-irradiation with fission neutrons at integrated doses in the range 5/spl times/10/sup 14/ to 1/spl times/10/sup 16/ neutrons/cm/sup 2/. The original GaAs material properties were found to have a significant influence on the neutron pre-irradiated photoconductor response times and sensitivities for integrated doses up to 1/spl times/10/sup 15/ neutrons/cm/sup 2/.
