Gallium Arsenide Photoconductive Detectors for Ultra Fast, High Dose Rate Pulsed Electron and Bremsstrahlung Radiation Measurements

George Kharashvili¹, Marc Mitchell¹, Wendland Beezhold¹, Vakhtang Makarashvili¹,  Randy Spaulding¹, Wayne Wingert²

⁽¹⁾Department of Physics, Idaho Accelerator Center, Idaho State University,.

⁽²⁾Department of Physics, University of Utah.

Real time radiation dose measurements are challenging in high dose rate environments such as those used for studying radiation effects on electronic devices or biological agents. Dosimetry needs at particle accelerator facilities require development of devices with fast (tens of picoseconds) response to pulsed radiation, linear response over a wide range of dose rates (up to 10¹¹ Gy/s), high resistance to radiation damage, and successful operation in mixed gamma and neutron environments. Gallium arsenide photoconductive detectors (GaAs PCD) have been shown to exhibit many of these desirable characteristics, especially fast time response, when neutron irradiation is used to introduce displacement damage in crystalline lattice of GaAs, hence improving time response characteristics of the devices at the expense of their sensitivity.  GaAs PCDs with 3 different neutron irradiation levels (0, ~10¹⁴, and 5 X 10¹⁵ n/cm² (1-MeV (GaAs) equivalent) were fabricated at ISU. The devices were tested with 7, 20 and 38-MeV electron pulses produced by linear accelerator operating at the L-band frequency of 1.3-GHz and the S-band frequency of 2.8-GHz, and 33-ns long, 7-MeV maximum energy bremsstrahlung pulses produced by a pulse-power accelerator. Time response characteristics and dose-rate ranges of application of the PCDs were determined. This talk presents a summary of the GaAs PCD development and characterization work performed at ISU.