Response of PCDs to low-energy protons

The authors report work done at the Los Alamos National Laboratory Ion Beam Facility to measure photoconductive detector (PCD) sensitivity to intense, subnanosecond pulses of low-energy protons as a function of proton energy. The PCDs were of two types: iron-doped indium phosphide (InP:Fe) and gallium arsenide (GaAs:ND). Some of the GaAs detectors had been neutron-damaged to improve their time response characteristics. Bunched protons varying in energy from 2 to 13 MeV were used for the measurement. The protons were diffused through aluminium foils to ensure that the full active area of the PCDs was uniformly irradiated. A nonintercepting beam monitor (NIBM) was installed in the beam line to record the magnitude and time structure of each proton bunch. A silicon detector was used to calibrate the NIBM. The silicon detector of known proton sensitivity was then removed and replaced by the PCDs. By computing the ratio of the PCD response to the NIBM response and knowing the NIBM response relative to the silicon detector, the PCD detector response to the silicon detector was calibrated. The PCDs were observed to be less efficient at detecting lower energy protons.<>