Detection of High Energy Protons by Thin-Window Lithium-Drifted Germanium Counters

Recent developments in producing thin-window Li-drifted germanium detectors have enabled us to investigate their response to 29- and 40-MeV protons. The window is of negligible thickness for long-range particles, probably about 0.5 μ, although a precise measurement has not been made. Resolutions of 28 and 44 keV (FWHM) were obtained on 29- and 40-MeV protons, respectively. After subtracting nondetector contributions, mainly the energy spread in the cyclotron beam, the resolutions obtained approach the theoretical limit for a Ge detector. A brief discussion of the response of a 0.5 cm thick, high-voltage Li-drifted silicon detector is also presented. Although extensive measurements have yet to be performed, these devices appear to be capable of a resolution approximately equal to that for Ge detectors for 29-MeV protons.