Variable Temperature Performance of a Si(Li) Detector Stack

New experimental data is presented which displays 137Cs resolution of both single Si(Li) devices and a detector stack 2 cm in height as a function of temperature (85 K <T <245 K). We also discuss variations in photopeak shape which indicate that detector charge collection may be temperature dependent over the range of interest. I. INTRODUC_ON We have previously reported laboratory experimental data and Monte Carlo analysis for a Si(Li) gamma-ray detector stack [1,2]. This configuration is intended to provide moderate resolution [full-width at half-maximum (FWHM) 5-10 keV @ 1 MeV)] over a broad temperature range (<90 K to 230 K). This temperature range is consistent with the needs of spaceborne applications using ambient (passive) cooling for orbiting platforms _100 K) or for Mars surface operations (130 K-230 K). Such an approach provides an attractive alternative to the poorer resolution of scintillators (-60 keV @ 1.3 MeV) and the cryogenic cooling requirements of HPGe (< 100 K). For simplicity in the earlier work, experimental resolution data was collected at 175 K [1]. DC leakage current indicated that acceptable device performance (FWHM < 10keV @ 662 keV) could be expected up to-230 K, where leakage current was- 10 hA. However, it is well known that leakage current is only one contributor to detector performance, and it has been suggested that detector performance often degrades as a function of temperature faster than indicated by DC measurements. In addition, the literature provides little experimental data on the performance of Si(Li) detectors at temperatures above that of liquid nitrogen (-77 K) [1]. This current work addresses that absence of data, providing variable temperature resolution measurements from 85 K to 245 K