Hypercryogenic Detector-Fet Unit--Core of High-Resolution Spectrometer

A hypercryogenic high-resolution x-ray and ¿-ray spectrometer is described. The spectrometer consists of a lithium-drifted germanium detector and a germanium-junction field-effect transistor (JFET) preamplifier. The detector is operated at its optimum temperature, which is in the range of 10-30° K. The JFET´s are operated at liquid helium temperature. This results in 0.28 keV FWHM preamplifier resolution with a slope of 0.018 keV/pF. Resolutions of the order of 0.4 keV are obtained with low capacitance detectors for low-energy x rays. The ¿ rays of 57Co are measured with 0.68 keV FWHM. The described spectrometer was used to study some aspects of the trapping effects in germanium detectors.