Single-transistor option for high-resolution gamma-ray spectroscopy in hostile environments

We designed and realized a low-noise charge preamplifier for HPGe (High Purity Germanium) gamma-ray detectors, able to operate at a distance of 3 to 6 m from the detector. One transistor only is placed in close proximity to the detector. Such a setup is required in applications where the detector works in hostile environments that could damage or destroy the electronic circuitry. Using 3 m RG62 cables and a 23 pF detector capacitance we obtained a noise of ~1.07 keV fwhm at 2 µs shaping time, so fully compatible with gamma-spectroscopy requirements. By compensating the preamplifier so as to completely eliminate the ringings in its response function we obtained a rise-time of ~46ns with 3 m cables and of ~80ns with 5 m cables. With a different approach, or using a lower compensation capacitance and eliminating the ringings through a numerical post filter, we obtained a faster rise time of ~33 ns, with a detector-preamplifier distance of 5 m, while maintaining the low-noise performance. This latter setup is adequate for spectroscopy and tracking of gamma rays with segmented HPGe detectors.