Low-noise amplification of γ-ray detector signals in hostile environments

We designed and realized a low-noise charge preamplifier for HPGe (High Purity Germanium) γ-ray detectors, able to operate at a distance of 3 m 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 γ-spectroscopy requirements. By compensating the preamplifier so as to completely eliminate the ringing in its response function we obtained a rise-time of ∼46 ns with 3 m cables and of ∼80 ns with 5 m cables. With a different approach, or using a lower compensation capacitance and eliminating the ringing 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 γ-rays with segmented HPGe detectors.