LC circuit as a pulse-height analyser for NaI gamma spectrometry

An LC circuit used as anode load of a photomultiplier tube converts its output current pulse into a damped harmonically oscillating voltage. Its amplitude is not only proportional to the transferred charge but it can be also readily encoded by the count of the successive maxima it passes until it falls below a predefined voltage level. Thus, a scintillation spectrometer may be realised in a very simple way, bypassing the classical (but rather sophisticated) solutions based on pulse-shaping amplifiers and amplitude-to-digital converters. The structure, spectral response and some experiments with a 256-channel ‘LC spectrometer’ are discussed. A 7% energy resolution has been achieved at 662 keV (with a ∅45×40 mm NaI(Tl) crystal). Despite some uncommon features (arising from the logarithmic channel-energy dependence), this spectrometer has useful potential in at least two fields of scintillation gamma-spectroscopy—as a portable dose-rate meter or in the study of the soft component of the cosmic rays.