Helium-filled proportional counter for low-temperature operation (4.2–300 K) and its application to cryogenic resonance-electron Mössbauer spectroscopy

Abstract

The operation of a proportional counter filled with helium gas has been investigated at low temperatures down to 5 K. It has been found for the first time that a helium‐filled counter cooled at temperatures below 30 K works well in the proportional region, but with low gas gains (≤100). The operation at low temperatures (≤30 K) is attributed to the complete removal of impurities from helium gas as well as the extreme depression of the reaction frequency of metastable heliums. The absence of impurities results in eliminating the Penning effect, i.e., an ionization process of impurity atoms or molecules by collisions with metastable helium, which spreads electron avalanches in both space and time if helium gas contains a slight amount of impurities (1–10³ ppm). Continuous discharges caused by the photoeffect of ultraviolet photons, which are mostly produced in decay channels of metastable helium, are thermally quenched at low temperatures below 30 K. The helium‐filled counter provides us with a new method to detect nuclear radiations at very low temperatures. The present counter technique has been successfully applied to the resonance‐electron Mössbauer spectroscopy near liquid‐helium temperature (∼5 K).