A low background beta-ray scintillation spectrometer using a coincidence method with a Geiger counter

Abstract

The design and performance of a new type of β-ray scintillation spectrometer suitable for measuring very low β-ray activities of solids are described. The spectrometer consists of a scintillation counter using a plastic scintillator and a gas flow G-M counter located in a hollow of the scintillator, and the coincidence operation between these two counters is applied. Cosmic ray counts are rejected by pulse height analysis. Inside the 10 cm lead shield the background counting rate is less than that of conventional low background counters using anti-coincidence shields, and a typical background counting rate of 0.15 cpm for the energy range from 0.5 to 2.5 MeV was obtained. This system can also be used as a low background counting device in a limited energy range. For relatively high energy β-ray emitters, the coincidence countings are used between scintillation pulses and G-M pulses. In this case, the background is reduced by rejecting cosmic ray counts, high and low energy components of the γ-ray background and noise or spurious counts of the detectors. For low energy β-ray emitters, on the other hand, the anti-coincidence countings are suitable, then the cosmic ray counts and high energy components of the γ-ray background can be rejected.