Alpha spectrometry: Avoiding recoil contamination of solid state alpha detectors

Abstract

Due to its low background, alpha spectrometry is capable of determining very low activity concentrations of alpha emitters in all types of samples, including environmental samples. This low background can be lost due to detector contamination caused by recoil nuclei, which can even render the detector useless. In this paper, the thickness of a thin film used to cover the source is calculated analytically. This film, capable of retaining these nuclei and avoiding this contamination, allows all the alpha particles emitted by the source to reach the detector. The energy loss of the alpha particles passing through it was also estimated in order to identify the peaks in the spectrum, including the unexpected ones. The validity of the calculations carried out and the effectiveness of the film in retaining the recoil nuclei were verified using thorium samples. Finally, the effect of applying a negative potential to the source on the retention of these nuclei was studied. The study was carried out using a PIPS detector under vacuum conditions (0.1 mm Hg) with the samples placed at a distance of 5 mm from the detector. The recoil suppression systems of some commonly used commercial instruments were also tested.