Alpha Background in Multi-Grid Neutron Detectors

TL;DR

This paper investigates alpha background sources in Multi-Grid neutron detectors, measuring emission rates from different materials and demonstrating that Ni plating significantly reduces background noise.

Contribution

It provides quantitative measurements of alpha emission rates from various materials and shows that Ni plating effectively lowers background counts in detector prototypes.

Findings

Alpha emission from composite Al/B4C is 280 times higher than pure Al.

Ni plating reduces alpha emission rate by approximately 1170 times.

Background rate in the second prototype was about 20% of the first.

Abstract

Alpha emission from actinide impurities in Al is a source of background counting rate in Multi-Grid type detectors of thermal neutrons. The alpha emission rates from samples of radio-purity Al and \mathrm{Al/B_{4}C} composite, used in grid construction, were measured on a large-area, low background spectrometer. Although the alpha emission rate from the composite was a factor \sim280 higher than radio-pure Al, \mathrm{25\:\mu m} Ni plating of the composite reduced the rate by a factor \sim1170. Background counting rates in two Multi-Grid prototypes were compared. They used identical configurations of \mathrm{B_{4}C}-coated, radio-pure Al normal blades for the grids, but the first employed radio-purity Al for the radial blades, while the second used Ni-plated \mathrm{Al/B_{4}C} on the radial blades. The background rate from the second prototype was around 20% of that from the first.