New ⁶Li Sandwich Counter for Measurement of Neutron Spectra in Fast Neutron Systems

Abstract

A new form of ⁶Li sandwich counter has been developed for use in measurements of neutron spectra in fast critical assemblies. The counters have two large surface area diodes approached very close to each other, on one of which is evaporated the target ⁶Li. This arrangement proves to provide a ten-fold increase of detection efficiency, while the resolution is improved by approximately ½ compared with currently used counters. The new counters were first tested on mono-energetic neutrons, after which neutron spectrum measurements were performed on natural uranium blocks, in the fast source reactor “YAYOI”, in the FCA IV-l-P and in the FCA V-3 core. The resulting spectra are compared with the measurements made with other types of counter and with calculated data. Proof was obtained that the new counter can serve practically and usefully for in-core measurements of fast neutron energy spectrum between 0.8 and 5 MeV.

KEYWORDS:

• ⁶Li sandwich counters
• neutron spectra
• fast critical assemblies
• natural uranium blocks
• fast source reactor
• in-core spectrometry
• high detection efficiency
• resolution
• unfolding method