9-Inch Moderated Neutron Detector - Model 42-31H
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Introduction

The Ludlum Model 42-31H Neutron Detector is designed to detect thermal and fast neutrons (0.025 eV to approximately 12 MeV). Neutrons are detected indirectly through nuclear reactions which result in energetically charged particles such as alpha which are often found associated with intense fields of gamma rays. Therefore it is important to choose a method of neutron detection with the ability to discriminate against those gamma rays in the detection and measurement processes.

The Model 42-31H is intended for use with portable counting instruments, and is fitted with a top bracket for convenient mounting. The instrument consists of a cadmium-loaded polyethylene sphere surrounding the 3He detector. A study demonstrates that the 9-inch cadmium-loaded sphere has a response similar to that of a 10-inch diameter rem-responding sphere.