Apparatus for controlling neutrons escaping from an elemental analyzer

Abstract

In an apparatus for neutron-capture-based on-line elemental analysis of bulk substances, the control of neutrons which escape from the volume in which the analyzed substance is placed improves accuracy and reduces potential radiation hazards. The apparatus includes a neutron source, which exposes the analyzed bulk substance momentarily contained within the instrument to a flux of neutrons. The analyzed substance captures some of these neutrons by (n,.gamma.) reactions, producing prompt gamma rays which are detected to provide the composition measurement. The placement of neutron absorbers around the volume containing the bulk substance and the neutron source and the proper geometrical relationship between the various parts of the instrument provide this neutron control. The materials used in controlling escaping neutrons and in the instrument structure are chosen to avoid interfering radiations. The materials and geometries herein provide neutron control in a manner which does not add significantly to the number of detected background events resulting from the scattering of measured capture gamma rays or from the production of additional gamma rays in the neutron-absorbing materials or in the surrounding structure. Absorbing and controlling escaping neutrons provides fewer neutron interactions in the gamma-ray detector and less scattering of the capture gamma rays, resulting in improved accuracies.