Abstract
The self-powered neutron detector (SPND) is a widely used flux monitor in thermal nuclear reactors. Although this is a mature technology, the current state of the art is tuned for a thermal neutron spectrum, so many of the devices currently in use lack sensitivity to fast neutrons. Because current in SPNDs is produced through nuclear reactions with the neutron flux inside a reactor, sensitivity in SPNDs is determined by the neutron cross section of the neutron-sensitive portion of the detector, termed the emitter. This neutron cross section drops by orders of magnitude between thermal and fast neutron energies for many emitters in currently used SPNDs, with a corresponding drop in current from the detector. This paper discusses efforts to develop a fast-spectrum self-powered neutron detector (FS-SPND) that is sensitive to neutrons with energies ranging from 0.025 eV up to 1 MeV. An in-depth analysis of Evaluated Nuclear Data File (ENDF)/B-VII.1 neutron-capture cross sections was performed, and four new materials were identified that are suitable emitter candidates for use in measuring fast neutrons. All four materials are stable mid-shell nuclei in the region between doubly magic132Sn and208Pb. Each candidate was simulated with the Geant4 Monte Carlo simulation toolkit to optimize overall detector efficiency.
Highlights
Self-powered neutron detectors (SPNDs) have been a common diagnostic tool for intra-core neutron flux mapping in thermal nuclear reactors for more than 60 years [1], [2]. They are useful flux monitors because they are durable, compact, and simple, and they produce a signal proportional to local neutron flux without requiring an external source of power. Signal in these detectors is a current source driven by the electrons generated from nuclear reactions within the emitter that make it out to the collector
self-powered neutron detector (SPND) insulators are generally made of magnesium oxide, aluminum oxide, or are a vacuum
Five emitter candidates were identified for prompt-type SPNDs, four of which are new, and two of which are suitable for delayed-type SPNDs, and both of which are well known SPND emitters
Summary
Self-powered neutron detectors (SPNDs) have been a common diagnostic tool for intra-core neutron flux mapping in thermal nuclear reactors for more than 60 years [1], [2]. They are useful flux monitors because they are durable, compact, and simple, and they produce a signal proportional to local neutron flux without requiring an external source of power. Signal in these detectors is a current source driven by the electrons generated from nuclear reactions within the emitter that make it out to the collector.
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