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Proceedings Paper

Fast neutron source detection at long distances using double-scatter spectrometry
Author(s): Leon Forman; Peter E. Vanier; Keith Welsh
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Paper Abstract

Fast neutrons can be detected with relatively high efficiency, >15%, using two planes of hydrogenous scintillator detectors where a scatter in the first plane creates a start pulse and scatter in the second plane is separated by time-offlight. Indeed, the neutron spectrum of the source can be determined as the sum of energy deposited by pulse height in the first added to the energy of the second found by time-of-flight to the second detector. Gamma rays can also create a double scatter by Compton interaction in the first with detection in the second, but these events occur in a single time window because the scattered photons all travel at the speed of light. Thus, gamma ray events can be separated from neutrons by the time-of-flight differences. We have studied this detection system with a Cf-252 source using Bicron 501A organic scintillators and report on the ability to efficiently detect fast neutrons with high neutron/gamma detection ratios. We have further studied cosmic-ray neutron background detection response that is the dominant background in long range detection. We have found that most of the neutrons are excluded from the time-of-flight window because they are either too high in energy, >10MeV, or too low, < 10 keV. Moreover, if the detection planes are position-sensitive, the angular direction of the source can be determined by the ratio of the energy of scattered protons in the first detector relative to the position and energy of the scattered neutron detected in the second. This ability to locate the source in theta is useful, but more importantly increases the signal to noise relative to cosmic-ray produced neutrons that are relatively isotropic. This technique may be used in large arrays to detect neutrons at ranges up to 0.5 kilometer.

Paper Details

Date Published: 20 January 2004
PDF: 8 pages
Proc. SPIE 5198, Hard X-Ray and Gamma-Ray Detector Physics V, (20 January 2004); doi: 10.1117/12.509667
Show Author Affiliations
Leon Forman, Brookhaven National Lab. (United States)
Peter E. Vanier, Brookhaven National Lab. (United States)
Keith Welsh, SUNY/Stony Brook (United States)

Published in SPIE Proceedings Vol. 5198:
Hard X-Ray and Gamma-Ray Detector Physics V
Larry A. Franks; Arnold Burger; Ralph B. James; Paul L. Hink, Editor(s)

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