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Title: Analysis of the scintillation mechanism in a pressurized {sup 4}He fast neutron detector using pulse shape fitting

An empirical investigation of the scintillation mechanism in a pressurized {sup 4}He gas fast neutron detector was conducted using pulse shape fitting. Scintillation signals from neutron interactions were measured and averaged to produce a single generic neutron pulse shape from both a {sup 252}Cf spontaneous fission source and a (d,d) neutron generator. An expression for light output over time was then developed by treating the decay of helium excited states in the same manner as the decay of radioactive isotopes. This pulse shape expression was fitted to the measured neutron pulse shape using a least-squares optimization algorithm, allowing an empirical analysis of the mechanism of scintillation inside the {sup 4}He detector. A further understanding of this mechanism in the {sup 4}He detector will advance the use of this system as a neutron spectrometer. For {sup 252}Cf neutrons, the triplet and singlet time constants were found to be 970 ns and 686 ns, respectively. For neutrons from the (d,d) generator, the time constants were found to be 884 ns and 636 ns. Differences were noted in the magnitude of these parameters compared to previously published data, however the general relationships were noted to be the same and checked with expected trendsmore » from theory. Of the excited helium states produced from a {sup 252}Cf neutron interaction, 76% were found to be born as triplet states, similar to the result from the neutron generator of 71%. The two sources yielded similar pulse shapes despite having very different neutron energy spectra, validating the robustness of the fits across various neutron energies.« less
Authors:
; ;  [1] ;  [2]
  1. University of Florida, Nuclear Engineering Program, Gainesville, FL 32611-6400 (United States)
  2. Arktis Radiation Detectors Ltd., Räffelstrasse 11, 8045 Zürich (Switzerland)
Publication Date:
OSTI Identifier:
22454488
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Advances; Journal Volume: 5; Journal Issue: 3; Other Information: (c) 2015 Author(s); Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS; 36 MATERIALS SCIENCE; CALIFORNIUM 252; COMPARATIVE EVALUATIONS; ENERGY SPECTRA; EXCITED STATES; FAST NEUTRONS; HELIUM; HELIUM 4; INTERACTIONS; LEAST SQUARE FIT; NEUTRON GENERATORS; NEUTRON SPECTROMETERS; PULSE SHAPERS; SCINTILLATIONS; SIGNALS; SPONTANEOUS FISSION; TRIPLETS