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Title: Measurement of U-235 Fission Neutron Spectra Using a Multiple Gamma Coincidence Technique

The Los Alamos Model of Madland and Nix predicts the shape of the fission neutron energy spectrum for incident primary neutrons of different energies. Verifications of the model normally are limited to measurements of the fission neutron spectra for energies higher than that of the primary neutrons because the low-energy spectrum is distorted by the admixture of elastically and inelastically scattered neutrons. This situation can be remedied by using a measuring technique that separates fission from scattering events. One solution consists of using a fissile sample so thin that fission fragments can be observed indicating the occurrence of a fission event. A different approach is considered in this paper. It has been established that a fission event is accompanied by the emission of between seven and eight gamma rays, while in a scattering interaction, between zero and two gammas are emitted, so that a gamma multiplicity detector should supply a datum to distinguish a fission event from a scattering event. We proceed as follows: A subnanosecond pulsed and bunched proton beam from the UML Van de Graaff generates nearly mono-energetic neutrons by irradiating a thin metallic lithium target. The neutrons irradiate a 235U sample. Emerging neutron energies are measured withmore » a time-of-flight spectrometer. A set of four BaF2 detectors is located close to the 235U sample. These detectors together with their electronic components identify five different events for each neutron detected, i.e., whether four, three, two, one, or none of the BaF2 detectors received one (or more) gamma rays. We present work, preliminary to the final measurements, involving feasibility considerations based on gamma-ray coincidence measurements with four BaF2 detectors, and the design of a Fission-Scattering Discriminator under construction.« less
Authors:
; ; ; ; ; ; ; ; ;  [1]
  1. Department of Physics and Applied Physics, University of Massachusetts Lowell, One University Avenue, Lowell, MA 01854 (United States)
Publication Date:
OSTI Identifier:
20722357
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Conference Proceedings; Journal Volume: 769; Journal Issue: 1; Conference: International conference on nuclear data for science and technology, Santa Fe, NM (United States), 26 Sep - 1 Oct 2004; Other Information: DOI: 10.1063/1.1945187; (c) 2005 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS; AVAILABILITY; COINCIDENCE SPECTROMETRY; ENERGY SPECTRA; FISSION; FISSION FRAGMENTS; FISSION NEUTRONS; GAMMA DETECTION; GAMMA RADIATION; INELASTIC SCATTERING; LOS ALAMOS; MULTIPLICITY; NEUTRON SPECTRA; PROTON BEAMS; TIME-OF-FLIGHT SPECTROMETERS; URANIUM 235; VAN DE GRAAFF ACCELERATORS