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Title: Moderator materials for the Spallation Neutron Source

The Spallation Neutron Source (SNS) is a neutron source providing intense neutron fluxes that will be used for performing a large variety of neutron scattering experiments. SNS is to be completed and start operation in 2005. Protons will be accelerated to 1 GeV, stored in an accumulator ring, and then injected into a neutron-producing target. After leaving the target (Hg in the ca/se of SNS), the neutrons are prepared for experiments by first using a moderator to impose energy and width requirements on the neutron pulse. One of the most important ingredients is the moderator material. Four materials that are commonly used and that were considered for use in SNS are liquid hydrogen (L-H{sub 2}), liquid water (L-H{sub 2}O), liquid methane (L-CH{sub 4}), and solid methane (S-CH{sub 4}). The spectra (neutron current versus neutron energy) for these four materials are shown. As may be seen, at low neutron energies (<10 MeV), the most effective moderator is S-CH{sub 4}, which produces up to four times as many neutrons in this energy range as L-H{sub 2}. The problem with the material is the internal storage of energy that can be spontaneously and explosively released. At energies of just above 10 MeV, themore » most effective moderator material is L-CH{sub 4}. Polymerization problems, however, preclude its use at high powers (again such as in SNS), where the buildup of undesirable materials becomes prohibitive. This is, however, an important energy range for neutron experiments. Preliminary consideration is being given to a composite moderator that contains two adjacent sections, one of L-H{sub 2} and one of L-H{sub 2}O, which produces a spectrum that is very similar to L-CH{sub 4}.« less
Authors:
 [1]
  1. Oak Ridge National Lab., TN (United States)
Publication Date:
OSTI Identifier:
678120
Report Number(s):
CONF-990605-
Journal ID: TANSAO; ISSN 0003-018X; TRN: 99:009105
Resource Type:
Journal Article
Resource Relation:
Journal Name: Transactions of the American Nuclear Society; Journal Volume: 80; Conference: 1999 annual meeting of the American Nuclear Society (ANS), Boston, MA (United States), 6-10 Jun 1999; Other Information: PBD: 1999
Country of Publication:
United States
Language:
English
Subject:
07 ISOTOPE AND RADIATION SOURCE TECHNOLOGY; 43 PARTICLE ACCELERATORS; NEUTRON SOURCES; ACCELERATOR FACILITIES; MODERATORS; HYDROGEN; WATER; METHANE; NEUTRON SPECTRA; COMPARATIVE EVALUATIONS