Moderator materials for the Spallation Neutron Source

Journal Article · Wed Sep 01 04:00:00 EDT 1999 · Transactions of the American Nuclear Society

OSTI ID:678120

Charlton, L A ^[1]

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1. Oak Ridge National Lab., TN (United States)

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, the 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}.

• OSTI ID: 678120
• Report Number(s): CONF-990605--
• Journal Information: Transactions of the American Nuclear Society, Journal Name: Transactions of the American Nuclear Society Vol. 80; ISSN 0003-018X; ISSN TANSAO
• Country of Publication: United States
• Language: English

Related Subjects

07 ISOTOPE AND RADIATION SOURCES
43 PARTICLE ACCELERATORS
ACCELERATOR FACILITIES
COMPARATIVE EVALUATIONS
HYDROGEN
METHANE
MODERATORS
NEUTRON SOURCES
NEUTRON SPECTRA
WATER