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Neutron Cross Section Standards

Summary:

NIST continues to be deeply involved with measurements and evaluations of neutron cross section standards.  NIST maintains a limited experimental effort focused on improvements to the database of the standards.

Description:

Measurements have been completed at Ohio University of the important hydrogen scattering angular distribution standard at 14.9 MeV neutron energy in an NIST-Ohio University-LANL collaborative experiment.  This work was initiated as a result of problems that became apparent in evaluations of this cross section.  The work has been published in Phys. Rev. C82 014001 (2010). These data were obtained by detecting the scattered protons from scattering of neutrons on hydrogen.  The large uncertainty for our point near 60 degrees in the CMS is a result of significant background at smaller angles using the proton detection method.  A new experiment is now underway in which the scattered neutrons are being detected.  With this method measurements can be made at smaller CMS angles with smaller uncertainties.  Only one experiment has been done (in 1967) at small CMS angles and that experiment indicates higher cross sections near zero degrees in the CMS.  Also some improvements to measurements at 10 MeV by this collaboration were published in Phys. Rev. C82 039901 (2010).  Plans have been made to measure this cross section using a Time Projection Chamber which will provide higher counting rates than are possible with other methods.

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Lead Organizational Unit:

pml

Staff:

Neutron Physics Group

Alan K. Thompson

NIST Associate:

Allan D. Carlson

David M. Gilliam