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Correction for variable moderation and multiplication effects associated with thermal neutron coincidence counting [electronic resource].

Published
Los Alamos, N.M. : Los Alamos Scientific Laboratory, 1978.
Oak Ridge, Tenn. : Distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy.
Physical Description
Pages: 22 : digital, PDF file
Additional Creators
Los Alamos Scientific Laboratory and United States. Department of Energy. Office of Scientific and Technical Information
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Summary
A correction is described for multiplication and moderation when doing passive thermal neutron coincidence counting nondestructive assay measurements on powder samples of PuO/sub 2/ mixed arbitrarily with MgO, SiO/sub 2/, and moderating material. The multiplication correction expression is shown to be approximately separable into the product of two independent terms; F/sub Pu/ which depends on the mass of /sup 240/Pu, and F/sub ..cap alpha..n/ which depends on properties of the matrix material. Necessary assumptions for separability are (1) isotopic abundances are constant, and (2) fission cross sections are independent of incident neutron energy: both of which are reasonable for the 8% /sup 240/Pu powder samples considered here. Furthermore since all prompt fission neutrons are expected to have nearly the same energy distributions, variations among different samples can be due only to the moderating properties of the samples. Relative energy distributions are provided by a thermal neutron well counter having two concentric rings of /sup 3/He proportional counters placed symmetrically about the well. Measured outer-to-inner ring ratios raised to an empirically determined power for coincidences, (N/sup I//N/sup O/)/sup Z/, and singles, (T/sup O//T/sup I/)/sup delta/, provide corrections for moderation and F/sub ..cap alpha..n/ respectively, and F/sub Pu/ is approximated by M/sub 240//sup X//M/sub 240/. The exponents are calibration constants determined by a least squares fitting procedure using standards' data. System calibration is greatly simplified using the separability principle. Once appropriate models are established for F/sub Pu/ and F/sub ..cap alpha..n/, only a few standards are necessary to determine the calibration constants associated with these terms. Since F/sub Pu/ is expressed as a function of M/sub 240/, correction for multiplication in a subsequent assay demands only a measurement of F/sub ..cap alpha..n/.
Report Numbers
E 1.99:la-ur-78-2477
E 1.99: conf-781007-10
conf-781007-10
la-ur-78-2477
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Note
Published through SciTech Connect.
01/01/1978.
"la-ur-78-2477"
" conf-781007-10"
IAEA symposium on nuclear material safeguards, Vienna, Austria, 2 Oct 1978.
Baron, N.
Funding Information
W-7405-ENG-36
View MARC record | catkey: 14398466