NEUTRON MULTIPLICITY AND ACTIVE WELL NEUTRON COINCIDENCE VERIFICATION MEASUREMENTS PERFORMED FOR MARCH 2009 SEMI-ANNUAL DOE INVENTORY Page: 4 of 9
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Analytical Development SRNL-STI-2009-00302
Savannah River National Laboratory page 3 of 8
Table 1. SRNL SNM inventory items meeting requirements for March 2009
Item Number Declared Content SNM Description
50014668 101. 4 gram Pu Pu metal from FB-Line 3/99
50015480 60 .2 9 gram Pu Pu oxide from FB-Line 1/99
50015426 59 . 25 gram PU Pu oxide from FB-Line 1/99
50015514 64.0 gram Pu Pu oxide from LANL 11/07
2002026A 102 gram HEU Pillow-like assimilation of U-Al solid
F1001 99 gram HEU U-Al slab with no flexibility
The accuracy and precision of all three instruments to perform passive NMC
measurements of items of total Pu mass 0.78 g and 7.2 g with known isotopics is
documented in reference 8. The passive NMC technique measures neutron coincidence
events to determine effective Pu-240 content, and total Pu is predicted from the known
isotopic content. Thus, the uncertainty of the total Pu measurement is directly related to
the uncertainty in the known isotopic distribution of the sample. Such isotopics is
established generally with a y-ray acquisition, but had not been established for four of the
five 50-material items of Table 1. The isotopic information available for each is shown
in Table 2.
Table 2. Isotopic Information available for the SNM items of Table 1.
Item Pu-238 Pu-239 Pu-240 Pu-241 Unaccounted U-235
Number Fraction Fraction Fraction Fraction Pu Fraction Enrichment
50014668 0.927 0.059 0.014
50015480 0.94 0.0153 0.0002 0.0445
50015426 0.932 0.0174 0.00152 0.049
50015514 0.9372 0.0628 0
Pu Measurement Results
AD analyzed the five 50-material items in each of the three NMC instruments in its possession in
the passive NMC mode for determination of Pu-240 and total Pu content. The enriched uranium
item 2002026A was analyzed in the Aquila AWCC instrument in the active mode for
determination of HEU content. For both passive and active neutron coincidence analyses, the
instrument acquisition parameters are extremely important. Coincidence gate width, deadtime
correction equations, instrument counting efficiency, and doubles- and triples-gate fractions
directly affect the analytical results for passive NMC analysis. The coincidence gate width and
correction for accidental coincidence directly affect the analytical results for active coincidence
analyses. All of these had been previously accurately determined experimentally for all three
instruments. The acquisition parameters are not listed in this report but are documented in
Laboratory Notebook WSRC-NB-98-00064114) and appear in the hard copy printed output of all
results.5 Individual measured values for each Pu content from the three instruments appear in
Table 3. We discuss results thoroughly below.
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Dewberry, R.; Ayers, J.; Tietze, F. & Klapper, K. NEUTRON MULTIPLICITY AND ACTIVE WELL NEUTRON COINCIDENCE VERIFICATION MEASUREMENTS PERFORMED FOR MARCH 2009 SEMI-ANNUAL DOE INVENTORY, article, February 5, 2010; South Carolina. (https://digital.library.unt.edu/ark:/67531/metadc929439/m1/4/: accessed April 19, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.