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Application of Triple Coincidence for the
Detection of Small Amounts of Special Nuclear
I. Dioszegia, C. Salwena , and L. Formanb
a Brookhaven National Laboratory, Upton, New York 11973-500, USA
bIon Focus Technology Inc., Miller Place, New York 11764, USA
Abstract. We constructed a device that measures two y-rays and one neutron from spontaneous
fission and any resulting multiplication chains. It extends the associated particle technique
based upon correlated counting of the multiplicity of gamma-rays and neutrons released in
spontaneous- or neutron-induced fission. There are two advantages in incorporating a third
detector in the design over the standard two-detector version. First, we found that random
uncorrelated events dominate the background of coincident counting with a gamma-ray- and
neutron-detector. These might be suppressed by requiring an additional coincidence. Second,
the time history of gamma-ray emission between the two gamma-ray detectors is related to
multiplication in the target media. Multiplication in highly enriched uranium is much greater
than in depleted uranium.
Keywords: Special Nuclear Material, Spontaneous Fission.
PACS: 25.85.Ca, 29.40.Mc.
We are developing1 a device that identifies Special Nuclear Material (SNM) by
detecting spontaneous fission y-rays and neutrons. Spontaneous fission emits several
neutrons and y-rays simultaneously, but also may exhibit a fast die-away component
resulting from fission multiplication via chain reactions. In our device, we exploit a
very short coincidence window to reduce the random background of y-radiation
coming from the target material's radioactive decay modes, and from the neutrons and
y-rays generated by cosmic rays. When there are large amounts of material nearby,
cosmic-rays generate considerable numbers of fast neutrons whose energy distribution
is similar to that of the fission neutrons (the so-called ship effect); therefore, filtering
out these ship-effect neutrons is of the utmost importance.
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DIOSZEGI, I.; Salwen, C. & and Forman, L. Application of Triple Coincidence for the Detection of Small Amounts of Special Nuclear Materials, article, June 12, 2011; United States. (digital.library.unt.edu/ark:/67531/metadc843272/m1/3/: accessed November 16, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.