17 April 2008 An equivalent n-source for WGPu derived from a spectrum-shifted PuBe source
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We have designed, built, and laboratory-tested a unique shield design that transforms the complex neutron spectrum from PuBe source neutrons, generated at high energies, to nearly exactly the neutron signature leaking from a significant spherical mass of weapons grade plutonium (WGPu). This equivalent "X-material shield assembly" (Patent Pending) enables the harder PuBe source spectrum (average energy of 4.61 MeV) from a small encapsulated standard 1-Ci PuBe source to be transformed, through interactions in the shield, so that leakage neutrons are shifted in energy and yield to become a close reproduction of the neutron spectrum leaking from a large subcritical mass of WGPu metal (mean energy 2.11 MeV). The utility of this shielded PuBe surrogate for WGPu is clear, since it directly enables detector field testing without the expense and risk of handling large amounts of Special Nuclear Materials (SNM) as WGPu. Also, conventional sources using Cf-252, which is difficult to produce, and decays with a 2.7 year half life, could be replaced by this shielded PuBe technology in order to simplify operational use, since a sealed PuBe source relies on Pu-239 (T½=24,110 y), and remains viable for more than hundreds of years.
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Gabriel Ghita, Glenn Sjoden, James Baciak, Scotty Walker, Spring Cornelison, "An equivalent n-source for WGPu derived from a spectrum-shifted PuBe source", Proc. SPIE 6945, Optics and Photonics in Global Homeland Security IV, 694504 (17 April 2008); doi: 10.1117/12.777475; https://doi.org/10.1117/12.777475

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