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Securing special nuclear material: Recent advances in neutron detection and their role in nonproliferation
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Image of FIG. 1.
FIG. 1.

Examples of neutron-detection systems used for interdiction (left), search (middle), and characterization (right) missions.

Image of FIG. 2.
FIG. 2.

Comparison of multiplicity distributions for plutonium isotopes undergoing spontaneous fission (s.f.), thermally induced fission (therm), and fission at 2 MeV [Ens98]. The shift between the spontaneous fission and induced fission distributions plays an important role in multiplicity measurements.

Image of FIG. 3.
FIG. 3.

Plot of cross section for neutron-induced fission vs neutron energy. The multiplication of SNM is a function of these cross sections and the energy spectrum as well as the multiplicity of emitted fission neutrons.

Image of FIG. 4.
FIG. 4.

Plot of probability vs energy for spontaneous neutron emission from various isotopes. Curves are based on Watt parameters from Table I. Data points are measurements of from [Vla01]. For the applications discussed in this article, the slight differences in these spectra are not significant.

Image of FIG. 5.
FIG. 5.

Comparison of fission neutron distributions emanating from a sphere of without (unmoderated) and with (moderated) a hydrogenous cover.

Image of FIG. 6.
FIG. 6.

Comparison of ambient background energy distribution with those from AmBe and a fission sources.

Image of FIG. 7.
FIG. 7.

Interaction cross sections as a function of energy for materials relevant to neutron detection.

Image of FIG. 8.
FIG. 8.

Fission spectrum flux after various thicknesses of moderation. Calculation courtesy of Sean Robinson, Pacific Northwest National Laboratory.

Image of FIG. 9.
FIG. 9.

An assembly of miniature ionization chambers sandwiched between two readout boards that can be distributed throughout a moderator. Photograph courtesy of Roger Kisner, Oak Ridge National Laboratory.

Image of FIG. 10.
FIG. 10.

Photograph revealing PMTs on the inside of a prototype water cerenkov detector. Photograph courtesy of Steve Dazeley, Lawrence Livermore National Laboratory.

Image of FIG. 11.
FIG. 11.

Lithium-doped scintillating fibers used for thermal-neutron detection. Photograph courtesy of Mary Bliss, Pacific Northwest National Laboratory.

Image of FIG. 12.
FIG. 12.

A 200-kg array of liquid scintillators used for characterizing fast-neutron emissions from SNM. Photograph courtesy of Les Nakae, Lawrence Livermore National Laboratory.

Image of FIG. 13.
FIG. 13.

A pressurized bubble chamber assembly. Photograph courtesy of David Jordan, Pacific Northwest National Laboratory. Reprinted from Applied Radiation and Isotopes, Vol. 63, D. V. Jordan, J. H. Ely, A. J. Peurrung, L. J. Bond, J. I. Collar, M. Flake, M. A. Knopf, W. K. Pitts, M. Shaver, A. Sonnenschein, J. E. Smart, and L. C. Todd, “Neutron detection via bubble chambers,” pp. 645–653, ©2005, with permission from Elsevier.

Image of FIG. 14.
FIG. 14.

Coded aperture thermal neutron camera (left) and neutron Image of six moderated sources (right). The sources were located 2 m from the imager and separated by 0.3 m.


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Table I.

Neutron emission properties of prominent SNM isotopes.

Generic image for table
Table II.

Maximum energy deposition in elastic scattering.

Generic image for table
Table III.

Properties of common thermal neutron-capture isotopes and for comparison.


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Scitation: Securing special nuclear material: Recent advances in neutron detection and their role in nonproliferation