ison, who is featured in the Highlight “Future Leaders” between Chapters 5 and 6, is part of this team. Only very small targets of americium-240 will be possible, making the fission cross section measurement another challenge. For the fission measurement, the very high neutron intensity capability of the Lead Slowing-Down Spectrometer (LSDS) at the Los Alamos Neutron Science Center will be used. The LSDS will also be used to measure another fission reaction of interest for uranium devices—in particular, the fission of uranium-237. Like americium-240, uranium-237 is very radioactive and difficult to produce and chemically separate. In these experiments, uranium-237 is produced by irradiation of uranium-236 in the high-flux reactor at Oak Ridge National Laboratory. Uranium-237 has a half-life of 6.75 days, and handling the irradiated sample to chemically separate uranium-237 requires use of Oak Ridge’s hot cell facilities. Once the targets are fabricated, the fission measurements will be carried out at Los Alamos using the LSDS.

The committee hopes that the validity of our nation’s nuclear forensics schemes will never need to be tested directly. Confidence in the program capability is greatly enhanced by the tight coupling between the fundamental nuclear data community, radiochemists, and the weapons design community. It hopes as well that broadcasting the capabilities of nuclear forensics to identify the source of a nuclear device and its fuel will deter advocates of such unthinkable acts.

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FIGURE FOR 2 Plutonium (Pu) and americium (Am) reaction chains. One of the pieces in a nuclear forensics puzzle is the amount of plutonium-241 in a nuclear device, which can be determined after an explosion. The figure illustrates all of the neutron-induced reactions that need to be understood to deduce the original amount of plutonium-241 in the device and the fluence of high-energy neutrons in the subsequent explosion. These include reactions on americium-241, the daughter from radioactive decay of plutonium-241. The relative abundance of americium-240 in the explosion debris would provide key information for forensic analyses, because americium-240 can only be produced by high-energy (En > 6.67 MeV) neutrons. SOURCE: Courtesy of A. Haynes, Los Alamos National Laboratory.



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