Grants and Contracts Details
The development of a comprehensive understanding of the process of neutron-induced fission of the actinides is of fundamental importance in many applied areas of nuclear technology, most notably in the design and operation of reactors and weapons, and in nuclear waste transmutation. While much is currently known about the basic fission process in these materials, important gaps remain in our knowledge of the details of fission. For example, it is known that "high energy" fission neutrons lead to the production of helium in reactors, yet the neutron yields near 10 MeV currently are not well measured. Various models are used to predict the distribution of fission neutron energies, but these must be tested against direct measurements. On the one hand, while the average neutron multiplicity is rather well known, it is much less certain how the neutrons are distributed in energy. And since a sizable fraction of the neutrons are emitted below 1 MeV where currently direct measurements do not exist, the average neutron multiplicity data cannot be used to constrain the high energy region. In short, our rather incomplete knowledge of the details of fission in uranium and plutonium limits our ability to understand processes which use these materials in technological application of importance to our national security and economy. The basic physics of nuclear fission is understood primarily as a competition between two energies: the Coulomb energy associated with the distribution of nuclear charge, and the surface energy of the nucleus as determined, for example, in a liquid drop model. As the nuclear deformation increases, so too does the surface energy increase. But as the deformation increases, the Coulomb energy decreases. In a high-Z nucleus where these two terms are of a similar magnitude, the net result is to produce a potential barrier to fission which is typically on the order of only about 6 MeV. In a heavy odd-N target nucleus, the pairing energy associated with the capture of a slow neutron is sufficient to allow fission to occur with high probability, while
|Effective start/end date||1/11/10 → 6/30/13|
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