Gordon Wendell Misch

There is a growing realization that neutrinos can be used as a diagnostic tool to better understand the inner workings of a nuclear weapon. Robust estimates demonstrate that an Inverse Beta Decay (IBD) neutrino scintillation detector built at the Nevada Test Site with a 1000-ton active target mass at a standoff distance of 500 m would detect thousands of antineutrino events per nuclear test. This would provide less than 4% statistical error on the measured antineutrino rate and 5% error on antineutrino energy. Extrapolating this to an error on the test device explosive yield requires knowledge from evaluated nuclear databases, non-equilibrium fission rates, and assumptions on internal neutron fluxes. Initial calculations demonstrate that the total number of neutrinos emitted per fission in the first 103 s after a short pulse of 239Pu fission is about a factor of two less than that from Pu fissioning under steady state conditions. Furthermore, there are significant energy spectral differences as a function of time after the pulse that must be considered. These and other model dependencies will be discussed in the paper. In the absence of nuclear weapons testing, many of the technical and theoretical challenges of a full nuclear test could be mitigated with a low cost smaller scale 20 ton fiducial mass IBD demonstration detector placed near a pulsed reactor. Potential reactors include the Texas A&M University TRIGA 1 GW–10 ms pulsed facility or the Sandia Annular Core Research Reactor. The short duty cycle and repeatability of pulses would provide critical real environment testing and measurements, which would be valuable for planning a possible real test shot in the future. Furthermore, the antineutrino rate as a function of time data would provide unique constraints on fission databases and model assumptions. Finally, there are impactful science drivers such as sensitive searches for ∼1 eV2 sterile neutrinos and ∼MeV scale axions.

⁸⁵Kr is an s-process branch point nucleus: the competition between neutron capture and β decay influences the production of nearby nuclides. Its evolution is complicated by the existence of a long-lived isomer that β-decays on a much shorter timescale than the ground state. We calculate the effective thermal transition rates between the ground and isomeric states along with estimates of their thermal β-decay rates in a suite of nucleosynthesis computations to assess the consequences of this isomer on isotopic abundances. A central finding in this study is that the s-process flow with the isomer included under astrophysical conditions relevant for the s-process creates a shift in abundance yield of the important radioactivity ⁸⁷Rb by a factor of ∼2.4 relative to the case when the ⁸⁵Kr is taken to be internally equilibrated when neutron exposures approach the main branch limit. On the other hand, the ⁸⁸Sr/⁸⁶Sr ratio is little affected because the bulk of the flow through ⁸⁵Kr is still via beta decay, whether the isomer is taken into account or not.

The U.S. Department of Energy's Office of Scientific and Technical Information

The U.S. Department of Energy's Office of Scientific and Technical Information

The U.S. Department of Energy's Office of Scientific and Technical Information