The neutron-induced reaction cross sections of 242m Am were measured at the Los Alamos Neutron Science Center using the Detector for Advanced Neutron-Capture Experiments array along with a compact parallel-plate avalanche counter for fission-fragment detection. A new neutron-capture cross section was determined, and the absolute scale was set according to a concurrent measurement of the well-known 242m Am(n,f) cross section. The (n,γ) cross section was measured from thermal to an incident energy of 1 eV at which point the data quality was limited by the reaction yield in the laboratory. Our new 242m Am fission cross section was normalized to ENDF/B-VII.1 to set the absolute scale, and it agreed well with the (n,f) cross section reported by Browne et al. from thermal energy to 1 keV. The average absolute capture-to-fission ratio was determined from thermal to En = 0.1 eV, and it was found to be 26(4)% as opposed to the ratio of 19% from the ENDF/B-VII.1 evaluation.
A differentially pumped windowless Ne gas target and a Ne beam produced with the ATLAS accelerator at Argonne National Laboratory were used to measure angle-averaged excitation functions for binary decay of Ne + Ne into low-lying states of Ne + Ne and Mg + 0, in the region of excitation energy in Ca from 51.4 to 58.2 MeV ( Ne beam energies from 61.8 to 75.4 MeV). The Ne + Ne mass partition displays little correlated structure and there exists no evidence of intermediate width resonances in these channels with branching ratios comparable to those seen in the Mg + Mg system. Angular distributions for the elastic channel are consistent with those obtained using optical-model calculations. The excitation functions for the low-lying channels in Mg + 0 do contain some structures, with widths varying from 400 to 800 keV in the c.m. system. PACS number(s): 25.70.Ef, 25.70.Hi
We have designed and tested software for the acquisition and analysis of high-resolution gamma-ray spectra during on-site inspections under the Comprehensive Nuclear-Test-Ban Treaty (CTBT). The On-Site Inspection RadioIsotopic Spectroscopy-OSIRIS-software filters the spectral data to display only radioisotopic information relevant to CTBT on-site inspections, e.g., 131 I. A set of over 100 fission-product spectra was employed for OSIRIS testing. These spectra were measured where possible, or generated by modeling. The test spectral compositions include non-nuclear-explosion scenarios, e.g., a severe nuclear reactor accident, and nuclear-explosion scenarios such as a vented underground nuclear test. Comparing its computer-based analyses to expert visual analyses of the test spectra, OSIRIS correctly identifies CTBT-relevant fission product isotopes at the 95% level or better.
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