[en] The international monitoring system exists to verify compliance with the terms of the comprehensive test ban treaty. About 10% of the member stations will be capable of detecting radioxenon, which can be produced in nuclear detonations or through civilian processes. We have studied the activation of radioxenon by the prompt, intense spectrum of 14-MeV neutrons produced at the National Ignition Facility. While 14-MeV neutrons are not currently a significant contributor to the production of radioxenon, we find that radioxenon produced through activation of environmental xenon by 14-MeV neutrons would be distinguishable from activation by nuclear tests. (author)

[en] We determined fission yields of xenon ("1"3"3"mXe, "1"3"5Xe, "1"3"5"mXe, "1"3"7Xe, "1"3"8Xe, and "1"3"9Xe) resulting from 14 MeV neutron induced fission of depleted uranium at the National Ignition Facility. Measurements begin approximately 20 s after shot time, and yields have been determined for nuclides with half-lives as short as tens of seconds. We determined the relative independent yields of "1"3"3"mXe, "1"3"5Xe, and "1"3"5"mXe to significantly higher precision than previously reported. The relative fission yields of all nuclides are statistically indistinguishable from values reported by England and Rider (ENDF-349. LA-UR-94-3106, 1994), with exception of the cumulative yield of "1"3"9Xe. Considerable differences exist between our measured yields and the JEFF-3.1 database values. (author)

[en] Fission gas isotopic compositions are sensitive to a variety of reactor operating parameters that include the neutron flux, neutron fluence at different neutron energies, and operating temperature. Measurements of fission gas isotopic compositions thus have potential to constrain reactor simulations for nuclear forensics and safeguards applications. In this paper, we present Kr and Xe isotope measurements from a suite of samples obtained from locations that span the axial length a fuel pin with a well-characterized irradiation history and compare these data to spatially resolved reactor simulations. We observed positive correlations between fluence sensitive isotopic ratios and burnup and between a flux sensitive ratio and power, although some discrepancies are observed between the measured data and model predictions. These differences may be due to simplifications in the model and/or inaccuracies in the cross sections. A much broader measurement to model comparison is required to better understand the discrepancies. (author)

[en] Nuclear weapons represent one of the most immediate threats of mass destruction. In the event that a procured or developed nuclear weapon is detonated in a populated metropolitan area, timely and accurate nuclear forensic analysis and fallout modeling would be needed to support attribution efforts and hazard assessments. Here we demonstrate that fissiogenic xenon isotopes retained in radioactive fallout generated by a nuclear explosion provide unique constraints on (1) the timescale of fallout formation, (2) chemical fractionation that occurs when fission products and nuclear fuel are incorporated into fallout, and (3) the speciation of fission products in the fireball. Our data suggest that, in near surface nuclear tests, the presence of a significant quantity of metal in a device assembly, combined with a short time allowed for mixing with the ambient atmosphere (seconds), may prevent complete oxidation of fission products prior to their incorporation into fallout. Xenon isotopes thus provide a window into the chemical composition of the fireball in the seconds that follow a nuclear explosion, thereby improving our understanding of the physical and thermo-chemical conditions under which fallout forms. - Highlights: • Radioactive fallout generated by nuclear explosions contains fissiogenic xenon isotopes. • Xe isotopes provide constraints on timescales of fallout formation and the speciation of fission products in the fireball. • Our data indicate that macroscopic fallout forms rapidly (<3 s). • Chemical fractionation trends suggest that fission products may not have been fully oxidized prior to incorporation