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The neutron activation of gold is the basis of an implosion performance diagnostic at the National Ignition Facility at Lawrence Livermore National Laboratory. In support of this diagnostic, a series of γ-ray spectrometric measurements of the decay of ¹⁹⁶Au^m2 (J^π = 12^-) was performed to improve the currently accepted literature values of the nuclear data associated with its half-life, γ-ray energies, and γ-ray intensities. It was determined that ¹⁹⁶Au^m2 decays with a half-life of 9.603 h ± 0.23%. The relative intensities of the γ rays emitted during its decay were also measured, and an absolute decay branch of 0.3352 ±more » 2.9% was determined for the emission of the 188.2-keV photon, which arises from a nuclear transition whose multipolarity is predominantly M1. Properties of other products arising in the reaction of ¹⁹⁷Au with fast neutrons were measured, as were selected production cross sections. Finally, the ¹⁹⁶Au^m2/¹⁹⁶Au^g isomer ratio measured in the ¹⁹⁷Au(n; 2n) reaction at 14.1 MeV was found to be 0.0731 ± 2.6%.« less

Isomore » tope harvesting is a method of collecting the long-lived radioisotopes that build up during the operation of ion-beam facilities in a way that is useful for subsequent research. As a demonstration of this method for the collection of a group IV metal at a fragmentation facility, the high-energy ${}_{88}\mathrm{Zr}$ secondary beam produced from a 140-MeV/u ${}_{92}\mathrm{Mo}$ primary beam at the National Superconducting Cyclotron Laboratory (NSCL) was stopped in a water target. The setup aimed to mimic the aqueous beam dump that will be implemented at the Facility for Rare tope Beams (FRIB). The collected ${}_{88}\mathrm{Zr}$ and accompanying ${}_{88}\mathrm{Y}$ decay daughter were radiochemically extracted from the solution and made into target samples suitable for neutron-capture cross-section measurements. These samples were then irradiated at two reactor facilities, and the ${}_{88}\mathrm{Zr}$ average thermal-neutron-capture cross section ( ${\sigma }_T$) and resonance integral ( $I$) were determined to be ${\sigma }_T=(8.04\pm 0.63)\times {10}^5$ b and $I=(2.53\pm 0.28)\times {10}^6$ b. The ${\sigma }_T$ value agrees well with previous results and $I$, determined for the first time here, was found to be the largest measured resonance integral by two orders of magnitude. The ${}_{88}\mathrm{Y}$ thermal-neutron-capture cross section was determined to be less than $1.8\times {10}^4$ b. This work demonstrates the steps needed to make cross-section measurements with samples produced via aqueous isotope harvesting.« less

A large area solid radiochemistry collector was deployed at the National Ignition Facility (NIF) with a collection efficiency for post-shot, solid target debris of approximately 1% of the total 4π solid angle. The collector consisted of a 20-cm diameter vanadium foil surrounded by an aluminum side-enclosure and was fielded 50 cm from the NIF target. The collector was used on two NIF neutron yield shots, both of which had a monolayer of ²³⁸U embedded in the capsule ablator 10 μm from the inner surface. Fission and activation products produced in the ²³⁸U were collected, and subsequent analyses via gamma spectroscopymore » indicated that the distribution of fission products was not uniform, with peak and valley fission products preferentially collected on the vanadium and low- and high-mass fission products primarily located on the aluminum side-enclosure. The results from these shots will be used to design future nuclear data experiments at NIF.« less

The solid debris collection capability at the National Ignition Facility has been expanded to include a third line-of-sight assembly. The solid radiochemistry nuclear diagnostic measurement of the ratio of gold isotopes is dependent on the efficient collection of neutron-activated hohlraum debris by passive metal disks. As a result, the collection of target debris at this new location is more reliable in comparison to the historic locations, and it appears to be independent of collector surface ablation.

A series of indirectly driven capsule implosions has been performed on the National Ignition Facility to assess the relative contributions of ablation-front instability growth vs. fuel compression on implosion performance. Laser pulse shapes for both low and high-foot pulses were modified to vary ablation-front growth and fuel adiabat, separately and controllably. Three principal conclusions are drawn from this study: (1) It is shown that reducing ablation-front instability growth in low-foot implosions results in a substantial (3-10X) increase in neutron yield with no loss of fuel compression. (2) It is shown that reducing the fuel adiabat in high-foot implosions results inmore » a significant (36%) increase in fuel compression together with a small (10%) increase in neutron yield. (3) Increased electron preheat at higher laser power in high-foot implosions, however, appears to offset the gain in compression achieved by adiabat-shaping at lower power. These results taken collectively bridge the space between the higher compression low-foot results and the higher yield high-foot results.« less