Robert Casperson | 18-ERD-013
In this project, we developed a new experimental capability at Lawrence Livermore National Laboratory, leveraging the capabilities of the Laboratory's recently acquired Photonuclear Reactions for Isotopic Signature Measurements (PRISM) accelerator, which is a gamma-ray bremsstrahlung platform, to conduct photonuclear experiments. We successfully fielded a number of experimental measurements of relevance to several mission areas. The PRISM accelerator was tuned and characterized at lower energy than previously achieved, enabling measurements in the gamma-ray energy range of interest for most applications. In support of gamma-ray beam interrogation of special nuclear materials, unique photo-fission signatures were identified, providing enhanced capabilities for distinguishing uranium isotopes. Photonuclear cross sections of relevance to Livermore's National Ignition Facility were measured on thulium for the first time, demonstrating a capability that could benefit science and security applications ranging from nuclear astrophysics to nuclear forensics. Pivoting toward upcoming nuclear data needs for stockpile stewardship, we performed an exploratory study of neutron-scattering measurements using a photo-fission, neutron-time-of-flight source. We also developed short-pulse accelerator tunes and simulations of nuclear data impact.
The project enabled scientists to pursue new ideas using one of the most fundamental probes in science. The expanded energy range developed during the project enables measurements across the photonuclear energy range of highest interest for applications. Unique isotopic signatures were identified with photo-fission delayed neutrons, which should provide the Defense Threat Reduction Agency and Department of Homeland Security with additional tools to better distinguish uranium isotopes. Demonstration of successful photonuclear cross-section measurements allows Livermore to respond to requests for new photonuclear data and pursue measurements of astrophysical and NNSA-relevant applications. Progress towards a photo-fission, neutron-time-of-flight source brings us closer to locally fielding integral neutron-induced measurements of interest for stockpile stewardship.
Publications, Presentations, and Patents
Casperson, R. J., et al. 2019. "Nuclear Science and Security Experiments with PRISM." APS April Meeting 2019, Denver, CO, April 2019. LLNL-PRES-771840
Johnson, M. S. 2018. "Nuclear Data Requirements for Nuclear Security Applications." Fifth Joint Meeting of the Nuclear Physics Divisions of the APS and JPS, Waikoloa Village, HI, October 2018. LLNL-PRES-760145
Soltz, R. A., et al., 2019. "Fissile material detection using neutron time-correlations from photofission," AIP Advances, 9, 025011. LLNL-JRNL-760386