Lawrence Livermore National Laboratory



Nicholas Scielzo

Overview

Nuclear reactions are the mechanism for forging elements in the cosmos, the source of energy for both stars and nuclear weapons, the principal probes used to study nuclear properties, and the primary diagnostic signatures for stockpile stewardship and nuclear forensics. Yet, most reaction experiments have been confined to the small fraction of all nuclei that are stable, and a theoretical foundation for reactions with a true predictive capability is lacking. The Facility for Rare Isotope Beams (FRIB), the flagship U.S. facility in low-energy nuclear science, will offer the opportunity to rectify the long-standing gap in understanding reactions on radioactive nuclei.

Our work brought together the experimental nuclear physics, radiochemistry, nuclear theory, and high-performance computing expertise of Lawrence Livermore National Laboratory's Nuclear and Chemical Sciences Division to develop new techniques that will be needed to exploit FRIB beams to better understand nuclear reactions. Novel isotope-harvesting techniques were developed to demonstrate that samples could be collected at the National Superconducting Cyclotron Laboratory at Michigan State University for direct measurements of long-lived radioisotopes. For isotopes too short-lived for direct measurement, indirect approaches were developed that would ultimately be used with high-intensity FRIB radioactive beams. Finally, to better interpret experimental results and reliably extend predictions beyond the available data, a foundation was established for a fully microscopic and unified description of the structure, interactions, and dynamics of two reacting nuclei that moves beyond empirical models.

Impact on Mission

This work positioned our project team for a leadership role at FRIB, enabling Livermore to maintain a world-class nuclear science program and compete for future talent and funding, both of which are vital for continuing support of the Laboratory’s nuclear stockpile stewardship mission. Our research and strong partnerships developed among nuclear physics, radiochemistry, and nuclear theory/modeling groups at Livermore and the broader scientific community developing programs at FRIB positioned Livermore to advance astrophysics, the Laboratory's stockpile stewardship mission focus area, and its core competencies in nuclear, chemical, and isotopic science and technology.

Publications, Presentations, Etc.

Dreyfuss, A., et al., 2018. "Clustering and Alpha-Capture Reaction Rates from First-Principle Structure Calculations for Nucleosynthesis." State of the Art in Nuclear Cluster Physics. LLNL-PROC-755912.

Escher, J. 2017. "Capture Reactions on Unstable Isotopes: Connecting Indirect Measurements to the Desired Cross Sections." 6th Workshop on Nuclear Level Densities and Gamma Strength, Oslo, Norway, May 2017. LLNL-ABS-725539.

——— . 2017. Capture Reactions on Unstable Isotopes: Determining Unknown Cross Sections from Indirect Measurements." 16th International Symposium on Capture Gamma-Ray Spectroscopy and Related Topics, Shanghai, China, September 2017. LLNL-ABS-725501.

——— . 2017. "Capture Reactions on Unstable Isotopes: Theory Developments for Connecting Measured Observables to the Desired Cross Sections." 3rd International Conference on Advances in Radioactive Isotope Science, Keystone, CO, May/June 2017. LLNL-ABS-720617.

Escher, J., et al. 2017. "Report on INT Program INT-17-1a." SciTech Connect. April 19. www.osti.gov/scitech/biblio/1357334. LLNL-TR-729382.

——— . 2017. "Toward Predictive Theories of Nuclear Reactions Across the Isotopic Chart: Web Report." SciTech Connect. May 12. https://www.osti.gov/scitech/biblio/1357406. LLNL-TR-731172.

——— . 2018. "Capture Cross Sections for Unstable Isotopes from Surrogate Reaction Data and Theory." 15th Varenna Conference on Nuclear Reaction Mechanisms, Villa Monastero, June 2018. LLNL-ABS-745500.

——— . 2018. "Neutron Capture Cross Sections for Short-Lived Nuclei from Surrogate Reaction Data and Theory." Nuclear Structure 2018, East Lansing, MI, August 2018. LLNL-ABS-752022.

Fronczyk, K. and J. Escher. 2018. "Neutron Capture Cross Sections for Unstable Nuclei with Surrogate Reaction Data." Joint Statistical Meetings, Vancouver, BC, Canada, July 2018. LLNL-ABS-749458.

Gorton, O. and J. Escher. 2018. "Neutron Capture from Surrogate Reaction Data: Assessing Model Uncertainties." Compound-Nuclear Reactions and Related Topics, Berkeley, CA, September 2018. LLNL-ABS-754291.

Jones, M., et al. 2018. "Examination of the Low Energy Enhancement of the Gamma-Ray Strength Function of Fe-56." Physical Review C, 97(2) 024327. LLNL-JRNL-758362.

Larsen, A. 2018. "Enhanced Low-Energy Gamma-Decay Strength of Ni-70 and its Robustness within the Shell Model." Physical Review C 97, 054329. LLNL-JRNL-758361.

Lewis, R., et al. 2019. "Experimental Constraints on the Zn-73(n, gamma)Zn-74 Reaction Rate." Physical Review C 99, 034601. LLNL-JRNL-760243.

Liddick, S., et al. 2016. "Experimental Neutron Capture Rate Constraint Far from Stability." Physical Review Letters 116(24): 242502. LLNL-JRNL-678694.

——— . 2018. Nuclear Astrophysics with Radioactive Beams." 6th International Conference on Fission and Properties of Neutron-Rich Nuclei. LLNL-ABS-758657.

Loveless, C., et al. 2018. "Harvesting 48V at a Radioactive Beam Facility." American Chemical Society 225th Annual Meeting, New Orleans, LA, March 2018. LLNL-ABS-739442.

Mercenne, A., et al. 2018. "A New Ab Initio Approach for Nuclear Reactions Based on the Symmetry-Adapted No-Core Shell Model." GANIL Topical Meeting: Nuclear Structure and Reactions for the 2020s, Caen, France, October 2018. LLNL-ABS-751669.

Ratkiewicz, A., et al. 2017. "Validating the (d,p(gamma)) Reaction as a Surrogate for (n,(gamma)) on Rare Isotopes Using the 95Mo(d,p(gamma)) Reaction." 3rd International Conference on Advances in Radioactive Isotope Science, Keystone, CO, May/June 2017. LLNL-ABS-721479.

——— . 2018. "Towards Neutron Capture on Exotic Nuclei: Demonstrating the (d,p) Reaction as a Surrogate for (eta,gamma)." Compound-Nuclear Reactions and Related Topics, Berkeley, CA, September 2018. LLNL-ABS-752504.

——— . 2018. "Isotope Harvesting of 88Zr for Neutron-Capture Cross-Section Measurements." American Chemical Society 225th Annual Meeting, New Orleans, LA, March 2018. LLNL-ABS-740274.

——— . 2019. "Towards Neutron Capture on Exotic Nuclei: Demonstrating (d,p gamma) as a Surrogate Reaction for (n,gamma)." Physical Review Letters 122, 052502. LLNL-JRNL-751443.

Shusterman, J., et al. 2018. "Isotope Harvesting of 88Zr and the Measurement of its Neutron-Capture Cross Section." MARC, Kailua-Kona, HI, April 2018. LLNL-ABS-743182.

——— . 2019. "The Surprisingly Large Neutron Capture Cross-Section of Zr." Nature 565(7739): 328. LLNL-JRNL-744886.

Spyrou, A., et al. 2017. "Neutron-Capture Rates for Explosive Nucleosynthesis: The Case of Ni-68(n,gamma)Ni-69." Journal of Physics G: Nuclear and Particle Physics, 44(4): 044002. LLNL-JRNL-705342.

Tonchev, A., et al. 2017. "Pygmy and Core Polarization Dipole Modes in 206Pb: Connecting Nuclear Structure to Stellar Astrophysics." Physics Letters B 773 (October 10): 20-25. doi:10.1016/j.physletb.2017.07.062. LLNL-JRNL-716577.

——— . 2018. "The s-Process branching-point at 205PB." Fall Meeting of the APS Division of Nuclear Physics, Pittsburgh, PA, October 2017. LLNL-ABS-734221.

Tveten, G., et al. 2016. "Completing the Nuclear Reaction Puzzle of the Nucleosynthesis of Mo-92." Physical Review C, 94(2): 025804. LLNL-JRNL-704523.

Ureche, A., et al. 2017. "Statistical Properties of short-lived 92Sr for National Security Applications." 6th Workshop on Nuclear Level Densities and Gamma Strength, Oslo, Norway, May, 2017. LLNL-ABS-726618.