Orateur
Description
The Facility for Rare Isotope Beams provides new opportunities to extend the known nuclear landscape and investigate the production of nuclei far from stability. Recent experiments at FRIB have demonstrated the discovery potential of projectile fragmentation and related reaction mechanisms over a broad range of primary-beam masses.
New isotopes have been produced and identified in experiments employing ¹⁹⁸Pt and ⁸²Se primary beams [1,2]. These measurements combined high-intensity primary beams, optimized fragment-separator settings, and event-by-event particle identification to reach production cross sections near current experimental sensitivity limits. More recent experiments using ¹⁴⁴Sm, ²⁰⁸Pb, and ²³⁸U beams have further expanded the range of reaction systems investigated at FRIB, and previously unknown isotopes were observed in several of these campaigns.
The interpretation and planning of such experiments require reliable predictions of rare-isotope production. Comparisons between experimental yields and reaction-model calculations provide important information on fragmentation, abrasion-ablation, nucleon-removal, and fission-related mechanisms. These studies are closely connected with the active development of the LISE++ program [3], including improvements to reaction models, production-rate predictions, fragment-separator transmission calculations, and tools for experiment planning and online analysis. The combined experimental and computational effort is used to optimize the selection of primary beams and production targets, separator settings, and the balance between the transmission of isotopes of interest and experimental background.
Future searches may benefit from primary beams that have not yet been extensively explored at FRIB. In particular, a ²³²Th beam may provide complementary access to neutron-rich nuclei through fragmentation and fission-like processes. Possible regions of interest and the reaction-mechanism considerations guiding the development of such experiments will be discussed. Further opportunities will emerge as FRIB increases the available primary-beam power and implements the planned upgrade toward beam energies of up to 400 MeV/u, extending the range of reaction mechanisms and production conditions available for new-isotope searches.
This contribution will summarize recent new-isotope searches at FRIB, the experimental and modeling tools used to plan and analyze them, and prospects for extending the known nuclear landscape with future beams, higher beam power, and increased beam energy.
Acknowledgments
This work was supported in part by the U.S. National Science Foundation under Grant No. PHY-23-10078. FRIB is a U.S. Department of Energy Office of Science user facility operated by Michigan State University under Award No. DE-SC0023633.
References
[1] O. B. Tarasov et al., “Observation of New Isotopes in the Fragmentation of ¹⁹⁸Pt at FRIB,” Physical Review Letters 132, 072501 (2024), DOI: 10.1103/PhysRevLett.132.072501.
[2] O. B. Tarasov et al., “Discovery of New Isotopes in the Fragmentation of ⁸²Se and Insights into Their Production,” Physical Review C 112, 034604 (2025), DOI: 10.1103/573p-7fjp.
[3] O. B. Tarasov and D. Bazin, “LISE++: Exotic Beam Production with Fragment Separators and Their Design,” Nuclear Instruments and Methods in Physics Research B 376, 185–187 (2016), DOI: 10.1016/j.nimb.2016.03.021.