From Reaction Mechanisms to Rare-Isotope Beam Design with LISE++

Oleg B. Tarasov (Facility for Rare Isotope Beams, Michigan State University, USA)

Reliable production and delivery of rare isotopes require a consistent treatment of nuclear-reaction mechanisms, fragment kinematics, charge-state evolution, interactions with matter, and separator ion optics. These ingredients are brought together in the LISE++ framework, which is widely used for the planning, optimization, and analysis of experiments with in-flight fragment and recoil separators [1].
This seminar will review selected developments in the description of projectile fragmentation, abrasion-ablation, abrasion-fission, nucleon-removal, and multistep reactions. Particular attention will be given to the role of excitation-energy distributions and nuclear binding energies in determining production cross sections far from stability. Recent measurements with an ⁸²Se beam at the Facility for Rare Isotope Beams (FRIB) provide an important test of empirical ΔBE systematics and model predictions for very neutron-rich nuclei [2]. FRIB provides high-intensity heavy-ion beams and the Advanced Rare Isotope Separator for producing, separating, and identifying rare isotopes over a broad region of the nuclear chart [3].
The seminar will also present recent developments in LISE++ aimed at improving production-rate calculations, reaction-model calibration, uncertainty estimates, multistep-reaction simulations, and the coupling of reaction-product distributions to separator transmission and ion-optical calculations. Particular attention will be given to reverse trajectory reconstruction, in which measured focal-plane positions, angles, and velocities are propagated backward through the separator ion optics to reconstruct reaction-product momentum distributions at the production target. This method provides direct experimental benchmarks for reaction-kinematics models, transmission calculations, and separator acceptance [4]. A recent Bayesian-inspired model-averaging study combines abrasion-ablation calculations based on multiple nuclear-mass models to quantify uncertainties in predicted fragmentation cross sections [5].
Selected results from FRIB and RIKEN will be used as benchmarks for the reaction models and computational methods. The emphasis will be on how experimental data guide model development and how improved reaction and separator calculations can support future rare-isotope experiments at existing and next-generation facilities.

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 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.
[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 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.
[4] M. Bowry et al., “Abrasion-Fission Reactions at Intermediate Energies,” Physical Review C 108, 034604 (2023), DOI: 10.1103/PhysRevC.108.034604.
[5] O. B. Tarasov, “Quantifying Uncertainty in Physics-Based Predictions of Rare-Isotope Production Cross Sections via Bayesian-Inspired Model Averaging Across Nuclear Mass Tables,” accepted for publication in Physical Review C, DOI: 10.1103/rd5c-4m5w.