Extending Progress in Multi-Step Abrasion Reaction Mechanisms

A major objective of rare isotope beam facilities is the exploration of unstable isotopes far from stability, characterized by extreme proton-to-neutron ratios and short lifetimes. Production probabilities for these exotic nuclei are extremely low, a challenge addressed through the use of high-power accelerators. Recent experimental results from RIKEN [1–3], focused on the search for new isotopes, have measured production cross sections that significantly exceed predictions from the LISE⁺⁺ Abrasion-Fission 3EER model [4], particularly in the more neutron-rich regions. These findings underscore the need for a substantial revision of Abrasion-Fission models (3EER and IFN [5]) for neutron-rich rare-earth isotope production and suggest a notable contribution from multi-step reactions.

Updates to the LISE models incorporating dedicated multi-step reaction analyses are presented and compared with experimental in-flight fission data. The impact of multi-step processes is discussed both for in-flight fission and for projectile fragmentation of a ⁴⁸Ca beam, in the context of recent FRIB results. The analysis is conducted using the latest LISE⁺⁺ framework, which extends the Abrasion-Ablation model to include secondary reaction steps. The potential of using new differential binding energy (dBE) systematics [6] to extract multi-step reaction factors is introduced.