Identification of MNT fragments produced by an energy-degraded 238 U beam on a 209 Bi target at the FRS Ion Catcher

An experiment on multi-nucleon transfer (MNT) reactions was performed at the FRS Ion Catcher at GSI-FAIR, where an energy-degraded ²³⁸U beam reacted with a ²⁰⁹Bi target inside the Cryogenic Stopping Cell (CSC). Target-like fragments (TLF) produced in the CSC were extracted and identified using a Multiple-Reflection Time-of-Flight Mass Spectrometer (MR-TOF-MS). The yields of eight mass-identified A = 210 and A = 211 nuclei were analyzed as a function of degrader thickness, which determines the incoming ²³⁸U beam energy, by comparing their dependence on degrader thickness with that of elastic-scattering products. The results indicated that they are produced in MNT reactions. This experiment is the first in which a broad range of MNT fragments was observed in an ion catcher following beam energy degradation from the relativistic realm to the MNT range, just above the Coulomb barrier. It sets the stage for further MNT experiments that are planned at the FRS Ion Catcher with different targets and unstable secondary ion beams.