Speaker
Description
In neutron-rich astrophysical environments, independent isotopic fission yields (IIFYs) of heavy progenitors are fundamental for shaping the r-process abundance pattern, as they directly determine the isotopic distribution in the rare-earth and second-peak regions via fission recycling. Since experimental data for heavy fissioning systems relevant to the r-process are largely unavailable, theoretical models are required, making experimental benchmarks essential.
We present results from a novel broadband method for measuring IIFYs through direct mass measurements using the Multiple-Reflection Time-of-Flight Mass Spectrometer (MR-TOF-MS) at the FRS Ion Catcher (FRS-IC) at GSI. Fission products from a $^{252}$Cf spontaneous fission source are thermalised in a cryogenic stopping cell and transported to the MR-TOF-MS, where they are identified and counted with high mass resolving power. The non-scanning, broadband nature of the technique reduces relative systematic uncertainties between isotopes, while element-dependent efficiencies are addressed using a self-consistent Monte Carlo approach benchmarked against known mass fission yields.
We report results for 60 IIFYs in the heavy-mass region (Z = 56-63), including 34 first-time measurements, with sensitivities down to 10$^{-4}$. The results generally agree with previous measurements where available, but reveal systematic deviations from evaluated data libraries and theoretical models. These findings provide new experimental constraints for fission-yield models and evaluations. Future measurements of $^{254}$Cf, together with the present $^{252}$Cf results, will provide additional constraints on fission-yield models in a region of particular relevance for fission recycling in r-process nucleosynthesis.