Speaker
Description
Measurements of independent isotopic fission yields (IIFYs) provide access to the underlying probability distribution of products resulting from fission. The knowledge of IIFY distributions contributes to our understanding of the nuclear fission process in more depth with respect to mass yield distributions. A better understating of the fission process has wide implications, including the abundance of elements through nucleosynthesis, nuclear structure and reactions, and nuclear waste management and safety [1].
We will present the first results of a novel method for measuring IIFYs of 252Cf spontaneous fission (SF) via direct mass measurements [2], at the FRS Ion Catcher (FRS-IC) at GSI, Germany [3]. Fission products were generated from a 252Cf source that was installed inside the cryogenic stopping cell (CSC) [4], and were identified and counted with the multiple-reflection time-of-flight mass spectrometer (MR-TOF-MS) [5] of the FRS-IC, utilizing well-established measurement and data analysis methods [6]. The high performance of the MR-TOF-MS can resolve isobars unambiguously, even with limited statistics. The non-scanning nature of the MR-TOF-MS ensures minimal relative systematic uncertainties in IIFY amongst fission products.
Our high-accuracy mass results constitute by themselves new important data, as they include first (or first direct) mass measurements at the N≈90 and Z=56-62 region. We compare our results to existing data of indirect measurements and to the Atomic Mass Evaluation 2020 (AME2020) [7].
The analysis for extracting IIFYs includes isotope-dependent efficiency corrections for all components of the FRS-IC. In particular, we applied a self-consistent technique that takes into account the element- dependent survival efficiencies in the CSC, due to chemical reactions with the buffer gas.
Our IFY results, which cover several tens of fission products in the less-accessible high-mass peak down to fission yields at the level of 10-5, are generally similar to those of the NuDat 2 database [8]. Nevertheless, they reveal some structures that are not observed in the database smooth trends.
These are the first results of a planned campaign to investigate IIFY distributions of spontaneous fission at the FRS-IC. Upcoming experiments will extend our results to wider Z and N ranges, lower fission yields, and other spontaneously-fissioning actinides.
References:
[1] Dimitriou, P., Hambsch, F.-J., & Pomp, S. (2016). Fission Product Yields Data: Current status and perspectives Summary Report of an IAEA Technical Meeting (INDC(NDS)--0713). International Atomic Energy Agency (IAEA)
[2] Mardor et al., EPJ Web of Conferences 239, 02004 (2020)
[3] W. R. Plass et al., Nucl. Inst. Meth. B 317, 457 (2013)
[4] M. Ranjan et al., Nucl. Inst. Meth. A 770, 87 (2015)
[5] T. Dickel et al., Nucl. Inst. Meth. A 777, 172 (2015)
[6] S. Ayet San Andres et al., Phys. Rev. C 99, 064313 (2019)
[7] M. Wang et al., Chinese Phys. C 45 030003 (2021)
[8] National Nuclear Data Center, information extracted from the NuDat 2 database, https://www.nndc.bnl.gov/nudat2/