Speaker
Description
Almost all elements heavier than iron are primarily produced through
the slow s- and rapid r- neutron-capture processes, which contribute about 50% each to the observed abundances [1]. The s-process, branching-point nuclei such as 192Ir play a crucial role, as neutron capture competes with β-decay affecting nucleosynthesis.
In this study, the $^{192}\mathrm{Ir}(n,\gamma)^{193}Ir$ and $^{193}\mathrm{Ir}(n,\gamma)^{194}\mathrm{Ir}$ reactions were investigated indirectly using data from the Oslo Cyclotron Laboratory. The $^{193,194}\mathrm{Ir}$ nuclei were populated via the $^{192}\mathrm{Os}(\alpha,t\gamma)$ and $^{192}\mathrm{Os}(\alpha,d\gamma)$ reactions. Due to the instability of 192Ir, its neutron-capture cross section cannot be measured directly. Instead, nuclear level densities and γ-ray strength functions were extracted using the Oslo Method [2] and used as input to the TALYS reaction code to calculate neutron-capture cross sections and Maxwellian-averaged cross sections (MACS). The $^{193}\mathrm{Ir}(n,\gamma)$ reaction results were compared to existing data for benchmark purposes [3].
The resulting $^{193}\mathrm{Ir}$ MACS values were implemented in the STAREVOL stellar evolution code [4] to assess their impact on the s-only isotope $^{192}\mathrm{Pt}$.
The results show that a reduced $^{192}\mathrm{Ir}(n,\gamma)$ reaction probability enhances β-decay branching, increasing the production of $^{192}\mathrm{Pt}$. Overall, the experimentally constrained data reduced the nuclear-physics uncertainty in the predicted $^{192}\mathrm{Pt}$ abundance by approximately 20%, providing improved
constraints for s-process nucleosynthesis models. In the workshop final
results of this study will be presented.
[1] Arnould, M., Goriely, S., and Takahashi, K. 2007.
[2] Schiller, A. et al. 2000.
[3] Zerkin, V. V., and Pritychenko, B. 2018
[4] L. Siess, E. Dufour, M. Forestini. 2000
This work is based on research supported in part by the National Re-
search Foundation of South Africa (Grant Number:PMDS22070734847),
SAINTS Prestigious Doctoral Scholarship, U.S. Department of Energy,
Office of Science, Office of Nuclear Physics under Contract No. DE-AC02-
05CH11231 and the SARChI under grant No REP-SARC180529336567.