Speakers
Description
The slow neutron capture ($s$-) process is responsible for the formation of half of the elements heavier than iron in the Universe. Despite the long time scale of this process, the long half-life of some isotopes throughout the $s$-process reaction flow creates branching points that lead to the division of the nucleosynthesis path. ${79}$Se ($t_{1/2} = 3.27 \times 10^5$ y [1]) represents one of the most relevant and debated s-branching nuclei [2] for two main reasons. On the one hand, the existence of quantum states in ${79}$Se, whose population varies with temperature, makes the s-process path sensitive to temperature. On the other hand, the observed abundances of the s-only isotopes of krypton (${80,82}$Kr) are very well-known from meteoric data. Thus, by comparing these abundances with those predicted by stellar models, information about the thermal conditions of the stellar media in which the $s$-process occurs can be obtained. To this aim hydrodynamic stellar models need experimental data on the neutron capture cross section of all isotopes involved in the branching.
In this context, we have measured the neutron capture cross section of ${80}$Se at CERN n_TOF, with very high energy resolution for the first time [3]. Although there is a previous measurement on of ${80}$Se(n,$\gamma$) [4], it suffers from a very limited energy resolution and a short neutron-energy range, as it can be appreciated in Fig. 1. These drawbacks have been remarkably improved in this time-of-flight measurement that covers the entire energy range of astrophysical interest between 1 eV and 100 keV. One hundred and thirteen resonances have been characterized, ninety-eight of them for the first time. The impact is sizable, being the MACS at kT = 8 keV 36\% smaller than the recommended value in KADoNiS [5]. In this work we present final results together with a discussion of their astrophysical implications.
[1] G. Jörg et al., Applied Radiation and Isotopes, 68(12):2339–2351, 2010.
[2] F. Kappeler et al., Reports on Progress in Physics, 52(8):945–1013, August 1989.
[3] V. Babiano-Suárez et al., CERN-INTC-2018-005, INTC-P-536, 2018.
[4] G. Walter et al., Astron. Astrophysic, 167:186-199, 1986.
[5] I. Dillmann et al., Nuclear Data Sheets, 120:171–174, 2014.
