n_TOF: Measurements of Key Reactions of Interest to AGB Stars

Abstract

In the last 20 years, the neutron time-of-flight facility n_TOF at CERN has been providing relevant data for the astrophysical slow neutron capture process (s process). At n_TOF, neutron-induced radiative capture (n,γ) as well as (n,p) and (n,α) reaction cross sections are measured as a function of energy, using the time-of-flight method. Improved detection systems, innovative ideas and collaborations with other neutron facilities have lead to a considerable contribution of the n_TOF collaboration to studying the s process in asymptotic giant branch stars. Results have been reported for stable and radioactive samples, i.e., 24,25,26Mg,26Al, 33S, 54,57Fe, 58,59,62,63Ni, 70,72,73Ge, 90,91,92,93,94,96Zr, 139La, 140Ce, 147Pm, 151Sm, 154,155,157Gd, 171Tm, 186,187,188Os, 197Au, 203,204Tl, 204,206,207Pb and 209Bi isotopes, while others are being studied or planned to be studied in the near future. In this contribution, we present an overview of the most successful achievements, and an outlook of future challenging measurements, including ongoing detection system developments.

Advances and new ideas for neutron-capture astrophysics experiments at CERN n_TOF

“…The fundamental role of neutron-induced reactions in the formation of the heavy elements in the universe was already evident in 1948 [1,2,3,4], although it was probably the first observation of technetium in S-type stars [5] and the subsequent quantitative theory of nucleosynthesis [6,7], which triggered and guided an enormous experimental effort, that still prevails today [8,9,10,11,12,13,14]. This article describes some experimental developments primarily aimed at measuring nuclear data of interest for nucleosynthesis studies in hydrostatic stages of stellar evolution, namely asymptotic giant branch (AGB-) and massive-stars [10,15].…”

“…1). Following this logic, many neutron-capture experiments were made at n TOF over the last 20 years [13] and many more experiments on stable isotopes will follow in the coming years. The new measurements will benefit, not only from the enhanced accuracy approach described below in Sec.…”

“…As shown in Fig. 1 several s-process branching nuclei have been measured with high accuracy [10,13], but there is still a significant number of them that have not been accessed yet owing to limitations in state-of-the-art detection systems and sample-production capabilities. Sec.…”

Nuclear astrophysics activities at the n_TOF facility at CERN

“…So far, the n_TOF collaboration has provided nuclear data using the TOF method for a large number of intriguing physics cases (see for instance ref. [3] and references therein). In the near future, the effort will be on activation measurements as well.…”

NEAR: A New Station to Study Neutron-Induced Reactions of Astrophysical Interest at CERN-n_TOF

“…So far, cross-sections have been measured in both EAR1 and EAR2 experimental areas for more than a hundred reactions and the data have been successfully exploited in modelling stellar and primordial nucleosynthesis (see, for instance, refs. [4,5]).…”