In stellar environments neutron capture reactions produce 99% of all elements heavier than iron via the so-called s- (slow) and r- (rapid) process. Neutron capture cross sections are the key variables to model these astrophysical processes. Neutron activations with energies of tens of keV, simulating stellar conditions in the laboratory, and subsequent measurements of the reaction products by accelerator mass spectrometry (AMS) can be used to determine these cross sections. AMS, an ultrasensitive technique for the determination of isotopic ratios, is the method of choice for characterising reactions resulting in long-lived radionuclides (kyr‑Myr) and thus complements on-line (in-beam) measurements of the reaction products. The main challenges in AMS measurements are interferences from stable isobars. The high energies achievable with the ANU Heavy Ion Accelerator (>200 MeV) are ideal to tackle these difficulties, also for isotopes in the most challenging intermediate mass region (m >50).

This presentation will focus on new nucleosynthesis studies of the intermediate mass nuclide ⁹²Zr, which is one of the matching points between two components of the s-process, taking part in different stellar environments, and the “neutron poison” ³⁵Cl, which due to its relatively high abundance may have an impact on the total neutron budget in stars.

Dr Stefan Pavetich received his PhD in Physics from the Technical University of Dresden. His PhD work focused on ion source development for Accelerator Mass Spectrometry and was conducted at the Helmholtz-Zentrum Dresden-Rossendorf. Currently, he is a Postdoctoral Fellow in the Department of Nuclear Physics at the ANU investigating neutron -, proton - and alpha capture reactions relevant for nucleosynthesis in stellar environments. He has participated in interdisciplinary studies using AMS including reconstruction of irradiation histories of meteorites and groundwater modelling in arid regions in Israel and Oman.