Constraining the neutron capture reaction on Zr isotopes for astrophysical processes

Understanding the origin of the elements in the universe is one of the major challenges in nuclear science. Most elements heavier than iron are made in neutron capture processes in environments such as asymptotic giant branch stars, core-collapse supernovas, and neutron-star mergers. Therefore, neutron capture reaction rates play an important role in explaining the abundance pattern of elements. However, the involved nuclei are often short-lived, and no experimental neutron capture reaction data exists. For this reason, indirect techniques to constrain the neutron capture reaction rates have been developed. One of the quantities needed to constrain neutron-capture reactions is the gamma-ray strength function, i.e. the probability of the nucleus to emit a gamma ray of particular energy and multipolarity. A low-energy enhancement (LEE) in gamma-ray strength function was observed in many isotopes along the nuclear chart, with a significant impact on the neutron-capture reaction rate. It remains unclear which isotopes should be expected to have this LEE and how strong it should be. The present work focuses on the evolution of the LEE in neutron-rich Zr isotopes and its impact on the neutron-capture reaction rate. The experiment was done at Argonne National Lab using the SuN Detector.