Dr Connor O'Shea
About
Biography
Dr. Connor O’Shea is a Post-doctoral Research Fellow in Nuclear Astrophysics in the School of Mathematics and Physics at the University of Surrey. His research focuses on the study of exotic nuclei relevant to explosive stellar environments, with particular emphasis on understanding the nuclear structure and reactions that govern the synthesis of elements in stars. Dr. O’Shea has extensive experimental experience at international facilities across the world, including FRIB and Argonne National Laboratory in the USA, TRIUMF in Canada, and CERN in Switzerland. His work combines gamma-ray spectroscopy with nuclear reaction techniques, including fusion-evaporation and nucleon-transfer reactions, to investigate proton-rich nuclei and constrain astrophysical reaction rates.
Areas of specialism
Publications
Recent models of the rapid proton (rp) capture process indicate that a competition between the 59Cu(p, gamma)60Zn and 59Cu(p, alpha)56Ni reactions may result in the formation of a nickel-copper (NiCu) cycle that traps the flux of material between 56Ni and 60Zn. Here, we report the identification of 15 proton-unbound levels in 60Zn, populated via 59Cu(d, n) transfer, which govern the rate of the 59Cu(p, gamma)60Zn reaction in XRBs. Precise excitation energies for levels in 60Zn were obtained from observed gamma decays, and spectroscopic factors were determined from angle-integrated cross sections. Incorporating these results into stellar-model calculations, we find that with experimentally constrained uncertainties a NiCu cycle in XRBs is indeed possible, though we limit its branching strength to less than 38%. While modest, such a branching has significant impact on the light curve, motivating further studies of the relevant rates. Our calculations also indicate that a significant NiCu cycle leads to an increase in the amount of odd-A nuclei in the burst ashes, which may affect Urca cooling processes in neutron star crusts.
The observation of active Ti-44 in supernova remnants offers the potential to solve one of the most debated questions in modern astrophysics, the exact underlying explosion mechanism of core collapse supernovae (CCSNe). In particular, a comparison between the predicted synthesized yield of Ti-44 and the ejected flux is expected to allow for a determination of the mass cut of the star. Unfortunately, such comparisons are currently severely hindered by large uncertainties in the nuclear reactions governing the production and destruction of Ti-44. On this note, the astrophysical V-45(p, gamma)Cr-46 reaction is expected to play a decisive role. We present the first experimental information on resonant states in the V-45(p, gamma)Cr-46 reaction. Excitation energies have been measured with high precision for ten previously unknown, low-spin, proton-unbound states in Cr-46, and spin-parity-assignment constraints have been made using observed gamma-decay patterns and shell-model calculations. We find that an l = 1 resonance at 714 keV dominates the V-45(p, gamma)Cr-46 reaction for the entire temperature range of alpha-rich freezeout. Moreover, the nominal rate is found to be similar to 25-50% of previous estimates for T > 1.2 GK, indicating an increase in Ti-44 production in CCSNe of similar to 20-35%.