Speaker
Description
The neutron dripline in oxygen isotopes presents a clear challenge and unique opportunity for studies of shell evolution and nuclear structure. The heaviest observed bound isotope of flourine (Z=9) has 22 neutrons, whereas oxygen -- with only one fewer proton, Z=8 -- can only bind 16 neutrons. This striking anomaly is a result of an increase in the spacing between the nu(d3/2) orbital and the nu(s1/2 d5/2) orbitals, which was only explained by the inclusion of three-body forces [1]. As such, measurements relating to the ν(d3/2) orbital in oxygen isotopes are of significant interest, in order to test our current models. Unfortunately, comprehensive spectroscopy close to the dripline is limited by the intensity and quality of radioactive isotope beams. In this work, we instead search for ν(d3/2) orbital occupation in the the high-energy states of a less-exotic isotope.
The single-neutron transfer reaction 19O(d,p)20O has been performed at GANIL using a high-quality radioactive beam of the near-stable isotope 19O [2]. This beam was impinged on a solid CD2 target (both with and without gold foil backing) and states up to and above the neutron separation energy were populated. The resulting 20O heavy recoil, ejected proton, and prompt gamma-ray emissions were detected using the state-of-the-art MUGAST+AGATA+VAMOS triple-coincidence experimental set-up. Bound states populated by s-wave and d-wave transfer have been identified, and angular distributions of at least three unbound states between 7.6 MeV and 9.0 MeV have been observed, accessed for the first time through the 19O(d,p) channel.
Notably, the success of the MUGAST+AGATA+VAMOS campaign is of particular relevance to the low-energy nuclear community due to the recent confirmation of a second campaign starting in 2029. Given the advancements in the AGATA and MUGAST/GRIT projects, it is projected that the second campaign will have much increased solid angule coverage -- 2pi in gamma-rays and 4pi in light charged particles.
[1] T. Otsuka et al. Phys. Rev. Lett. 105, 032501 (2010)
[2] I. Zanon et al. Phys. Rev. Lett. 131, 262501 (2023)
