title: Gamma-ray spectroscopy of neutron-rich scandium isotopes
Creators: name: Zidarova, Radostina
Publisher: name: UNSPECIFIED
Year: 2025

description: With the advances in radioactive isotope science, nuclei far from the valley of beta-stability have become available for nuclear physics experiments. Data on exotic nuclei obtained in the last decades report on the interesting phenomena taking place at the edges of the nuclear chart. The standard magic numbers - 2, 8, 20, 28, 50, 82, and 126, known from the nuclear shell model, appear to not be uniform and can weaken and disappear, while new neutron and proton numbers obtain magic character. An example is the appearance of the neutron N = 32 and N = 34 magic numbers in the calcium isotopes. The establishment of magicity includes a series of experiments such as measurements of excited state energies, reduced transition probabilities, masses and
cross sections. The region around calcium has been extensively investigated in the last decade implementing all mentioned techniques, and others, in order to determine the persistence of the new magic numbers. While the N = 32 subshell closure has been confirmed both below and above calcium, the N = 34 subshell closure seems to disappear when protons are added to ^{54]Ca. The N = 34 isotope of scandium, with one proton more than calcium, makes a perfect ground to test the shell evolution in the pf -shell. Towards the neutron rich side, scandium is approaching the N = 40 island of inversion, IoI, which is characterized by increased deformation and energetically-favoured intruder configurations in the ground states. In light of recent results on neutron-rich N = 36, 38 Ca isotopes, information on the scandium isotones will bring more understanding to the limits of the IoI. The Shell Evolution And Search for Two-plus energies At RIBF project, known as SEASTAR, aims at a systematic investigation of the neutron-rich edge of the nuclear chart, including the nuclei around the new magic numbers N = 32, 34, as well as the N = 40 Island of Inversion. The third SEASTAR campaign took place in 2017 at RIKEN-RIBF and produced the data on the N = 34 isotope of scandium, as well as the first spectroscopy of the ^{57,59}Sc, which will be presented in this work. The primary beam of ^{70}Zn was accelerated to 345 MeV/u and impinged on a ^{9}Be target, producing a beam of fission reaction products. The neutron-rich radioactive isotopes were selected and identified on an event-by-event basis in the BigRIPS fragment separator. A second target of liquid hydrogen was used to induce knockout reactions, while the surrounding Time Projection Chamber allowed for precise reaction vertex determination. In this way a good Doppler correction of the detected gamma-rays was achieved. The DALI2^{+} array was used for the γ-ray detection. The
outgoing fragments were identified using the SAMURAI magnet.
The neutron-rich ^{55,57,59}Sc isotopes were investigated via in-beam gamma-ray spectroscopy following direct and indirect proton and neutron removal reactions, as well as inelastic scattering. For all three isotopes level schemes were build. In the case of ^{55}Sc the obtained level scheme was compared to the one reported in literature. All level schemes were compared to state-of-the-art shell model calculations. The A3DA and SDPF-MUr interactions were implemented, which have been successfully used for the description of nuclei in the same region.