Negative Parity States in ³⁹Cl Configured by Crossing Major Shell Orbits

Traditional "magic numbers" were once regarded as immutable throughout the nuclear chart. However, unexpected changes were found for unstable nuclei around N = 20. With both proton and neutron numbers around the magic number of 20, the neutron-rich ³⁹Cl isotope provides a good test case for the study of the quantumstate evolution across the major shell. In the present work, the negative parity states in ³⁹Cl are investigated through the β decay spectroscopy of ³⁹S. Newly observed γ transitions together with a new state are assigned into the level scheme of ³⁹Cl. The spin parity of 5/2^- for the lowest negative parity state in ³⁹Cl is reconfirmed using the combined γ transition information. These systematic observations of the negative parity states in ³⁹Cl allow a comprehensive comparison with the theoretical descriptions. The lowest 5/2^- state in ³⁹Cl remains exotic in terms of comparisons with existing theoretical calculations and with the neighboring isotopes having similar single-particle configurations. Further experimental and theoretical investigations are suggested.