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 quantum-state evolution across the major shell. In the present work, the negative parity states in ^39Cl are investigated through the \beta decay spectroscopy of ^39S. Newly observed \gamma 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 \gamma 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.