The higher-spin structure of 38 Cl (N = 21) was investigated following the 26 Mg( 14 C, pn) reaction at 30 and 37 MeV beam energies. The outgoing protons were detected in an E − ∆E Si telescope placed at 0 • close to the target with a Ta beam stopper between the target and telescope. Multiple γ rays were detected in time coincidence with the protons using an enhanced version of the FSU γ detection array. The level scheme was extended up to 8420 keV with a likely spin of 10 . A new multishell interaction was developed guided by the experimental information. This FSU interaction was built by fitting to the energies of 270 experimental states from 13 C to 51 Ti. Calculations using the FSU interaction reproduce observed properties of 38 Cl rather well, including the spectroscopic factors. The interaction has been successfully used to interpret the 1p1h and 2p2h configurations in some nearby nuclei as well. I. INTRODUCTIONThe evolution of shell structures, specially with increasing proton-neutron imbalance, can provide valuable insights into the finite many-body problem. The exploration of an exotic region in the chart of nuclides with extreme N/Z ratios, the so called "island of inversion" region, has cast doubt on the persistence of the classical magic numbers and revealed the fragility of the shell gaps that lead to the magic numbers. The nuclei with Z = 10 ∼ 12 and N ≈ 20 have been found to have ground states dominated by the intruder configurations from the upper f p shell orbitals [1-6] and the anomalous property was interpreted as the reduction of the N = 20 shell gap. The immediate question emerged after the revelation of the shell gap reduction was how does this change happen along an isotopic or isotonic chain.Explaining this trend of shell evolution or structural evolution has been a great challenge to the nuclear structure models. The monopole parts of the shell model Hamiltonian have long been recognized to play the major role in the evolution of shell structure. While some models [7,8] are very successful in explaining the very neutron rich sd shell isotopes, they were unable to explain the intruder states of some nuclei within the same isotopic chain [9], or simply some other sd nuclei which are not even very neutron rich [10]; meaning that their monopoles are not well determined to explain the shell gap evolution. This demonstrates the need of a more comprehensive shell model treatment for the intruder states of the sd-shell nuclei which are sensitive to the shell gaps and, hence, very informative to describe the shell gap evolution.The current experimental investigation focuses on the structure of moderately neutron rich 38 Cl with Z = 17 and N = 21 having the valence protons in the sd shell and one valence neutron within the f p shell. Both normal and intruder states of 38 Cl are valuable to understand the N = 20 shell gap evolution. This nucleus has long been recognized as providing a window into the interactions between π0d 3/2 and νf 7/2 nucleons, since the first 4 states (2 − , 5 − , 3 − , and 4 ...

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New half-lives for exotic isotopes approaching the neutron drip-line in the vicinity of N ∼ 28 for Z = 12 − 15 were measured at the Facility for Rare Isotope Beams with the FRIB Decay Station initiator. The first experimental results are compared to the latest quasi-particle random phase approximation (QRPA) and shell model (SM) calculations. Overall, the measured half-lives are consistent with the available theoretical descriptions and suggest a well-developed region of deformation below 48 Ca in the N =28 isotones. The erosion of the Z=14 sub-shell closure in Si is experimentally confirmed at N =28, and a reduction in the 38 Mg half-life is observed as compared to its isotopic neighbors, which does not seem to be predicted well based on the decay energy and deformation trends. This highlights the need for both additional data in this very exotic region, and for more advanced theoretical efforts.

High-spin states in 39 Ar were populated using the 27 Al(14 C, pn) reaction at 25.6 MeV. The deexciting γ rays were measured with the FSU γ detector array along with evaporation protons in a Si E-∆E telescope. The known high-spin level scheme was extended up to over 11 MeV with a dozen new levels above the neutron decay threshold. The decay pattern appears somewhat atypical for heavy-ion fusion-evaporation reactions. The structure of 39 Ar is discussed in terms of the new FSU cross-shell spsdpf interaction fitted to a wide range of nuclei. This interaction has proved quite successful in accounting for the level scheme of 39 Ar, including the previously suggested fully aligned πf 7/2 ⊗ νf 7/2 17/2 + state and previously discovered analogs of the lowest states in 39 Cl.

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