Gamma-ray spectroscopy and lifetime measurements using the Doppler shift attenuation method (DSAM) were performed on the nucleus Mg28 near the N=20 "island of inversion," which was populated using a C12(O18,2p)Mg28 fusion-evaporation reaction to investigate the impact of shell evolution on its high-lying structure. Three new levels were identified at 7203(3), 7747(2), and 7929.3(12) keV along with several new gamma rays. A newly extracted B(E2;41+→21+) of 42(7) e2fm4 indicates reduced collectivity in the yrast band at high spin, consistent with ab initio symmetry adapted no-core shell model (SA-NCSM) calculations. At high excitation energy, evidence for the population of intruder orbitals was obtained through identification of negative parity levels [Iπ=(0,4)-, (4,5)-]. Calculations using the SDPF-MU interaction indicate that these levels arise from single neutron excitation to the pf shell and provides evidence for the lowering of these intruder orbitals approaching the island of inversion.
Publication Source (Journal or Book title)
Physical Review C
Williams, J., Ball, G., Chester, A., Domingo, T., Garnsworthy, A., Hackman, G., Henderson, J., Henderson, R., Krücken, R., Kumar, A., Launey, K., Measures, J., Paetkau, O., Park, J., Sargsyan, G., Smallcombe, J., Srivastava, P., Starosta, K., Svensson, C., Whitmore, K., & Williams, M. (2019). Structure of Mg 28 and influence of the neutron pf shell. Physical Review C, 100 (1) https://doi.org/10.1103/PhysRevC.100.014322