부산대학교 도서관

Gamma-ray spectroscopy and lifetime measurements using the Doppler shift attenuation method (DSAM) were performed on the nucleus 28Mg near the N=20 "island of inversion," which was populated using a 12C(18O,2p)28Mg 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;4+1→2+1) 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. [ABSTRACT FROM AUTHOR]