7 research outputs found
Isospin symmetry in B(E2) values: Coulomb excitation study of Mg-21
The ~=~ nucleus Mg has been studied by Coulomb
excitation on Pt and Pd targets. A 205.6(1)-keV
-ray transition resulting from the Coulomb excitation of the
ground state to the first excited state in
Mg was observed for the first time. Coulomb excitation cross-section
measurements with both targets and a measurement of the half-life of the
state yield an adopted value of
~=~13.3(4)~W.u. A new excited
state at 1672(1)~keV with tentative assignment was also
identified in Mg. This work demonstrates large difference of the
values between
~=~, ~=~21 mirror nuclei. The difference is investigated in
the shell-model framework employing both isospin conserving and breaking USD
interactions and using modern \textsl{ab initio} nuclear structure
calculations, which have recently become applicable in the shell.Comment: 8 pages, 6 figures, submitted to Phys. Rev. C, Rapid Communicatio
Structure of Mg-28 and influence of the neutron pf shell
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+â21+) 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 [IÏ=(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