title: Measurement of the spin and magnetic moment of 31Mg: evidence for a strongly deformed intruder ground state.
abstract: Unambiguous values of the spin and magnetic moment of 31Mg are obtained by combining the results of a hyperfine-structure measurement and a beta-NMR measurement, both performed with an optically polarized ion beam. With a measured nuclear g factor and spin I=1/2, the magnetic moment mu(31Mg)=-0.88355(15)mu(N) is deduced. A revised level scheme of 31Mg (Z=12, N=19) with ground state spin/parity I(pi)=1/2(+) is presented, revealing the coexistence of 1p-1h and 2p-2h intruder states below 500 keV. Advanced shell-model calculations and the Nilsson model suggest that the I(pi)=1/2(+) ground state is a strongly prolate deformed intruder state. This result plays a key role for the understanding of nuclear structure changes due to the disappearance of the N=20 shell gap in neutron-rich nuclei.
authors.affiliation: Instituut voor Kern- en Stralingsfysica, Katholieke Universiteit Leuven, B-3001 Leuven, Belgium.
authors.forename: G
authors.initials: G
authors.lastname: Neyens
authors.forename: M
authors.initials: M
authors.lastname: Kowalska
authors.forename: D
authors.initials: D
authors.lastname: Yordanov
authors.forename: K
authors.initials: K
authors.lastname: Blaum
authors.forename: P
authors.initials: P
authors.lastname: Himpe
authors.forename: P
authors.initials: P
authors.lastname: Lievens
authors.forename: S
authors.initials: S
authors.lastname: Mallion
authors.forename: R
authors.initials: R
authors.lastname: Neugart
authors.forename: N
authors.initials: N
authors.lastname: Vermeulen
authors.forename: Y
authors.initials: Y
authors.lastname: Utsuno
authors.forename: T
authors.initials: T
authors.lastname: Otsuka