First observation of an excited state in the neutron-rich nucleus31Na

Abstract

The first excited state in the neutron-rich Nϭ20 isotope 31 Na was observed at 350͑20͒ keV via intermediate energy heavy-ion scattering, which is dominated by the Coulomb excitation mechanism. This state appears to be a rotational excitation built on a strongly deformed ground state. The yield of the ␥ ray deexciting this state can be reproduced by a shell model calculation which takes ( f 7/2 ,p 3/2 ) intruder configurations into account.

Direct experimental evidence for a multiparticle-hole ground state configuration of deformedMg33

“…Later a similar observation was also reported for 33 Mg [3]. The onsets of deformations in the nuclei 32 Mg [4], 31 Na [5], and 30 Ne [7] at N = 20 shell closure were also observed. These phenomena were proposed to originate due to substantial contributions from so-called intruder pf configurations over the normal sd shell in the ground state wave functions.…”

“…The observation of the breakdown of traditional magic numbers [1] in exotic nuclei far from the β-stability line has been an important issue in nuclear structure physics and significant effort has been put into both experimental investigations [2][3][4][5][6][7][8][9][10][11][12] and theoretical studies [13][14][15][16]. The first observation of the disappearance of the so-called magic number was reported by Thibault et al [2], based on mass measurements of the neutron-rich 31,32 Na isotopes [2].…”

Correlations beyond the mean field in magnesium isotopes: angular momentum projection and configuration mixing

“…In addition, the low excitation energy of the first 2 + 1 excited state [15,16] in 32 Mg and the ratio E(4 + )/E(2 + ) = 2.6 are consistent with the expectations for a rotational state. Recently, evidence for a rotational band in 31 Na has also been obtained [17]. Although indirect, another evidence for the deformed nature of the 32 Mg ground state comes from the strong ground state deformation of 34 Mg inferred from the large value of the B(E2, 0 + 1 → 2 + 1 ) transition probability measured [18] in this nucleus and the E(4 + )/E(2 + ) ratio of 3.18 [19,20] which is very close to the rotational limit.…”

Single-neutron knockout from intermediate energy beams ofMg30,32: Mapping the transition into the “island of inversion”

“…Subsequent observations revealed a region of deformation around the N = 20 isotones with Z 12 [2][3][4][5][6][7][8][9]. Shell-model calculations performed for a broad range of nuclei in this vicinity indicate that two-particle-two-hole (2p-2h) configurations across the N = 20 shell gap are lower in energy than normal configurations for nuclei with 20 N 22 and 10 Z 12, illustrated in Fig.…”