Quadrupole Collectivity in32,34,36,38Siand the

R. W. Ibbotson

¹

,

T. Glasmacher

²

,

B. A. Brown

³

et al.

Abstract

The b-unstable nuclei 32,34,36,38 Si have been produced by projectile fragmentation and studied by inbeam Coulomb excitation. Excited states at 1399 6 25 keV and 1084 6 20 keV have been identified for the first time in 36 Si and 38 Si, respectively, and tentatively assigned J p 2 1 . The B͑E2; 0 1 1 ! 2 1 1 ͒ values leading to these states and the previously identified 2 1 1 states in 32,34 Si have been measured, and are compared to shell model calculations. Our results indicate that the 2 1 1 state in 34 Si has a large fp-shell intruder component, and that the 2 1 1 states in the N . 20 silicon isotopes can be reproduced assuming an N 20 shell closure. [S0031-9007(98)

Ground-state configuration of neutron-rich Al35 via Coulomb breakup

“…That large deformation was explained by considering intruder effects which suggest a clear vanishing of the shell gap between the sd and pf shells around N = 20 [4]. Later, in many neutron-rich nuclei around N ∼ 20 and 28, large deviations in the nuclear structure from conventional shell models were observed [5][6][7][8][9][10][11]. These observation have been explained by considering tensor interactions, three-body interaction, etc.…”

“…[12]. Large quadrupole collectivity in 32,34,36,38 Si [10] indicates a large fp-shell intruder component in its 2 + 1 excited state. Recently, a p-wave halo structure was also observed in 31 Ne [8] and 37 Mg [9].…”

Tensor interaction in mean-field and density functional theory approaches to nuclear structure

“…[90], and concerns the tensor effect on the shape evolution of the Si isotopes. The basic questions in this case are: is the tensor-force-driven deformation present in other neutron-rich Si isotopes, especially 30 Si with a possible N = 16 subshell, since some models (e.g., the FRDM) predicted a spherical shape for this nuclei [91] while the large B(E2) value suggested its deformed nature [92]. For this purpose, the authors of Ref.…”

Properties of Intruder States in 34Al and 34Si

“…Despite limited statistics and the high level of background, the branching ratio for the decay of the 2 + 1 state to the 0 + 2 and 0 + 1 states has been extracted taking into account the gamma efficiencies and the relevant Si detector efficiencies : R(2 [16].…”

“…The sd → pf neutron excitations were not considered and therefore it was not possible up to now to describe nuclei in which these excitations are important, such as in the Island of Inversion. In order to account for this type of excitations, two ingredients have to be added : -i-the off-diagonal cross shell sd-p f matrix elements; they have been taken from the Lee-KahanaScott-G matrix [22] and scaled as for the description of the superdeformed states in 40 Ca [23] that are similarly built on multiparticles-multiholes excitations, -ii-the second ingredient are the neutron single particle energies for the sdpf shells on a core of 16 O. For the sd one, the standard USD [24] are used whereas for pf the choice was done in order to -i-reproduce the results of the previous SDPF interaction in the limit of no excitation and -ii-to reproduce the energy of the 0 …”