Normal and intruder configurations in Si34 populated in the β− decay of Mg34

Abstract

The structure of 34 Si was studied through γ spectroscopy separately in the β − decays of 34 Mg and 34 Al at the ISOLDE facility of CERN. Different configurations in 34 Si were populated independently from the two recently identified β-decaying states in 34 Al having spin-parity assignments J π = 4 − dominated by the normal configuration π(d 5/2 ) −1 ⊗ ν(f 7/2 ) and J π = 1 + by the intruder configuration π(d 5/2 ) −1 ⊗ ν(d 3/2 ) −1 (f 7/2 ) 2 . The paper reports on spectroscopic properties of 34 Si such as an extended level scheme, spin and parity assignments based on log(f t) values and γ-ray branching ratios, absolute β feeding intensities and neutron emission probabilities. A total of 11 newly identified levels and 26 transitions were added to the previously known level scheme of 34 Si. Large scale shell-model calculations using the sdpf-u-mix interaction, able to treat higher order intruder configurations, are compared with the new results and conclusions are drawn concerning the predictive power of sdpf-u-mix, the N = 20 shell gap, the level of mixing between normal and intruder configurations for the 0 + 1 , 0 + 2 and 2 + 1 states and the absence of triaxial deformation in 34 Si.

In-beam $γ$-ray spectroscopy of $^{32}$Mg via direct reactions

“…While the locations of negative-parity states down to 34 Si were discussed previously in Ref. [83], the present work established the lowest firmly-assigned negative-parity state in 32 Mg at 2858 keV, further extending the systematics. It can be seen that the lowest negative-parity states remain around 4 MeV from 40 Ca to 34 Si, but at 32 Mg it suddenly drops by 1.4 MeV.…”

“…Level systematics of the N = 20 isotones. The levels in32 Mg are taken from the present work, while those in34 Si are from Ref [83]…”

Structure of Si33 and the magicity of the N=20 gap at Z=14Jongile1, Lemasson2, Sorlin3 et al. 2020Phys. Rev. CSelf Cite10030View full textAdd to dashboardCite

“…The resulting experimental cross section is 111 ± 7 mb. With the calculated inclusive knockout cross section, from Table II, of σ inc th =125 mb, we obtain R s = 0.89 (6), which is consistent with the systematics for other systems [32]. The overall effective neutron separation energy, derived by weighting the separation energy to each bound shell-model final state by its partial cross section, is 9.07 MeV, and hence the neutron-proton separation energy asymmetry [33] is ∆S = −9.71 MeV.…”

“…It has the properties of a spherical, doubly-magic nucleus, e.g. a high 2 + 1 energy at 3325 keV and the tentative spherical 2 + state at an even higher energy of 5348 keV [5,6], a low B(E2; 0 + 1 → 2 + 1 ) value [7], and a drop in the neutron separation energy (S n ) beyond N = 20 by about 5 MeV [8]. Its N = 20 gap was corroborated by the energy of the 4 − , 5 − states [6].…”

“…For example, the nearby 34 Al nucleus has ground and intruder configurations separated by only 46.6 keV [9]. It follows that deformed configurations, shape coexistence [6,10], and possibly triaxial shapes were predicted [11] and searched for [6,12,13] in the properties of the first few excited states of 34 Si. The abrupt transition from the closed-shell ground state of 34 Si to the intruder-dominated ground state of 32 Mg [14][15][16], with only two protons removed from the 0d 5/2 orbit, is attributed to the subtle balance between the magnitude of the proton and neutron shell gaps that prevent nuclear excitations and the pairing and quadrupole correlations that scale with the amount of particle-hole excitations across these gaps.…”