Identification of the crossing point at N=21 between normal and intruder configurations

Abstract

The β − decay of 34 Mg was used to study the 34 Al nucleus through γ spectroscopy at the Isotope Separator On-Line facility of CERN. Previous studies identified two 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. Their unknown ordering and relative energy have been the subject of debate for the placement of 34 Al inside or outside the N = 20 "island of inversion." We report here that the 1 + intruder lies only 46.6 keV above the 4 − ground state. In addition, a new half-life of T 1/2 = 44.9(4) ms, that is twice as long as the previously measured 20(10) ms, has been determined for 34 Mg. Large-scale shell-model calculations with the recently developed SDPF-U-MIX interaction are compared with the new data and used to interpret the mechanisms at play at the very border of the N = 20 island of inversion.

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

“…The density of states of such nuclei is high. Recently, a level scheme of excited states of 34 Al [40] was proposed from the β-decay studies of 34 Mg. With knowledge of the excited states of 34 Al from the literature, a detailed GEANT4 simulation was performed to understand the the sum-energy spectrum obtained from the present experiment. The detection efficiency of the sum-energy spectrum using the Crystal Ball spectrometer under experimental conditions was obtained.…”

“…A primary beam of 40 Ar (531A MeV), delivered by the Heavy Ion Synchrotron (SIS18) at GSI (Helmholtzzentrum für Schwerionenforschung GmbH), Darmstadt was fragmented, and a group of short lived radioactive isotopes ( 29-31 Na, [31][32][33] Mg, 34,35 Al, etc.) with similar mass-to-charge ratio (A/Z between 2.55 to 2.85) were separated by the FRagment Separator (FRS) [32] according to their magnetic rigidity.…”

“…In this respect, 35 Al would be an interesting nucleus to explore. In 1979 Simons et al [13] first identified the neutron-rich nucleus 35 Al produced in fragmentation of 40 Ar. Four decades later, except for some theoretical calculations [14][15][16][17][18], limited experimental information regarding the ground-state configuration of 35 Al is available.…”

Normal and intruder configurations in Si34 populated in the β− decay of Mg34Lică1, Rotaru2, Borge3 et al. 2019Phys. Rev. CSelf Cite14170View full textAdd to dashboardCite

“…1(a), is the same as the one briefly described in Ref. [28]. It represents the high β-γ efficiency configuration of IDS.…”

“…Indeed, it was observed in Ref. [28] that more than 99% of the β decay of 34 Mg (T 1/2 = 44.9(4) ms) proceeds through the 1 + isomeric state of 34 Al, which subsequently populates mainly the low-spin positive parity states in 34 Si. As for the 34 Al beam, 89(3)% of ground (4 − , T 1/2 = 53.73(13) ms) and 11(3)% of isomeric (1 + , T 1/2 = 22.1(2) ms) state were deduced from transitions in 34 Si decaying from high-spin states (e.g.…”