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

R. Lică , F. Rotaru , M.J.G. Borge , S. Grévy (1, 2) , F. Negoiţă , A. Poves , O. Sorlin (1) , A.N. Andreyev , R. Borcea , C. Costache , H. de Witte , L.M. Fraile , P.T. Greenlees , M. Huyse , A. Ionescu , S. Kisyov , J. Konki , I. Lazarus , M. Madurga , N. Mărginean , R. Mărginean , C. Mihai , R.E. Mihai , A. Negret , R.D. Page , J. Pakarinen , S. Pascu , V. Pucknell , P. Rahkila , E. Rapisarda , A. Şerban , C.O. Sotty , L. Stan , M. Stănoiu , O. Tengblad , A. Turturică , P. van Duppen , R. Wadsworth , N. Warr

1 GANIL - Grand Accélérateur National d'Ions Lourds
2 CENBG - Centre d'Etudes Nucléaires de Bordeaux Gradignan

The β− decay of Mg34 was used to study the Al34 nucleus through γ spectroscopy at the Isotope Separator On-Line facility of CERN. Previous studies identified two β-decaying states in Al34 having spin-parity assignments Jπ=4− dominated by the normal configuration π(d5/2)−1⊗ν(f7/2) and Jπ=1+ by the intruder configuration π(d5/2)−1⊗ν(d3/2)−1(f7/2)2. Their unknown ordering and relative energy have been the subject of debate for the placement of Al34 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 T1/2=44.9(4)ms, that is twice as long as the previously measured 20(10) ms, has been determined for Mg34. 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.

Domaines: Physique Nucléaire Expérimentale [nucl-ex]

R. Lică, F. Rotaru, M.J.G. Borge, S. Grévy, F. Negoiţă, et al.. Identification of the crossing point at $N=21$ between normal and intruder configurations. Phys.Rev.C, 2017, 95 (2), pp.021301. ⟨10.1103/PhysRevC.95.021301⟩. ⟨hal-01554689⟩