Abstract
Abstract The first excited 2 + state of 36Ca has been identified by its γ-decay, exploiting the two-step fragmentation technique at the FRS-RISING setup at GSI. This is the heaviest T z = − 2 nucleus in the Segre chart in which a γ-decay of an excited state has been observed. A stable beam of 40Ca at 420 A MeV impinged on a primary 9Be target. Out of the secondary beam of fragmentation products, 37Ca was separated by the FRS and struck on a second 9Be target at the final focus of the FRS. The energy for the 2 1 + decay of 36Ca was determined to be 3015(16) keV, which is 276 keV lower than in its T = 2 mirror 36S. This mirror energy difference (MED) is discussed in the framework of shell model calculations using a 16O core, the sd shell isospin symmetric interaction USD and experimental single-particle energies from 17O and 17F. The results show that the MED within the sd shell provide a sensitive test for the evolution of the N, Z = 14 , 16 subshell gaps towards the driplines. Especially the N, Z = 16 gap is determined by Thomas–Ehrman shift in the A = 17 , T = 1 / 2 isospin doublet, while Coulomb effects are found to have marginal influence.
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