The first excited 2+ state of 36Ca has been identified by its gamma -decay, exploiting the two-step fragmentation technique at the FRS-RISING setup at GSI. This is the heaviest Tz=-2 nucleus in the Segre chart in which a gamma -decay of an excited state has been observed. A stable beam of 40Ca at 420A 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 21+ 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.
The T=2 mirrors 36Ca and 36S : a test for isospin symmetry of shell gaps at the driplines / P. Doornenbal, P. Reiter, H. Grawe, T. Otsuka, A. Al-Khatib, A. Banu, T. Beck, F. Becker, P. Bednarczyk, G. Benzoni, A. Bracco, A. Bürger, L. Caceres, F. Camera, S. Chmel, F.C.L. Crespi, H. Geissel, J. Gerl, M. Górska, J. Grebosz, H. Hübel, M. Kavatsyuk, O. Kavatsyuk, M. Kmiecik, I. Kojouharov, N. Kurz, R. Lozeva, A. Maj, S. Mandal, W. Meczynski, B. Million, Z. Podolyák, A. Richard, N. Saito, T. Saito, H. Schaffner, M. Seidlitz, T. Striepling, Y. Utsuno, J. Walker, N. Warr, H. Weick, O. Wieland, M. Winkler, H.J. Wollersheim. - In: PHYSICS LETTERS. SECTION B. - ISSN 0370-2693. - 647:4(2007), pp. 237-242. [10.1016/j.physletb.2007.02.001]
The T=2 mirrors 36Ca and 36S : a test for isospin symmetry of shell gaps at the driplines
A. Bracco;F. Camera;F.C.L. Crespi;
2007
Abstract
The first excited 2+ state of 36Ca has been identified by its gamma -decay, exploiting the two-step fragmentation technique at the FRS-RISING setup at GSI. This is the heaviest Tz=-2 nucleus in the Segre chart in which a gamma -decay of an excited state has been observed. A stable beam of 40Ca at 420A 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 21+ 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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