High-spin states in the Tz =,1=2 nucleus 55 Ni.pdfVIP

Z. Phys. A Short Note Manuscript-Nr. (will be inserted by hand later) Short Note High-spin states in the T z = 1=2 nucleus 55Ni D. Rudolph1;2, C. Baktash2, M.J. Brinkman2, M. Devlin3, H.-Q. Jin4;?, D.R. LaFosse3, M. Leddy5, I.Y. Lee6, A.O. Macchiavelli6, L.L. Riedinger4, D.G. Sarantites3, and C.H. Yu2 1 Sektion Physik der Universitat Munchen, D-85748 Garching, Germany 2 Oak Ridge National Laboratory, Oak Ridge, TN 37831, U.S.A. 3 Washington University, St. Louis, MO 63130, U.S.A. 4 University of Tennessee, Knoxville, TN 37966, U.S.A. 5 Schuster Laboratory, University of Manchester, Manchester M13 9PL, United Kingdom 6 Lawrence Berkeley National Laboratory, Berkeley, CA 94720, U.S.A. 2. April 1997 Abstract. High-spin states of the isospin Tz = 1=2 nucleus 55Ni have been identi ed for the rst time by means of the reaction 28Si(36Ar,2n) at 143 MeV beam energy. The Gammasphere array together with ancil- lary detectors was used to detect rays in coincidence with evaporated light particles. The level scheme of 55Ni comprising four transitions is compared to its mirror partner 55Co and shell-model calculations in the fp shell. Doubly magic nuclei occupy a unique place in nu- clear structure: they and their nearby neighbours de ne the single-particle energies and the two-body matrix- elements of the residual interaction which form the buil- ding blocks of (large scale) shell-model calculations. The- refore, spectroscopic data of these nuclei serve both as the source and the constraints on the parameter sets that de ne the eective nuclear forces. Among the unstable doubly-magic nuclei the region around 56Ni is readily ac- cessible via heavy-ion induced reactions. However, high- spin states in the A  60 region have eked out a sha- dowy existence until now: The excitation schemes com- prise very few high-spin levels { at most 5 to 10 [1]. Con- trary, the A  60 nuclei have been extensively studied with light-ion induced transfer reactions (cf. Ref. [2, 3]). With a pr