Decay Studies of Tz=-1 and -2 nuclei and the “isopin quasi selection rule”
B. Rubio 1*, F. Molina 1, Y. Fujita 2, W. Gelletly 3
1 Instituto de Física Corpuscular Valencia (IFIC)
2 Univ of Osaka
3 Univ. of Surrey
In this talk I will present the results of several decay studies we have performed at GSI and GANIL using fragmentation reactions. The aim of these experiments was to obtain precise Gamow-Teller transition probabilities, B(GT) values, for the beta decay of Tz=-1 or Tz=-2 nuclei and to compare the results with those obtained in the mirror process, ie, Charge Exchange reactions using Tz=+1 and Tz=+2 targets. The latter were obtained previously at RCNP (Osaka).The experiments at GSI were performed using fragmentation of 58Ni beams, only two nucleons away from the N=Z line. In these experiments very high statistics (more than 1 million decays in each case) could be obtained for the decays of 54Ni, 50Fe, 46Cr and 42Ti. This together with the high efficiency of the RISING array (15 Euroball CLUSTER detectors) allowed us to determine the half life with high accuracy, more precise than values in the literature by up to two orders-of-magnitude, as well as weak beta feeding to levels up to 4 MeV. Ground state to ground state feeding was also determined. The Tz=-1 and -2 nuclei heavier than 54Ni are difficult to populate because the available beams lie further away from the N=Z line. We have nevertheless studied 58Zn (Tz=-1) produced in the fragmentation of 64Zn, and 56Zn (Tz=-2) made in double charge exchange reactions on 58Ni at the GANIL facility. I will present our preliminary results including clear examples of the isospin “ M1 quasi-selection rule”
Figure. Upper panel;spectrum from the 46Ti (3He, t) 46V reaction measured at RCNP-Osaka ( T. Adachi et al, Phys. Rev C73 (2006) 024311), the peaks correspond to excited 1+ states populated in Gamow-Teller transitions. Lower panel; RISING gamma spectrum in coincidence with beta particles after fragmentation of 58Ni and in-flight separation of the fragments at GSI_FRS. The peaks correspond to delayed gamma rays from the beta decay of 46Cr de-exciting 1+ states to the ground state of 46V.