beta-decay study of Ni-54,Ni-55 produced by an element-selective laser ionsource

beta-decay studies of the neutron-deficient Ni-54,Ni-55 isotopes have been performed at the Leuven isotope separator on-line facility (LISOL) at Louva in-la-Neuve. The nuclei of interest are produced using an element-selective laser ion source coupled to the on-line mass separator. The half-life of N i-55 (T-1/2= 204+/-3 ms) was remeasured precisely and the beta(+) decay of Ni-54 was observed for the first time. The beta(+)-decay Gamow-Teller stren gth [B(GT)] associated with the (J(pi)=1(+)) level at 937.2 keV in the daug hter nucleus Co-54 was deduced. The beta(+) GT strength of 1.09+/-0.25 obta ined from the measured half life of Ni-54 (T-1/2 = 106+/-12 ms) and branchi ng ratio (I-beta=22.4 +/- 4.4%) towards this level is in agreement with the GT strength obtained from (p,n) reaction studies on Fe-54 [B(GT-) = 1.172/-0.078]. [S0556-2813(99)03405-6].