Halflife of Ni-56 in cosmic rays

A measurement of the Ni-56 cosmic ray abundance has been discussed as a pos sible tool to determine the acceleration time scale of relativistic particl es in cosmic rays. This conjecture will depend on the halflife of totally i onized Ni-56 which can only decay by higher-order forbidden transitions. We have calculated this halflife within large-scale shell model calculations and find t(1/2) approximate to 4 x 10(4) years, only slightly larger than t he currently available experimental lower limit, but too short for Ni-56 to serve as a cosmic ray chronometer.