A measurement of the 56Ni cosmic ray abundance has been discussed as a possible tool to determine the acceleration time scale of relativistic particles in cosmic rays. This conjecture will depend on the halflife of totally ionized 56Ni 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} approx 4 times 10^4 years, only slightly larger than the currently available experimental lower limit, but too short for 56Ni to serve as a cosmic ray chronometer.
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