of cobalt 59 Cobalt is the only stable cobalt isotope . 22 radioisotopes have been characterized with the most stable being 60 Co with a half-life of 5.2714 years, 57 Co with a half-life of 271.79 days, 56 Co with a half-life of 77.27 days, and 58 Co with a half-life of 70.86 days. All