This forum can help if you follow these guidelines.
As a guess right now, you have a version of Geant that requires setting the /process/had/rdm/thresholdForVeryLongDecayTime 1.0e+60 year in your macro since depending on geant version, this number may default to 1 year. This is long enough for F18, Cu54, and Co64 which have half lives of 109 minutes, 75 nanoseconds, and 300 microseconds, respectively, but not long enough for Co60 with a half life of 5.27 years.
RDecay01 has the physics lists you probably need. It even includes a Co60 macro file example.
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