Cobalt-60 decay table

​The half life of Cobalt-60 is 5.272 years.  This the time required for a quantity of Cobalt-60 to fall (decay) to half of its original value.  The decay factors below can be used to calculate the change in activity of a quantity of Cobalt-60 over a period of time.

Example:  ​To calcuate the decay of a Cobalt-60 source with an activity of 11,000Ci over a period of 10 years and 5 months.  

​                 11,000Ci (original activity) x 0.2685 (decay factor for 10 years) x 0.9467 (decay factor for 5 months) = 2,796Ci