The mass of cobalt-60 in a sample is found to have decreased from 0.800g to 0.200g in a period of 10.5 years. From this information, what is the half-life of cobalt?

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Answer 1 · 2018-05-24T22:41:50

Let's assume radioactive decay follows first order kinetics.

Recall,

#ln[A]_"t" = -kt + ln[A]_0#

#t_(1/2) = ln(2)/k#

Let's derive the rate constant,

#=> k = ln(([A]_"t")/([A]_0))/(-t) = 0.132"yr"^-1#

Hence, the half life of cobalt-60 is,

#t_(1/2) = ln(2)/k approx 5.25"yr"#