57Co decays to 57Fe by β+-emission. The resulting 57Fe is in its excited state and comes to the ground state by emitting γ-emission is 10–8 s. A sample of 57Co gives 5.0 × 109 gamma rays per second. How much time will elapse before the emission rate of gamma rays drops to 2.5 × 109 per second?

Given, 57Co decays by β+ and γ- emission. Rate of emission of gamma rays is 5.0 × 109.

As the emission rate reduce to half of the given value. So the amount of 57Co by β+-emission should reduce to half of the original amount.


Time elapsed for drop of emission rate to half is half life of the β+-emission.


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