`Co^57` decays to `Fe^57` by`beta^+` -emission.The resulting `Fe^57`is in its excited state and comes to the ground state by emitting `gamma`-rays.The half-life of `beta^+`-decay is 270 days and that of the `gamma`-emission is `10^(-8)`s.A sample of `Co^57` given `5.0xx10^9`gamma rays per second.How much time will elapse before the emission rate of gamma rays drops to `2.5xx10^9` per second ?

Answer

A, B, D

Explanation

According to the question , the emistion rate of `gamma-rays` will drop to the half when the `beta` + decays to half of its original amount and for this the sample would take 270 days
`:. This required time is 270 days `.