There are two radioactive substance A & B, Decay constant of B is two times that of A. initially, both have equal number of nuclei. After n half lives of A, rate of disintegration of both are equal. The value of ‘h’ is

Let  λA=λ  ∴  λB=2λ.If  is total number of nuclei in A & B at t = 0, times initial rate of distntegration of  A=λNo,and initial rate of disintegration of B=2λNoAs λB=2λA⇒TB=TA2After one half life of A−dNdtA=λNo2Equivalently, after two half lives of B−dNdtB=2λNo4=λNo2∴−dNdtA=−dNdtBn=1,i.e  After  one half life of A