At a given instant, say t = 0, two radioactive substance A and B have equal activities. the ratio $${{{R_B}} \over {{R_A}}}$$ of their activities after time t itself decays with time t as e^$$-$$3t. If the half-life of A is ln², the half-life of B is :

A sample of radioactive material A, that has an activity of 10 mCi(1 Ci = 3.7 $$ \times $$ 10¹⁰ decays/s), has twice the number of nuclei as another sample of a different radioactive materail B which has an activity of 20 mCi. The correct choices for half-lives of A and B would then be respectively :

At some instant, a radioactive sample S₁ having an activity 5 $$\mu $$Ci has twice the number of nuclei as another sample S₂ which has an activity of 10 $$\mu $$Ci. The half lives of S₁ and S₂ are :

If the series limit frequency of the Lyman series is $${\nu _L}$$, then the series limit frequency of the Pfund series is: