Lanthanum has a stable `La^(139)` and radioactive isotope `La^(138)` of half life `1.1 xx 10^(10)`
Channel: Doubtnut
Date: 2020-08-30

Lanthanum has a stable `La^(139)` and radioactive isotope `La^(138)` of half life `1.1 xx 10^(10)` years whose atoms are 0.1 % of those of the stable isotope. Estimate the rate of decay or activity of `La^(138)` with 1 kg of `La^(139)` Take Avogadro's number `N=6 xx10^(23) mol^(-1)`