One of the hazards of nuclear explosion is the generation of `.^(90)Sr` and its subsequent incorporation in bones. This nuclide has a half-life of `28.1` year. Suppose one micro-gram was absorbed by a new-born child, how much `Sr^(90)` will remain in his bones after 20 year?

Explanation

`t = (2.303)/(lambda)` log `("initial")/("remaining")`
`lambda = (0.693)/(28.1), t = 20 y`, initial `= 1 mu g` remaining `= x mu g`
`20 = (2.303)/(0.693) xx 28.1 log (1)/(x)`
`x = 0.61 mu g`