What mass of `Ra^(226)` whose `t_(1//2) = 1620` years will give the activity of 1 millicurie?

Explanation

Activity `= (0.693)/(t_(1//2)) xx (w)/(At.Wt) xx 6.023 xx 10^(23)`
`3.7 xx 10^(7) = (0.693)/(1620 xx 365 xx 24 xx 3600) xx (w)/(226) x 6.023 xx 10^(23)`
So `w = 10^(-3) g`