Question

1 gram of radium is reduced by 3.1 mg in 5 years by alpha decay.

Calculate the half-life of radium.

Answer 1

1 gm = 1000 mg

N = No e^-y t where y = lambda the decay constant

N / N0 = .9969

ln .9969 = - y t

-.00310 = - 5 y

y = .00310 / 5 = .000621

So the half-life = .693 / y

T^1/2 = .693 / .000621 = 1116 or about 1120 yrs