Question

A radioactive substance of 1 g is reduced to 2.1 mg in 5 years by alpha decay.
Calculate the half-life of the substance

Answer 1

Let us write the radioactive decay law in the form
M(t)=M_0 2^((-t)⁄T).(1)
Here M(t) is the mass of substance at time t, М_0 is the mass of substance at initial moment, T- is the half-life.
From equation (1) we obtain T=tln2/(ln M_0/M(t) )=0.562yrs.