Question

The half-life of 235U, an alpha emitter, is 7.1×10^8yr. Calculate the number of alpha particles emitted by 1.5 mg of this nuclide in 1.0 minute.

Answer 1

1.5 mg = 0.0015 g U-235

moles of U-235 = 0.0015 /(235) = 6.38 x 10^-6 mol U-235

number of atoms = 6.38 x 10^-6 x 6.02 x 10^23

                           = 3.84 x 10^18 atoms U-235

N = N0 x e^(kt)

k = 0.693 / 7.1×10^8

    = 9.76 x 10^-10 yr-1

1 min = 1.903 x 10^-6 yrs

N = 3.84 x 10^18 x e^(9.76 x 10^-10 x 1.903 x 10^-6)

N = 3.84 x 10^18 atoms