Question

If you have a 4.00 mg sample of a radionuclide known as Q-234, calculate the mass that will remain after 5.00 years given that the half life of Q-234 is 2.5 years.

Answer 1

A_o = A_t x 2ⁿ                  - equation 1

Where,

            A_o = Initial amount                                 = 4.0 mg (given)

            A_t = Amount remaining at time t           = ?      

            n = number of half-lives

Number of half-lives, n = total time elapsed / half-life period = 5.0 years / 2.5 years = 2

Putting the values in equation 1-

4.0 mg = A_t x 2²

Or, A_t = 4.0 mg / 4 = 1.0 mg

Hence, the amount of Q-234 remaining after 5.0 years = 1.0 mg