Calculate the half-life of the radioisotope

Question

4. A 160. mg sample of radium-224 weighs 20.0 mg after 9.0 years. Calculate the half-life of the radioisotope.

Answer 1

4. A 160. mg sample of radium-224 weighs 20.0 mg after 9.0 years. Calculate the half-life of the radioisotope.

You need to know that the weight of radium-224 is reduced to a half after one half-life decay

160 mg------> 80 mg ------> 40 mg ---------> 20 mg

Radium-224 after 3 half-life decay reached to 20 mg. The half-life is the total years divide 3 half-life:

9 yrs / 3 = 6 yrs t_1/2 = 6 yrs