Radiation seed therapy is a common method for treating some prostate cancers and brain tumors. Iodine-125, with a half-life of 60 days, is one isotope used for this treatment. How long does it take for the activity of iodine-125 to decrease to 5.0% of its initial value?

Question

Quizplus · Accepted Answer

The activity of a radioactive isotope decreases to a certain percentage of its initial value according to the formula: $ N(t) = N_0 \times (0.5)^{t/T_{1/2}} $. To find the time $ t $ when the activity is 5% of the initial value, we solve $ 0.05 = (0.5)^{t/60} $. Solving this gives $ t \approx 259 $ days.

Radiation Seed Therapy Is a Common Method for Treating Some