Question

Iodine-131 is a radioisotope with a half-life of 8 days and can be used in the treatment of thyroid cancer. Calculate the percentage of iodine-131 that would have decayed after 24 days

Answer 1

$N=N_0(\frac{1}{2})^{\frac{t}{t_{1/2}}}$ , where N is the amount at given time (in this case - the percentage remaining), N₀ is the initial amount (in this case it is equal to 100 percent), t is time, and t_1/2 is the half-life. Therefore,

$N=100\%\times(\frac{1}{2})^{\frac{24days}{8days}}=12.5\%$ (remaining).

Hence 100 - 12.5 = 87.5% would have decayed.

Answer: 87.5%