Question

Radioactive iodine (I-131) is an isotope of iodine that emits radiation and is used for various medical applications, such as in the treatment of thyroid cancer. The half-life for I-131 is 8 days. Based on the half-life of I-131, how many half-lives have to pass for a 200 mg sample of I-131 to decay down to 25 mg?

Answer 1

Half life is the time period in which half of the initial amount of an element will decay into a new element due to instability. For I-131, the half life is 8 days.

From 200 to 25 grams, let's see how many half lives are there:

200g -> 100g

100g -> 50g

50g -> 25g

Therefore for 200g of I-131 reach 25 grams, 3 half lives are necesseray, 3 half lives or 24 days