Question

2. The half-life of a radioactive element is important when considering its application in medicine. For example, iodine-131 is often used in the imaging of the thyroid. The reason is that iodine is readily absorbed by the thyroid gland. Another reason is the short half-life of iodine-131. I-131 gas has a half-life of 8.0 days.

a. If you started with 5 x 1010 iodine atoms, how many are left after approximately 1 month?
b. Why is it important that there will be very few I-131 left in your thyroid after 1 month of exposure?

Answer 1

a.
k = 0.693/t_1/2
Substitute k into the below

ln(No/N) = kt
No = 5E10
N = ?
k from above
t = 1 month but change that to days if you use half life in days.

b.
Basically you don't want to get bombarded with radioactive rays longer than necessary.