Fluorine-18, which has 1/2 life of 110 minutes, is used in PET scans. If 100 mg of fluorine-18 is shipped @8AM, how many milligrams of the radioisotope are still active if the sample arrives at the lab at 1:30 pm?

Answer 1

k = 0.693/t_1/2
ln(No/N) = kt
No = 18 mg
N = unknown
k from above.
t = minutes from 8 am to 1:30 pm.

OR, to keep the numbers a little more workable, you may wish to use t1/2 in hours (110/60), then use t = hours from 8:00 AM to 1/:30 pm.

Answer 2

0.50