Fluoride18 which has a halflife of 110 min is used in PET sc

Fluoride-18, which has a half-life of 110 min, is used in PET scans. If 100. mg of fluoride-18 are shipped at 8:00 am, how many milligrams of the radioisotope are still active if the sample arrives at the radiology laboratory at 1:30 pm? 3.13 mg 6.25 mg 12.5 mg 25.0 mg 50.0 mg 100. mg

Solution

Answer: 12.5mg

Time difference between 8am and 1:30 pm= 5:30 min = 330 minutes

Number of half lives = 330/110 =3

Initial concentration of F-18 = 100mg

100mg---->50mg---->25mg---->12.5mg