The half‑lives of different medical radioisotopes are given in the table. If the initial amount of arsenic‑74 is 2.3 mCi, how much arsenic‑74 is left in the body after 54 days?

Answer 1

17.5 days is the half life for As-74 according to the internet. Using this value and a simple formula of

FR = 0.5ⁿ we can find how much is remaining after 54 days.

FR = fraction remaining = ?

n = number of half lives that have elapsed = 54 days x 1 half life/17.5 days = 3.086 half lives

FR = 0.5^3.086

FR = 0.1178

amount remaining = 0.1178 x 2.3 mCi = 0.27 mCi left