Plz help don't know

Question

Iodine-131 is often used in nuclear medicine to obtain images of the thyroid.

If you start with 4.0*10^10 I-131 atoms, how many are left after approximately 1 month? I-131 has a half-life of 8.0 days.

Answer 1

First order decay.

FR = 0.5ⁿ

FR = fraction remaining = ?

n = number of half lives that have elapsed: assuming 30 days in 1 month, then 8 days = 8/30 = 0.267 half lives

FR = 0.5^0.267

FR = 0.831 (or 83.1% remains)

Atoms left = 0.831 x 4.0x10¹⁰ = 3.3x10¹⁰ atoms remain