Question

The function mc028-1.jpg gives the mass, m, of a radioactive substance remaining after h half-lives. Cobalt-60 has a half-life of about 5.3 years. Which equation gives the mass of a 50 mg Cobalt-60 sample remaining after 10 years, and approximately how many milligrams remain?
mc028-2.jpg; 0 mg
mc028-3.jpg; 0.05 mg
mc028-4.jpg; 13.5 mg
mc028-5.jpg; 25 mg

Answer 1

Use h = 10/5.3 half-lives.
m = 50*(1/2)^(10/5.3) ≈ 50*(1/2)^1.8868 ≈ 13.5 mg.

(So the correct choice is the one giving about 13.5 mg.)