The half life of a strontium-90 is 28 years. How long will it take a 100 mg sample to decay to 68 mg?

Answer 1

68 = 100(0.5)^t/28

0.68 = (0.5)^t/28

ln 0.68 = (t/28) ln 0.5

-0.3857 ≈ (t/28) -0.6931

0.5564 ≈ t / 28

15.580 ≈ t