Question

The half life of Cesium-137 is 30 years. After a nuclear accident, Cesium-137 was released near a major city and the radiation level was 1500 rads per hour. It is not safe to return permanently until the radiation is 5 rads per hour. How long before the population can return to live? (Round to nearest year.) Hint: don't round during the calculation!!!!

Answer 1

1500 (1/2)^(t/30) = 5
(1/2)^(t/30) = 1/300
t/30 log(1/2) = -log300
t = 30 log300/log2 = 246.86 yr

makes sense, since 1/256 = 1/2^8 and 8 half-lives are 240 years