After the Chernobyl nuclear accident, the concentration of ¹³7Cs in milk was proportional to the concentration of ¹³7Cs in the grass that cows consumed. The concentration in the grass was, in turn, proportional to the concentration in the soil. Assume that the only reaction by which ¹³7Cs was lost from the soil was through radioactive decay and the half-life for this isotope is 3 years. Calculate the concentration of ¹³7Cs in cow's milk after 5 years (units of Bq/L) if the concentration in milk shortly after the accident was 12,000 becquerels (Bq) per liter (a becquerel is a measure of radioactivity; 1 becquerel equals 1 radioactive disintegration per second).
