Question 30.6: Radioactivity in the air The average activity of air inside ...
Radioactivity in the air
The average activity of air inside homes in the United States is about 1.5 pCi per liter. What is the average activity of a liter of air, in Bq? In decays per hour?
SET UP We use the average value just cited, 1.5 pCi/L, along with the conversion factor \mathrm{1 Ci = 3.7 \times 10^{10} Bq.}
SOLVE \mathrm{1.5 pCi/L = (1.5 \times 10^{-12} Ci/L)\left(\frac{3.70 \times 10^{10} Bq}{1 Ci} \right) }
= 0.056 Bq.
Since 1 Bq = 1 decay/s, the number of decays in 1 hour is
(0.056 decays/s)(3600 s/h) = 200 decays/h.
REFLECT A level of activity of air of 1.5 pCi/L represents, on average, the decay of one Rn nucleus every 18 s in each liter of air. If the basement of a medium-size house has a volume of 10^6 L, the total activity of the air in this basement is about \mathrm{1.5 \times 10^{-6} Ci, or about 5 \times 10^4} disintegrations per second.
Practice Problem: If your lungs contain an average of 5.0 L of air, how many decays occur each minute? Answer: 17.