Question

Radon is a radioactive colorless, odorless gas that is produced in thorium and uranium decay chains. Its half-life is 3.8 days. Typical domestic exposures are approximately 100 Bq/m³ in buildings and 10 Bq/m³outdoors. What would the concentration be in Ci/m³ and approximately how many days would it take for an air sample taken indoors to be equivalent in activity to typical outdoor activity concentrations?

Answer 1

The conversion between the units Becquerel(Bq) and Curie(Ci) is

So,

So the indoor concentration is

and the outdoor concentration is

To find out how much time is required for the activity to reduce from 100Bq/m3 to 10 Bq/m3 :

Activity of a radioactive sample is given by

and this at time t₂ reduces to the outdoor value.

Dividing both equations, we get,

Taking log on both sides,

Substituting this in the equation,

It will take 12.6 days for the sample taken at indoor activity concentration to fall to the outdoor concentration levels.