i remember doing an experiment in school where we put an air filter in the basement for several hours, and it became measurably radioactive due to radon decay product dust accumulating. its a neat experiment anyone can carry out.

radon is heavier than air so i was surprised to see that there is apparently only about a 20% decrease in radon levels with each floor above ground. they say the decrease is actually due to ventilation. nonetheless their preliminary data that "1 in 10 multifamily [mostly low rise] residential properties are at or above 200 Bq/m" is skewed considering the sampling bias toward basements. at any rate, another single-family-detached L.