I love physics and I am a big fan of Dean W. Armstrong's blog. In a post from 2005, Armstrong attaches a coffee filter to a running vacuum cleaner and then takes a reading of the coffee filter with his Geiger counter to see "the decay of radioactive daughter products of radon-222".
Graphic of radon decay
Last week, being inspired by Armstrong, I decided to put my Geiger counter on the air filter of my 9-5 to see what would happen. I had just returned home from work when I did this experiment.
The Geiger counter on the stone fireplace mantle after running for five minutes.
The Geiger counter on top of the old filter after running for five minutes.
The Geiger counter on top of some Uranium ore (just for fun).
Visit Dean Armstrong's blog for the real information about what is going on. I was hoping for something a little more dramatic than five additional μRem/hour. I can get 17 μRem/h with the counter sitting on our kitchen table, but usually it is around 8-10 μRem/h in the house. The Uranium ore photo was right after I placed the counter on the sample, no real need to wait five minutes.
I previously tried the coffee filter experiment in our basement near the sump pump. Sadly (or luckily), I didn't see any noticeable jump in radiation.
My next experiment will be with the cabin air filter on the SAAB 9-5 when it needs replacement. I will also try testing the used oil filter at the next oil change.
NanoSense has some background information on radioactivity.
How Stuff Works article on Radon.