Awhile back I did some testing of using a USB based Geiger counter on a plane ride from Seattle to San Fran to detect cosmic rays- Dean used a Aware Electronics RM-70 to do the same on more on a Southwest Airlines flight to LAX. On the site you can see graphs from the flight as well as the decay of radioactive daughter products of radon-222 being captured on a coffee filter that filtered 15 minutes of air through a vacuum cleaner in someone’s basement in Ohio. Link.