Radiation and Radon
Radiation is all around us. As natural isotopes continuously degrade, they release α-particles, β-particles and γ-rays.
I live (relatively) close to a natural out-gassing area called the “Reading Prong” which is an area that extends from Reading, Pennsylvania up through northern New Jersey and southeastern New York. This area contains higher levels of uranium than surrounding areas of these associated states. 
I purchased a radiation monitor (Geiger Counter) from Aware Electronics in 2005 to monitor the radon levels in the basement. I settled on their product as it can be easily interfaced to a monitoring computer and the results can be graphed and updated regularly.
Currently, I am monitoring natural occurring radiation in the basement. The above graphs plot micro rads (uR) vs time.
1. Schutz, D. Geology of the Reading Prong. Environment. 1987: 29(2). pp:14-15
The graphs displayed on the data page are created with a batch file and some programs from Aware, including ‘joinrad.exe’ and a small DOS program called ‘bmp2gif.exe’. The latter program is needed because the graphing program only outputs a .bmp file (as far as I know). A copy of my batch file is available here.