In this instructable I will be demonstrating how to build a pocket radiation detector or "PIRD." The parts for this radiation detector will all be salvaged (that means no pricey GM tube off of ebay), but building will require steady hands and alot of patience! This is a "clicking" radiation detector, unlike many other DIY versions without a Gieger-Muller tube out there, and I have yet to see anyone try this concept and/or make one like it. Although it may not be as sensitive or practical as a standard geiger counter, it does detect background radiation (most likely gamma rays). Similar concepts are seen on the CERN website, demonstrating the potential to detect both alpha rays and background radiation: (http://teachers.web.cern.ch/teachers/archiv/hst2000/teaching/expt/new/new.htm) and on youtube (http://www.youtube.com/watch?v=RzglpP3D2tQ).
Here is a video testing it using a small amount of radioactive Americium found in a smoke detector: