My kit will not respond to bananas, at least not in an obvious way. I believe that a more sensitive pancake-style detector is required - bananas just aren't that radioactive. It may be possible to see a small signature using a large number of bananas (I hear some types are more radioactive than others) and a long sample time (extended data logging). It will not be an easy measurement.
Camping mantles made in the last several years are NOT radioactive. If you purchase a mantle from a sporting goods store, Target, etc it will NOT be radioactive, I have checked!
Also, my geiger kit will not detect much radioactivity from a smoke detector, so that is also not a good test source (and disassembly of a smoke detector is dangerous). The results will be disappointing, anyway.
Good test sources include:
- some granite countertops
- vaseline (depression) glass, available on eBay as uranium marbles
- orange/red Fiestware produced before the 1960s (eBay)
- old watches with Radium dials (probably pre-1960s, ordinary glow in the dark watches won't work)
- uranium or other radioactive ore samples (eBay, United Nuclear)
- thoriated welding rods (welding supply store, eBay)
- old camping mantles containing Thorium (eBay)
- some camera lenses with thoriated optics, but these are rare (maybe available from antique camera dealers or eBay)
More info here: http://mightyohm.com/blog/2012/02/feed- ... t-sources/