http://www.youtube.com/watch?v=x8ykex_h ... &index=262At 5m 45s Tom talks about electrostatic build-up caused by movement.
Possibilities...speculations...theories...one as good as the next?
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If you inhaled or ingested a gamma emitter, it should be present in the lungs or stomach primarily, perhaps the gastrointestinal tract? A torso reading might be different than a foot or hand?
A laundry soap radioactivity on your clothing? Measure your washing machine drum?
Water supply based radiation present on your skin after you rinse in the shower? A timed measurement on a bathtub full of water? Scan your bath soaps?
Food additives permeating your body/skin? Scan your foods?
Electromagnetic charge build-up from the movement of breathing? Hold your breath for a 1 minute timed measurement?
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I would start with Tom's method of 'progressive shielding' to narrow down what type of radiation...alpha/beta/gamma. Use a few sheets of paper, then a sheet of aluminum foil between the GM tube and your skin/clothing while taking a timed measurement...then move up to something like a ceramic/stoneware plate? I've found ceramics to be relatively dense material. A solid metal 'plate' such as a meat cleaver over the tube opening would probably suffice as well to block out everything but gamma.
Perform a baseline reading of each shielding type as well...the ceramic or metal may be radioactive by itself (granite can be very radioactive).
Record the uSv and CPM readings for each level of shielding and then do a subtraction from highest to lowest to get your various radiation types.
I hope this helps.
M.