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a) alpha spectrum for a 20mm x 20mm 226Ra source at 3 mm in front of the detector, b) alpha spectrum for the same source with our 12 micro-meter PET foil placed between source and detector, c) alpha spectrum taken with the experimental setup in Fig.1 with about 50 Bq 222Rn in the water sample. Integration time 10'000 s, started just after filling in the water. Error bars are +/- 1 sigma counting errors. (units) |