High dose values due to contaminated badges

In some cases extraordinary high radiation doses have been determined for radiation workers. These values only could be explained to be caused by contaminations of the cover of the dosimeters (badges). The aim of the present study is to find out the amount of radioactivity sufficient to produce a dose of 1.67 mSv. For this reason badges have been contaminated systematically with calibrated radioactive solutions, using a pipette. The badges have been covered by lead to avoid exposure towards each other. They have been stored for several days and evaluated afterwards. The contaminations have been performed with the nuclides F-18, P-32, Tc-99m, In-111, I-123, I-125 and I-131. In order to consider different times of contamination the results of the measurements have been converted for exposure times of 2, 14 and 30 days respectively. As a result just small amounts of radioactivity are causing relative high doses. Due to the radionuclide and - for nuclides of longer half lives in addition due to the point of time when a contamination occurred - the values differ significantly. Our study shows, that possible contaminations of the badges can be considered to be the reason for conspicuous high evaluated doses. (orig.)