340. Evaluation of worker inhaled activity after surface contamination

Abstract

Purpose The use of unsealed sources (either in nuclear medicine or in radiochemical bio-laboratories) involves the risk of internal contamination for workers after partial evaporation of the unsealed source during its use. This issue was already addressed in [1] , the aim of this work is to extend that work towards a comprehensive model taking into account also the airborne contamination after radionuclide evaporation from the cumulated surface contamination of the working area. Methods The above mentioned model takes into account the manipulation time (tm, the manipulated activity (A), the frequency of manipulations, the total time the workers spend in the laboratory (on an yearly basis), the air exchange ratio (R) and the half-life of the manipulated radionuclides. According to the actual working conditions, the model evaluates firstly the radionuclide air concentration as a function of time and thereafter the committed effective dose depending on the time spent in the laboratory by the worker. Results During tm the radioisotope manipulation determines both air contamination (AC) and probabilistic surface contamination (SC). After tm AC decreases due to R, whereas surface contamination increases after each manipulation, decreasing only through physical decay, thus leading to an asymptotic SC in the long run. SC is more relevant for long-life radioisotopes. Conclusions Application of the model to an actual bio-laboratory case shows that contribution to inhaled activity from surface contamination may be relevant or even dominant especially for long-life radionuclide (i.e. 3H and 14C). Great care should be used in cleaning the working surfaces after each manipulation to avoid or at last reduce to a reasonable level surface contamination. Smear test looks the test of choice to accurately verify the effective contamination level.