Experimental study of the collection efficiency of the CEA individual α-dosimeter for aerosol particles in the 0.001-0.1 μ size range

Personal α-dosimetry has been developed in France within the frame of a program devoted to evaluate hazards due to exposures of workers to radon or thoron gas, its daughters, and external irradiation, in uranium mines. To this end, the CEA has built an Integrated system of Individual Dosimetry of which the more recent version is now in operation in COGEMA Mine of La Crouzille. Principle of this α-dosimeter, which will be described further, is based on the use of ionographic film to detect α emitters of radioactive aerosols, previously collected on a membrane filter mounted in a special head. So, concentrations of radon-thoron daughters or potential α energy can be measured over the period of exposure. However, global radioactivity of mine atmospheres is ranged on particles from free atom dimensions to a few microns, and the corresponding size distribution depends on different uranium mining operations. Because some radioactive particles may be removed by a plate-out mechanism inside the dosimeter head, it is of prime importance to know the collection efficiency of the measuring head as a function of particle size, in order to avoid errors in exposure dose calculation. This is the purpose of the present work. (author)