Rapid estimation of inhaled particle size for internal dose during nuclear emergency medicine.

Information on particle size is one of the important factors for internal dose estimation at accidents with airborne radioactive materials. An autoradiography method has been investigated as a technique for the sizing of alpha-emitting particles. Concerning nuclear emergency medicine, the waiting time for dose estimation is limited. For determining the shortest estimation time, the exposure time of autoradiography was examined using PuO2 particles captured on HEPA filters. In this study, the effective counting efficiency of tracks produced by alpha particles was evaluated to be 0.31 by a numerical simulation. The minimum exposure time for PuO2 with aerodynamic diameter of 5 μm was found to be only 10 min. When any star-like alpha particle track was not detected after 6 h of exposure, even if the sample had significant radioactivity, the aerodynamic diameter was assumed to be less than 1 μm. When the radioactivity of PuO2 particles detected by autoradiography within 1 h was dominant of total activity, the aerodynamic diameter would be estimated to be over 5 μm. These results indicate that the precise dose estimation is useful for the decision of medical treatment.