Numerical Simulation on Dose Estimation from Nasal Swab Data at Nuclear Accident

Abstract

A nasal swab sample, which is taken immediately after an inhalation accident of radioactive aerosols, shows provisional intake radioactivity. In the case of an alpha emitter, much time is needed to determine the intake radioactivity using bioassay. A nasal swab sample would give a better estimation for early dose. In this study, the most hazardous size to our health and how to estimate the exposure dose were considered from the viewpoint of emergency medicine. A computer code, LUDEP, was used to calculate the aerosol deposition in respiratory tract and the committed effective dose. Assuming that the radioactivity detected in a nasal swab sample was equal to the radioactivity deposited in the extrathoracic region 1 (ET₁), the dose conversion factor (DCF_nasal) was evaluated based on the relationship between the ET₁-deposited radioactivity in Bq and the committed effective dose in mSv. The DCF_nasal showed a clear dependency on the aerosol particle size. It was indicated that the reference aerosol with the size of 5μm for occupational exposure in the ICRP publication does not always give dose estimation in safer side. In the case of insoluble plutonium-239, the maximum value of 2.6mSv Bq^-1 for DCF_nasal was found at 0.02μm in a heavy exercise level of an adult. Therefore, the maximum value would be applied to first estimation of the dose for nuclear emergency medicine.