Abstract
Calculations of radon-exposure doses have intensively made due to its importance from the standpoint of radiation protection. To determine radiation doses from radon inhalation, we should take into account the following exposure patterns: (1) Deposition of inhaled radon progeny; (2) Retention of radon gas in lung airways; (3) Biokinetics of inhaled radon gas. Almost all studies reported so far paid attention to the pattern (1), which was the greatest contributor to total radiation doses.
We have conducted radon exposure experiments using mice to observe their biological changes. Since organs other than lungs were also analyzed, absorbed doses of many organs and tissues must be assessed. Taking into account the above three patterns, we computed the doses for small laboratory animals with dose calculation models that have been established for humans. These assessments will be important for considering the radiation protection of environment.
The result of mice is shown here. Exposure pattern (1): the absorbed doses were 51.6, 4.6 and 35.9 nGy/(Bq/m3)/h for the tracheobronchial and alveolar regions, and whole lung, respectively. Exposure pattern (2): 0.036, 0.015 and 0.029 nGy/(Bq/m3)/h for the tracheobronchial and alveolar regions, and whole lung, respectively. Exposure pattern (3): 0.056, 0.029 and 0.002 nGy/(Bq/m3)/h for adipose tissue, red bone marrow and the rest (average), respectively. It was confirmed that, in descending order, the pattern (1), (2) and (3) give the high doses. This trend was seen for rats, which is the same as humans. In our presentation, we will talk about the dose calculation models used, the comparison of doses between humans and small animals, and future issues.
