The Dose to the Human Respiratory Tract by Inhalation of Short-lived 222Rn- and 220Rn-decay Products

Abstract

The deposition of Rn daughters in the different regions of the human respiratory tract is derived from the particle size of their carrier aerosol in ordinary, unfiltered air. The resulting mean distribution of the radioactivity in the respiratory tract is estimated, taking into account the clearance from the alveolar tissue and the ciliary transport in the bronchial tree. The radiation dose distribution in the epithelium of trachea and bronchi is calculated, taking into account the α-absorption in the mucus layer and the variation of stopping power with α-energy. The resulting mean absolute α-dose in different regions of the respiratory tract is given for each inhaled nuclide, especially at their natural level in atmospheric air and their maximum permissible level. The results indicate, that owing to the ciliary transport, a considerable fraction of the dose in the upper respiratory tract is due to the transfer of activity from the bronchioli and lower bronchi in the mucus stream. The highest dose should be expected in the lower bronchi.