varies linearly with depth through the stomach wall. The results do not change significantly when the diffusion coefficient is varied from 10-5 to 10-7 cm2 s-1. The number of radon atoms that decay in the vicinity of the stem cells can be obtained by

where

N(α)= the number of nuclear transformations of 222Rn occuring in the volume element dV per ingested Bq,

dVs = the volume of a spherical shell surrounding the assumed location of stem cells in the stomach wall (4φr2dr),

r = 3.928 cm, at a depth of 200 µm, and)

dr = 100 µm.

The result of this integration yields four nuclear transformations per becquerel of 222Rn after ingestion of 250 mL of water. That indicates that energy deposition by alpha particles in the vicinity of the radiosensitive cells will certainly not be uniform. Absorbed dose obtained by averaging energy deposition over the volume of interest for this situation should be interpreted with caution.

The model presented here assumes that there is no capillary involvement in the first 250 µm of tissue below the mucous layer in the stomach wall. If such capillaries were present in the region between the surface cells and the crypts containing the stem cells, the capillary blood flow would reduce radon penetration into the wall.

It must be emphasized that this is a very naive representation of the actual conditions in the stomach after an intake of water containing 222Rn. However, these simplifications can increase our understanding of the processes associated with the ingestion of radon by illustrating how assumptions about diffusion could influence internal dosimetry. These results can also provide a basis for the development of more-representative models.



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