Figure B.2

Diagram showing the geometry used in the model for diffusion of radon through the stomach wall.

The wall consists of mucous (50 µm), surface cells (50 µm) and tissue with crypts that contain the radiosensitive stem cells (200 µm) (E. Robbins 1998, personal communication). The stem cells are centered at a depth of 200 µm below the surface. It is assumed that blood flow removes all radon at a depth of 300 µm.

A solution for that situation is

The results depend on the selection of a diffusion coefficient for radon in the mucous and wall. The effective diffusion coefficient includes a retardation factor that accounts for absorption in the medium. There are no published values in the literature for the effective diffusion coefficient of radon in tissue. For this report, we have adopted a value obtained for xenon and assume a nominal value of D = 5 × 10^-6 cm² s^-1 for both the mucous and the stomach wall. The exact location of the radio-sensitive cells is also unknown. For this calculation, the absorbed dose is estimated at a depth of 200 µm which is 150 µm below the mucous.

Figure B.3 shows the results from the model with the concentration C(r)/C_o plotted at various times after intake. It can be seen that the concentration in the