The S value for heterogeneous distribution of radioiodine in the human follicle model. The S value for the follicle cell nuclei from the non-radiative transitions are given for homogeneously distributed (a)123I, (b)125I and (c)131I on concentric spherical shells in the human thyroid model. The contribution from Auger electrons (AE) (triangle), internal conversion electrons (CE) (square) and β particles (diamond) are shown separately together with the total value (circle). The surface source radius 0 μm indicates the centre of the follicle lumen, and the dashed lines represent the apical and basal follicle cell surfaces for the respective models. Error bars indicate the standard deviation of the mean value (SD) and are smaller than the symbol when not visible. Note the logarithmic scale on the ordinate.