The specific energy distributions in water caused by I-125 atoms, located in the centre of a sphere with a radius of 5 μm, were calculated using geant4. The dependence of the specific energy on the respective electron frequency distributions was investigated, since there has been a lack of knowledge of the explicit electron frequency distribution up to now. The electron frequency distribution was modelled as Poisson, log-normal, or uniform distribution. Among others, some differences in the specific energy distribution were found. The lowest average specific energy, however, was within the range of the highest average specific energy and vice versa.