Certain radioisotopes within the fuel probably became liberated from the molten fuel or fuel fragments as a result of the high temperature and chemical environment in the days following the accident. This is probably the source of the particles composed almost totally of ruthenium isotopes. Air samples indicated that the releases of molybdenum and ruthenium were substantially higher in the late phase of the radionuclide emission period than the releases of fuel fragments. This suggests that the release mechanism of molybdenum and ruthenium was by oxidation to volatile forms. Although fuel fragments themselves were not carried out very far, monitoring at many locations showed that the fission products in gaseous or aerosol form were transported over large distances from the site.
Distance tends to dilute the concentration of fission products in the atmosphere.
However, climatic and local weather conditions often resulted in local concentration onto relatively small areas, even at large distances. You may find that one of the two sites has a much faster access for you.