There are three natural radioactive families according to their decay, which are: the uranium series ( 238 U decreasing to stable 206 Pb), the actinium series ( 235 U decreasing to stable 207 Pb) and the thorium series ( 236 U ® 232 Th decreasing to stable 208 Pb). The three series all have radon gas as an intermediary element, but each with a different atomic mass ( 222 Rn, 219 Rn and 220 Rn). The three isotopes are inert gases at ambient conditions and all are alpha particles emitters. Soils

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... aturally emanate these radioactive gases in variable concentrations depending on composition and location. The radon radioactive emanation is a mass flow composed of radionuclides emitted to the atmosphere from the surface of the material, or transported to it. Emanation depends on the amount of radon atoms formed from the decay of radium and on the surface roughness of the material. Treatment such as polishing can be used to decrease radon gas emanation by closing open surface pores and reducing the specific surface area. This study aims at evaluating granite roughness of experimental plates of ornamental rocks using a systematic random sampling approach in order to minimise analysis time. To validate the systematic minimum area sampling results these were compared to measurements made over the whole reference area. It is concluded that measurements can be conducted in just a few locations using systematic random sampling, significantly reducing the time for obtaining estimates of the granite's roughness by factors 150-200.