Estimating granite roughness using systematic random sampling for the evaluation of radon gas emanation from ornamental granite rocks
T. M. El Hajj,a I. Tertuliano,b T. Vieira,c A. C. Chieregatia and H. Delboni Jr.a aDept. of Mining and Petroleum Engineering, University of Sao Paulo, Av. Prof. Mello Moraes 2373, 05508-030, Sao Paulo, Brazil. E-mail: [email protected]; [email protected]; [email protected] bDept. Of Mechanical Engineering, University of Sao Paulo, Av. Prof. Mello Moraes 2231, 05508-030, Sao Paulo, Brazil. E-mail: [email protected] cDept. Of Civil Engineering, University of Sao Paulo, Av. Prof. Almeida Prado 83, 05508-070, Sao Paulo, Brazil. E-mail: [email protected]
There are three natural radioactive families according to their decay, which are: the uranium series (238U decreasing to stable 206Pb), the actinium series (235U decreasing to stable 207Pb) and the thorium series (236U → 232Th decreasing to stable 208Pb). The three series all have radon gas as an intermediary element, but each with a different atomic mass (222Rn, 219Rn and 220Rn). The three isotopes are inert gases at ambient conditions and all are alpha particles emitters. Soils naturally 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.