Control of radon emanation at determination of activity concentration index for building materials

Radon emanation is a well-known source of uncertainty at determination of activity concentration index for building materials and NORM. To reduce this uncertainty both radon emanation coefficient of the sample material and radon leakage from the measuring container should be considered. Two different methods (the rapid method and precise method, which requires to keep the sample sealed for at least three weeks), which are based on the use of only gamma-ray spectrometer, are proposed for testing radon emanation. Both methods also allow simultaneous determination of the specific activity of radium and an assessment of radon exhalation rate from the surface of the finished building products. In addition, the method for determination of radon leakage from the container is proposed. The reliability of the sealing methods of containers is compared and standard PET-flasks with a high radon-tightness are offered. The criteria to control radon leakage and radon emanation coefficient are given for three types of test samples: (a) building materials, (b) natural materials of mineral origin (sands, clays, rocks etc.), and (c) artificial materials, such as absorbents, filters, radioactive wastes. A simplified screening test to control activity concentration index for building materials without a need to keep the sample sealed before the measurement is proposed.