Spatial distribution and time variation of radon concentration in a dwelling

The spatial distribution and time variation of 222Rn (radon) concentration and its relatives were measured for one year in a typical Japanese apartment of reinforced concrete. The purpose of measuring spatial distribution is to determine a representative position in a dwelling from which to form estimates of radon level and to conduct a radon level investigation. Electrostatic integration radon monitors were simultaneously operated at one-month intervals in bedroom, kitchen, living room, and veranda. Because the measurement results of mean concentration are likely to be atypical, kitchen is not a suitable place for investigating the indoor radon level. Living room could be used; however, bedroom should be better since occupant is likely to spend longer time there. The purpose of measuring time variation is to investigate the variation ranges in the equilibrium factor (F) as well as to determine the radon concentration, which is one of the major factors for the calculation of the annual effective dose due to radon. Therefore, the equilibrium equivalent concentration of radon (EEC Rn) and radon concentration were measured at one-month intervals. The annual mean of F=0.43±0.09 found for the dwelling agrees very well with the UNSCEAR (United Nations Scientific Committee on Effects of Atomic Radiation) value of 0.4 for indoors. In addition, it appears that the monthly F value for the dwelling varies over the range of factor three. The variation in the F value in this case is mainly based on changes in the life-styles and activities of the occupants, especially such things as ventilation due to the opening and shutting of windows and the operation of air-conditions. If it is necessary to determine an effective dose due to radon over a shorter period than one year, the time variation of each physical or environmental parameter including the F value should be taken into account. (author)