Variation of gross β radioactivity and 210Pb concentration in air dust

As part of environmental radiation monitoring around the nuclear fuel cycle facilities, we are carrying out continuous measurements of gross α and gross β radioactivities in air dust by dust monitors. Measured values of gross β radioactivity increased after a renewal of the dust monitors, because ZnS (Ag) scintillator became thinner and the counting efficiency of β-ray became higher. The variations of 210Pb concentration and gross β radioactivity in air dust showed similar pattern. This correlation after the renewal is higher than before the renewal. The similar variation patterns of the gross β radioactivity in air dust were observed at all monitoring stations. When precipitation data at Aomori monitoring station became higher, the gross β radioactivity in air dust tended to be lower. (author)