Difference in Concentration of Indoor Radon or Thoron Progeny in Daytime and Nighttime

Abstract

A portable integrating monitor for measuring both radon and thoron progeny concentrations was developed. The monitor gave the average equilibrium equivalent concenttrations of radon (E.E.R.) and thoron (E.E.T.) during five days. The calibration factor was calculated by Monte Carlo method. We selected four measurement locations : home, office, laboratory and outdoor. In the measurement at home, the both radon and thoron progeny concentrations in the nighttime were larger than in the daytime. On the other hand at the other locations the concentrations in the nighttime were same as in the daytime. The RT-ratio, which was defined as the ratio of E.E.T. to E.E.R., was about 0.10 indoors and about 0.02 outdoors. Therefore indoor thoron progeny concentration tends to be higher.