In connection with low-level γ-ray counting of natural samples, background due to 220Rn-and 222Rn-daughters was monitered. The results obtained for 4 months showed that the background γ-ray from 222Rn-daughters was more variable than that of 220Rn-daughters. An efficient air-conditioning was helpful to keep the background stable. It was practically equivalent to the use of N2-gas. Radiometric data for dust samples filtered from the laboratory air suggested that Rn-daughters tended to be removed by air-conditioning.
Improving the smear efficiency and the stability of smear method on the monitoring of radioactive floor surface contamination, wet smear method by a water sprayer was designed and examined. And as the temporary decontamination method applied to the wide spread radioactive floor surface contamination, the method by a vacuum cleaner (vacuum cleaner method) was examined. These examinations were carried out by the experiment using the lonleum floor sheets waxed and the various types of pharmaceutical compounds labeled with 99mTc. On wet smear method, the smear efficiencies were larger than 50% and coefficient of variations by far smaller than that of dry smear method (usual smear method) : for all the radiopharmaceuticals examined. These results showed the effectiveness of wet smear method. On vacuum cleaner method, the decontamination coefficients were comparatively large and almost same to that by wet duster method (decontamination method by using the wet duster) except Ringer's solution and DMSA what had less removable part of contamination. These results showed the effectiveness of vacuum cleaner method for the removable parts of contamination.