A large amount of contaminated rubbles were generated by the accident at the Fukushima Daiichi Nuclear Power Station (F1NPS). For safe decommissioning of F1NPS, it is important to evaluate the composition and concentration of radionuclides in the rubbles. In this paper, to characterize the rubbles collected at F1NPS, radiochemical analysis was operated. As a result of radiochemical analysis, gamma-ray-emitting nuclides 60Co, 137Cs and 154Eu, beta-ray-emitting nuclides 3H, 14C, 90Sr and 99Tc, and alpha-particle-emitting nuclides 238, 239+240Pu, 241Am and 244Cm were detected. In contrast, 94Nb and 152Eu concentrations were below the detection limit. Measured radioactive concentrations implied that 60Co and 90Sr concentrations depended on 137Cs concentration respectively. This analysis was characterized the radioactivity concentrations of the rubbles.
In order to understand the source of atmospheric radon concentration in the Gyokusendo which is the limestone cave on Okinawa Island, the radon concentrations in the drip water from the ceiling were measured using a liquid scintillation counter. The arithmetic mean (± standard deviation) of radon concentration was 8.7 ± 2.0 kBq m-3. This result suggests that the atmospheric radon in the cave was supplied from the drip water. When comparing the monthly precipitations which are considered to exert a profound influence on isotopic compositions of water seeping into a cave, the variation of radon concentration in the drip water was shown the delay of 60-90 days. The radon concentration in the soil water was estimated to be 47.3 kBq m-3. Furthermore, the radon concentrations in the percolation water at the cave over a period of 9 to 10 days were calculated to be 9.3-7.7 kBq m-3. The estimated radon concentration in the percolation water was almost equivalent with the measurement concentration in the drip water. These results suggest that the radon atoms in the drip water were generated from the soil above the cave. In other words, emanated radon from the soil particles might be the source of radon in the Gyokusendo.
A quantitative assessment was carried out to evaluate the performance of iodine adsorption cartridges attached to gas and powered air-purifying respirators, under radioactive iodine concentrations, temperatures, and humidity conditions simulating the post-earthquake conditions at Fukushima Daiichi Nuclear Power Station. The test was conducted at the temperature of 30℃, the radioactive iodine concentration (radioactive methyl iodine concentration) and humidity conditions were varied, radioactive methyl iodine was directly aerated into the adsorption cartridges for a maximum of 10 hours, and the radioactive iodine removal performance of the adsorption cartridges was assessed. Some adsorption cartridges demonstrated a radioactive iodine removal performance of 10 hours or more, while the performance of others decreased with higher relative humidity. Based on the results of these performance assessments, respirator-wearing guidelines at Fukushima Daiichi Nuclear Power Station were established.
This study aimed to estimate breast glandularity in Japanese women using patient exposure conditions and tissue-equivalent materials by a conventional method. Typical glandularities in Japanese women were compared with those in European women to verify the validity of the average glandular dose estimation manual based on the EUREF protocol. Glandularity was estimated from the data of 600 patients and the model breast of the tissue-equivalent materials which had various amounts of glandular contents and thicknesses. The model breasts were measured to examine the relationships between the thickness of the glandular contents and tube loading by using an automatic exposure control system. Then, equations were established to determine glandularity from patient data. The mean glandularity in the highest compressed breast thickness (CBT) group of 36-45 mm was 72%. The mean CBT of the 184 (31%) patients with glandularities exceeding 100% was 31 mm. Glandularities in patients with CBT of 30-70 mm in the present study were higher compared to those in European women by approximately 10-20%. The results suggest that the model breast of European women might not be a suitable reference standard for more than 30% of Japanese women, who have breasts with lower CBT.
Many studies of background levels in gamma-ray measurements using a high-purity germanium detector have been reported from various aspects such as its reduction and variation. In the present work, natural gamma-ray background was thoroughly measured in a year (283.5 days in total, n=271). One measurement time was almost all either 86,400 sec (1 day) or 100,000 sec. The data was first discussed in relation to radon concentrations in the laboratory. No correlations were found between the gamma-ray count rates from 214Pb and 214Bi and radon concentrations, meaning that radon just around the germanium detector was reduced to the negligible level by the introduction of nitrogen gas. Also, the count rates of major nuclides appeared to fluctuate with the normal distribution or its similar distribution, without seasonal variations. The coefficient of variance of a few up to several tens of percent was seen, which were larger than those calculated from counting statistics alone. Furthermore, summing of all gamma-ray spectra allowed us to see neutron-induced peaks that cannot be detected in usual short-term measurements. All data obtained here would be the knowledge useful for the practice of gamma-ray measurements.