In the Nuclear Science Research Institute, Japan Atomic Energy Agency (JAEA), in order to oxidize 14C, which exists in various chemical forms in exhaust, into 14CO2, a copper oxide (CuO) catalyst is introduced after heating to 600℃. Our goal was to establish a safer 14C monitoring system by lowering the heating temperature required for the catalyst; therefore, we developed a new hydrophobic palladium/silicon dioxide (Pd/SiO2) catalyst that makes the carrier's surface hydrophobic. In these experiments, catalysts CuO, platinum/aluminum oxide (Pt/Al2O3), palladium/zirconium dioxide (Pd/ZrO2), hydrophobic Pd/SiO2, and hydrophilic Pd/SiO2 were ventilated with standard methane gas, and we compared the oxidation efficiency of each catalyst at different temperatures. As a result, we determined that the hydrophobic Pd/SiO2 catalyst had the best oxidation efficiency. By substituting the currently used CuO catalyst with the hydrophobic Pd/SiO2 catalyst, we will be able to lower the working temperature from 600℃ to 300℃ and improve the safety of the monitoring process.
There is no radiation survey meter that can discriminate among alpha particles, beta particles, and gamma-rays with one material. Previously, undoped poly(ethylene terephthalate) (PET) has been shown to be an effective material for beta particle and gamma-ray detection. Here, we demonstrate a prototype survey meter for alpha particles based on undoped PET. A 140 × 72 × 1-mm PET substrate was fabricated with mirrored surfaces. It was incorporated in a unique detection section of the survey meter that directly detects alpha particles. The prototype exhibited an unambiguous response to alpha particles from a 241Am radioactive source. These results demonstrate that undoped PET can perform well in survey meters for alpha particle detection. Overall, the PET-based survey meter has the potential to detect multiple types of radiation, and will spawn an unprecedented type of radiation survey meter based on undoped aromatic ring polymers.
Radiation Effects Association has carried out radiation epidemiological study for nuclear industry workers during 1990-2010. We assembled a cohort of 204,103 workers. The average cumulative dose was 13.8 mSv (median 1.0 mSv, interquartile range (IQR) 0.0-10.7 mSv) and the average follow-up period was 14.2 year. The present report has not concluded that low-dose radiation increases cancer mortality based on the follow-up data through 2010. One reason is that analyses among 75,442 respondents― the average cumulative dose was 25.8 mSv (median 6.3 mSv, IQR 0.2-28.0 mSv) and the average follow-up period was 8.3 year―to the lifestyle surveys revealed the decrease of the ERR after adjusting for smoking habits or educational year, suggesting that confounder has a large effect on the association between radiation exposure and mortalities in the cohort. Another reason is that in analyses on all cohort members, no significant ERR was observed in all death, and leukemia excluding chronic lymphoid leukemia. Significant ERR was seen in all cancers excluding leukemia, but this significance of the ERR might be affected by confounder such as smoking, because the significance of the ERR in all cancers excluding leukemia originates in the significance of the ERR in lung cancer.
The accident at the Fukushima nuclear power plant in 2011 caused the release of large amounts of tellurium (Te) isotopes, with radio-cesium (Cs) and radio-iodine (I), into the environment. The total amounts of 127mTe and 129mTe released from the nuclear power plant were estimated as 1.1 × 1015 and 3.3 × 1015 Bq, respectively. At the location where the deposition of 129mTe was relatively large, the ratio of the radioactivity of 129mTe to that of 137Cs reportedly reached 1.49 on June 14, 2011. Since 127mTe has a relatively long half-life, it possibly contributed to the internal radiation dose at the early stage after the accident. In this paper, the ratio of the committed effective dose of 127mTe to that of 137Cs after the oral ingestion of rice was estimated by using various reported parameters. The relevant parameters are: 1) the deposition ratios of 127mTe, 129mTe, and 134Cs to 137Cs; 2) the deposition ratio of 127mTe to 129mTe; 3) the transfer factors of Te and Cs; and 4) the effective dose coefficients for 127mTe, 129mTe, 134Cs, and 137Cs. The ratios of the committed effective dose of 127mTe to that of 137Cs were calculated for adults after a single ingestion at the time of the rice harvest. The ratio was 0.45 where the 129mTe/137Cs in the soil was higher and 0.05 where the level of 129mTe/137Cs was average. The ratio of the committed effective dose from 129mTe and 127mTe to that from 137Cs for one year reached 0.55 and 9.03 at the location where the level of 129mTe/137Cs in the soil was higher. These data could indicate that radioactive Te should not be disregarded in reconstructing the internal radiation dose from food for one year after the accident.
Many nuclear facilities are located in Aomori Prefecture, Japan. However, no detailed dose rate distribution map of Aomori Prefecture, including its mountain regions has been reported since the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident. Thus, a car-borne survey which used a 3-in × 3-in NaI(Tl) scintillation spectrometer was done throughout the prefecture for the purposes of making a dose distribution map and estimating the annual external dose. These results have been published in the same issue of this journal. On the other hand, many researchers have performed car-borne surveys in Fukushima Prefecture after the FDNPP accident. In this paper, the methods of car-borne survey of the present author are explained in detail. 1) The relationship between the total counts per minute of a gamma-ray pulse height distribution and an absorbed dose rate in air is examined for the estimation of dose rate conversion factor. 2) The relationship between count rates outside and inside the car is examined for the estimation of the shielding factor by car body. 3) The uncertainties to the counts inside the car, the dose rate conversion factor and the shielding factor are evaluated according to the Guide to the Expression of Uncertainty in Measurement published by the Joint Committee for Guides in Metrology. 4) The gamma-ray pulse height distributions are unfolded using a 22 × 22 response matrix for the analysis of activity concentrations in soil of 40K, 238U and 232Th and the contributions of their nuclides to absorbed dose rate in air. 5) The distribution map of absorbed dose rate in air of Aomori Prefecture is drawn using the Generic Mapping Tool which was developed by Hawaii University.
Many nuclear facilities are located within Aomori Prefecture, Japan. However, no detailed dose rate distribution map of Aomori Prefecture, including its mountain regions has been reported since the Fukushima Daiichi Nuclear Power Plant accident. A car-borne survey which used a 3-in × 3-in NaI(Tl) scintillation spectrometer was carried out throughout the prefecture for the purposes of making a dose distribution map and estimating the annual external dose. The average absorbed dose rate in air and the annual effective dose were found to be 22 ± 5 nGy h-1 and 0.20 ± 0.08 mSv, respectively. These average values for all of Aomori Prefecture were respectively 44% and 59% of the nationwide average values. The average values with standard deviations of activity concentrations in soil of 40K, 238U and 232Th were 234 ± 148, 15 ± 6, 12 ± 6 Bq kg-1, respectively. The average values of contributions of 40K, 238U and 232Th to absorbed dose rates in air were 39%, 29% and 32%, respectively. The contributions of 134Cs and 137Cs to the absorbed dose rates in air were judged to be negligible.
137Cs is an important long-term contributor to radiation dose and risk following a nuclear accident. Its high abundance (about 6 atoms per 100 fissions), the 30.17 year physical half-life and its biological availability all made it of special concern in the Fukushima accident. After this event, extensive amounts of time and money were invested to clean-up and limit the transport of 137Cs into the food chain. However, since the biological and environmental half-lives of 137Cs are short, they limit its availability and exposure in people. This paper demonstrates how historical data on the environmental half-life of 137Cs in both milk and humans changes, in the absence of remedial action, and modifies dose and risk. 137Cs activity in milk from selected dairy farms and total body burdens in the farmers exposed to fallout in Utah were determined. The activity in milk decreased each year from spring to summer, while the activity in the farmers increased with time and varied by a factor of about ten (100-1,400 Bq). Fallout provided a continuing resupply of 137Cs into humans. If resupply were to be prevented or limited by remediation, 137Cs would clear from the body as a function of the effective half-life of 104 days measured in Fukushima. Blocking the entry of 137Cs would have reduced the body-burden in Utah farmers by a factor of almost ten. Data in this manuscript provides a baseline, from which the influence of remedial actions on dose and risk associated with evacuation and cleanup can be compared.