Airborne Radioactive Particles Research Articles

Identification of airborne radioactive spatial patterns in Europe – Feasibility study using Beryllium-7

The present study proposes a methodology to identify spatial patterns in airborne radioactive particles in Europe. The methodology is based on transforming the activity concentrations in the set of stations for each month (monthly index), due to the tightly spaced sampling intervals (daily to monthly), in combination with hierarchical and non-hierarchical clustering approaches, due to the lack of a priori knowledge of the number of clusters to be created. Three different hierarchical cluster methodologies are explored to set the optimal number of clusters necessary to initialize the non-hierarchical one (k-means).To evaluate this methodology, cosmogenic beryllium-7 (7Be) data, collected between 2007 and 2010 at 19 sampling stations in European Union (EU) countries and stored in the Radioactivity Environmental Monitoring (REM) database, are used. This methodology yields a solution with three distinguishable clusters (south, central and north), each with a different evolution of the 7Be monthly index. Clear differences between monthly indices are shown in both intensity and time trends, following a latitudinal distribution of the sampling stations.This cluster result is evaluated performing ANOVA analysis, considering the original 7Be activity concentrations grouped in each cluster. The statistical results (among clusters and sampling stations within clusters) confirm the spatial distribution of 7Be in Europe, and, hence, reinforce the use of this methodology. Finally, the impact of tropopause height on this grouping is successfully tested, suggesting its influence on the spatial distribution of 7Be in Europe.For airborne radioactive particles the analysis gave valuable results that improve knowledge of these atmospheric compounds in Europe. Hence, this work addresses a methodology to a grouping of airborne sampling stations, 1) allowing a better understanding of the distribution of 7Be activity concentrations in the EU, and 2) serving as a basis for further investigation of the heterogeneity of airborne radioactivity concentrations in Europe.

Size-distribution of airborne radioactive particles from the Fukushima accident

The particle size distribution of radioactive aerosols, which originated from the released radioactive materials from the Fukushima Daiichi nuclear power plant accident, has been observed using the Andersen-type classifier combined with a high volume air sampler. Estimated activity median aerodynamic diameters (AMADs) of 131I-, 134Cs- and 137Cs-aerosols were ranging from 0.56 to 0.60 μm, which were larger than that of 7Be-aerosols existing as an aerosol including cosmogenic radionuclide, about 0.2 μm.

Size distribution of radioactive particles collected at Tokai, Japan 6 days after the nuclear accident

Airborne radioactive particles released by the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident in 2011 were collected with a cascade low-pressure impactor at the Japan Atomic Energy Agency (JAEA) in Tokai, Japan, 114 km south of the FDNPP. Size-fractionated samples were collected twice, in the periods of March 17–April 1, 2011, and May 9–13, 2011. These size-fractionated samplings were carried out in the earliest days at a short distance from the FDNPP. Radioactivity of short-lived nuclides (several ten days of half-life) was determined as well as 134Cs and 137Cs. The elemental composition of size-fractionated samples was also measured. In the first collection, the activity median aerodynamic diameter (AMAD) of 129mTe, 140Ba, 134Cs, 136Cs and 137Cs was 1.5–1.6 μm, while the diameter of 131I was 0.45 μm. The diameters of 134Cs and 137Cs in the second collection were expressed as three peaks at <0.5 μm, 0.94 μm, and 7.8 μm. The 134Cs/137Cs ratio of the first collection was 1.02 in total, but the ratio in the fine fractions was 0.91. A distribution map of 134Cs/137Cs – 136Cs/137Cs ratios was helpful in understanding the change of radioactive Cs composition. The Cs composition of size fractions <0.43 μm and the composition in the 1.1–2.1 μm range (including the AMAD of 1.5–1.6 μm) were similar to the calculated compositions of fuels in the reactors No. 1 and No. 3 at the FDNPP using the ORIGEN-II code. The Cs composition collected in May, 2011 was similar to the calculation results of reactor No. 2 fuel composition. The change of Cs composition implies that the radioactive Cs was released from the three reactors at the FDNPP via different processes.

Internal radioactivity of temporary residents in Fukushima within one year after the radiological accident

Aim: In an attempt to estimate the chronological changes of health risk in Fukushima, the internal radiation doses of temporary residents in Fukushima were analyzed. Method: The internal radioactivity of 372 persons who were dispatched to the Fukushima prefecture at any time from April 2011 to March 2012 were examined using a whole body counter within 2 months after they left Fukushima. Result: 131I was only detected in April while 134Cs and 137Cs were found up to November 2011. The maximum committed effective dose and thyroid equivalent dose were 22.4 µSv and 0.1 mSv, respectively, which were observed in April 2011. The internal radioactivity was found in almost all of the interior and the coastal regions regardless of the distance from the Fukushima-Daiichi nuclear power plant. Comparison of internal doses evaluated by the whole body counter and by prediction from environmental radioactivity indicates that the intake of radioactivity in March, April and possibly May 2011, would be mainly attributable to the inhalation of airborne radioactive particles, whereas in June and later months ingestion of contaminated food would be the major route of radioactive intake. Conclusion: The risk for internal exposure existed for approximately six months after the radiological accident in almost the entire area of Fukushima, however, adverse health consequences by the radiation dose due to internal exposure seem to be negligible.

Preliminary study on aerosol particle addition calibration method for on-line quantitative analysis of airborne radioactive particles with ICP-MS

An ambient aerosol concentration enrichment system coupled with ICP-MS for real-time monitoring of airborne radioactive particles is now under development. ICP-MS is very sensitive to sample introduction conditions, so it is necessary to develop an easy-use calibration method for on-line quantitative analysis in field application. In this paper, a calibration method using standard solution instead of monodisperse particles was established and validated preliminarily. First of all, four parameters for the method were determined experimentally, including: uptake flow rate and nebulisation efficiency of the Microconcentric nebuliser, nebulisation/transport efficiency of Aridus Desolvating Sample Introduction System, and Relative Sensitivity Factor between 159 Tb and 174 Yb. Then, monodisperse terbium nitrate particles were generated by a commercial Vibrating Orifice Aerosol Generator. Continuous aerosols of ytterbium nitrate droplets were nebulised from standard solution. They were mixed together, desolvated through the membrane dryer and introduced into ICP-MS for on-line analysis of terbium nitrate particles. The air sampled from nuclear environment was also introduced into ICP-MS to investigate the effect of flow rate on instrument responses. Finally, atom numbers of 159 Tb in discrete terbium nitrate particles were determined using the calibration method and compared to the calculated value. Results show that when air flow rate increase from 10 mL min−1 to 100 mL min−1, the ratio of 159 Tb ion count to 174 Yb ion intensity keeps constant although instrument sensitivity decreases by a factor of 25. The relative standard deviation of 159 Tb atom number measured is better than 18%. The discrepancy with the calculated value could be attributed to the over-estimation of atom number in the particles generated by VOAG because there was some liquid leakage in the VOAG.

Radiation surveillance using an unmanned aerial vehicle

Radiation surveillance equipment was mounted in a small unmanned aerial vehicle. The equipment consists of a commercial CsI detector for count rate measurement and a specially designed sampling unit for airborne radioactive particles. Field and flight tests were performed for the CsI detector in the area where 137Cs fallout from the Chernobyl accident is 23–45 kBq m −2. A 3-GBq 137Cs point source could be detected at the altitude of 50 m using a flight speed of 70 km h −1 and data acquisition interval of 1 s. Respective response for 192Ir point source is 1 GBq. During the flight, the detector reacts fast to ambient external dose rate rise of 0.1 μSv h −1, which gives for the activity concentration of 131I less than 1 kBq m −3. Operation of the sampler equipped with different type of filters was investigated using wind-tunnel experiments and field tests with the aid of radon progeny. Air flow rate through the sampler is 0.2–0.7 m 3 h −1 at a flight speed of 70 km h −1 depending on the filter type in question. The tests showed that the sampler is able to collect airborne radioactive particles. Minimum detectable concentration for transuranium nuclides, such as 239Pu, is of the order of 0.2 Bq m −3 or less when alpha spectrometry with no radiochemical sample processing is used for activity determination immediately after the flight. When a gamma-ray spectrometer is used, minimum detectable concentrations for several fission products such as 137Cs and 131I are of the order of 1 Bq m −3.

イメージングプレートを利用したエアフィルタの捕集性能の簡易評価法

Collection performance such as collection efficiency and surface collection efficiency is considerably important in order to select a suitable filter for the measurement of the concentrations of airborne radioactive particles. A simple method with imaging plates is proposed to evaluate the collection performance of air filters. By comparing the collection performance of some filters with natural airborne radioactivity as a test aerosol, it was confirmed that the method could reliably evaluate the collection performance of filters.

Pneumotoxic effects of radioactive dust (RD) from a nuclear power plant in Kozloduy, Bulgaria.

Airborne radioactive particles isolated from the reactor halls of nuclear power plants are a potential risk to the respiratory system of the working staff. Such radioactive dust (RD) from the Nuclear Power Plant, Kozloduy, Bulgaria was investigated. The RD was administered intratracheally to 60 male Wistar rats as an aqueous suspension and the biological effects are estimated, using sensitive biological markers in bronchoalveolar lavage fluid (BALF) and important parameters of the pulmonary antioxidant defense. The results obtained show that RD increases the total cell number, the activities of the lactate dehydrogenase and alkaline phosphatase as well as the protein content in BALF. The activities of superoxide dismutase and catalase in lung homogenate are decreased while activity of the glutathione peroxidase and the content of non-protein sulfhydrils is elevated. It is concluded that the RD causes transitory toxic effect on lung tissue and changes the correlation between the elements of the pulmonary antioxidative defense.

ＨＥＰＡフィルタの捕集効率と除染係数

It is very important in a nuclear air cleaning system that HEPA (High Efficiency Particulate Air) filter is for reduction of releasing amounts of airborne radioactive particles. HEPA filter, by definition, has a minimum collection efficiency of 99.97% for 0.3μm particles. However, DF (Decontamination Factor), which is necessary for safety management, can not be directly derived from the efficiency. And the current standard defined for 0.3μm particles has no scientific justification, because it has been found that the most penetrating particle size through HEPA filter is not always 0.3μm.In the present paper, a numerical experiment was made in order to estimate a relationship between DF and the efficiency. And new standard, in which the minimum DF is able to be easily obtained, was proposed. In the multistage filtration system, it was found that lower values of DF was possible to be experimentally indicated in the second and the third stages, even if the collection performance of the each filter is the same.

Radiogenic lung cancer in man: Exposure-effect relationship

Comparisons are made of lung cancer data from five groups of miners exposed to a wide range of levels of air-borne radioactive particles. Partly because of variable quality of the data for the different groups, alternative estimates of lung cancer risk are used: incidence or mortality rates, ratio of observed to expected rates and proportion of lung cancer to all deaths. These three criteria agree that lung cancer in mining groups tends to be directly proportional to mean radiation exposure. After assuming linearity of this relationship and absence of a dose-rate effect, it is estimated that one rad to the bronchial walls of one million persons produces about one lung cancer per year, and that the average integral dose required to produce one lung cancer is 1.3 × 10 5 gm rad. An exposure of 120 WLM (estimated to equal 360 rad) appears to double the lung cancer incidence characteristic of the general population.

Determination of the Respiratory Deposition and Size of Airborne Radioactive Particles by Graded Filtration

Determination of the Respiratory Deposition and Size of Airborne Radioactive Particles by Graded Filtration

The Solubility of Airborne Radioactive Particles

Abstract Membrane filters of various pore sizes were used to collect airborne radioactive particles. The samples were counted for beta radioactivity, then washed with solvents. The filters were counted to determine the insoluble fraction, and the filtrate was passed through exchange resins to determine the gross ionic form. The radioactive particles showed about 40 per cent solubility in water at pH 7. The solubility increased with a pH change in either direction, but was greater for the low pH. The solubility also increased with decreasing particle size.

The solubility of airborne radioactive particles.

Abstract Membrane filters of various pore sizes were used to collect airborne radioactive particles. The samples were counted for beta radioactivity, then washed with solvents. The filters were counted to determine the insoluble fraction, and the filtrate was passed through exchange resins to determine the gross ionic form. The radioactive particles showed about 40 per cent solubility in water at pH 7. The solubility increased with a pH change in either direction, but was greater for the low pH. The solubility also increased with decreasing particle size.