135Cs activity and 135Cs/137Cs atom ratio in environmental samples before and after the Fukushima Daiichi Nuclear Power Plant accident

Innovative ICP-MS/MS Method To Determine the 135Cs/137Cs Ratio in Low Activity Environmental Samples

The ¹³⁵Cs/¹³⁷Cs isotopic ratio is a powerful tool for tracing the origin of radioactive contamination. Since the Fukushima accident, this ratio has been measured by mass spectrometry in several highly contaminated environmental matrices mainly collected near nuclear accident exclusion zones and former nuclear test areas. However, few data were reported at ¹³⁷Cs environmental levels (<1 kBq kg^-1). This is explained by the occurrence of analytical challenges related to the very low radiocesium content at the environmental level with the large presence of mass interferences, making ¹³⁵Cs and ¹³⁷Cs measurements difficult. To overcome these difficulties, a highly selective procedure for Cs extraction/separation combined with an efficient mass spectrometry measurement must be applied on a quantity of ca. 100 g of soil. In the current research, an innovative inductively coupled plasma-tandem mass spectrometry (ICP-MS/MS) method has been developed for the ¹³⁵Cs/¹³⁷Cs ratio measurement in low activity environmental samples. The use of ICP-MS/MS led to a powerful suppression of ¹³⁵Cs and ¹³⁷Cs interferences by introducing N₂O, He, and, for the first time, NH₃, into the collision-reaction cell. By adjusting the flow rates of these gases, the best compromise between a maximum signal in Cs and an effective interference elimination was achieved allowing a high Cs sensitivity of more than 1.10⁵ cps/(ng g^-1) and low background levels at m/z 135 and 137 lower than 0.6 cps. The accuracy of the developed method was successfully verified by analyzing two certified reference materials (IAEA-330 and IAEA-375) commonly used in the literature as validation samples and three sediment samples collected in the Niida River catchment (Japan) impacted by the Fukushima fallout.

New Approach To Understanding the Experimental 133Cs NMR Chemical Shift of Clay Minerals via Machine Learning and DFT-GIPAW Calculations

Structural determination of adsorbed atoms on layered structures such as clay minerals is a complex subject. Radioactive cesium (Cs) is an important element for environmental conservation, so it is vital to understand its adsorption structure on clay. The nuclear magnetic resonance (NMR) parameters of ¹³³Cs, which can be determined from solid-state NMR experiments, are sensitive to the local neighboring structures of adsorbed Cs. However, determining the Cs positions from NMR data alone is difficult. This paper describes an approach for identifying the expected atomic positions on clay minerals by combining machine learning (ML) with experimentally observed chemical shifts. A linear ridge regression model for ML is constructed from the smooth overlap of atomic position descriptor and gauge-including projector augmented wave (GIPAW) ab initio data. The constructed ML model predicts the GIPAW data to within a 3 ppm root-mean-squared error. At this stage, the ¹³³Cs chemical shifts can be instantaneously calculated from the Cs positions on any clay layers using ML. The inverse analysis, which derives the atomic positions from experimentally observed chemical shifts, is developed from the ML model. The input data for the inverse analysis are the layer structure and the experimentally observed chemical shifts. The Cs positions for the targeted chemical shifts are then output. Inverse analysis is applied to montmorillonite, and the resultant Cs positions are found to be consistent with previous results (Ohkubo, T.; et al. J. Phys. Chem. A 2018, 122, 9326-9337). The Cs positions on saponite clay are also clarified from experimentally observed chemical shifts and inverse analysis.

Long-term variation of 90Sr and 137Cs in environmental and food samples around Qinshan nuclear power plant, China

Environmental radioactivity monitoring in the surroundings of nuclear facilities is important to provide baseline data for effective detection in case of any radioactive release in the region. In this work, we report for the first time the long-term monitoring data of ¹³⁷Cs and ⁹⁰Sr in environmental and food samples around Qinshan nuclear power plant in 2012–2019. The distribution levels, temporal variations and source terms of ¹³⁷Cs and ⁹⁰Sr in the investigated samples were discussed. The annual effective dose (AED) for the local population from the ingestion of foods was also evaluated. Peak values of ⁹⁰Sr and ¹³⁷Cs concentrations and ¹³⁷Cs/⁹⁰Sr activity ratio were observed in total atmospheric deposition in 2016 and some water and food samples in the following years. This seems to be associated to an additional radioactive input, mostly likely from the operational release of a local facility. This demonstrates that ⁹⁰Sr and ¹³⁷Cs, especially the ¹³⁷Cs/⁹⁰Sr activity ratio, are sensitive indicators for detecting potential radioactive releases. Nevertheless, overall ⁹⁰Sr and ¹³⁷Cs activity concentrations measured during 2012–2019 in this work were at the background levels with average AED far below the internationally permissible limit and recommendation.

Support activities in Namie Town, Fukushima undertaken by Hirosaki University

This paper does not necessarily reflect the views of the International Commission on Radiological Protection.Several radiation monitoring research projects are underway on dose assessment, biological analysis, and risk communication under an agreement with Namie Town. Indoor radon and thoron progeny concentrations have been measured using passive-type monitors to estimate internal doses due to inhalation. In addition, airborne radiocaesium concentrations at five points in Namie Town have been analysed using a high-purity germanium detector to estimate internal doses for comparison with radon. External radiation doses from natural and artificial radionuclides have also been estimated using an in-situ gamma-ray spectrometer. Other support activities are mentioned briefly in this article.

Determination of Characteristic vs Anomalous 135Cs/137Cs Isotopic Ratios in Radioactively Contaminated Environmental Samples

A contamination with the ubiquitous radioactive fission product ¹³⁷Cs cannot be assigned per se to its source. We used environmental samples with varying contamination levels from various parts of the world to establish their characteristic ¹³⁵Cs/¹³⁷Cs isotope ratios and thereby allow their distinction. The samples included biological materials from Chernobyl and Fukushima, historic ashed human lung tissue from the 1960s from Austria, and trinitite from the Trinity Test Site, USA. After chemical separation and gas reaction shifts inside a triple quadrupole ICP mass spectrometer, characteristic ¹³⁵Cs/¹³⁷Cs isotope signatures (all as per March 11, 2011) were obtained for Fukushima- (∼0.35) and Chernobyl-derived (∼0.50) contaminations, in agreement with the literature for these contamination sources. Both signatures clearly distinguish from the characteristic high ratio (1.9 ± 0.2) for nuclear-weapon-produced radiocesium found in human lung tissue. Trinitite samples exhibited an unexpected, anomalous pattern by displaying a low (<0.4) and nonuniform ¹³⁵Cs/¹³⁷Cs ratio. This exemplifies a ¹³⁷Cs-rich fractionation of the plume in a nuclear explosion, where ¹³⁷Cs is a predominant species in the fireball. The onset of ¹³⁵Cs was delayed because of the longer half-life of its parent nuclide ¹³⁵Xe, causing a spatial separation of gaseous ¹³⁵Xe from condensed ¹³⁷Cs, which is the reason for the atypical ¹³⁵Cs/¹³⁷Cs fractionation in the fallout at the test site.

External Cesium-137 doses to humans from soil influenced by the Fukushima and Chernobyl nuclear power plants accidents: a comparative study

External exposure to gamma-photon irradiation from soil contamination due to nuclear power plant (NPP) accidents has significant contribution to human radiation exposure in the proximity of the NPP. Detailed absorbed doses in human organs are rarely reported in the literature. We applied the Monte Carlo Neutron Particle (MCNP) transport code to calculate and compare the absorbed doses in different human organs. The absorbed doses by gamma-photon radiation were from cesium-137 (137Cs) in soil contaminated by the two major NPP accidents. More serious and wide-spread impacts of the Chernobyl NPP accident on soil contamination in Ukraine, Belarus, Russia and countries as far as Sweden and Greece were due to the inland location, radiative plume transport pathway and high 137Cs emission strength (9 times the Fukushima emission). Based on our MCNP calculations, the largest absorbed dose was found in skin. The maximum calculated external 137Cs annual effective dose received from the Chernobyl accident was 10 times higher relative to the Fukushima accident. Our calculated effective doses at various influenced areas were comparable to those available in the literature. The calculated annual effective doses at areas near the Fukushima and Chernobyl NPPs exceeded the ICRP recommendation of 1 mSv yr-1.

Determination of Ultratrace Level 135Cs and 135Cs/137Cs Ratio in Small Volume Seawater by Chemical Separation and Thermal Ionization Mass Spectrometry

The atomic ratio of ¹³⁵Cs/¹³⁷Cs is a powerful fingerprint for distinguishing the source terms of radioactive contamination and tracing the circulation of water masses in the ocean. However, the determination of the ¹³⁵Cs/¹³⁷Cs ratio is very difficult due to the ultratrace level of ¹³⁵Cs (<0.02 mBq/m³) and ¹³⁷Cs (<2 Bq/m³) in the ordinary seawater samples. In this work, a sensitive method was developed for determination of ¹³⁵Cs concentration and ¹³⁵Cs/¹³⁷Cs ratio in seawater using chemical separation combined with thermal ionization mass spectrometry (TIMS) measurement. Cesium was first preconcentrated from seawater using ammonium molybdophosphate-polyacrylonitrile column chromatography and then purified using cation exchange chromatography to remove the interferences. With this method, decontamination factors of 6.0 × 10⁶ for barium and 1800 for rubidium and a chemical yield of more than 60% for cesium were achieved. By using glucose as an activator, the ionization efficiency of cesium was significantly improved to 50.6%, and a constant high current of Cs⁺ (20 V) can be maintained for more than 180 min, which ensures sensitive and reliable measurement of low level ¹³⁵Cs and ¹³⁷Cs. Detection limits of 4.0 × 10^-17 g/L for both ¹³⁵Cs and ¹³⁷Cs for 200 mL seawater were achieved, which enables the accurate determination of ¹³⁵Cs concentration and ¹³⁵Cs/¹³⁷Cs ratio in a small volume of seawater samples (<200 mL). The developed method has been validated by analysis of seawater reference material IAEA-443. Seawater samples collected from the Greenland Sea, Baltic Sea, and Danish Straits have been successfully analyzed for ¹³⁵Cs concentrations and ¹³⁵Cs/¹³⁷Cs ratios, and the results showed that ¹³⁵Cs concentrations in the seawater of the Baltic Sea is much higher than that in the Greenland Sea, which is attributed to the high deposition of Chernobyl accident derived radiocesium in the Baltic Sea region.

Isotopic ratios of uranium and caesium in spherical radioactive caesium-bearing microparticles derived from the Fukushima Dai-ichi Nuclear Power Plant

Spherical radioactive caesium (Cs)-bearing microparticles (CsMPs) were emitted during the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident in March, 2011. The emission source (timing) and formation process of these particles remain unclear. In this study, the isotopic ratios of uranium (²³⁵U and ²³⁸U) and caesium (¹³³Cs, ¹³⁴Cs, ¹³⁵Cs, and ¹³⁷Cs) isotopes in the five spherical CsMPs (ca. 2 μm in size) sampled at 50 km west of the FDNPP were determined using secondary ion mass spectrometry and laser ablation-ICPMS, respectively. Results showed that the ²³⁵U/²³⁸U ratios of CsMPs were homogeneous (1.93 ± 0.03, N = 4) and close to those estimated for the fuel cores in units 2 and 3, and that the Cs isotopic ratios of CsMP were identical to those of units 2 and 3. These results indicated that U and Cs in the spherical CsMPs originated exclusively from the fuel melt in the reactors. Based on a thorough review of literatures related to the detailed atmospheric releases of radionuclides, the flow of plumes from the FDNPP reactor units during the accident and the U and Cs isotopic ratio results in this study, we hereby suggest that the spherical CsMPs originate only from the fuel in unit 2 on the night of 14 March to the morning of 15 March. The variation range of the analysed ²³⁵U/²³⁸U isotopic ratios for the four spherical particles was extremely narrow. Thus, U may have been homogenised in the source through the formation of fuel melt, which ultimately evaporating and taken into CsMPs in the reactor and was released from the unit 2.

Sources and variation of isotopic ratio of airborne radionuclides in Western Arctic lichens and mosses

This research concerned radioactivity of lichens and mosses from coastal zones of the Canadian Arctic and Alaska. Over 50 samples were collected from 7 positions during two scientific expeditions in 2012 and 2013. The tundra contamination caused by anthropogenic radionuclides was relatively low, reaching mean values with SD's of: 17.4 ± 3.5 Bq/kg for ⁹⁰Sr, 14.0 ± 2.9 Bq/kg for ¹³⁴Cs, 38.4 ± 7.5 Bq/kg for ¹³⁷Cs, 0.86 ± 0.24 Bq/kg for ^239+240Pu, 0.065 ± 0.017 Bq/kg for ²³⁸Pu and 0.50 ± 0.13 Bq/kg for ²⁴¹Am. The increase of activity concentration with increasing latitudes was noticed mostly in regard to ⁹⁰Sr, Pu isotopes and ²⁴¹Am. The analysis of isotopic ratios exhibited dominant contribution of the global fallout (+SNAP 9A satellite re-entry fallout) for the presence of plutonium isotopes and ²⁴¹Am. The Fukushima fallout signature was identified in a few lichens from Alaska. However, the influence of additional unknown factor on the occurrence of ⁹⁰Sr and ¹³⁷Cs has been detected in western part of Canadian Arctic. Natural radioisotopes of thorium and uranium were found throughout the entire investigated region and the average values of activity concentration with SD's were as follows: 2.92 ± 0.47 Bq/kg for ²³⁰Th, 2.61 ± 0.48 Bq/kg for ²³²Th, 4.32 ± 0.80 Bq/kg for ²³⁴U and 3.97 ± 0.71 Bq/kg for ²³⁸U. Examined Western Arctic tundra was not affected with any technically enhanced natural radioactivity.

Theoretical study on the ability of bicyclic cryptands to separate alkali-metal isotopes by ion exchange

Cryptand [2.2.2] collects heavier isotope ¹³⁷Cs more readily than [3.2.2] that gives a potential minimum at d = d_e.

Spatial pattern of plutonium and radiocaesium contamination released during the Fukushima Daiichi nuclear power plant disaster

Plutonium and radiocaesium are hazardous contaminants released by the Fukushima Daiichi nuclear power plant (FDNPP) disaster and their distribution in the environment requires careful characterisation using isotopic information. Comprehensive spatial survey of ¹³⁴Cs and ¹³⁷Cs has been conducted on a regular basis since the accident, but the dataset for ¹³⁵Cs/¹³⁷Cs atom ratios and trace isotopic analysis of Pu remains limited because of analytical challenges. We have developed a combined chemical procedure to separate Pu and Cs for isotopic analysis of environmental samples from contaminated catchments. Ultra-trace analyses reveal a FDNPP Pu signature in environmental samples, some from further afield than previously reported. For two samples, we attribute the dominant source of Pu to Reactor Unit 3. We review the mechanisms responsible for an emergent spatial pattern in ^134,135Cs/¹³⁷Cs in areas northwest (high ¹³⁴Cs/¹³⁷Cs, low ¹³⁵Cs/¹³⁷Cs) and southwest (low ¹³⁴Cs/¹³⁷Cs, high ¹³⁵Cs/¹³⁷Cs) of FDNPP. Several samples exhibit consistent ^134,135Cs/¹³⁷Cs values that are significantly different from those deposited on plant specimens collected in previous works. A complex spatial pattern of Pu and Cs isotopic signature is apparent. To confidently attribute the sources of mixed fallout material, future studies must focus on analysis of individual FDNPP-derived particles.

Can 129I track 135Cs, 236U, 239Pu, and 240Pu apart from 131I in soil samples from Fukushima Prefecture, Japan?

In the present study, ¹²⁹I activities and ¹²⁹I/¹²⁷I atom ratios were measured in 60 soil samples contaminated by the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident. The ¹²⁷I concentrations, ¹²⁹I activities, and ¹²⁹I/¹²⁷I atom ratios in dry-weight were observed to be 0.121–23.6 mg kg⁻¹, 0.962–275 mBq kg⁻¹, and (0.215–79.3) × 10⁻⁷, respectively. The maximum values of both ¹²⁹I activities and ¹²⁹I/¹²⁷I atom ratios in Japanese soil increased about three orders of magnitude due to this accident. The equation logy = 0.877logx + 0.173 (Pearson’s r = 0.936; x, ¹²⁹I concentration; y, ¹³¹I concentration; decay-corrected to March 11, 2011) instead of a simple constant may be a better way to express the relationship between ¹²⁹I and ¹³¹I in Japanese soil affected by both global fallout and FDNPP accident fallout. In addition, a moderate correlation was observed between ¹²⁹I and ¹³⁵Cs (logy = 0.624logx + 1.01, Pearson’s r = 0.627; x, ¹²⁹I activity; y, ¹³⁵Cs activity). However, ¹²⁹I presented larger fractionations with less volatile radionuclides, such as ²³⁶U, ²³⁹Pu, and ²⁴⁰Pu. These findings indicated ¹³⁵Cs could be roughly estimated from ¹²⁹I or ¹³¹I; this is advantageous as fewer ¹³⁵Cs data are available and ¹³⁵Cs/¹³⁷Cs is being considered a promising tracer during radiocesium source identification.

Isotopic compositions of 236U, 239Pu, and 240Pu in soil contaminated by the Fukushima Daiichi Nuclear Power Plant accident

Six years after the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, data for ²³⁶U and ²³⁶U/²³⁸U have remained limited to a few heavily contaminated samples. In the present study, activities of ²³⁶U, ²³⁹Pu, and ²⁴⁰Pu, along with other U isotopes in 46 soil samples both heavily and lightly contaminated by this accident were measured by inductively coupled plasma–mass spectrometry (ICP-MS) and triple-quadrupole ICP-MS. The ²³⁶U activities and ²³⁶U/²³⁸U atom ratios in these soil samples were in the range of (0.469–24.4) × 10⁻⁵ Bq kg⁻¹ and ((0.099–1.35) × 10⁻⁷), respectively. Higher ²⁴⁰Pu/²³⁹Pu atom ratios (0.245–0.312) and ²³⁸Pu/^239+240Pu activity ratios (0.859–1.62) indicated Pu contamination originated from this accident and global fallout in some samples. For those soil samples along with black substances collected along roads in Fukushima Prefecture, high linear correlations were presented between ²³⁶U activities and ^239+240Pu activities (Pearson’s r = 0.755, p < 0.01), and between ²³⁶U activities and ²³⁸Pu activities (Pearson’s r = 0.844, p < 0.01). The analysis of these soil samples confirmed the release of ²³⁶U, although in trace amounts, during the FDNPP accident.