Low level detection of <Superscript>135</Superscript>Cs and <Superscript>137</Superscript>Cs in environmental samples by ICP-MS

The measurement of fission product cesium isotopes ¹³⁵Cs and ¹³⁷Cs at low femtogram (fg) 10⁻¹⁵ levels in ground water by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) is reported. To eliminate the natural barium isobaric interference on the cesium isotopes, in-line chromatographic separation of the cesium from barium was performed followed by high sensitivity ICP-MS analysis. A high efficiency desolvating nebulizer system was employed to maximize ICP-MS sensitivity ~10 cps/fg. The three sigma detection limit for ¹³⁵Cs was 2 fg/mL (0.1 μBq/mL) and for ¹³⁷Cs 0.9 fg/mL (0.0027 Bq/mL) measured from the standard with analysis time of less than 30 min/sample. Cesium detection and 135/137 isotope ratio measurement at very low femtogram levels using this method in a spiked ground water matrix is also demonstrated.     

Concentration of <Superscript>137</Superscript>Cs in seawater surrounding East Malaysia

Studies of ¹³⁷Cs distribution in East Malaysia were carried out as part of a marine coastal environment project. The results of measurements will serve as baseline data and background reference level for Malaysia coastline. Twenty-one locations were identified along the coastline of East Malaysia, and from each location water samples were collected at the surface of the seawater. Ten near-shore locations were also selected and seawater was collected at three different depths. Large volumes of seawater were collected and the co-precipitation technique was employed to concentrate cesium. A known amount of ¹³⁴Cs tracer was added as yield determinant, followed by addition of copper(II) nitrate salt and a solution of potassium hexacyanoferrate(II) trihydrate, to precipitate the total cesium. The precipitate slurry was oven dried at 60 °C for 1–2 days, finely ground and counted using gamma-ray spectrometry. The activity of ¹³⁷Cs was determined by measuring the peak area under the photopeak of the gamma-spectrum at 661 keV, which is equivalent to gamma-intensity corrected for detection efficiency, percentage of gamma-ray abundance of the radionuclide and recovery of ¹³⁴Cs tracer. There were no significant differences of ¹³⁷Cs activities both in surface and bottom water samples at 95% confidence level. The activity of ¹³⁷Cs (for all samples) was found to be in the range of 1.47 to 3.36 Bq/m³ and 1.69 to 3.32 Bq/m³ for Sabah and Sarawak, respectively.     

Soil-to-plant transfer factors of fallout <Superscript>137</Superscript>Cs and native <Superscript>133</Superscript>Cs in various crops collected in Japan

In order to compare the soil-to-plant transfer factors (TFs) of fallout ¹³⁷Cs and those of native stable ¹³³Cs, concentrations of these isotopes were determined in various crops and the associated soils collected throughout Japan. The results showed that TF-¹³⁷Cs was 11 times higher than TF-native ¹³³Cs for brown rice, while those values were almost the same for leafy vegetables. Possibly, fallout ¹³⁷Cs would be more mobile and more easily adsorbed by plants than native ¹³³Cs in the soil because a part of the ¹³³Cs is in a soil structure where it is hard to replace with ¹³⁷Cs. However, ¹³⁷Cs and native ¹³³Cs have reached an approximately isotopic equilibrium in the bioavailable fraction in the soils, therefore, the TF-native ¹³³Cs can be used for long-term transfer of ¹³⁷Cs in the environment.     

Migration processes of <Superscript>137</Superscript>Cs and <Superscript>90</Superscript>Sr in compartments of a lake ecosystem

Summary The dispersion of radioactive substances in the environment following nuclear weapon tests in atmosphere since 1954 and accidents to nuclear plants, like that in Chernobyl in 1986, have allowed us to study the migration processes of some radionuclides in complex ecosystems such as lakes are. In the present paper the behavior of ¹³⁷Cs and ⁹⁰Sr in different compartments of the Monterosi Lake (central Italy) was assessed. The ¹³⁷Cs concentration was measured in lake water as well as sediment, stream water, aquatic plant and fish samples. ⁹⁰Sr concentration in water and sediments was also determined. A total inventory of 4206±76 Bq ^. m^-2 and 958±79 Bq ^. m^-2 (on 27/6/01) has been found for ¹³⁷Cs and ⁹⁰Sr, respectively. The experimental data presented here allow to calibrate theoretical models predicting the temporal trend of radionuclide concentration in similar ecosystems. Moreover, information on cesium and strontium migration processes can be extended to other pollutants having similar environmental behavior.     

Relationships among <Superscript>137</Superscript>Cs, <Superscript>133</Superscript>Cs,and K in plant uptake observed in Japanese agricultural fields

Plant uptake of radiocesium (¹³⁷Cs) was investigated in consideration of the relationships with naturally existing ¹³³Cs and potassium (K). We first determined plant-unavailable fraction of ¹³⁷Cs in soil by batch sorption and sequential extraction methods with a radiotracer. Then, using the data obtained from the batch sorption and extraction methods, we clarified the relationships of plant-available and plant-unavailable fractions between ¹³⁷Cs, ¹³³Cs, and K in soil. Additionally, ¹³⁷Cs concentrations in crop were estimated using ¹³⁷Cs in soil and several factors, i.e. fixation ratio of ¹³⁷Cs in soil, cation exchange capacity, and K concentration in crop. The results implied that the fixation ratio of ¹³⁷Cs in soil was a very important key to understanding ¹³⁷Cs plant uptake.     

Comparison of thermal ionization mass spectrometry and Multiple Collector Inductively Coupled Plasma Mass Spectrometry for cesium isotope ratio measurements

In the nuclear domain, precise and accurate isotopic composition determination of elements in spent nuclear fuels is mandatory to validate neutron calculation codes and for nuclear waste disposal. The present study presents the results obtained on Cs isotope ratio by mass spectrometric measurements. Natural cesium is monoisotopic (¹³³Cs) whereas cesium in spent fuels has 4 isotopes (¹³³Cs, ¹³⁴Cs, ¹³⁵Cs, and ¹³⁷Cs). As no standard reference material is available to evaluate the accuracy of Cs isotopic measurements, a comparison of cesium isotopic composition in spent nuclear fuels has been performed between Thermal Ionization Mass Spectrometry (TIMS) and a new method involving Multiple Collector Inductively Coupled Plasma Mass Spectrometry (MC-ICPMS) measurements. For TIMS measurements, isotopic fractionation has been evaluated by studying the behavior of cesium isotope ratios (¹³³Cs/¹³⁷Cs and ¹³⁵Cs/¹³⁷Cs) during the analyses. For MC-ICPMS measurements, the mass bias effects have been corrected with an external mass bias correction using elements (Eu and Sb) close to cesium masses. The results obtained by the two techniques show good agreement: relative difference on ¹³³Cs/¹³⁷Cs and ¹³⁵Cs/¹³⁷Cs ratios for two nuclear samples, analyzed after chemical separation, ranges from 0.2% to 0.5% depending on the choice of reference value for mass bias correction by MC-ICPMS. Finally the quantification of the ¹³⁵Cs/²³⁸U ratio by the isotope dilution technique is presented in the case of a MOx (mixed oxide) spent fuel sample. Evaluation of the global uncertainties shows that this ratio could be defined at an uncertainty of 0.5% (k = 2). The intercomparison between two independent mass spectrometric techniques is fundamental for the evaluation of uncertainty when no isotopic standard is available.     

Global fallout levels of <Superscript>99</Superscript>Tc and activity ratio of <Superscript>99</Superscript>Tc/<Superscript>137</Superscript>Cs in the Pacific Ocean

Summary Global fallout levels of ⁹⁹Tc and ¹³⁷Cs of surface seawater in the Pacific Ocean were measured. The ⁹⁹Tc concentrations ranged from 0.62 to 3.33 mBq^. m^-3and 5 of 6 samples showed less than 1 mBq^. m^-3except one sample taken in the Great Barrier Reef, Australia. The ¹³⁷Cs concentrations ranged from 2.13 to 3.14 Bq^. m^-3, showing a gradual decrease in the North Pacific toward the equator and a constant level in the South Pacific. The ⁹⁹Tc/¹³⁷Cs activity ratios ranged from 2.5^. 10^-4to 2.9^. 10^-4, which is very close to that calculated theoretically from the fission yield.     

Mixing of atmospheric <Superscript>210</Superscript>Pb and <Superscript>7</Superscript>Be and <Superscript>137</Superscript>Cs and <Superscript>90</Superscript>Sr fission products in four characteristic soil types

Depth distribution of atmospheric ²¹⁰Pb and ⁷Be and ⁹⁰Sr and ¹³⁷Cs fission products was measured in two types of aeolian soils (desert dust and volcanic ash), irrigated paddy soil and strongly acidic soil. The depth dependence of ²¹⁰Pb, ⁷Be and ¹³⁷Cs show that these radionuclides have been diffused as solid soil particles in surface soil layers. In aeolian soil layers, about 50% of ⁹⁰Sr were diffused in surface soil layer and the remaining 50% had penetrated to deeper layers. The half of the fission particles containing ⁹⁰Sr were shown to have decomposed over the past 35 years.     

Distribution of <Superscript>137</Superscript>Cs, <Superscript>40</Superscript>K and <Superscript>7</Superscript>Be in silver fir-tree (<Emphasis Type="Italic">Abies alba</Emphasis> L.) from Gorski Kotar,Croatia

Distribution of ¹³⁷Cs, ⁴⁰K and ⁷Be in tissues of the silver fir-tree was studied. Samples of the shoots were taken at six locations in Croatia during five years. Shoots were cut according to the year of growth and analyzed. Distribution between needles and twigs was also studied. Samples of the tree rings and the bark were taken at three locations. ¹³⁷Cs and ⁴⁰K showed very similar distributions. ¹³⁷Cs and ⁴⁰K activities were age-dependent and increased in decreasing age of twigs and needles. The highest activities were measured in the youngest twigs. The highest ⁷Be activities were found in the twigs.     

Bioaccumulation of gamma emitting radionuclides in Polysiphonia fucoides

The article presents the results of a study on the bioaccumulation abilities of Polysiphonia fucoides, a red algae specific to the southern Baltic Sea, towards (of) gamma emitting isotopes. A laboratory experiment was carried out to determine changes in the activities of some isotopes—⁵⁴Mn, ⁵⁷Co, ⁶⁵Zn, ^110mAg,¹¹³Sn, ¹³⁴Cs, ¹³⁷Cs and ²⁴¹Am—occurring in P. fucoides exposed to a seawater medium containing these isotopes over the course of 1 month. All analyzed isotopes showed the greatest increase of radioactive activity in plant tissue in the first 24 h of exposure. The temporary concentration factors of cesium isotopes were increasing linearly during the experiment from 114 to 274 in the case of ¹³⁷Cs, and from 144 to 351 in the case of ¹³⁴Cs. The level of the initial concentration factor of cesium isotopes in the plant proved to be independent of the initial concentration of the isotope in seawater and it took the lowest (125 dm³ kg^?1) level among the studied isotopes. In the case of a mixture of gamma emitting isotopes, a linear relation between the individual isotope activity in P. fucoides and its initial concentration in seawater was established after the first day of exposure; the isotopes initial concentration factors ranged from 767 to 874 dm³ kg^?1. Having reached the maximal concentration level, a statistically significant decline in radioactivity concentrations of the five isotopes in the plant tissue was observed. A half-life of biological removal of the isotopes from the plant tissue was established at: 3.8 days in the case of ⁵⁴Mn, 4 days—⁵⁷Co, 4 days—⁶⁰Co, 4.2 days—¹³⁷Cs and ²⁴¹Am—3.5 days.     

Determination of <Superscript>137</Superscript>Cs and <Superscript>90</Superscript>Sr in the bottom sediments from the Barents Sea

The aim of this paper was to determine the extent of contamination by anthropogeneous radionuclides ¹³⁷Cs and ⁹⁰Sr in the bottom sediments from the Barents Sea based on the radioactive activity of the samples taken up in August 1991, among others, from the area close to New Land Island and Francis Joseph Archipelago. The results are based on the phenomenon of vertical migration, in the bottom sediments which is of significant importance from the natural environment point of view.     

Distribution of <Superscript>137</Superscript>Cs, <Superscript>40</Superscript>K, <Superscript>232</Superscript>Th and <Superscript>238</Superscript>U in coastal marine sediments of Margarita Island,Venezuela

This work presents the results of ¹³⁷Cs, ⁴⁰K, ²³²Th and ²³⁸U concentration (Bq kg⁻¹) values in coastal marine sediments collected from 38 sites along the coastline of the island of Margarita, Venezuela. The purpose was to determine baseline values for these radionuclides in surface marine sediments and to detect if there were any anomalously high concentration values. Only three of the 38 sediments analyzed had measurable values above the detection limit of 0.9 Bq kg⁻¹ for ¹³⁷Cs and the highest only being 1.4 Bq kg⁻¹. While, the concentration (Bq kg⁻¹) ranges for the primordial radionuclides, ⁴⁰K, ²³²Th and ²³⁸U were as follows: 12.2–211.7, <1.5–9.8 and <4.4–20.7, respectively. These concentration ranges for the primordial radionuclides can be considered as baseline values for surface marine sediments for areas that are considered not polluted by man or contaminated by nature. Finally, the concentration range of ¹³⁷Cs can also be employed as baseline values, which only seem to have been the result of the atmospheric testing of nuclear weapons in the past.     

Measuring <Superscript>137</Superscript>Cs, <Superscript>40</Superscript>K and decay products of <Superscript>226</Superscript>Ra and <Superscript>232</Superscript>Th in samples of different nature by a multidetector spectrometer

A coincidence method for measuring ¹³⁷Cs, ⁴⁰K, ²²⁶Ra and ²³²Th decay products activity in soil, vegetation and fish samples, was applied to the six-crystal gamma-coincidence spectrometer PRIPYAT-2M. In this way, some problems appeared in simultaneous measurement of ¹³⁷Cs, ²²⁶Ra and ²³²Th by NaI(Tl) detectors and the PRIPYAT-2M spectrometer were solved. The obtained results were agreeable with the HPGe spectrometer ones.     

Improvement of <Superscript>137</Superscript>Cs analysis in small volume seawater samples using the Ogoya underground facility

¹³⁷Cs in seawater is one of the most powerful tracers of water motion. Large volumes of samples have been required for determination of ¹³⁷Cs in seawater. This paper describes improvement of separation and purification processes of ¹³⁷Cs in seawater, which includes purification of ¹³⁷Cs using hexachloroplatinic acid in addition to ammonium phosphomolybdate (AMP) precipitation. As a result, we succeeded the ¹³⁷Cs determination in seawater with a smaller sample volume of 10 liter by using ultra-low background gamma-spectrometry in the Ogoya underground facility. ¹³⁷Cs detection limit was about 0.1 mBq (counting time: 10⁶ s). This method is applied to determine ¹³⁷Cs in small samples of the South Pacific deep waters.     

Chemometrics of the distribution and origin of <Superscript>226</Superscript>Ra, <Superscript>228</Superscript>Ra, <Superscript>40</Superscript>K and <Superscript>137</Superscript>Cs in plants near the West Macedonia Lignite Center (Greece)

Summary The distribution and origin of ⁴⁰K, ²²⁶Ra, ²²⁸Ra and ¹³⁷Cs has been investigated in trees, mosses and lichens in the basin of the West Macedonia Lignite Centre. In tree leaves ¹³⁷Cs is negligible, while the ²²⁶Ra and ²²⁸Ra concentrations are affected by the fly ash particles. Concerning ²²⁶Ra and ²²⁸Ra values of mosses and lichens, which are systematically larger than those of unpolluted areas, the application of chemometrics proved that they originate mainly from the lignite fly ash.     

Long-term transfer of <Superscript>137</Superscript>Cs from soil to mushrooms in a semi-natural environment

The radioactive contamination following the Chernobyl accident resulted in high concentrations of ¹³⁷Cs in several mushrooms species. Mushroom samples were collected in a forest environment between 1986 and 2007 and the transfer of ¹³⁷Cs to two edible species, Suillus variegatus and Cantharellus spp., was investigated. The ¹³⁷Cs uptake by the collected samples did not decrease over time and in Cantharellus spp. a significant increase was observed. Most of the ¹³⁷Cs in soil still appears to be available for uptake and radioactive decay of the radionuclide is likely the main factor for the reduction of ¹³⁷Cs in a forest ecosystem.     

The <Superscript>137</Superscript>Cs distribution in sediment profiles from the Yangtze River estuary: a comparison of modeling and experimental results

It has been generally accepted when estimating sedimentation rates using the ¹³⁷Cs dating method that the position of the ¹³⁷Cs maximum in a sediment profile represents the year 1963. In this paper we validated this approach by developing a model in which the annual ¹³⁷Cs global fallout flux for the Yangtze River estuary was established on the basis of the Tokyo flux corrected for precipitation rates observed in Shanghai. As the ¹³⁷Cs maxima in the sediment deposition profiles depend on the sedimentation rates, the sub-sampling intervals were calculated accordingly. Higher measured than the calculated values were found in some cores, what may be due to fluctuating sedimentation rates and an additional deposition of ¹³⁷Cs from land-based sources. The study provides useful information on the reliability of the measured ¹³⁷Cs maxima in sediment profiles frequently used for dating of sediments in marine (coastal regions, open seas) as well as in terrestrial (lakes) environments.     

Determination and spatial distribution of <Superscript>137</Superscript>Cs in soils,mosses and lichens near Kavanayen,Venezuela

The activity of ¹³⁷Cs was determined in soils, mosses, lichens and other vegetation along the Caruay River and near the town of Kavanayen. The range of values for the soils was from <1.2 Bq·kg⁻¹ of ¹³⁷Cs (our detection limit) to 14.1 Bq·kg⁻¹. The range of ¹³⁷Cs activities in the mosses ranged from 9.9 to 17.9 Bq·kg⁻¹ with a mean value of 13.4±4 Bq·kg⁻¹; all the moss samples were found along the river. While the ¹³⁷Cs activities in the lichens ranged from 9.1 to 29.8 Bq·kg⁻¹; the two values along the river were about three factors higher than the one near Kavanayen. It was concluded that the ¹³⁷Cs activities in the soils, mosses and lichens are much higher along the river in respect to the nearby town of Kavanayen.     

Radioactivity in the Exclusive Economic Zone of east coast Peninsular Malaysia: distribution trends of <Superscript>137</Superscript>Cs in surface seawater

Large volumes of surface seawater samples were collected from thirty locations in the Exclusive Economic Zone (EEZ) of the east coast Peninsular Malaysia on June 2008 to study the activity concentrations of ¹³⁷Cs. The results will serve as additional information to the existing baseline data and is very useful for monitoring fresh input of anthropogenic radionuclide into Malaysian marine environment. In this study, the activity concentrations of ¹³⁷Cs were determined using co-precipitation technique, followed by Gamma Spectrometry measurement. The mean activity concentration of ¹³⁷Cs ranged between 3.40 and 5.89 Bq/m³. Higher activity concentrations were observed at the coastal and towards the south of Peninsular Malaysia and were aligned with the high turbidity. These may due to the rapid diffusion of ¹³⁷Cs from suspended particulates and fine sediments into surface seawater. The activity concentrations of ¹³⁷Cs observed in this study were slightly higher than the concentrations reported in seawater at the Straits of Malacca, Vietnam and Philippines. This might be because the study area received more input of ¹³⁷Cs that originated from global fallout and then deposited on land which later being transported subsequently into the coastal zone due to siltation and erosion processes. It could also be attributed to the intrusion of river waters containing higher concentrations of ¹³⁷Cs.     

Separation of cesium-137 from uranium fission products via a Neoflon® column supporting tetraphenylboron

Cesium is a member of the Group I alkali metals, very reactive earth metals that react vigorously with both air and water. The chemistry of cesium is much like the chemistry of neighboring elements on the periodic table, potassium and rubidium. This close relation creates many problems in plant-life exposed to cesium because it is so easily confused for potassium, an essential nutrient to plants. Radioactive ¹³⁴Cs and ¹³⁷Cs are also chemically akin to potassium and stable cesium. Uptake of these radioactive isotopes from groundwater by plant-life destroys the plant-life and can potentially expose humans to the radioactive affects of ¹³⁴Cs and ¹³⁷Cs. Much experimental work has been focused on the separation of ¹³⁷Cs from uranium fission products. In previous experimental work performed a column consisting of Kel-F supporting tetraphenylboron (TPB) was utilized to separate ¹³⁷Cs from uranium fission products. It is of interest at this time to attempt the separation of ¹³⁴Cs from 0.01M EDTA using the same method and Neoflon in the place of Kel-F as the inert support. The results of this experiment give a separation efficiency of 88% and show a linear relationship between the column bed length and the separation efficiency obtained.