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.     

Determination of Cs and Cs in environmental samples: A review

Radionuclides of caesium are environmentally important since they are formed as significant high yield fission products (¹³⁵Cs and ¹³⁷Cs) and activation products (¹³⁴Cs and ¹³⁶Cs) during nuclear fission. They originate from a range of nuclear activities such as weapons testing, nuclear reprocessing and nuclear fuel cycle discharges and nuclear accidents. Whilst ¹³⁷Cs, ¹³⁴Cs and ¹³⁶Cs are routinely measurable at high sensitivity by gamma spectrometry, routine detection of long-lived ¹³⁵Cs by radiometric methods is challenging. This measurement is, however, important given its significance in long-term nuclear waste storage and disposal. Furthermore, the ¹³⁵Cs/¹³⁷Cs ratio varies with reactor, weapon and fuel type, and accurate measurement of this ratio can therefore be used as a forensic tool in identifying the source(s) of nuclear contamination. The shorter-lived activation products ¹³⁴Cs and ¹³⁶Cs have a limited application but provide useful early information on fuel irradiation history and have importance in health physics.     

Electrochemical immobilization of Cs in single-crystalline SYNROC

The development of a disposal technique for the radiotoxic ¹³⁷Cs in nuclear wastes is one of the most urgent issues in nuclear fuel technology. An effective disposal method of ¹³⁷Cs is to immobilize it in a synthetic rock (SYNROC) material: cesium titanate hollandite, ¹³⁷Cs_xTi₈O₁₆ (I4/m, , ). Practical applications of ¹³⁷Cs_xTi₈O₁₆ have been restricted so far because the conventional synthetic method requires strong chemical reducers and reaction temperatures higher than 1250 °C. In this report, we present a milder preparation method of Cs_xTi₈O₁₆ by electrolysis of a mixture of Cs₂MoO₄ and TiO₂ in ambient atmosphere at 900 °C. The Cs content in the resultant single-crystalline Cs_1.35Ti₈O₁₆ is competitive with the highest value in polycrystalline Cs_1.36±0.03Ti₈O₁₆ prepared by the conventional synthetic method. The electrochemical preparation of Cs_1.35Ti₈O₁₆ is a promising way to immobilize a high quantity of ¹³⁷Cs ions in a stable form of single-crystalline SYNROC.     

Specificity of Lichen Species in Respect to 137Cs Binding

Abstract

The aim of this work was to investigate the significance of species specificity on the efficiency of ¹³⁷Cs isolation from lichens. It was shown that a 5% solution of both ammonium oxalate and phosphoric acid was able to solubilize 77.5% of ¹³⁷Cs from Cetraria islandica, 47.6% from Cladonia fimbriata and 46.4% from Usnea barbata. Since the tested lichen species had similar specific radioactivities (i.e. amount of ¹³⁷Cs) the difference could be explained by the existence of different types of bonds between radiocesium and the corresponding binding sites. Crystals precipitated from these extracts incorporated most of the soluble ¹³⁷Cs. The amount and specific radioactivity of the crystals varied between lichen species which could also be interpreted as the presence of specific ions in each lichen that either participated in crystal formation or inhibited the process. The potential of a tested solution to extract and “concentrate” ¹³⁷Cs in crystalline form may be a tool to correlate mass and radioactivity of ¹³⁷Cs.     

Determination of 135Cs in nuclear power plant wastes by ICP-MS and k 0-NAA

A radiochemical method for the determination of ¹³⁵Cs in radioactive wastes has been adopted/developed. For the separation of cesium from other elements ammonium-molybdophosphate precipitation and cation exchange chromatography were used. The chemical yield of the method was about 60–100 %. ¹³⁵Cs was measured by two methods. In neutron activation analysis (NAA), Cs was irradiated with reactor neutrons. ¹³⁶Cs was detected by gamma spectrometry, wherefrom the activity/mass of ¹³⁵Cs was calculated according to the k ₀-standardization technique. The Cs containing fractions were measured by inductive coupled plasma mass spectrometry, as well. NAA and ICP-MS techniques were comparatively evaluated and a good agreement between the results was found. The activity concentration of ¹³⁵Cs in a couple of waste samples originating from VVER-440 type nuclear reactors was in the range of 1–5 Bq L^?1 (20–120 ng L^?1) while ¹³⁷Cs activity concentrations varied between 0.1 and 1 MBq L^?1.     

Comparing the capability of collision/reaction cell quadrupole and sector field inductively coupled plasma mass spectrometers for interference removal from 90Sr, 137Cs,and 226Ra

Here we report a quantitative comparison of sector field inductively coupled plasma mass spectrometry (ICP-SFMS) and collision/reaction cell inductively coupled plasma quadrupole mass spectrometry (ICP-QMS) for the detection of ⁹⁰Sr, ¹³⁷Cs, and ²²⁶Ra at ultra-trace levels. We observed that the identification and quantification of radioisotopes by ICP-MS were hampered by spectral (both isobaric and polyatomic ions) and non-spectral (matrix effect) interferences. ICP-QMS has been used to eliminate the isobaric ⁹⁰Sr/⁹⁰Zr interference through the addition of O₂ into the collision cell as a reactant gas. Zr⁺ ions were subsequently converted into ZrO⁺, whereas Sr⁺ ions were not reactive. In addition, the isobaric interference of ¹³⁷Ba on ¹³⁷Cs was eliminated by the addition of N₂O gas in the cell, which led to the formation of BaO⁺ and BaOH⁺ products, whereas Cs⁺ remained unreactive. Furthermore, He and H₂ were used in the collision/reaction cell to eliminate polyatomic ions formed at m/z 226. A comparison of the results obtained by ICP-SFMS after a chemical separation of Sr from Zr and Cs from Ba was performed. Finally, to validate the developed analytical procedures, measurements of the same samples were performed by γ-ray spectroscopy.     

Determination of135Cs in sodium from an in-pile loop by activation analysis

Several months after shut-down,¹³⁷Cs and¹³⁴Cs were the main activities in coolant residues from an in-pile sodium loop where a fuel pin had failed at 40000 MWd/t burn-up, FR2-reirradiation of coolant residues increased¹³⁴Cs and generated¹³⁶Cs, thus indicating the presence of stable¹³³Cs and of long-lived¹³⁵Cs in the samples. The amount of¹³⁵Cs calculated from¹³⁶Cs activities was of the same quantity as the number of¹³⁷Cs atoms.     

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.     

Mass selective separation applied to radioisotopes of cesium

A technique that uses the intrinsic mass‐based separation capability of a quadrupole mass spectrometer has been used to resolve spectral radiometric interference of two isotopes of the same element. In this work the starting sample was a mixture of ¹³⁷Cs and ¹³⁴Cs and was (activity) dominated by ¹³⁷Cs. This methodology separated and ‘implanted’ ¹³⁴Cs that was later quantified for spectral features and activity with traditional radiometric techniques. This work demonstrated a ¹³⁴Cs/¹³⁷Cs activity ratio enhancement of >4 orders of magnitude and complete removal of ¹³⁷Cs spectral features from the implanted target mass (i.e. 134). Copyright © 2016 John Wiley & Sons, Ltd.     

Half-life of134Cs determined by gamma spectrometry

The half-life of¹³⁴Cs obtained by gamma spectrometry from the change of the¹³⁴Cs to¹³⁷Cs activity ratio is 2.04±0.03 years.     

A simple preparation of calibration curve standards of134Cs and137Cs by serial dilution of a standard reference material

Two sets of calibration standards for¹³⁴Cs and¹³⁷Cs were prepared by small serial dilution of a natural matrix standard reference material, IAEA-154 whey powder. The first set was intended to screen imported milk powders which were suspected to be contaminated with¹³⁴Cs and¹³⁷Cs. Therefore the concentration range of the calibration standards were about 40–400 Bq/kg. The precision of the preparation of the standard with about 7 Bq/kg of¹³⁴Cs and 39 Bq/kg of¹³⁷Cs at measurement time was 7.4% and 3.2%, respectively. The preparation of a similar standard by spiking the matrix with radioisotope solutions resulted in a poorer precision, about double that of the former technique. The other set of calibration standards was prepared to measure the environmental levels of¹³⁷Cs in commercial Venezuelan milk powders. Their concentration ranged from 3–10 Bq/kg of¹³⁷Cs. The accuracy of these calibration curves was checked by using IAEA-152 and A-14 milk powders. Their measured values were in good agreement with their certified values. Finally, it is shown that these preparation techniques by serial dilution of a standard reference material were simple, rapid, precise, accurate and cost-effective.This work was partly funded by a research contract PC-075 from the Consejo Nacional de Investigaciones Científicas y Tecnológicas (CONICIT).     

Studies of the vertical distribution of134Cs,137Cs,238Pu,239, 240Pu,241Pu,241Am and210Pb in ombrogenous mires at mid-latitudes

Six peat cores taken from three unmodified blanket and raised bogs in Ireland were sectioned and analyzed for a range of radionuclides including¹³⁴Cs,¹³⁷Cs,²³⁸Pu,²³⁹Pu,²⁴¹Am, and²¹⁰Pb.¹³⁴Cs and¹³⁷Cs were measured by high resolution gamma-spectrometry, while the transuranium nuclides were determined after chemical separation by alpha-spectrometry.²⁴¹Pu, present on the electroplated discs together with Pu(), was measured directly by low-level liquid scintillation counting. Core chronologies were established by measuring the unsupported²¹⁰Pb component using low energy photon spectrometry (LEPS). From the resulting profiles, relaxation depths and migration rates for the above mentioned radionuclides have been determined and differences in the values of these parameters interpreted.²³⁸Pu/^239,240Pu and²⁴¹Pu/^239,240Pu ratios have been examined carefully and are discussed in some detail. Finally, the contribution from Chernobyl to the total radiocaesium inventory in each core has been established using the¹³⁴Cs/¹³⁷Cs ratio observed in the initial fallout from Chernobyl.     

Vertical Distribution of137 Cs in The Lacustrine Areas and Preliminary Results of 7Be Activity in Snow Samples at Terra Nova Bay (ANTARCTICA)

Abstract

¹³⁷ Cs activity in samples from lacustrine areas around the Italian base in Antarctica is reported as an integration of a previous work. Preliminary data of cosmogenic ⁷ Be activity determined in snowfalls, total atmospheric depositions, soil and air particulate collected during the 1990–91 and 1991–92 Italian expeditions in Antarctica is presented. The results obtained point out the efficiency of snow in the processes of air particulate scavenging and provide useful information for the development of research in Antarctica in the study of air/snow transfer processes by means of natural radionuclides.     

Distribution of 131I, 134Cs, 137Cs and 239,240Pu concentrations in Korean rainwater after the Fukushima nuclear power plant accident

Radionuclides such as ¹³¹I, ¹³⁴Cs, ¹³⁷Cs, and ^239,240Pu in Korean rainwater have been analyzed by Korea Research Institute of Standards and Science (KRISS) since the Fukushima nuclear power plant accident in March 2011 to investigate the activity level, distribution pattern, and temporal variation and to assess the radiation dose the public is exposed to. The concentration of ¹³¹I in the Korean rainwater samples varied between 0.033 (minimum detectable activity; MDA) and 1.30 Bq kg^?1 and the concentrations tended to decrease exponentially with time. The concentrations of ¹³⁴Cs and ¹³⁷Cs in rainwater ranged from 0.01 to 334 ± 74 and 0.29 ± 0.01 to 276 ± 1 mBq kg^?1, respectively. The mean activity ratio of ¹³⁷Cs/¹³⁴Cs in the rainwater samples collected from April 18 to May 12 was estimated to be 0.44 ± 0.21, and this value is lower than that (ca. 1) observed in Fukushima, Japan, when there was an escape from the nuclear reactors. When an attempt was made to analyze Pu isotopes in rainwater samples, no Pu isotopes were detected above the MDA in any of the rainwater samples. Although the locations investigated were different from Asia to Europe, the concentrations of ¹³¹I, ¹³⁴Cs and ¹³⁷Cs in the rainwater are comparable, which suggests a global contamination of ¹³¹I, ¹³⁴Cs, and ¹³⁷Cs occurred because of the Fukushima nuclear power plant accident.     

Accumulation of <Superscript>137</Superscript>Cs and <Superscript>40</Superscript>K in aboveground organs of tropical woody fruit plants

Distribution of ⁴⁰K and ¹³⁷Cs in tissues of the Citrus aurantifolia was measured by gamma spectrometry. A simple theoretical model is also proposed to describe the temporal evolution of ⁴⁰K activity concentration in such tropical woody fruit species. This model exhibits close agreement with the ⁴⁰K experimental results, in the leaf growing and fruit ripening processes of lemon trees.     

A new approach to determine Pm in irradiated fuel solutions

Developments carried out in the Laboratory of Isotopic, Nuclear and Elementary Analyses in order to quantify ¹⁴⁷Pm in spent nuclear fuels analyzed at the CEA within the framework of the Burn Up Credit research program for neutronic code validation are presented here. This determination is essential for safety-criticality studies.The quantity and the nature of the radionuclides in irradiated fuel solutions force us to separate the elements of interest before measuring their isotopic content by mass spectrometry. The main objective of this study is to modify the separation protocol used in our laboratory in order to recover and to measure the ¹⁴⁷Pm at the same time as the other lanthanides and actinides determined by mass spectrometry.A very complete study on synthetic solution (containing or not ¹⁴⁷Pm) was undertaken in order to determine the yield of the various stages of separation carried out before obtaining the isolated Pm fraction from the whole of the elements present in the spent fuel solutions. With the lack of natural tracer to carry out the measurement with the isotope dilution technique, the great number of isotopes in fuel, the originality of this work rests on the use of another present lanthanide in fuel to define the output of separation. The yields were measured at the conclusion of each stage of separation with two others lanthanides in order to show that one of them could be used as a tracer to correct the measurement of the ¹⁴⁷Pm with the separation yield. The total yield (at the conclusion of the two stages of separation) was measured at the same time by ICP-MS and liquid scintillation. This last determination made it possible to validate the use of the ¹⁴⁷Sm (natural) to measure the ¹⁴⁷Pm in ICP-MS since the outputs determined in liquid scintillation and ICP-MS (starting from the radioactive decrease of the source having been used to make the synthetic solution) were equivalent. It is the first time that such measurement is performed in ICP-MS.The measurement of the ¹⁴⁷Pm was finally taken on fuels UOx and MOx by using the ¹⁵³Eu like a tracer of the separation yield. The results obtained are in very good agreement with those obtained from neutronic calculation code.     

131I,134Cs and137Cs concentrations in 1986 for some Roumanian foodstuffs

Results of post-Chernobyl measurement on some foodstuff samples /eggs, meat, fruit, honey, medicinal herbs/ from South-Eastern Roumania are presented. Gamma-ray spectrometry was used; the radioactive concentration values are given in nCi.kg^–1 wet weight. A strong decrease in concentrations for eggs from 6–7 May /3.0–7.4 nCi for¹³¹I, 0.25–0.40 nCi for¹³⁴Cs, 0.40–0.85 nCi for¹³⁷Cs per one egg, mainly in the yolk/ to 19–25 May /0.3–1.0 nCi for¹³¹I, 0.15–0.25 nCi for¹³⁴Cs, 0.25–0.40 nCi for¹³⁷Cs/ was observed. The mean values for lamb meat /joint muscle/ were 500 nCi.kg^–1 for¹³¹I, 12 nCi.kg^–1 for¹³⁴Cs, 22 nCi.kg^–1 for¹³⁷Cs /18–25 May/. Relatively reduced values were found for fruits, e.g. compared to dairy products¹. In May–June 1986, the food consumption in Roumania was strictly limited and controlled by competent authorities.     

Characterization of sealed radioactive sources: uncertainty analysis to improve detection methods

A radioactive ¹³⁷Cs source has been analyzed for the radioactive parent ¹³⁷Cs and stable decay daughter ¹³⁷Ba. The ratio of the daughter to parent atoms is used to estimate the date when Cs was purified prior to source encapsulation (an “age” since purification). The isotopes were analyzed by inductively coupled plasma mass spectrometry (ICP-MS) after chemical separation. In addition, Ba was analyzed by isotope dilution ICP-MS (ID-ICP-MS). A detailed error analysis of the mass spectrometric work has been undertaken to identify areas of improvement, as well as quantifying the effect the errors have on the “age” determined. This paper reports an uncertainty analysis to identifying areas of improvement and alternative techniques that may reduce the uncertainties. In particular, work on isotope dilution using ICP-MS for the “age” determination of sealed sources is presented. The results will be compared to the original work done using external standards to calibrate the ICP-MS instrument.     

Determination of131I,134Cs,137Cs in plants and cheese after Chernobyl accident in Roumania

Various samples from the south-east region of Roumania/greens, fodder, cheese/were analyzed for¹³¹I,¹³⁴Cs and¹³⁷Cs concentrations in May and July 1986 by -ray spectrometry. The concentrations are reported in nCi. kg^–1 wet weight. For greens, a considerable decrease was observed for¹³¹I/to 3.0–7.0 nCi. kg^–1/,¹³⁴Cs/to 0.5–2.0 nCi.kg^–1/ and¹³⁷Cs /to 1.0–4.0 nCi. kg^–1/ from the first half /5–15 May/ till the end of May 1986. For cheese, maximum values were measured between 5 and 15 May /sheep cottage cheese: 500–800 nCi.kg^–1 for¹³¹I, 25–50 nCi. kg^–1 for¹³⁴Cs, 40–80 nCi. kg^–1 for¹³⁷Cs/; at the beginning of July a considerable decrease /to 5–10 nCi. kg^–1 for¹³¹I, 1.2–2.0 nCi.kg^–1 for¹³⁴Cs, 2.2–3.0 nCi. kg^–1 for¹³⁷Cs/ was observed. In autumn 1986 a small increase up to 2.0–3.0 nCi. kg^–1 for¹³⁴Cs and 3.4–5.0 nCi. kg^–1 for¹³⁷Cs /in November/ was reported. The population's internal possible contamination was strongly limited by the authorities' severe control of the food-stuff.     

Distribution of 137Cs and 134Cs in the North Pacific Ocean: impacts of the TEPCO Fukushima-Daiichi NPP accident

Impact of the TEPCO Fukushima-Daiichi NPP accident, FNPP1, to the North Pacific Ocean occurred through two pathways, namely direct release and atmospheric deposition to wide ocean surface. We collected more than 100 seawater samples in the North Pacific Ocean in April and May 2011 by seven commercial ships as VOS. Since the sample volume was 2 l each, we measured radiocaesium activity at Ogoya Underground Facility to obtain reliable activity. ¹³⁷Cs was detected at all stations and ¹³⁴Cs was detected at most of the stations in the North Pacific Ocean. The ¹³⁷Cs activity ranged from around 1 to 1,000 Bq m^?3 with activity ratios of ¹³⁴Cs/¹³⁷Cs close to 1 which is a signature of radiocaesium originated from the FNPP1 accident. At east of the International Date Line north of 40°N in the Pacific Ocean in April 2011, the ¹³⁴Cs activity ranged from 2 to 12 Bq m^?3.