Detecting137Cs breakthrough in an ion exchange process

High-level radioactive wastes can be transformed to low-level wastes by removing¹³⁷Cs through selective ion exchange processes. Since the short-lived daughter,¹³⁷ⁱⁿBa produces the 662-keV gamma-ray normally attributed to¹³⁷Cs, equilibrium may be broken, and observation of the 662-keV gamma-ray cannot be used to detect cesium breakthrough. Two detectors viewing the output line, but separated sufficiently to measure the^137mBa decay between them, are used to detect¹³⁷Cs breakthrough based on deviation from the normal^137mBa decay. Detection evaluated for the process separation time, counting time, fractional breakthrough detectable, and accuracy and confidence of the measurements are discussed.     

Modeling of 137Cs migration in cores of marine sediments of Mumbai Harbor Bay

The vertical concentration profile of ¹³⁷Cs in cores of marine sediment of Mumbai Harbor Bay has been studied by the compartment and the diffusion-convection models. Based on the measured concentrations of ¹³⁷Cs in the sediment layers, the various transport parameters such as sedimentation rate, residence half- time, effective migration velocity, diffusion coefficient and the convective velocities were determined. The sedimentation rate was determined to be 1.61, 1.03 0.69 and 1.25 cm year^?1 from the slope of lines obtained from the depth profile of ¹³⁷Cs in cores using a least-square fitting method at site 1, 2, 3 and 4 respectively. The mean residence half-times, ranging from 11 to 35 years were observed to be the highest at the upper layers (up to 8 cm) of all sites and decreased with sediment depth. Subsequently, the ranges of mean value of effective vertical migration velocity in the same layers were between 0.15 and 0.46 cm year^?1. As expected, the vertical migration in the upper sediment layers was very slow and thereafter increased slowly in the succeeding layers (12 cm onwards) of all sites with a mean ranging from 1.11 to 4.13 cm year^?1. The obtained migration velocities were quite higher than those reported in literatures for global fallout. The convective velocity and diffusion coefficient at each site were assumed to be constant in the whole depth and calculated under the assumption of steady state. Using a depth-zoned bioturbational mixing model, the estimated biological diffusion coefficients ranged from 7 × 10^?7 to 3.8 × 10^?6 cm² s^?1 which were within the literature values reported for shallow coastal environments and deep sea.     

Determination of 137Cs in Soil Samples by Low-Level Compton Suppression Gamma-Counting

We have used Compton suppression gamma ray counting to effectively measure ¹³⁷Cs in undisturbed environmental samples weighing only one hundred grams of material. Our results have shown that Compton suppression is ideal in determining low levels (1–3 Bq/kg) of ¹³⁷Cs in soil samples, while the Compton advantage is negligible for higher concentrations. Quality assurance and quality control experiments show that for samples weighing 100–200 grams, gamma-ray attenuation is significant (up to 10% difference) when analyzing different soil compositions.     

Determination of40K and137Cs concentration in selected honey samples

Seventeen honey samples collected at different sites during 1992 have been measured using the method of -spectroscopy. Measurements were performed by a low background high purity germanium spectrometer of a relative efficiency of 14.5% and an energy resolution of 1.7 keV. Using natural -ray sources to determine efficiency, it has been shown that out of 17 samples of natural honey only two (of meadow type) have specific activity of¹³⁷Cs greater than 0.5 Bq kg^–1. The remaining samples have the same¹³⁷Cs concentrations as before May, 1986. Predominant activity in all samples comes from the⁴⁰K radionuclide, indicating natural honey.     

Extraction-chromatographic separation of137mBa from137Cs

The possibilities of extraction-chromatographic separation of^137mBa from¹³⁷Cs in genetic succession were studied, using columns filled with support beads loaded with the extractant H⁺[)–(3)–1,2–B₉C₂H₁₁]₂Co^–, further referred to as dicarbolide-H⁺, in nitrobenzene. The dependence of the amount of separable activities on experimental conditions was established. Optimal conditions were selected for the separation process. The effects of isotopic and nonisotopic carriers of^137mBa on the separation and the degree on saturation of extraction-chromatographic column with Ba²⁺ ions were evaluated. The effects of acidity of the elution solutions, of flow-through velocity, the amount of elution solution and the quality of carrier beads on the separation process were assessed. The extraction-chromatographic yield was calculated and the number of possible repeated elution cycles for^137mBa with saline and some other eluents was determined.     

Determination of90Sr and137Cs in mushrooms following the Chernobyl fallout

After the Chernobyl accident high concentrations of radionuclides were found in Sweden in mushrooms and the contents of⁹⁰Sr and¹³⁷Cs were measured. The level of⁹⁰Sr was generally low and, in proportion to¹³⁷Cs, 2–3 orders of magnitude lower than in the fallut. The contents of¹³⁷Cs varied among species and extreme local variations occurred. The ratio¹³⁴Cs/¹³⁷Cs diverged from other biological samples leading to the conclusion that old fallout was involved in the uptake.     

Determination and correlation of 137Cs and unsupported 210Pb activities in soil

To ascertain the feasibility of using ¹³⁷Cs and ²¹⁰Pb in soil erosion models a Compton suppression system with a Be window was used to simultaneous detect both of the naturally occurring isotopes. In particular, the system allowed the use of only 20 g of soil material instead of the usual needed 0.5-1.0 kg in similar soil studies.     

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.     

Comparison of different methods to determine the retardation factor of 137Cs transport through granite in column experiments

Retardation factor (Rf) is the most frequently used indicator to describe the transport of radionuclides through geological substances. In this work, we compare the Rf values determined by four methods including direct experimental data, model fitting curve, integration technique and modeling at two relative concentration (C/C ₀) 0.5 and 1.0 in a case study of Cs transport through crushed granite. A simple Q-test indicated all Rf values are valid at 96% confidence level. Meanwhile, the T-test demonstrated that the precision of Rf value is 4.21±0.39 at 90% and ±0.45 at 95% confidence level, which is about 9.3% and 10.7% of the average value of the Rf value. An uncertainty window of 10% is recommended in Rf value determination.     

Rapid determination of 137Cs in environmental samples--purification of 137Cs by ammonium molybdophosphate column separation]

A rapid method for the determination of 137Cs in environmental samples was proposed. The principal technic employed in this study is based on column separation of 137Cs using ammonium molybdophosphate mixed with glass fiber to eliminate contribution of natural radionuclides such as 40K and 87Rb. The separation of cesium from potassium and rubidium was performed by the elution with 0.5m ammonium nitrate solution. The time required for separation of cesium was five hours as compared with the conventional cation exchange separation which required thirteen hours. The chemical yield of cesium carrier was normally more than 90 percent. The results obtained were compared with that by the conventional methods using Bio-Rex cation exchange separation and the good agreement between the two methods was obtained.     

Determination of131I,134Cs,137Cs in grass and cheese after Chernobyl accident in Austria

Various samples from Styria /grass/ and Salzburg /cheese/ were analyzed for¹³¹I,¹³⁴Cs and¹³⁷Cs concentration during April–July 1986 by -ray spectrometry. The concentrations are reported in nCi kg^–1 wet weight. The concentration values found for¹³¹I 0.2–17.2 nCi kg^–1 /grass/, 0.1–0.5 nCi kg^–1 /cheese/, for¹³⁴Cs 1.1–6.2 nCi kg^–1 /grass/, 0.2–1.3 nCi kg^–1 /cheese/, for¹³⁷Cs 1.6–15.7 nCi kg^–1 /grass/, 0.3–2.2 nCi kg^–1 /cheese/. While radioactivity of¹³¹I,¹³⁴Cs and¹³⁷Cs in cheese samples increases from May to June, it decreases in grass samples from May to July 1986.     

Some biological factors related to the 137Cs concentration of marine organisms

Marine Ecology Research Institute has been studying the factors controlling the concentration of radionuclides in marine biota. Weight of fish seemed to be an important factor controlling the concentration of ¹³⁷Cs because of the good correlation observed between the weight and the concentration of ¹³⁷Cs. Food habits also seemed to be an important factor because fishes in higher trophic levels tended to indicate higher concentration factors and a positive correlation was observed between the concentrations of predator fishes and those of the foodstuff. Gender could be another factor controlling the concentration of ¹³⁷Cs because the difference of ¹³⁷Cs between gender was observed in rockfish and marbled sole.     

Leaching behavior of137Cs in cement

To assess the safety of disposal of a radioactive waste-cement composite, the leaching of¹³⁷Cs from a waste composite into a surrounding fluid has been studied. Leaching tests were carried out in accordance with a method recommended by IAEA.¹ The leachability was measured as a function of bentonite clay to cement ratio. The fraction of¹³⁷-Cs leached from a specimen of Portland cement is 0.03–0.13 at a leaching time of 400 d. Results presented in this paper are examples of data obtained in a 10 y mortar and concrete testing project, which will influence the design of the engineered trench system for a future Yugoslav radioactive waste storage center.^2,3     

Vertical distributions of global fallout 137Cs and 14C in a Japanese forest soil profile and their implications for the fate and migration processes of Fukushima-derived 137Cs

Vertical distributions of global fallout ¹³⁷Cs and ¹⁴C were investigated in a Japanese forest soil in 2001. Even 38 years after the fallout, ¹³⁷Cs was still observed mostly in the uppermost 5 cm. A preferential accumulation of ¹³⁷Cs was found in a 1-cm-thick transition layer between organic-rich A and underlying B horizons. This unique observation indicated that ¹³⁷Cs migrated through the A horizon at a rate of 0.20 % year⁻¹ and the transition layer acted as a barrier for ¹³⁷Cs migration to deeper layers. The vertical distributions of ¹³⁷Cs and ¹⁴C were significantly correlated, suggesting a coupled downward migration of ¹³⁷Cs and organic matter on a time scale of decades, along the same physical pathways.

     

Determination of137Cs and134Cs radioisotopes in various mushrooms from Austria one year after the Chernobyl incident

Many mushrooms from Austria collected between May 25 and September 21, 1987 were analyzed for¹³⁷Cs and¹³⁴Cs by -spectroscopy one year after the reactor accident at Chernobyl. The following concentrations /nCi kg^–1 wet weight/ were found:¹³⁷Cs 0.4–43.2 nCi kg^–1,¹³⁴Cs 0.1–16.4 nCi kg^–1. The concentration of cesium isotopes in Cantharellus cibarius /Klagenfurt/ and Xerocomus badius /Upper-Austria, Mühlviertel/ were considerably higher than the tolerance level /5 nCi kg^–1/.     

Comparison of food processing retention factors of 137Cs and 40K in vegetables

Removal of radiocesium from food by processing is of great concern following the accident of TEPCO’s Fukushima Daiichi Nuclear Power Plant accident. To provide more Cs removal rates, we studied the applicability of K data using edible plant samples. Values were compared for ¹³⁷Cs and ⁴⁰K of the food processing retention factors, F _r (total activity in processed food/total activity in raw food), and they were found to be close to the 1:1 line and highly correlated (R = 0.96, p < 0.001). Thus, K can be an analogue to estimate radiocesium removal rates by food processing of vegetables. Using the literature K values, we calculated the K removal rates (%), that is, (1 ? F _r) × 100, for ten vegetable types to provide potential Cs removal rates. The average percent of K removal were as follows: dried pulses, 33; fresh pulses, 15; leafy vegetables, 52; fruit vegetables, 7; flower vegetables, 44: root crops, 18; tubers, 16; ferns, 93: mushrooms, 32; and others, 30.     

Investigation of adsorption and vertical migration of137Cs in three kinds of soil at Lublin vicinity

The results of field, column and laboratory studies carried out on three types of mineral soils are encloses presented. Based on the field tests, average migration rates of¹³⁷Cs were calculated. The highest rate was found for the brown soil (FAO/UNESCO—Cambisol). Cesium migrated with the lowest rate in the podzol soil (FAO/UNESCO—Cambic Podzol). The column experiments confirmed the above observation. In laboratory tests the adsorption and desorption isotherms of Cs were determined on samples taken from 0–2 cm layers of each soil profile. It was found from the calculated partition coefficients that Cs is always irreversibly bonded to some extent, but it appears to be completely and irreversibly immobilized on the podzol soil. The permanent retention of cesium in the podzol soil was also confirmed by microcalorimetric studies. The desorption energy was negligibly small and amounted to −0.21 mJ/g. In the brown soil, containing prevailing amounts of loamy minerals, the desorption energy was found to be 106.89 mJ/g. The investigations are supplemented by the sorption kinetics measurements. These indicate that the adsorption equilibrium is reached after a dozen, up to twenty or so minutes.     

Determination of137Cs and134Cs in air samples collected near Belgrade /Yugoslavia/ following the Chernobyl accident

This paper presents the results of measurements of¹³⁷Cs and¹³⁴Cs content in air sampled during May 1986. Maximum concentrations:¹³⁷Cs 2.94±0.01 Bq m^–3 and¹³⁴Cs 1.38±0.01 Bq m^–3 were registered on May 3. Several other long lived radionuclides having -energies in the region 33 keV to 1365 keV were registered in the same samples two years later. The results of measurements of the total -activity in air for the same period are also presented.     

Vertical migration of 85Sr, 137Cs and 131I in various arable and undisturbed soils

The vertical migration of ⁸⁵Sr, ¹³⁷Cs and ¹³¹I in some arable and undisturbed single-contaminated soils was studied by gamma-spectrometry measurements under lysimetric laboratory conditions during irrigation of the soil profiles with wet atmospheric precipitation for about one year, except ¹³¹I. A new simple exponential compartment (box) model was derived, which makes it possible to calculate the migration rate constants and migration rates in the individual soil layers (vertical sections) as well as the total vertical migration rate constants and total vertical migration rates of radionuclides in the bulk soil horizon. The relaxation times of radionuclides in respective soil horizons can also be evaluated.     

The biological half-life of137Cs in snails

The biological half-life of¹³⁷Cs in snails Helix pomatia after a single administration of contaminated diet has been investigated. The calculation was based on the retention of¹³⁷Cs in snails in vivo. It was found that loss of cesium from snails can be explained by a two-exponential retention curve leading to biological loss constants _{B 1}=0.27 d^–1 and _{B 2}=0.024 d^–1, which correspond to biological half-lives of T_{B 1}=2.5 d and T_{B 2}=28.5 d respectively. The equation describing the retention of¹³⁷Cs in snails is also presented.