Showing papers in "Journal of Radioanalytical and Nuclear Chemistry in 2002"

Essential and trace element contents of some Nigerian medicinal plants

Abstract: The energy-dispersive X-ray fluorescence (EDXRF) spectroscopy has been used for the determination of essential and trace elements" contents of some twenty Nigerian medicinal plants. The accuracy and precision of the technique were assured by analyzing the European Community Bureau Reference Standard BCR 62 (Olive Leaves). Fourteen elements, namely K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Se, Br, Rb, Sr were detected with toxic heavy metal such as Cd, As, Pb, Hg were detected in the samples. The ranges of elemental concentrations varied from 7.7.104 to 1.6 mg/kg in the herbs. The results show that many of these plants contain elements of vital importance for human metabolism and prevention and healing of diseases.

Sorption and thermodynamic behavior of zinc(II)-thiocyanate complexes onto polyurethane foam from acidic solutions

Abstract: The uptake of Zn(II)-SCN complex onto polyurethane foam (PUF) has been investigated in detail with respect to different composition and variable concentration of electrolyte, zinc, thiocyanate ions and PUF, and equilibration time. The sorption data followed both Langmuir and Dubinin-Radushkevich (D-R) sorption isotherms over the entire concentration range of zinc investigated whereas Freundlich sorption isotherm is obeyed upto 13.6.10-3M concentration. The Langmuir constants Q = 202±7 mmole.g-1 and of b = (1.78±0.31.104 dm3.mole-1 and of D-R paraneter X m = 493±1 mmole.g-1, b = activity coefficient = -0.028±0.0002 and of sorption energy E = 13.2±0.5 kJ.mole-1 and Freundlich constants 1/n = 0.42±0.03 and c m = 6.47±1.7 mmole.g-1 were evaluated. The influence of temperature variation on sorption have yielded DH = -77.5±2.9 kJ.mole-1, DS = -5±0.09 J.mole-1.K-1 and DG = -6.67±0.05 kJ.mole-1. The effect of common anions and cations on the sorption has been examined. Sulphate, ascorbate and bromide ions enhances the sorption to some extent whereas nitrite, Pb(II), Fe(III), Al(III), Cu(II) and Co(II) decrease to sorption significantly. A possible mechanism has been envisaged for Zn(II)-SCN sorption onto PUF.

Thermodynamic parameters of Cs+ sorption on natural clays

Abstract: The sorption behavior of Cs+ on kaolinite, chlorite-illite, and bentonite clays as a function of time, cation concentration, and temperature was studied using the radiotracer method. Sorption data were well represented by Freundlich and Dubinin-Radushkevich type isotherms. Bentonite was found to have the highest sorption capacity and the highest exchange affinity to Cs+. In all three cases Cs+ sorption was found to be exothermic with DH° (kJ/mol) –13, –8, –19 and DS° (J/mol.K) –15, 31, and –3 for kaolinite, chlorite-illite, and bentonite, respectively. Negative DG° values were obtained in all cases, indicating the spontaneity of sorption. The magnitudes of DG° suggest that ion exchange is the primary sorption mechanism.

Extraction of uranium, thorium and lanthanides using Cyanex-923: Their separations and recovery from monazite

Abstract: The extraction behavior of uranium, thorium and lanthanides, represented by cerium and ytterbium, by Cyanex-923 has been investigated. The effect of different variables like the concentration of acids, metal ion and extractant, nature of diluent and temperature has been studied. A composition for the extracted U(VI) and Th(IV) species has been proposed. Based on the partition data some important binary and ternary separations involving the aforesaid metal ions have been achieved. The proposed procedure has been applied for the recovery of uranium, thorium and lanthanide fraction from monazite sand. The stability and regeneration capacity of the extractant have been evaluated.

Cesium sorption from concentrated acidic tank wastes using ammonium molybdophosphate-polyacrylonitrile composite sorbents

Abstract: Ammonium molybdophosphate-polyacrylonitrile (AMP-PAN) composite sorbents have been evaluated for the removal of cesium from Idaho National Engineering and Environmental Laboratory (INEEL) concentrated acidic tank waste. Batch contacts were performed to qualitatively evaluate the effects of increased nitric acid, sodium and potassium. An equilibrium isotherm was generated with simulated concentrated tank waste solutions and fit to the Langmuir equation. Additional batch contact experiments were performed to determine if mercury, plutonium and americium would sorb onto AMP-PAN. Dynamic sorption was evaluated in column tests employing 1.5 cm3 columns operating at 5, 10 and 20 bed volumes of flow per hour. Results indicate, as expected, that dynamic cesium sorption capacity is reduced as the flowrate is increased. Calculated dynamic capacities for cesium were 22.5, 19.8 and 19.6 mg Cs/g sorbent, for 5, 10 and 20 bed volume per hour flows, respectively. The thermal stability of loaded AMP-PAN was evaluated by performing thermogrovimetric analysis (TGA) on samples of AMP, PAN (polymer), and AMP-PAN. Results indicate that AMP-PAN is stable to 400 °C, with less than a 10% loss of weight, which is at least partially due to loss of water of hydration. The evaluation of AMP-PAN indicates that it will effectively remove cesium from concentrated acidic tank waste solutions.

Certified reference material for radionuclides in seawater IAEA-381 (Irish Sea Water)

Abstract: A certified reference material (CRM) for radionuclides in seawater, IAEA-381 (Irish Sea Water), is described and the results of certification are presented. The material has been certified for nine radionuclides (40K, 90Sr, 137Cs, 237Np, 238Pu, 239Pu,240Pu, 239,240Pu and 241Am). Information on massic activities with the corresponding 95% confidence intervals are given for eight radionuclides (3H, 125Sb, 234U, 235U, 236U, 238U, 241Pu and 244Cm). Less reported radionuclides include 60Co, 99Tc, and 242Pu. The CRM may be used for quality assurance/quality control of the analysis of radionuclides in environmental water samples, for the development and validation of analytical methods and for training purposes. The material is available from the IAEA in 5 kg units.

Sorption characteristics of Am(III), Sr(II) and Cs(I) on bentonite and granite

Abstract: The ability of the back-fill and the host rock materials to take up radioisotopes like 241Am, 85,89Sr and 137Cs has been examined as a function of contact time, pH, amount of sorbent, sorbate concentration, and the presence of complementary cations. A batch technique using actual borehole water from the granite formation has been utilized. In general, the uptake of nuclides by bentonite is much higher than that with granite. The sorption order of nuclides on bentonite is Am>Cs>Sr. The presence of complementary cations, Na+, K+, Ca2+ and Mg2+ depresses the sorption of Cs and Sr on bentonite. The sorption data have been interpreted in terms of Freundlich and Langmuir isotherm equations. Utilizing the Langmuir isotherm equation, the monolayer capacity, Vm,and the binding constant, K, have been evaluated. The change in free energy for the sorption of nuclides on bentonite has also been calculated.

Biosorption of americium-241 by Saccharomyces cerevisiae

Abstract: The biosorption of radionuclide 241Am from solution by Saccharomyces cerevisiae (S. cerevisiae), and the effects of experimental conditions on the adsorption were investigated. The preliminary results showed thatS. cerevisiae is a very efficient biosorbent. An average of more than 99% of the total 241Am could be removed by S. cerevisiae of 2.1 g/l (dry weight) from 241Am solutions of 17.54–4386.0 mg/l (2.22 MBq/l–555 MBq/l) with adsorption capacities of 7.45–1880.0 mg/g biomass (dry weight) (0.94 MBq/g–237.9 MBq/g). The adsorption equilibrium was achieved within 1 hour and the optimum pH ranged 1–3. No significant differences on 241Am adsorption were observed at 10–45 °C, or in solutions containing Au3+ or Ag+, even 2000 times above 241Am concentration. The relationship between concentrations and adsorption capacities of 241Am indicated the biosorption process should be described by the Freundlich adsorption isotherm.

Sorption of cesium on copper hexacyanoferrate/polymer/silica composites in batch and dynamic conditions

Abstract: The sorption of cesium ions from aqueous solutions on composite sorbents was investigated in static (by the batch method) and dynamic (on column) conditions. The composite sorbents consisted of copper hexacyanoferrate retained by an anion-exchange polymeric layer bound to porous silica beads. The influence of cesium concentration and solution flow rates on cesium sorption were studied. The cesium sorption isotherm obtained is of the Langmuir type. The shape of the breakthrough curves and the sorption capacity for cesium depend on the preparation procedure of the composites.

Natural radioactivity in soil samples of Kocaeli basin, Turkey

Abstract: The city of Kocaeli is in the western part of Anatolia in Turkey and has a population of approximately 1.000.000. There is no information about radioactivity in the Kocaeli soils samples so far. For this reason, the concentrations of the natural radionuclides in soil samples from 27 different sampling stations in Kocaeli Basin and its surroundings have been determined. The results have been compared with other radioactivity measurements in different country"s soils. The typical concentrations of 137Cs, 238U, 40K, 226Ra, 232Th found in surface soil samples ranged from 2±0.6 to 25±6 Bq/kg, from 11±4 to 49±10 Bq/kg, from 161±30 to 964±127 Bq/kg, from 10±4 to 58±11 Bq/kg, and from 11±3 to 65±13 Bq/kg, respectively.

Determination of uranium isotopes in environmental samples by alpha-spectrometry

Abstract: A new and accurate method for the determination of uranium isotopes (238U, 234U and 235U) in environmental samples by alpha-spectrometry has been developed. Uranium is preconcentrated from filtered water samples by coprecipitation with iron(III) hydroxide at pH 9-10 using an ammonia solution and the precipitate is dissolved in HNO3 and mineralized with H2O2 and HF; uranium in biological samples is ashed at 600 °C, leached with Na2CO3 solution and mineralised with HNO3, HF and H2O2; uranium in soil samples is fused with Na2CO3 and Na2O2 at 600 °C and leached with HCl, HNO3 and HF. The mineralized or leaching solution in 2M HNO3 is passed through a Microthene-TOPO (tri-octyl-phosphine oxide) column; after washing, uranium is directly eluted into a cell with ammonium oxalate solution, electrodeposited on a stainless steel disk and measured by alpha-spectrometry. The lower limits of detection of the method is 0.37 Bq.kg-1 (soil) and 0.22 mBq.l-1 (water) for 238U and 234U and 0.038 Bq.kg-1 (soil) and 0.022 mBq.l-1 (water) for 235U if 0.5 g of soil and 1 litre of water are analyzed. Five reference materials supplied by the IAEA have been analyzed and reliable results are obtained. Sample analyses show that, the 238U, 234U and 235U concentrations are in the ranges of 0.30-103, 0.49-135 and 0.02-4.82 mBq.l-1 in waters, of 1.01-7.14, 0.85-7.69 and 0.04-0.32 Bq.kg-1 in mosses and lichens, and of 25.6-53.1, 26.4-53.8 and 1.18-2.48 Bq.kg-1 in sediments. The average uranium yields for waters, mosses, lichens and sediments are 74.5±9.0%, 80.5±8.3%, 77.8±4.9% and 89.4±9.7%, respectively.

242Pu as tracer for simultaneous determination of 237Np and 239,240Pu in environmental samples

Abstract: A procedure has been developed using 242 Pu as tracer for simultaneous determination of 237 Np and 239,240 Pu in environmental samples. The validity of the method has been demonstrated by ICPMS and α-spectroscopy for up to 10 gram soil and sediment, seawater up to 200 litres. The paper describes a suitable chemical procedure for Np and Pu including a quantitative pre-concentration of neptunium and plutonium, preparation of Np 4+ and Pu 4+ , Np(NO3)6 2– and Pu(NO3)6 2– . The ratio of 237 Np/ 242 Pu (or 237 Np/ 239 Pu) before and after the procedure has been determined using 10 g soil (free from Np and Pu) Rbefore/Rafter = 1.004±3.3% (S.D n = 20) and 1 litre seawater Rbefore/Rafter = 1.019±1.9% (S.D., n = 12). Results from the intercomparison samples IAEA-135, IAEA-381 and from environmental samples are presented.

Distribution characteristics of rare earth elements in plants from a rare earth ore area

Abstract: The contents of eight rare earth elements (La, Ce, Nd, Sm, Eu, Tb, Yb and Lu) in various plant species taken from a rare earth ore area were determined by instrumental neutron activation analysis. For a given plant, the REE patterns in root, leaf and host soil are different from each other. The REE distribution characteristics in roots of various species are very similar and resemble those in the surface water. The results of this study suggest that there is no significant fractionation between the REEs during their uptake by the plant roots from soil solution. However, the variation of the relative abundance of individual REE occurs in the process of transportation and deposition of REEs in plants.

The uranium(VI) extraction mechanism of D2EHPA-TOPO from a wet process phosphoric acid

Abstract: This paper reports the results of an investigation into the solvent extraction of uranium from technical grade phosphoric acid using industrially available extractants as D2EHPA and TOPO diluted in technical grade kerosene. Preliminary tests showed that, the effect of different parameters such as uranium oxidation stage, temperature and the molar ratio of D2EHPA/TOPO on the uranium recovery was in good agreement with those of previous investigations. However, a detailed investigation into the effect of phosphoric acid concentration, organic concentration and acid/organic phase ratios suggested that the mechanism of D2EHPA/TOPO synergism was rather complex and it presented a different character depending on the acid concentration.

Comparative study on Th(IV) sorption on alumina and silica from aqueous solutions

Abstract: The effects of pH, ionic strength and concentration on the sorption of Th(IV) on alumina and silica were investigated and the sorption isotherms of Th(IV) on alumina and silica at different pH values were determined. It was found for both sorbents that the absorbability of silica is less than that of alumina. The relative sorption rate of silica is similar to that of alumina. The sorption edges are similar to each other, that the insensitivity of sorption to ionic strength is about the same. These similarities between the sorbents suggest that the speciation of Th(IV) in aqueous solutions plays a significant, but subtle role, in controlling the sorption process, because the charges of both sorbents are distinctly different. The mechanism of Th(IV) sorption on alumina is distinctly different from that of the sorptions of Cs+, Eu3+ and Yb3+ on alumina, and similar to that of the sorption of Co(II) on alumina.

Sorption of uranyl ions on silica: Effects of contact time, pH, ionic strength, concentration and phosphate

Abstract: The sorption of UO22+ and phosphate on silica were simultaneously studied. The effect of contact time between the solid phase and aqueous solution, pH and ionic strength on the UO22+ sorption in the absence and the presence of phosphate was investigated. The effect of contact time between the solid phase and aqueous solution, pH and ionic strength on the phosphate sorption was investigated too. The isotherms of UO22+ and phosphate sorption at different pH values were determined. It was found that as compared with the sorption in the absence of phosphate, the sorption of UO22+ on silica in the presence of phosphate is increased at low pH and decreased at high pH; the abruptly increased with increasing pH in the pH range 3-6; the sorption is gradually decreased with increasing pH in the pH range 2-12; the sorption insensitive and the sorption of phosphate is sensitive to ionic strength.

Radionuclide variations in the air over Monaco

Abstract: Radionuclides in aerosols and precipitation have been analyzed by IAEA-MEL in Monaco since 1987 and 1999, respectively, to identify their behavior in the atmosphere and delivery into the northwestern Mediterranean Sea. While the concentration of 7Be in aerosols has been affected by the stratospheric-tropospheric mixing and precipitation, the concentration of 137Cs in aerosols has been influenced by a combination of local meteorological conditions and re-suspension of 137Cs from soil. Higher concentrations of 7Be, 137Cs, 239,240Pu and 241Am in precipitation occurred during spring and summer. The highest deposition rates of these radionuclides were observed in spring and autumn during periods of high precipitation. A good correlation was found between the amount of precipitation and depositional flux for 7Be, but not for 137Cs, 239,240Pu and 241Am. This indicates that the wet process as well as the dry process seem to be important factors in determining the annual deposition for transuranic radionuclides and 137Cs.

Natural radioactivity in Algerian bottled mineral waters

Abstract: The activity concentrations of some radionuclides in Algerian bottled mineral waters were determined using CR-39 nuclear track detectors for 222Rn, and a high resolution gamma-ray spectrometry for 226Ra, 232Th and 40K. The mean specific activities of 222Rn , 226Ra, 231Th and 40K in the drinking mineral waters were 7±4 Bq.l-1, 26±11 mBq.l-1, 30±13 mBq.l-1 and 1±0.5 Bq.l-1, respectively. These values are comparable with concentrations reported for other countries. The effective doses due to intake of these radionuclides as a consequence of direct consumption of drinking mineral waters have been determined. The estimated effective doses were 56.8 mSv.y-1 for 222Rn, 3.94 mSv.y-1 for 226Ra, 4.45 mSv.y-1 for 232Th and 3.33 mSv.y-1 for 40K. Contribution of these radionuclides to the effective dose due to ingestion and inhalation of all terrestrial radionuclides is estimated to be only 0.012%.

Radiation-induced degradation and crosslinking of poly(ethylene oxide) in solid state

Abstract: The effects of g-irradiation on solid poly(ethylene oxide) (PEO) of an initial weight-average molecular weight of 6.3.105 Da were investigated by gel permeation chromatography and viscometry. The parameters studied were changes in number- and weight-average molecular weight, molecular weight distribution and viscosity of PEO in aqueous solution. Irradiation of poly(ethylene oxide) powder in the presence of oxygen leads to the dominance of chain scission reactions. Their high radiation-chemical yield [G(scission) » 2.5.10-6 mol/J] indicates the occurrence of effective chain reactions. Upon irradiation in vacuum, crosslinking and scission occur side-by-side and the changes in molecular weight are less pronounced in the studied dose range (up to 20 kGy). Scission dominates for doses up to ca. 15 kGy, while for higher doses intermolecular crosslinking gains in importance. The competition between these processes seems to depend not only on the applied dose but also to be influenced by the inhomogenity of the material (molecular weight and/or possibly the crystallinity). Parallel occurrence of scission and crosslinking leads to the broadening of the molecular weight distribution.

atmospheric deposition of heavy metals around the lead and copper-zinc smelters in Baia Mare, Romania, studied by the moss biomonitoring technique, neutron activation analysis and flame atomic absorption spectrometry

Abstract: The mosses Pleurozium schreberi, Pseudoscleropodium purumandRhytidiadelphus squarrosus were used as biomonitors to study the atmospheric deposition of metals around the lead and copper-zinc smelters in Baia Mare. Samples representing the last three years" growth of moss or its green part, collected on the ground at 28 sites located 2-17 km from the source area, were analyzed by instrumental neutron activation analysis using epithermal neutrons (ENAA) and by flame atomic absorption spectrometry (FAAS). A total of 31 elements were determined, including most of the heavy metals characteristic of emissions from this kind of industry. The observed data for Pb, As, Cu, and Cd are all high compared with those observed in other regions of Europe with similar industries, but the concentrations in moss approach regional background levels at a distance of about 8 km from the main source area. Factor analysis of the data distinguishes two industrial components, one characterized by Pb, Cu, As, and Sb, and another one by Zn and Cd. A strong crustal component including five major elements (Na, Mg, Al, Ti, Fe) and an additional number of trace elements (Sc, V, Cr, Cs, Ba, REE, Th) also appears to be derived mainly from industrial sources. The mean I value in the present material is 5 times lower than the corresponding level in moss in Norway, and also consistently lower than elsewhere in Europe, a fact which evidences the endemic character of the examined area due to iodine depletion.

Separation of lanthanides using ion-interaction chromatography with HDEHP coated columns

Abstract: A rapid and high resolution separation of lanthanides by HPLC technique has been developed using Di-(2-ethylhexyl) phosphoric acid (HDEHP) coated reverse phase column and a-hydroxy isobutyric acid as the complexing reagent for elution. A gradient elution technique has been developed for achieving the separation of the entire lanthanide series. Isocratic elution procedure has also been developed for the separation of lighter (La to Gd) as well heavier lanthanides (Lu to Tb). This paper describes the separation methods developed and their application for the determination of lanthanides in a fission product mixture.

Adsorption of radioactive iodide by natural zeolites

Abstract: Two natural zeolites from Iranian deposits (clinoptilolite and natrolite) were characterized and their ability for adsorption of iodide from nuclear wastewaters was evaluated. The adsorption behavior was studied on natural and modified zeolites by g-spectrometry using 131I as radiotracer. Adsorption isotherms and distribution coefficient (Kd) were measured. The results showed that clinoptilolite is a more promising zeolite for removal of iodide compared to natrolite. Furthermore, the adsorption was higher in silver, lead and thallium forms, whereas the lowest desorption was observed in lead modified zeolite.

Study of 137Cs, 90Sr, 239,240Pu, 238Pu and 241Am behavior in the Chernobyl soil

Abstract: The vertical distribution of 137Cs, 90Sr, 239,240Pu, 238Pu and 241Am was determined in soil samples collected from the Chernobyl exclusion zone in 1994. The results show very close distribution profiles for all radionuclides, with about 90% of the total activity of each nuclide lying between the surface and the fourth centimeter. Sequential extraction methods were used to determine the association of radionuclides in soil. The data on vertical distribution of radionuclide species were used to calculate their vertical migration parameters.

Uranium sorption on amorphous titanium and zirconium phosphates modified by Al3+ or Fe3+ ions

Abstract: The sorption of uranium from aqueous solutions on titanium and zirconium phosphates in H+ and K+ forms modified by iron or aluminum ions has been investigated. The modified pattern of porosity is much better, than for none modified analogous, owing to their increased sorption capacity and kinetics of uranium absorption. The modified sorbents display selectivity towards uranium, that allows to purify solutions up to the content of uranium below the limit of its analytical definition.

Structural studies on organotin(IV) complexes formed with ligands containing {S,N,O} donor atoms

Abstract: A number of complexes of ligands containing {O,N,S} donor atoms (2,3,4,6-tetra-O-acetyl-b-D-thioglucopyranoside, 1-thio-b-D-glucose, 2-aminomercaptopurine, 4-amino-2-mercaptopyrimidine and 2-amino-6-mercaptopurine-9-D-riboside) with di-n-butyltin(IV) oxide, diphenyltin(IV) oxide, tribenzyltin(IV) chloride, and trimethyltin(IV) chloride were prepared in the solid state. It was found that the complexes contain the organotin(IV) moiety and the ligand in a ratio of 1:1 or 2:1. The FTIR and Raman spectra clearly demonstrated that the organotin(IV) moieties react with the {S} atom of the ligands, while di-n-butyltin(IV) oxide is coordinated to the deprotonated hydroxy group. In several cases, the basic part of the ligands also participates in complex formation. Comparison of the experimental Mossbauer D values with those calculated on the basis of the pqs concept revealed that the organotin(IV) moiety has trigonal-bipyramidal geometry, and in certain cases tetrahedral geometry too. Some of the complexes contain the organotin(IV) cation in two different surroundings.

137Cs dating of lake cores from the Nahuel Huapi National Park, Patagonia, Argentina: Historical records and profile measurements

Abstract: Historical records of short lived (140Ba, 131I, 103Ru and 95Zr+95Nb) and long-lived (137Cs and 90Sr) fission products by fallout measurements performed in Argentina since 1959 were analyzed in order to define the main characteristics of 137Cs fallout time evolution in the Nahuel Huapi National Park, Patagonia, Argentina. Sedimentary cores were sampled from Lake Nahuel Huapi and Lake Morenito, which are located within Nahuel Huapi National Park. 137Cs specific activity profiles were measured and 210Pb dating was performed in each core. The time evolution of 137Cs fallout shows different characteristics than records taken in the Northern Hemisphere.137Cs specific activity profiles of the cores studied reproduce the fallout time sequence observed in the historical records, and the chronology obtained shows excellent agreement with 210Pb dating.

Extraction of U(VI) by cyanex-272

Abstract: Extraction of U(VI) from HNO3, HCl and HClO4 media using cyanex-272 (bis[2,4,4 trimethyl pentyl] phosphinic acid)/n-dodecane has been carried out. In the case of HNO3 and HClO4 media, the distribution ratio (D) value first decreases and then increases, whereas from HCl medium it first decreases and then remains constant with increase in H+ ion concentration. At lower acidities, U(VI) was extracted as UO2(HA2)2 by an ion exchange mechanism, whereas at higher acidities as UO2(NO3)2 .2(H2A2) following a solvation mechanism. The D for U(VI) by cyanex-272, PC-88A and DEHPA at low acidities follows the order cyanex-272 > PC-88A > DEHPA. Also, cyanex-272 was found to extract U(VI) more efficiently than TBP at 2M HNO3. The effect of diluents on the extraction of U(VI) by cyanex-272 followed the order cyclohexane > n-dodecane > CCl4 > benzene. The loading of U(VI) into cyanex-272/n-dodecane from 2M HNO3 has shown that at saturation point, cyanex-272 was 78% loaded. No third phase was observed at the saturation level. The stripping of U(VI) from the loaded organic phase was not possible with water, it was poor with acetic acid and sodium acetate but quantitative with oxalic acid, ammonium carbonate and sodium carbonate.

Some aspects of environmental radioactivity around the former Soviet Union"""s Semipalatinsk nuclear test site: Local fallout Pu in Ust"""-Kamenogorsk district

Abstract: The 137Cs, 238Pu and 239,240Pu activity concentrations were determined together with the atomic ratios of 240Pu/239Pu for the soil samples at 19 sites from the Ust"""-Kamenogorsk district, located more than 300 km east of the Semipalatinsk nuclear test site (SNTS). The mean areal deposition of 137Cs ranged from 1,500 to 4,100 Bq/m2. However, some hot spot-like areas showing high concentrations of 5,500–7,700 Bq/m2 were foundat some sites within the city. The 239,240Pu levels ranged from <50 to 510 Bq/m2, however most of them ranged between 120–200 Bq/m2. These levels are nearly the same as those around the Semipalatinsk City. At most of the sites within the city and its adjacent areas, both nuclides were found in the soil layers up to a depth of 30 cm. A fraction of 20–50% of 239,240Pu was not leached by hot digestion with concentrated HNO3 containing a small amount of H2O2. Generally, such tightly bound fraction showed a trend to decrease with increasing distance from the SNTS. The fraction of these radionuclides that were deposited in Ust"""-Kamenogorsk district from global and from SNTS fallouts have been determined using the 240Pu/239Pu atomic ratios in both Pu fractions: one which can be leached with hot HNO3 + H2O2 and another that is a non-leacheable for each soil layer of core samples. As a result a fraction of 21–80% (mostly 30–60%) of total 239,240Pu were found to be due to the local fallout of Pu from the SNTS debris. For 137Cs, the contribution (mostly 10–20%) of local fallout from the SNTS were estimated to be far lower as compared to 239,240Pu.

Retention of Cs on zeolite, bentonite and their mixtures

Abstract: The sorption behavior of cesium on zeolite and bentonite minerals and their mixtures was studied by means of a batch method and a tracer technique. All experiments were carried out in the presence of CsCl spiked with 137Cs and NaCl as a supporting electrolyte in varying concentrations. The distribution coefficients (K D) did not show significant differences at low Cs+ loadings while they decreased in the high loading region. Freundlich and D-R isotherms were applied to the adsorption data of zeolite and bentonite. Adsorption capacities and mean energies calculated from D-R isotherm parameters decreased by increasing ionic strength on both minerals. The identification of the specific uptake sites was attempted on the basis of the Freundlich isotherm. Experimentally observed distribution coefficients of Cs on two mineral mixtures were smaller than theoretically calculated values, except at the highest NaCl concentration.

Diffusion of 3H, 99Tc, 125I, 36Cl and 85Sr in granite, concrete and bentonite

Abstract: Understanding the characteristics of diffusion is essential in the assessment of radionuclide release through the backfill of waste repository. The diffusion behavior of 3H, 99Tc, 125I, 36Cl and 85Sr in granite, concrete and bentonite was studied in a specially designed diffusion cell. Diffusion coefficients (D, Da) and time-lag (ta) were measured, break-trough curves were plotted and experimental data were interpreted to predict diffusion rates. The results showed that tritium, iodine and chlorine could be considered as non-sorbing tracers, while technetium was weakly and strontium was strongly sorbed (no break-through was observed during the period of the experiments).