Nuclear Chemical Effects in the Paragenetic Mineral Association Based on Polycrase

A natural polymineral compound in which the major uranium-containing mineral is polycrase (Ti- Ta-niobate) described by the formula АВ₂О₆ was chosen as a model for studying the behavior of recoil atoms produced by α-decay of actinides. Polycrase, despite its metamict structure, is characterized by the following features distinguishing it from Ti-Ta-niobates of the formula А₂В₂О₇ (pyrochlore and betafite): (1) 1/3 of uranium atoms preserve the initial valence state, U(IV); (2) the U(IV) fraction is characterized by the isotope activity ratio AR(²³⁴U/²³⁸U) close to that at secular equilibrium; (3) the uranium atoms that underwent oxidation “memorize” their radiogenic origin; as a result, the AR(²³⁴U/²³⁸U) ratio in the U(VI) fraction is 0.90, and in the most altered part of the mineral it decreases to 0.77; (4) the parent uranium is relatively stable in the metamict structure of polycrase: The half-leaching time for ²³⁸U atoms is 2 times longer than that in betafite, zircon, or sphene.     

Radiogenic 234U and 210Po in humus acids of dyctionemic shale

Radiochemical analysis is made of different fractions of humic and fulvic acids separated from organic matter of graptolitic argillite (dyctionemic shale) of the Baltic basin. The relation between the decalcination of humates and fulvates and the isotopic composition of U is studied. The tightness of binding to humus substances, including humin, is different for ²³⁸U and ²³⁴U, which is probably due to preferential stabilization of the radiogenic uranium in the oxidation state +4. Based on the experiments on precipitation of humates at pH 0–2, it is suggested that the thiol groups of humic acids are involved in chemical binding of ²¹⁰Po. Experiments on partial decalcination of humates in 1 M HNO₃ revealed stronger binding of the radiogenic Po as compared to ^208,209Po. The results were interpreted in terms of the known models.     

Influence of the nature of oxygen-containing minerals on their sorption ability toward U(VI)

Sorption of U(VI) on natural and synthetic oxygen-containing minerals was studied. With respect to the sorption ability toward U(VI), natural minerals can be ranked in the order iron-containing > aluminum-containing > silicon-containing, and synthetic minerals, in the order iron-containing ≈ silicon-containing ≫ aluminum-containing. It was demonstrated by the example of Fe(OH)₃, α-FeO(OH), and γ-FeO(OH) that crystalline minerals bind U(VI) at pH values corresponding to natural media (pH > 7.5) better than do amorphous minerals. The ionic strength does not affect the U(VI) sorption owing to formation of strong inner-sphere complexes on the mineral surface. The presence in solution of complexing agents in small amounts can enhance the U(VI) sorption owing to formation of ternary surface complexes, whereas large excess of the ligand decreases the sorption because of the shift of the equilibrium toward formation of soluble complexes migrating in the environment by long distances with water streams.     

Recovery of <Superscript>137</Superscript>Cs and <Superscript>90</Superscript>Sr from wastewater by sorption on finely dispersed minerals under static conditions

The natural minerals clinoptilolite and tripoli were used for sorption treatment of liquid radioactive waste (LRW) to remove ¹³⁷Cs and ⁹⁰Sr. The efficiency of sorption recovery of these radionuclides with finely dispersed mineral sorbents under static conditions was studied in relation to the sorption time, pH, size of mineral granules, sorbent amount, salt content and chemical composition of solutions, and number of successive sorption steps. The distribution coefficient of radionuclides between the sorbent and aqueous phase and the sorption capacity of sorbents for radionuclides were determined. It was found that treatment of real salt-containing LRW from the Leipunskii Institute of Energy Physics, State Scientific Center of the Russian Federation, with the natural sorbents decreased their activity by 2–3 orders of magnitude owing to recovery of ¹³⁷Cs and ⁹⁰Sr.     

Dose effect for South Serbians due to 238U in natural drinking water

The use of depleted uranium ammunition in South Serbia during the 1999 Kosovo conflict raised a great deal of public concern in the Balkans. Radioactivity levels of 238U in 20 wells and lake water samples were checked from the viewpoint of internal radiation exposure for South Serbian subjects. We have measured 238U concentration using inductively coupled plasma mass spectrometry, whereas thermal ionisation mass spectrometry has been used for the measurement of isotope ratios, e.g. 234U/238U and 235U/238U. The concentration of uranium in water samples varies in the range 1.37-63.18 mBq/L. 234U belongs to the 238U natural radioactive decay series, and at secular equilibrium, the abundance ratio, 234U/238U, corresponds to the ratio of their half-lives. The 234U/238U activity ratio varies in the range 0.88-2.2 and 235U/238U isotope ratio varies from 0.00698 to 0.00745. These findings indicate that uranium in water was a mixture of natural and anthropogenic origin. The annual effective dose due to 238U was estimated to be in the range 9.2 x 10(-5)-2.1 x 10(-3) mSv.     

Radionuclides in ground waters from observation holes in the Shelter local area

The volume activity of ³H, ⁹⁰Sr, ¹³⁷Cs, ²³⁴U, ²³⁵U, ²³⁸U, ²³⁸Pu, ^239+240Pu, and ²⁴¹Am in ground waters from observation holes 1-G-6-G in the north section of the Shelter local area of the Chernobyl Nuclear Power Plant (CNPP) was measured. The distribution of radionuclides in the suspension fractions of the ground waters was evaluated. The main contribution to the pollution of ground waters with uranium is due to natural uranium isotopes: ^234,235,238U. The activity ratios of ²³⁸Pu, ^239+240Pu, and ²⁴¹Am in ground waters are similar to those in the spent fuel of 4th CNPP block.     

The development of a method for the preparation of large amounts of 234Th-purified 238U-oxide

High purity ²³⁸U-oxide in amounts up to 60 g is required for capture cross-section measurements. The material needs to be purified for the ²³⁴Th daughter of ²³⁸U in order to reduce the natural γ background. It has been shown that 60 g of U₃O₈ can be purified by cation-exchange and retransformed in U₃O₈ in about 20 h. When the target is ready for use the ²³⁴Th content is 2% of the saturation value.     

The State of Disequilibrium between U and Th Series Isotopes in Marine Sediments from the Sudanese Red Sea Coast

The geochemical behavior of U, Th series nuclides in surface marine sediments collected fromthe Red Sea coastal environment of Sudan was examined using daughter/parent and nonisotopic activity ratios. Pronounced anomalous behavior of several series of nuclides has been observed, particularly at shallower depths. On the average, the ²³⁴U/²³⁸U ratio is fairly constant and close to 1.13, suggesting scavenging of ²³⁴U from the overlying water column. In shallow-water sediments collected from the biologically productive area of the fringing reef and from the tidal-flat of Sanganeb atoll, compared to harbor and deep-sea sediments, ²³⁸U was found in large excess relative to ²³²Th. The ²²⁸Th/²³²Th disequilibrium indicates rapid sedimentation at shallower sites, which agrees well with data reported in the literature for similar environments. Depletion was observed of precursor thorium isotopes (²³⁰Th, ²³²Th) with respect to their mobile daughter isotopes of radium (²²⁶Ra, ²²⁸Ra). On the other hand, there is surface enrichment of ²²⁸Th and ²¹⁰Po with respect to their progenitors ²²⁸Ra and ²²⁶Ra, as demonstrated by the ²²⁸Th : ²²⁸Ra and ²¹⁰Po : ²²⁶Ra activity ratio, which is greater than unity in all the sediments analyzed. The ²¹⁰Po/²²⁶Ra ratio is fairly constant (average 3.2).     

Uranium isotopes in public drinking water and dose assessment for man in Poland

238U, 234U and 235U were determined in tap water from municipal water pipes that drew their supply from surface water or ground water in various locations in Poland. Average activity concentrations of 238U, 234U and 235U in tap water from surface water were 9.6 +/- 7.1, 12.8 +/- 9.7 and 0.41 +/- 0.31 Bq m(-3), respectively, whereas from ground water they were 4.5 +/- 6.0, 5.7 +/- 6.9 and 0.19 +/- 0.27 Bq m(-3), respectively. Activity concentrations of 234U were higher than 238U. Ratios of 234U/238U ranged from 1.07 to 2.60, indicating the lack of equilibrium between these isotopes. The average 235U/238U ratio was 0.043 +/- 0.008, being close to 0.046 for natural uranium. Average annual intake with water and food was 7.6 +/- 5.1 Bq for 238U and 9.5 +/- 6.6 Bq for 234U. Annual committed effective doses calculated from these intakes for adults were 0.34 +/- 0.23 and 0.47 +/- 0.32 microSv, respectively; 235U contributed to the total dose from the uranium isotopes by about 2%.     

A Method for Determining the Isotope Composition of U, Pu, Am, and Cm in "Hot" Particles and Spent Nuclear Fuel

A method was proposed for determining the content of ^234-238U, ^238-242Pu, ^241-243Am, and ^242-244Cm in "hot" fuel particles and spent nuclear fuel. The method is based on high-precision measurement of the -activity in the sample and calculation of the relative contributions of individual nuclides or radionuclide groups to the total activity. Partitioning of U, Pu, Am, and Cm was carried out by ion-exchange chromatography. The contents of ²³⁴U, ²³⁶U, ²³⁸U, ²³⁸Pu, ^239+240Pu, ²⁴²Pu, ²⁴¹Am, ^242mAm, ²⁴³Am, ²⁴²Cm, and ²⁴⁴Cm in "hot" particles sampled in the Chernobyl area were reported. The applicability of the method proposed to determining the radionuclide composition of spent nuclear fuel was discussed.     

An accurate method to measure alpha-emitting natural radionuclides in atmospheric filters: Application in two NORM industries

In this work, an accurate method for the measurement of natural alpha-emitting radionuclides from aerosols collected in air filters is presented and discussed in detail. The knowledge of the levels of several natural alpha-emitting radionuclides (²³⁸U, ²³⁴U, ²³²Th, ²³⁰Th, ²²⁸Th, ²²⁶Ra and ²¹⁰Po) in atmospheric aerosols is essential not only for a better understanding of the several atmospheric processes and changes, but also for a proper evaluation of the potential doses, which can inadvertently be received by the population via inhalation.The proposed method takes into account the presence of intrinsic amounts of these radionuclides in the matrices of the quartz filters used, as well as the possible variation in the humidity of the filters throughout the collection process. In both cases, the corrections necessary in order to redress these levels have been evaluated and parameterized. Furthermore, a detailed study has been performed into the optimisation of the volume of air to be sampled in order to increase the accuracy in the determination of the radionuclides.The method as a whole has been applied for the determination of the activity concentrations of U- and Th-isotopes in aerosols collected at two NORM (Naturally Occurring Radioactive Material) industries located in the southwest of Spain. Based on the levels found, a conservative estimation has been performed to yield the additional committed effective doses to which the workers are potentially susceptible due to inhalation of anthropogenic material present in the environment of these two NORM industries.     

An efficient FE model and Least Square Error method for accurate calculation of transverse shear stresses in composites and sandwich laminates

Accurate evaluation of transverse stresses in laminated composites and sandwich plates using 2D FE models involves cumbersome post-processing techniques. In this paper a simple and efficient method has been proposed for accurate evaluation of through-the-thickness distribution of transverse stresses in composites and sandwich laminates by using a displacement based C⁰ FE model (2D) derived from Refined Higher Order Shear Deformation Theory (RHSDT) and a Least Square Error (LSE) method. The C⁰ FE model satisfies the inter-laminar shear stress continuity conditions at the layer interfaces and zero transverse shear stress conditions at the top and bottom of the plate. In this model the first derivatives of transverse displacement have been treated as independent variables to circumvent the problem of C¹ continuity associated with the above plate theory (RHSDT). The LSE method is applied to the 3D equilibrium equations of the plate problem at the post-processing stage, after in-plane stresses are calculated by using the above FE model based on RHSDT. Thus the proposed method is quite simple and elegant compared to the usual method of integrating the 3D equilibrium equations at the post-processing stage for calculation of transverse stresses in a composite laminate. In the proposed method, the first two equations of equilibrium are utilized to compute the transverse shear stress variation through the thickness of a laminated plate whereas the third equation of equilibrium gives the normal stress variation. Accuracy of the proposed method is demonstrated in the numerical examples through comparison of the present results with those obtained from different models based on higher order shear deformation theory (HSDT) and 3D elasticity solutions.     

Accurate calculation of transverse shear stresses for soft-core sandwich laminates

Accurate evaluation of transverse stresses in soft-core sandwich laminates using the existing 2D finite element (FE) models involves cumbersome post-processing techniques. In this paper, a simple and robust method is proposed for accurate evaluation of through-the-thickness distribution of transverse stresses in soft-core sandwich laminates by using a displacement-based C⁰ continuous 2D FE model derived from refined higher-order shear deformation theory (RHSDT) and a least square error (LSE) method. In this refined higher-order shear deformation theory (RHSDT), the in-plane displacement field for the face sheets and the core is obtained by superposing a global cubically varying displacement field on a zigzag linearly early varying displacement field. The transverse displacement is assumed to have a quadratic variation within the core, and it remains constant in the faces beyond the core. The proposed C⁰ FE model satisfies the condition of transverse shear stress continuity at the layer interfaces and the zero transverse shear stress condition at the top and bottom of the sandwich plate. The nodal field variables are chosen in an efficient manner to circumvent the problem of C¹ continuity requirement of the transverse displacements associated with the RHSDT. The LSE method is applied to the 3D equilibrium equations of the plate problem at the post-processing stage, after in-plane stresses are calculated by using the above FE model based on RHSDT. Thus, the proposed method is quite simple and elegant compared to the usual method of integrating the 3D equilibrium equations at the post-processing stage for the calculation of transverse stresses in a sandwich laminates. The accuracy of the proposed method is demonstrated in the numerical examples through the comparison of the present results with those obtained from different models based on HSDT and 3D elasticity solutions.     

Fourier transform infrared spectroscopic estimation of crystallinity in SiO<Subscript>2</Subscript> based rocks

We present here optical properties and crystallinity index of quartz (SiO₂) in natural rocks samples from the Mikir and Khasi hills, Assam, India. Infrared spectroscopy has been used to study the structure of quartz in rock samples and estimate the mining quality of quartz mineral, which is substantiated by calculating the crystallinity index. Systematic investigations of structure have been carried out in between 10 μm (1000 cm⁻¹) and 20 μm (500 cm⁻¹) bands of silicates. Investigation is based on the assignment of infrared bands to certain structural groups of SiO₄ tetrahedra. The crystallinity of samples has been ascertained by comparing the ratio of intensity of the characteristic peak at 778 and 695 cm⁻¹ with the corresponding ratio for a standard sample. The crystallinity parameter is calculated by using a standard procedure which can be used to estimate the distribution of quartz in various rocks for mining purpose. The infrared spectroscopic investigation is found to be an ideal tool for structure elucidation and for estimating quartz crystallinity of the natural samples.     

Modeling frost heave in freezing soils

A generalized model for secondary frost heave in freezing fine-grained soils is presented. The cryostatic suction effect, which causes an increase in upward water permeation, ice-lens growth during freezing, and, as a consequence, the increase of soil heave, is considered to be the main mechanism of moisture transfer. Although the model in this paper has a number of approaches in common with the model of Fowler and Krantz (1994) it differs in at least several important respects. We recognize the need to determine the distribution of the moisture within the frozen fringe by approximation of the experimental data for the equilibrium unfrozen water content. This distribution is the result of the complicated interaction between water, ice and the mineral skeleton during the freezing process. The generalization of the Clapeyron relation, which is used in the work cited above, only estimates the drop in initial freezing temperature and does not define the connection with the external temperature gradient ∇T, which is responsible for the frost heave process. This very important aspect is discussed in detail in the Introduction to our paper. Another difference is the fact that our solution is based on a dimensionless system of equations. We take into account the ratio Pe/Ste ≠ 1 (where Pe << 1). This approach allows us to obtain both a more general solution as well as analyze frost heave and propagation of the freezing front as they depend upon the convective (Pe) and phase transition (Ste) characteristics (criteria) of the process. The theoretical results derived from our solution of the analysis for fine-grained soils are compared, in good agreement, with experimental investigations and numerical models. A singularity of the solution at the initial point in time is discussed. In this respect the asymptotic solution for short and long times is obtained. The results are compared with both solutions (modeling and asymptotic). The model presented predicts the frost heave and freezing processes in porous media with reasonable accuracy and satisfactorily reflects observed phenomena, and thus can be suitable for engineering practice.     

Mass spectrometric determination of 234U/238U ratio with improved precision

A new mass spectrometric method is proposed for measurement of 234U/238U ratio with a single Daly electron multiplier detector using the general peak jump method. The method is based on precise measurement of the 235U/238U ratio and 234U/235U ratio, which are used to calculate the 234U/238U ratio using the equation 234U/238U = 235U/238U x 234U/235U. The results show a significant improvement, i.e., more than 35 times better precision in measuring the (234)U/(238)U ratio with this method (sigma = 2.9 x 10(-8)) as compared to direct measurement of 234U/238U (sigma = 1.1 x 10(-6)). The method widens the applicability of the single collector system, and it will potentially be helpful to improve the precision in the case of the static multicollector system also.     

Sorption of 90Sr and 137Cs on Natural Sorbents in Model Environmental Systems

Sorption of ⁹⁰Sr and ¹³⁷Cs from both tap drinking water and water of Beloyarsk storage basin on samples of natural ion exchangers, glauconite concentrate and white alluvial clay, was studied under static conditions. The distribution coefficients of ⁹⁰Sr and ¹³⁷Cs between these sorbents and water were studied as influenced by the equilibration time and water type. With white alluvial clay and glauconite concentrate the sorption equilibrium is reached within 90 and 270 days, respectively. Sorption characteristics of these natural sorbents allow them to be recommended for water decontamination from ⁹⁰Sr and ¹³⁷Cs.     

Dynamics and thermodynamics of quasi-one-dimensional helium deposited on carbon nano-bundles

No Heading The thermodynamics of monoatomic gas (helium) adsorbed on one-dimensional groove positions on carbon nanolube bundles has been investigated theoretically. The model of lattice gas type is based on account of equilibrium conditions between two subsystems: quasi-one-dimensional helium in grooves and three-dimensional helium atmosphere closed within the free volume of an experimental cell (the total amount of helium atoms in the system is taken to be constant). The analytical calculations of the energy and the heat of adsorption have been compared with the experimental data.¹PACS: 68.35.Dv, 68.35.Ja, 68.65.+g     

Comparative and competitive adsorption of cadmium, copper, nickel, and lead ions by Iranian natural zeolite

The competitive adsorption behavior of cadmium (Cd²⁺), copper (Cu²⁺), nickel (Ni²⁺), and lead (Pb²⁺) ions using Iranian natural zeolite has been studied in order to determine its applicability in treating industrial wastewater. Tests to determine both the rate of adsorption and the uptake at equilibrium were performed under batch conditions from single- and multi-component solutions. The optimum conditions for the treatment process were investigated by observing the influence of pH levels, the presence of competing ions, varying the mass of zeolite and different contact time. Adsorption kinetics of the zeolite followed first-order kinetics, showing about 100 % of Pb²⁺ removal within 40 min and reaching an equilibrium state within 24 h for Cd²⁺, Cu²⁺, and Ni²⁺. The results indicated that removal of metals from single- and multi-component solutions is best described by a Freundlich isotherm, in which the distribution coefficient was in the following order: Pb²⁺ > Cu²⁺ > Cd²⁺ > Ni²⁺. In the multi-component solutions, metals exhibit competitive adsorption on the zeolite. The adsorption is reduced to 90, 53, 30, and 22 % of single component of Cu²⁺, Ni²⁺, Cd²⁺, and Pb²⁺, respectively. However, the total adsorption was higher than single component. Finally, soil solution saturation indices and speciation of metals was assessed using Visual MINTEQ 2.6 software, and probability of precipitation of minerals supported by scanning electron microscopy. The research indicates that Cd²⁺ and Ni²⁺ retention by zeolite can be viewed as the result of ion exchange reaction, but Pb²⁺ and Cu²⁺ retention is both due to ion exchange and precipitation. These results show that Iranian natural zeolite particularly effective in removing cationic heavy metal species from industrial wastewater.