Desorption of 90Sr and 137Cs from Flood Plain Deposits of the Sozh River and Rocks of the Adjacent Catchment Areas

Desorption of ⁹⁰Sr and ¹³⁷Cs from flood plain warps, meadow sod, humus-containing sandy loam, peat, clays, limonite, meadow marl, and friable rocks of the adjacent catchment areas (moraine clay, loam, sandy loam) was studied. ¹³⁷Cs is sorbed the most strongly on clays by the mechanism of isomorphic ion-exchange incorporation into the crystal lattice of montmorillonite-type minerals. ¹³⁷Cs is also tightly fixed on buried and peaty soils due to association with the poorly mobile species of humic acids and humin. The strong fixation of ⁹⁰Sr on amorphous iron hydroxides is caused by its association with poorly soluble ferrite-type minerals. Sorption of ⁹⁰Sr on peaty soils can be attributed to their association with aluminum and iron-containing organomineral complexes. ¹³⁷Cs sorbed on flood plain warps, sandy loams, and loams exhibits increased mobility and is leached with all the tested desorbing solutions. These deposits apparently contribute maximally to the redistribution of radiocesium over flood plain and the adjacent catchment areas. The desorption efficiency of cations of the desorbing solutions decreases in the order Cs⁺ > K⁺ > Fe^{3 +} > NH₄ ⁺ > Ca^{2 +} > H⁺ for radiocesium and Fe^{3 +} > Sr^{2 +} > K⁺ > H⁺ > Ca^{2 +} > NH₄ ⁺ for radiostrontium.     

Coprecipitation of microamounts of radionuclides on chitosans of various molecular weights in solutions

Coprecipitation of ²³³U, ²³⁹Pu, ²⁴¹Am, ¹⁵²Eu, ⁹⁰Sr, ⁹⁰Y, and ⁶⁰Co on chitosans of various molecular weights (MW) was studied. Low-molecular-weight chitosan (LMWC) with MW of 5 kDa (5 × 10³ g mol⁻¹) proved to be a more effective coprecipitant than high-molecular-weight chitosan (HMWC) with MW of 700 kDa (7 × 10⁵ g mol⁻¹). With HMWC, the degree of coprecipitation (α) was 80% for ¹⁵²Eu and ⁹⁰Y, 99% for ²³³U and ²⁴¹Am, and 85% for ²³⁹Pu. For ⁶⁰Co, α monotonically increased with an increase in the chitosan concentration in solution and reached 40% at [HMWC] = 5 g l⁻¹. For ⁹⁰Sr, α did not exceed 3% in the entire examined range of chitosan concentrations. With LMWC, the α values for An, ¹⁵²Eu, and ⁹⁰Y differed insignificantly (92–99%). For ⁶⁰Co and ⁹⁰Sr, α increased to 40% in the range of chitosan concentrations from 0 to 1 g l⁻¹. The presence of inorganic salts in solution considerably decreases α of UO₂²⁺ with chitosans but does not noticeably affect the behavior of Am, Pu, and Eu. The effect of salts on the efficiency of ²³³UO^2/2+ coprecipitation on HMWC decreases in the order Na₂SO₄ > NaCl > Na₂CO₃ > NaNO₃ > Na₃PO₄. Based on the results obtained, a procedure suitable for expedition conditions was developed for preconcentration of Pu from seawater on chitosan, with simultaneous separation of Pu from U, for radioecological monitoring of natural waters. The specific activity of Pu in samples of near-bottom seawater of gulfs of the Novaya Zemlya archipelago was (150–170) ± 20 mBq m⁻³. The results are well consistent with the published data.     

Specific features of deuterium and tritium labeling of SB258585

Samples of SB258 585 labeled with hydrogen isotopes were synthesized. [²H]SB258 585 containing one ²H atom per molecule and [³H]SB258585 with the molar radioactivity of 15 Ci mmol^?1 were obtained in preparative amounts. From 0.18 to 1.5 ²H atoms were incorporated, on the average, into an SB 258 585 molecule depending on the reaction conditions. The isotope exchange efficiency strongly depends not only on the catalyst-substrate ratio and on the reaction temperature, but also on processes occurring on the support surface. The isotope effects strongly influence the degree of deuterium or tritium incorporation into the samples in cases when the organic compound largely decomposes in the course of the reaction.     

Heat Capacity Measurements of 3He-4He Mixture Films

We report heat capacity measurements from our on-going experiments on two-dimensional liquid ³He on superfluid ⁴He thin films absorbed on Nuclepore. The ³He coverage dependence of the heat capacity for 0.02–0.50 bulk-density layers of ³He with 3.10 bulk-density layers of ⁴He over the temperature range 40≤T≤200 mK is presented. We find the effective mass of ³He on 3.10 layers of ⁴He is greater than that on 4.33 layers of ⁴He, consistent with our previous magnetic susceptibility measurements.     

Back-scattering study of heavy-ion distribution in semiconductors

The three-dimensional distribution of ⁸⁴Kr ions implanted into a Si substrate with 180 keV energy to a dose of 2 × 10¹⁶ ions/cm² has been measured by a back-scattering technique with 1.5 MeV ⁴He⁺. The distribution was observed as a distorted curve due to the influence of the ⁸⁴Kr ions on the specific energy loss of the ⁴He⁺. By considering the correction of the distortion, it is shown that the experimental results are in good agreement with theoretical predictions, and it is concluded that in quantitative discussions on the profile of impurity atoms in heavily doped material the influence of the impurity atoms on the specific energy loss cannot be neglected.     

Use of 3He++ in RBS analysis of CMT and related epilayers

The advantages of using a beam of ³He⁺⁺ extracted from conventional accelerator equipment for RBS analysis of CMT - related materials are described. Results obtained on an epilayer of HgTe grown on a CdTe substrate are compared with results of ⁴He⁺ beam RBS. The improved mass resolution combined with the lower energy loss rate of the ³He beam on penetration provides a much enhanced profiling depth both for Hg in the near-surface region and for diffusion effects at the interface. The method should extend to other heavy-element materials.     

Superfluidity of4He films adsorbed on hydrogen plated graphite

The superfluidity of⁴He on graphite with various preplatings of HD is under investigation using a torsional oscillator. Results for a bilayer of HD follow a similar pattern to those obtained earlier on pure⁴He films and are consistent with third sound measurements on graphite plated with a bilayer of hydrogen. In our case the first⁴He layer solidifies, consistent with behaviour observed in NMR studies of³He on a similarly prepared substrate. At a coverage of 11nm^–2 there is the onset of a region in which the transition temperature increases rapidly with coverage and the transition itself becomes sharper. At certain coverages pronounced signatures have been observed in the period shift and dissipation, which may indicate a further phase transition in the film at lower temperatures.     

Extraction-chromatographic isolation of 90Y for medical purposes

A procedure is described for isolating ⁹⁰Y from its equilibrium mixture with ⁹⁰Sr. It is based on extraction-chromatographic separation of ⁹⁰Sr and ⁹⁰Y on columns packed with a solid extractant based on di-2-ethylhexyl hydrogen phosphate. Further purification of ⁹⁰Y is made by its sorption on a column with an yttrium-specific sorbent based on octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide in TBP, and then on a cation-exchange resin. The whole process is performed in a nitric acid solution, which, in contrast to hydrochloric acid solutions, does not cause strong corrosion of stainless steel equipment, thus facilitating decontamination of the final product from inactive impurity cations.     

Production of Lutetium-177: Process Aspects

Papers dealing with the ¹⁷⁷Lu production technology are analyzed with the aim of evaluating the readiness of the existing processes to setting up regular large-scale production, which is the necessary condition for the progress of the market of ¹⁷⁷Lu-based radiopharmaceuticals. This is now on the initial step of its development. The ¹⁷⁷Lu production processes are based on irradiation of isotopically enriched ¹⁷⁶Lu or ¹⁷⁶Yb with reactor neutrons, followed by radiochemical processing of the irradiated targets. Specific production features are analyzed with emphasis on process aspects of the reactor and radiochemical stages. The evaluation shows that the presently reached level of the ¹⁷⁷Lu production technology allows only the current demand of nuclear medicine for this radionuclide, corresponding to the initial step of its clinical use, to be met. Further growth of the market of ¹⁷⁷Lu radiopharmaceuticals requires the upgrading of existing or construction of new facilities, which is possible only with significant improvement of both reactor and radiochemical processes.

     

Sorption of long-lived radionuclides onto main types of rocks of the Novaya Zemlya Archipelago

The ability of black carbonaceous siltstones and silt sandstones, lime sandstones, gray limestones, carbon–silicon carbonate schists with pyrite, and other rocks that most widely occur on the Novaya Zemlya Archipelago to sorb ¹³⁷Cs, ⁹⁰Sr, ^239+240Pu, and ²⁴¹Am was studied. The distribution coefficients K _d (cm³ g^–1) are as follows: for ^239+240Pu, 2.7 × 10³–7.7 × 10³; for 241Am, 2.5 × 10³–1.8 × 10⁴; and for ¹³⁷Cs, 1.1 × 10²–2.0 × 10³. Strontium-85(90) it not noticeably sorbed (within the measurement uncertainty) by any of the rocks studied. ^239+240Pu, ²⁴¹Am, and ¹³⁷Cs are strongly sorbed onto the rocks studied and are not noticeably desorbed from them with distilled water. The data obtained are required for predicting the migration of long-lived radionuclides generated by nuclear explosion with surface waters from test sites on the Novaya Zemlya Archipelago.     

The rotating disc as a device to study the adhesive properties of endothelial cells under differential shear stresses

Hemocompatibility can be conferred on a biomaterial by covering this material with a monolayer of endothelial cells. The endothelial cell is an epithelial cell of mesenchymal origin, that features a specific phenotype with homotypic intercellular interactions and with specialized cell-matrix interactions. These interactions are mandatory to the normal barrier function and the non-thrombogenicity of the endothelial monolayer and are maintained in vivo at shear stresses ranging from 10^-5 to 10^-3 N cm^-2. The endothelial monolayer grafted on a biomaterial should meet similar requirements. We have constructed a rotating disc device to investigate the effects of differential shear stresses on cell-cell and cell-matrix interactions in a monolayer of endothelial cells grafted on a disc-shaped biomaterial. The range of shear stresses that are being applied by the device vary from 0–10^-4 N cm^-2 to 0–2×10^-3 N cm^-2. In a series of experiments with discs of plasma discharge treated polycarbonate (PC) that are coated with fibronectin, it has been shown that a monolayer of endothelial cells grafted on these discs starts to lose intercellular contacts and cell-fibronectin interactions at shear stresses of 10^-4 N cm^-2. Coating of the PC discs with a complex extracellular matrix, synthesized by arterial smooth muscle cells in culture, prior to endothelial cell seeding results in the formation of a monolayer, which retains its integrity at shear stresses up to 2×10^-3 N cm^-2.     

Chemical bath deposition of PbS nanocrystals: Effect of substrate

Nanocrystalline PbS layers have been deposited chemically on Si, Ge and GaAs substrates from alkaline solutions containing 0.05 mol l^− 1 of Pb(NO₃)₂, 0.04 mol l^− 1 of thiourea, 0.05 mol l^− 1 of triethanolamine, and 0.15 mol l^− 1 of NaOH. Rutherford backscattering spectroscopy, transmission electron and atomic force microscopy reveal that the chemical nature of the substrate has a profound influence on the structure and thickness of the deposited layers. It is found that a large lattice mismatch between the substrate and PbS results in formation of coarse-grained layers with a small effective thickness (e.g. PbS on Si). On the other hand, close matching of lattice constants leads to deposition of thicker layers with smaller grain size (e.g. PbS on Ge, GaAs).     

Superconducting properties of ion beam modified YBCO microbridges

We prepared ion beam modified microbridges based on thin sputtered or laser ablated YBCO films on SrTiO₃ substrates. The microbridges with a width of 10 μm were irradiated through slits in a 700 nm thick double layer resist mask. In our experiments we used O⁺ ions with an ion energy of 30 keV or 100 keV varying the dose between 10¹³ ions·cm⁻² and 10¹⁴ ions·cm⁻². We investigated the influence of film thickness and slit width on the superconducting properties of these junctions. We show the temperature dependence of the junctions properties on microwave radiation or external magnetic fields.     

Production of Neptunium and Plutonium Tracers in Nuclear Reactions of 236U with 21-to-60-MeV 3He Ions1

Production of ²³⁶Pu, ²³⁷Pu, and ²³⁵Np by the reactions ²³⁶U(³He,t^-)²³⁶Pu, ²³⁶U(³He,2n)²³⁷Pu, and ²³⁶U(³He,p3n)²³⁵Np with 43- and 60-MeV ³He ion beams on the K-130 cyclotron of the University of Jyvüaskylüa was studied. The cross sections for the reactions were determined. The curves of yields with thick targets were derived from the cross sections. The results are discussed and compared with previous data on the other reactions yielding the same final products.     

Procyanidins Gels : Influence of Ions on the Celification of Carraghenan Solutions

Abstract

The formulation of procyanidin gels based on carraghenans is described. Gelling vehicles were selected to obtain stable, limpid gels of satisfactory viscosity and pH compatible with antiulcer therapy. Effort was focused on the study of the influence of cations (Na⁺, K⁺, Ca⁺⁺) and associated anions (chloride, citrate, gluconate), on the gelification : the best results were obtained with trisodium-citrate.     

Sorption of 137Cs and 90Sr Ionic Species on Soil of Various Types

Sorption of ¹³⁷Cs and ⁹⁰Sr ionic species on soils with different agrochemical features was studied. The dependence of ¹³⁷Cs sorption on peaty-bog soil on the ratio of the solid and liquid phases shows that sorption occurs by the ion-exchange mechanism. The correlation between the potassium content in soils and     

Extraction generator of 223Ra for nuclear medicine

A novel ²²⁷Ac/²²³Ra extraction generator for nuclear medicine was developed. Its operation is based on selective extraction of ²²³Ra with a solution of chlorinated cobalt dicarbollide and polyethylene glycol in a polar diluent from a solution of a mineral acid and a complexing agent. Radium is stripped to any appropriate aqueous solution on adding TBP into the extractant. Trials performed in the manual mode showed that ²²³Ra is efficiently separated from the parent isotopes ²²⁷Ac and ²²⁷Th (decontamination factor of ²²³Ra from ²²⁷Ac and ²²⁷Th >10⁶). It is the most convenient to use the ²²³Ra generator for the radionuclide production in a regional center, because it allows fairly simple production of large batches of ²²³Ra, avoiding problems associated with the need for skilled staff for working with the generator in a medical center and with the radiation-induced degradation of the matrix (ion-exchange resin).     

Phase formation and modification of corrosion property of nitrogen implanted Ti-Al-V alloy

In the present investigation, polished samples were implanted with nitrogen ion at an energy of 60 keV and implantation doses were 1×10¹⁶, 5×10¹⁶, 1×10¹⁷ and 6×10¹⁷ ions/cm². Glancing incidence X-ray diffraction was employed on the implanted specimens to understand the phases formed with increasing dose. The valence states of nitrogen, titanium and carbon on the sample surfaces were analyzed by X-ray photoemission spectroscopy. The corrosion resistance was examined by the electrochemical methods in a solution with pH=10 at room temperature in order to determine the optimum dose that can give good corrosion resistance in a simulated nuclear reactor condition. Scanning electron microscopy was used to observe the topographies of nitrogen-implanted Ti-Al-Zr after potentiodynamic measurement. It was found that implanted nitrogen dissolved in titanium matrix with increasing dose and the resultant nitrides such as TiN and Ti₂N precipitated. Implantation of nitrogen ions into the surface of Ti-Al-V alloy improves its corrosion resistance, and the increase of the corrosion resistance depends on the nitrogen dose employed; the maximum improvement of the corrosion resistance was observed at a dose of 1×10¹⁷ N⁺/cm².     

Extraction of variable energy neutral hydrogen beams from the University of Manitoba Cyclotron

Neutral hydrogen beams with energies between 30 and 50 MeV and fluxes on target of up to 4 × 10¹² H⁰/(s cm²) have been successfully extracted from the University of Manitoba Cyclotron. Upon completion in October 1986, the facility is expected to deliver 10 to 50 MeV H⁰ beams with fluxes in excess of 10¹⁴ H⁰/s cm²).     

Development of a tandem generator system 229Th/225Ac/213Bi for repeated production of short-lived α-emitting radionuclides

²²⁹Th was isolated from a long-stored ²³³U sample using an anion exchanger and 8 M HCl. Thorium was separated from macroamounts of inactive impurities on an anion exchanger in aqueous-methanol HNO₃ solutions. A tandem generator system was developed for repeated isolation of ²²⁵Ac (α, 10 days) from the parent radionuclide ²²⁹Th (7.3 × 10³ years) sorbed on an anion-exchange column, with the subsequent sorption of Ac on a cation-exchange column and repeated elution of ²¹³Bi (α, 45.6 min) with dilute HCl and HBr solutions. The γ-ray spectra of the radionuclides at various steps of their isolation are presented. Alternative procedures for production and isolation of ²²⁵Ac and ²¹³Bi are described. The application potential and advantages of the newly developed tandem generator system are discussed.