Analysis of gamma-radioactivity of “hot particles” released after the Chernobyl accident

A particulate form (hot particles) of the radioactive fallout in Poland after the accident at the Chernobyl Nuclear Plant has been studied. Parameters of the effective reactor campaign are obtained from the characteristics of -activity of the hot particles. The numerical INV program written to calculate time evolution of eight isotopes in the reactor is described. On the basis of these calculations the measured hot particles are classified into two groups: those originating from the first load and those from younger fuel rods. A procedure for dating younger hot particles is proposed. The results of the analyses constitute a basis for other investigations of hot particles.     

Actinides in the near release from the Chernobyl NPP accident

Actinide elements concentrations in the products of near release from CNPP accident were estimated. The data on uranium,²³⁷Np,²⁴¹Am and plutonium and curium isotopes content in fuel particles are given. Sums of -emitting radionuclides and plutonium isotopes in reactor graphite particles and of uranium,²⁴²Cm,^239+240Pu isotopes in the soil and aerosol samples were also determined. By 1989 soil and dust contamination in near release of the accident is due to long-lived -emitting plutonium isotopes.     

Characterization and surface properties of amino-acid-modified carbonate-containing hydroxyapatite particles

The surface properties (nature, strength, and stability of interaction of functional groups) and bulk morphologies of a series of amino-acid-functionalized carbonate-containing hydroxyapatite (CHA) particles were investigated. It was found that the amino acids were both occluded in and presented on the surface of the CHA particles. Furthermore, their presence enhanced particle colloidal stability by retardation of Ostwald ripening and in some cases increasing the magnitude of the zeta-potential. Measurements of adsorption isotherms and zeta-potential titrations have shown that the amino-acid-surface interactions are weak and reversible at pH 9 and consistent with a model in which the carboxyl terminus interacts with calcium ions in the CHA lattice. Complexities in adsorption behavior are discussed in terms of different adsorption mechanisms that may be prevalent at different pHs.     

Radiocesium contamination in soil due to the Chernobyl accident

Three different cereal cultivated fields (rice, maize/wheat, wheat/barley) were selected and soil samples were collected in order to study the behaviour of the radiocesium deposited over the crops after the Chernobyl accident fall-out (April 1986) together with its distribution at different ground depths. For each field, soil samples were removed during the sowing (Oct–Nov '86), in Spring (Apr '87) and during the harvest time (Jun–Sept '87). The⁴⁰K concentration and stable potassium content in soil was also evaluated by nuclear spectrometry and by atomic absorption spectrometry. Beside soil sample measurements, the cultivated cereals produced in the 1986 harvest (rice, maize, wheat) were analyzed to evaluate the deposited contamination, and in order to evaluate the contamination during the growth and naturation we also analyzed whole plants (roots, stalks, grains) of the cultivated cereals (rice, wheat, barley) in 1987. Results are presented and discussed.     

Heavy metal contamination of surface soil around Gebze industrial area, Turkey

An increase in heavy metal pollution in the soils of Gebze (Turkey) due to intense industrialization and urbanization has become a serious environmental problem. There are two large organized industrial zones in Gebze; the Gebze Organized Industrial Zone (GOIZ) and the Dilovas? Organized Industrial Zone (DOIZ). The region hosts several industrial facilities which are the main source for hazardous wastes which include paint, plastic, electric, metal, textile, wood, automotive supply industry, food, cosmetics, packing, machinery, and chemicals. Soil samples were collected from these two industrial zones and analyzed for their metal contents. Results of the analysis show that the soils are characterized by high concentrations of Cd, As, Pb, Zn, Mn, Cu, Cr and Hg. Since concentrations of other elements do not exceed the permissible levels, they are not evaluated. Concentrations are 0.05-176 mg/kg of Cd, 10-1161 mg/kg of Cr, 7.87-725 mg/kg of Cu, 1.50-65.60 mg/kg of As, 17.07-8469 mg/kg of Pb, 1.96-10,000 mg/kg of Mn, 29.5-10,000 mg/kg of Zn, and 9-2721 μg/kg of Hg. Application of factor, cluster and correlation analysis showed that heavy metal contamination in soils originates from industrial activities and heavy traffic which are of anthropogenic origin. Contaminations in soils were classified as geoaccumulation index, enrichment factor, contamination factor, and contamination degree. Integrated pollution index (IPI) values indicate that heavy metal pollution levels of soils collected from industrialization sites are greater than those from distal parts of industrialization. Spreading of hazardous wastes from industrial facilities in the study area via rain or wind is the main source of soil pollution. In addition, traffic-related metal pollution is also observed.     

Contribution to the analysis of plutonium originated from the Chernobyl accident in soil

Four different procedures have been studied for the extraction of plutonium from soil sampled at Bragin, 40 km from Chernobyl. On extraction by leaching with conc. HNO₃ for 2 or 6 h the concentration of^{239, 240}Pu in soil was approximately by 30% lower than on extraction involving treatment with HF or fusion.     

Determination of239Pu in soil samples from Austria after the Chernobyl accident

As a consequence of the reactor accident at Chernobyl on Tuesday 29 April 1986 the environmental radioactivity in Austria increased for above the level recorded before. Depending on the amount of precipitation the deposition of radioactive fallout showed great differences. Many soil samples collected /during the period from June 15 to September 15/ from Lower-Austria, Styria and Burgenland were analyzed for²³⁹Pu. The concentration found for²³⁹Pu ranged between 2.9 and 9.2 fCi g^–1. The highest concentration was detected in the soil of south-eastern part of Austria /Radkersburg/.²³⁹Pu concentration increased with depth from which soil samples were taken.     

Plutonium isotopes in the surface air in Japan: Effect of Chernobyl accident

Plutonium isotope concentrations in the surface air at Tsukuba, Japan are reported during the period from 1981 to the end of 1986. The^239,240Pu concentration in the surface air, which showed a marked seasonal variation with a spring maximum and fall minimum, decreased until the end of 1985 according to the stratospheric residence time of 1.15 years. In May 1986, elevated^239,240Pu concentrations with high²³⁸Pu/^239,240Pu activity ratios were observed. The serial trend of plutonium concentration in the surface air is similar to the concentrations of the Chernobyl-released radionuclides. These findings suggest that a significant part of the plutonium in the surface air in May 1986 was due to the Chernobyl fallout. The size distribution of plutonium bearing particles indicates that plutonium isotopes were mechanically released in the Chernobyl accident. The surface air concentration of plutonium from the Chernobyl accident was much lower than the concentrations of the volatile fission products, and increased the monthly mean^239,240Pu concentration by only 0.03 Bqm^–3.     

Distribution of non-exchangeable organically bound tritium activities at the surface soil around Qinshan Nuclear Power Plant

The tritium deposited in the soil formed the non-exchangeable organically bound tritium (NE-OBT). Most of the NE-OBT locates at the surface. In this study, higher NE-OBT activity appeared at the sampling sites in the prevailing wind direction. The distribution of NE-OBT activity in soil particle with different particle size implied that the NE-OBT might originate from soil organic matter. According to the correlation analyses, in the soil with particle size less than 53 μm, the NE-OBT might originate from soil organic matter, and in the soil with particle size between 250 and 2000 μm, it originated from HTO.

     

Depth profiles of long lived radionuclides in Chernobyl soils sampled around 10 years after the accident

Depth profiles of the long-lived radionuclides, ¹³⁷Cs, ⁹⁰Sr, Pu isotopes and ²⁴¹Am were examined in undisturbed sandy, peaty and Podsol soils in the Chernobyl 30 km exclusion zone sampled around 10 years after the accident. Two Podsol soils, which have different radioactive deposition characteristics, have also been examined. Activity ratios of ^239,240Pu/¹³⁷Cs, ⁹⁰Sr/¹³⁷Cs, and ²⁴¹Am/¹³⁷Cs in the 0-1 cm layer of the two Podsol soils differed very much. Speciation of the radionuclides by sequential selective extraction was examined in the soils. Depth profiles of the soils have been analyzed according to the speciation results and soil characteristics.     

Production of micron-sized polystyrene particles containing PEG near the particles surface

Polystyrene (PS) particles in the size range of 1-7 µm, containing poly(ethylene glycol) or PEG on the particles surface, were prepared by multi-step seeded polymerizations. Micron-sized PS particles were first prepared by dispersion polymerization using 2,2'-azobisisobutyronitrile as initiator and polyvinyl pyrrolidone as stabilizer. Conventional swelling method was then used to increase the size of the PS particles with a large amount of styrene in presence of oil soluble initiator, benzoyl peroxide. In the final step, the PS particles have been used to carry out seeded polymerization with small amount of styrene in presence of poly(ethylene glycol)-azo or PEGA initiator with average molecular weights of the PEG chains of 200 and 3000 g mol^-1 , respectively. The average size, size distribution, and surface morphology indicate that seeded polymerization in the final step with small amount of styrene in presence of PEGA is the best way to produce monodisperse polystyrene particles containing PEG near the particles surface.     

On the surface transition in small nonspherical particles

We discuss a theoretical model for a surface transition in a nonspherical geometry. We study the stationary states of coexistence within a droplet of given volume. We show that finite range interactions with the matrix act to stabilize a finite non-spherical surface layer which is thickest in zones of highest curvature. At a certain temperature, the core tends to a spherical shape, becomes unstable and coexistence is no longer possible.     

Characterization of the silica surface

Aerosil samples, heat-treated and then silylated with various silanes at various temperatures have been characterized by adsorption of benzene at 293 K. Adsorption and desorption isotherms were plotted and the specific surface areas were determined using the BET method. Cross-plots of adsorption were made between the silylated and the unsilylated samples to reveal in a simple way the resulting changes in surface properties. Modification of aerosils using silanes was found to alter the adsorptive properties of aerosils for benzene to extents depending on the silane used as well as the concentration of residual surface silanols.     

Transient cage formation around hot gold colloids dispersed in polymer solutions

Gold colloids dispersed in dilute to concentrated polymer solutions can efficiently be heated by laser irradiation and act as almost pointlike heat sources. In systems with positive Soret coefficients S(T) of the polymer, such as solutions of polystyrene in toluene, the polymer can almost entirely be removed from the particle surface. The colloid attracts the solvent and a transient cage of low viscosity and dramatically enhanced mobility is formed, which follows the motion of the particle with a certain retardation. Based on a complete parameterization of S(T)(M, c, T), we analyze in detail the stationary temperature, concentration, and viscosity profiles. Depending on the polymer molar mass and concentration on the distance to the glass transition temperature, the negative or positive feedback-loops are established that lead to either attenuation or self-amplification of the polymer depletion.     

Modification of the silica particles surface with perfluoroalkylmethyloxiranes

Silica particles have been prepared via the sol-gel process in the presence of perfluoropropyl- and perfluorobutylmethyloxiranes. Nanoparticles are formed in the presence of acidic catalyst. Under conditions of basic catalysis the attack of silanol group (formed in situ via hydrolysis of tetraethoxysilane) on the oxirane ring leads likely to the Si-O-C bond formation.     

Determination of uranium isotopic composition and 236U content of soil samples and hot particles using inductively coupled plasma mass spectrometry

As a result of the accident at the Chernobyl nuclear power plant (NPP) the environment was contaminated with spent nuclear fuel. The ²³⁶U isotope was used in this study to monitor the spent uranium from nuclear fallout in soil samples collected in the vicinity of the Chernobyl NPP. Nuclear track radiography was applied for the identification and extraction of hot radioactive particles from soil samples. A rapid and sensitive analytical procedure was developed for uranium isotopic ratio measurement in environmental samples based on double-focusing inductively coupled plasma mass spectrometry (DF–ICP–MS) with a MicroMist nebulizer and a direct injection high-efficiency nebulizer (DIHEN). The performance of the DF–ICP–MS with a quartz DIHEN and plasma shielded torch was studied. Overall detection efficiencies of 4×10^–4 and 10^–3 counts per atom were achieved for ²³⁸U in DF–ICP–QMS with the MicroMist nebulizer and DIHEN, respectively. The rate of formation of uranium hydride ions UH⁺/U⁺ was 1.2×10^–4 and 1.4×10^–4, respectively. The precision of short-term measurements of uranium isotopic ratios (n = 5) in 1 μg L^–1 NBS U-020 standard solution was 0.11% (²³⁸U/²³⁵U) and 1.4% (²³⁶U/²³⁸U) using a MicroMist nebulizer and 0.25% (²³⁵U/²³⁸U) and 1.9% (²³⁶U/²³⁸U) using a DIHEN. The isotopic composition of all investigated Chernobyl soil samples differed from those of natural uranium; i.e. in these samples the ²³⁶U/²³⁸U ratio ranged from 10^–5 to 10^–3. Results obtained with ICP–MS, α- and γ-spectrometry showed differences in the migration properties of spent uranium, plutonium, and americium. The isotopic ratio of uranium was also measured in hot particles extracted from soil samples.     

Determination of uranium isotopic composition and 236U content of soil samples and hot particles using inductively coupled plasma mass spectrometry

As a result of the accident at the Chernobyl nuclear power plant (NPP) the environment was contaminated with spent nuclear fuel. The 236U isotope was used in this study to monitor the spent uranium from nuclear fallout in soil samples collected in the vicinity of the Chernobyl NPP. Nuclear track radiography was applied for the identification and extraction of hot radioactive particles from soil samples. A rapid and sensitive analytical procedure was developed for uranium isotopic ratio measurement in environmental samples based on double-focusing inductively coupled plasma mass spectrometry (DF-ICP-MS) with a MicroMist nebulizer and a direct injection high-efficiency nebulizer (DIHEN). The performance of the DF-ICP-MS with a quartz DIHEN and plasma shielded torch was studied. Overall detection efficiencies of 4 x 10(-4) and 10(-3) counts per atom were achieved for 238U in DF-ICP-QMS with the MicroMist nebulizer and DIHEN, respectively. The rate of formation of uranium hydride ions UH+/U+ was 1.2 x 10(-4) and 1.4 x 10(-4), respectively. The precision of short-term measurements of uranium isotopic ratios (n = 5) in 1 microg L(-1) NBS U-020 standard solution was 0.11% (238U/235U) and 1.4% (236U/238U) using a MicroMist nebulizer and 0.25% (235U/238U) and 1.9% (236U/P38U) using a DIHEN. The isotopic composition of all investigated Chernobyl soil samples differed from those of natural uranium; i.e. in these samples the 236U/238U ratio ranged from 10(-5) to 10(-3). Results obtained with ICP-MS, alpha- and gamma-spectrometry showed differences in the migration properties of spent uranium, plutonium, and americium. The isotopic ratio of uranium was also measured in hot particles extracted from soil samples.     

Native surface structure of natural soil particles determined by combining atomic force microscopy and X-ray photoelectron spectroscopy

A procedure was developed for handling natural soil particles and probing their native surface structure by atomic force microscopy (AFM) under water. This procedure was used to investigate the nanometer scale organisation of organic matter at the surface of sand particles taken from three soil horizons. The latter were selected for the contrasted properties of their organic matter, namely Podzol E and Bh horizons and a Cambisol A–B horizon. The presence of an adsorbed layer was visualised at the surface of Podzol Bh and Cambisol particles in the form of aggregated structures that interacted with the AFM probe. Surface analysis by X-ray photoelectron spectrometry (XPS) confirmed the carbonaceous nature of this adsorbed layer. Displacement of organic matter by the scanning probe was directly evidenced for Podzol Bh sand particles. Such displacement was not observed for Cambisol particles. A dramatic effect of drying on the concentration, nanometer scale distribution and properties of the adsorbed organic matter was clearly demonstrated by combining AFM imaging and XPS analysis. The procedure developed here gives access to direct, nanoscale information of the surface structure of sand particles and offers promising prospects for the characterisation of other environmentally-relevant particles in native conditions.