Contribution to the external gamma dose rate from <Superscript>137</Superscript>Cs and <Superscript>40</Superscript>K activity concentrations determined in the vertical profile of sandy beaches

Sampling sites, located along the Calabria and Basilicata Regions coastal beaches (south of Italy), were selected to assess the external gamma dose rate in air, 1 m above ground, and to estimate the fraction attributable to the radiocesium and radiopotassium contents along the vertical sand profile. Mean values for the gamma dose rate were: 76±30 nGy·h⁻¹. ¹³⁷Cs and ⁴⁰K deposition densities in sand samples were determined for each sampling site (mean values 0.24±0.22 kBq·m⁻² and 178±88 kBq·m⁻², respectively). The ¹³⁷Cs external dose rate contribution was assessed using a Monte Carlo simulation code. The method gives an estimation of the contribution to the external gamma dose rate of each sand layer along the vertical profile. The dose rate associated with the ¹³⁷Cs content in sand was 0.16±0.14 nGy·h⁻¹. The cosmic radiation and ⁴⁰K contributions to the external gamma dose rate were estimated using the UNSCEAR methodologies. The values obtained were 34±3 nGy·h⁻¹ and 18±9 nGy·h⁻¹, respectively.     

Pulse radiolysis study of the oxidation of the I<Superscript>−</Superscript> ions with the radical anions Br<Subscript>2</Subscript><Superscript>·−</Superscript> in an aqueous solution: formation and properties of the radical anion BrI<Superscript>·−</Superscript>

The radiation chemical redox transformations in solutions of bromides in the presence of minor additives of iodides were studied by pulse radiolysis. The change in the concentrations of the Br⁻ and I⁻ ions changes the ratio of the formed short-lived radical anions Br₂ ^·−, BrI^·−, and I₂ ^·−. The spectrum of the mixed radical anion BrI^·− contains a broad optical band at 370 nm with ɛ₃₇₀ = 9650 L mol⁻¹ cm⁻¹. The reduction potential of the BrI^·−/Br⁻, I⁻ pair is 1.25 V. The rate constants for the forward and backward reactions Br₂ ^·− + I⁻ ⇌ BrI^·− + Br⁻ are k _f = 4.3·10⁹ and k _r = 1.0·10⁵ L mol⁻¹ s⁻¹, respectively; for the reactions BrI^·− ⇌ Br⁻ + I^·, k _f = 5.7·10⁸ s⁻¹ and k _r = 1.0·10¹⁰ L mol⁻¹ s⁻¹. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1787–1792, September, 2008.     

Influence of ammonium on the performance of a denitrifying culture under heterotrophic conditions

The effect of ammonium on a denitrifying reactor of the upflow anaerobic sludge blanket type was studied. At a constant nitrate loading rate (2500 mg NO ₃ ⁻ -N/[L · d]), using acetate as organic electron donor and at a C/NO ₃ ⁻ -N ratio of 1.23, an increase in the N₂ production rate was observed when the ammonium loading rate was increased (25, 250, and 500 mg NH ₄ ⁺ -N/[L · d]). Dissimilatory nitrate reduction to ammonium (DNRA) was not observed, and the N₂ production efficiency was increased from 84 to 100% or higher. Since NH ₄ ⁺ in the output was lower than in the input, it was suggested that it was used for nitrate reduction. At constant NH ₄ ⁺ -N/NO ₃ ⁻ -N and C/NO ₃ ⁻ -N ratios of 0.2 and 1.63, respectively, the molecular nitrogen production rate was increased at 300 and 500 mg NH ₄ ⁺ -N/(L · d), whereas at 200 mg NH ₄ ⁺ -N/(L · d) DNRA took place probably owing to culture conditions of low reductive power. Molecular nitrogen production was not observed under autotrophic conditions, and the addition of acetate to the culture recovered its high nitrogen removal rate. Experimental results and balances indicated that the consumed ammonium was used as an additional reductive source.     

Formations of Active Species and By-Products in Water by Pulsed High-Voltage Discharge

Formations of active species and by-products are different from bubbling different gases in a pulsed high-voltage discharge reactor. The identification of all the products and the formation rate determination of active species are quite important as the process is applied to wastewater disposal. Serials of measurements were conducted to do the identifications and determinations in this paper. Amounts of · OH all increased but that of H₂O₂ all decreased by bubbling gas. The · OH formation rate was 3.49 × 10⁻⁷, 3.56 × 10⁻⁷, 3.21 × 10⁻⁷ and 1.94 × 10⁻⁷ mol l⁻¹ s⁻¹ with bubbling nitrogen, argon, air and oxygen respectively, but it was 1.61 × 10⁻⁷ mol s⁻¹ l⁻¹ without bubbling. Without any bubbling, the H₂O₂ formation rate was up to 6.53 × 10⁻⁶ mol l⁻¹ s⁻¹, while it was 9.97 × 10⁻⁷, 1.663 × 10⁻⁷, 1.73 × 10⁻⁶ and 3.14 × 10⁻⁶ mol l⁻¹ s⁻¹ with bubbling nitrogen, argon, air and oxygen, respectively. NO₂⁻ and NO₃⁻ was detected in discharged water with bubbling nitrogenous gas. Their formation made the pH decreased.     

Photochemical degradation of typical halogenated herbicide 2,4-D in drinking water with UV/H<Subscript>2</Subscript>O<Subscript>2</Subscript>/micro-aeration

UV/H₂O₂/micro-aeration is a newly developed process based on UV/H₂O₂. Halogenated pesticide 2,4-dichlorophenoxyacetic acid (2,4-D) photochemical degradation in aqueous solution was studied under various solution conditions. The UV intensity, initial 2,4-D concentrations and solution temperature varied from 183.6 to 1048.7 μW·cm⁻², from 59.2 to 300.0 μg·L⁻¹ and from 15 to 30°C, respectively. The concentration of hydrogen peroxide (H₂O₂) and pH ranged from 0 to 50 mg·L⁻¹ and 5 to 9, and different water quality solutions (tap water, distilled water and deionized water) were examined in this study. With initial concentration of about 100 μg·L⁻¹, more than 95.6% of 2,4-D can be removed in 90 min at intensity of UV radiation of 843.9 μW·cm⁻², H₂O₂ dosage of 20 mg·L⁻¹, pH 7 and room temperature. The removal efficiency of 2,4-D by UV/H₂O₂/micro-aeration process is better than UV/H₂O₂ process. The photodecomposition of 2,4-D in aqueous solution follows pseudo-first-order kinetics. 2,4-D is greatly affected by UV irradation intensity, H₂O₂ dosage, initial 2,4-D concentration and water quality solutions, but it appears to be slightly influenced by pH and temperature. There is a linear relationship between rate constant k and UV intensity and initial H₂O₂ concentration, which indicates that higher removal capacity can be achieved by the improvement of these factors. Finally, a preliminary cost analysis reveals that UV/H₂O₂/micro-aeration process is more cost-effective than the UV/H₂O₂ process in the removal of 2,4-D from drinking water.     

Radiation-induced polymerization of β(−)pinene: A further insight

The radiolysis of β(−)pinene has been studied at five different radiation dose, namely at 50, 100, 150, 300 and 600 kGy with a dose rate of 2.2 kGy/h. At lower radiation dose, β(−)pinene showed a reduction of the optical activity, hence, the expected radioracemization appeared predominant. At higher radiation dose, an opposite and unexpected trend was observed: the optical activity increased almost linearly with the radiation dose. The increase of [α]_D of radiolyzed β(−)pinene was due to the formation oligomers, mainly a dimer and/or a trimer of β(−)pinene which remain soluble in the monomer but which displayed a higher optical activity than the starting monomer, contributing to the increase in the specific optical rotation. Simultaneously to the formation of the dimer/trimer the radiolysis of β(−)pinene induced also its polymerization into a poly(β(−)pinene) resin which was insoluble in the monomer and which was characterized by a high structural order and by the preservation of the chiral centers so that it showed an enhanced specific optical rotation which is ≈2 times that of the monomer. It is shown that poly(β(−)pinene) radiopolymer can be easily racemized in presence of a Friedel-Crafts catalyst. The kinetics of β(−)pinene radiation-induced oligomerization and polymerization can be described by a pseudofirst order rate constant k = 1.9·10⁻⁷·s⁻¹. The radiation chemical yield for the same reaction is G = 1.93·10⁻⁶ mol/J. The work shows that also the radiation-induced polymerization of chiral monomers may be a tool for the preservation and amplification of the optical activity of the monomer with implications for abiotic mechanisms of chiral amplification.     

Study of kinetics,equilibrium and isotope exchange in ion exchange systems. II

The kinetics of isotope exchange in the²³⁸U(VI)-²³³U(VI)-strongly acidic cation exchanger Ostion KS system was studied in the temperature range 275–307K and for total uranium concentration 2.94·10⁻⁴–1.75·10⁻² mol·l⁻¹ in UO₂(NO₃)₂ solution. The experimental results were evaluated by means of the “two-film mass-transfer model” and by the use of Fick's diffusion equations which have been proved more suitable for the system studied than McKay's equation. The influence of the temperature was evaluated using the Arrhenius equation. The diffusion character of the process follows also from the value of the activation energy (15.12 kJ·mol⁻¹). In comparison with the UO ₂ ²⁺ ↔H⁺ ion exchange⁶ the isotope exchange studied is faster and less dependent on temperature (the activation energy is substantially lower).     

Differential pulse polarographic study of thiamine (vitamin B1) in neutral and acidic aqueous solutions

The differential pulse (dp) polarograms of thiamine in neutral aqueous solutions exhibited six peaks at low depolarizer concentration (⋦10⁻⁴ mol dm⁻³) and only three peaks at concentrations ≥10⁻³ mol dm⁻³. Only one of these was found to correspond to the diffusion-controlled reduction of this compound at the dme and this was shown to be an irreversible two-electron process. The kinetic parameters derived from the dp polarograms were found to be in good agreement with those calculated from classical polarograms and were:E _1/2=−1·261 Vvs SCE,an _a=0·54 andD≈3·5×10⁻⁶ cm² sec⁻¹ for 10⁻³ mol dm⁻³ thiamine in 0·1 mol dm⁻³ acetate buffer (pH 6·5). The reduction product has been identified as dihydrothiamine. The effect of pH on the dpp of thiamine was studied in the pH range 0–7. In the pH region 5·5 to 7·0 only one peak attributable to the B₁ ⁺ form of thiamine is present. In the pH region 3·5–5·5 another dpp peak attributable to the protonated form (B₁H²⁺) of thiamine was also observed. At pHs less than 3 only one peak was observed which could be attributed to the doubly protonated form (B₁ H₂ ³⁺) of thiamine. Surfactants like triton-X-100 and CTABr were found to inhibit the electroreduction of thiamine due to the strong adsorption of these compounds on the dme. Thiamine itself was found to have an inhibitory effect on its own electroreduction, although to a smaller extent.     

Kinetics of reductive stripping of Pu(IV) in the tributylphosphate-kerosene/nitric acid-water system using dihydroxyurea

The kinetics of the reductive stripping of plutonium(IV) by dihydroxyurea (DHU) in 30% TBP/kerosene-HNO₃ system was studied with a constant interfacial area cell. The stripping rate of plutonium(IV) increases with the increase of the stirring speed of two phases and the interfacial area. The activation energy of this process is 28.4 kJ/mol. Under the given experimental conditions, the mass transfer of Pu is not controlled by redox reaction, but controlled by molecular diffusion from the organic phase to organic film layer and from the aqueous film layer to aqueous phase. The rate equation of reductive stripping (process is controlled by diffusion) was obtained as: r ₀ = k′[Pu(IV)]₀[DHU]_a ^0.16[HNO₃]_a ^−0.34. The rate constant k′ is (5.0±0.4)·10⁻² (mol/L)^0.18·min⁻¹ at 18.0°C.     

Pulse radiolytic investigation of the reaction of hydroxyl radicals with gentamycin

Hydroxyl radicals were generated radiolytically in N₂O-saturated aqueous solutions of the aminoglycoside antibiotic, gentamycin. Using the pulse radiolysis technique, the rate constant of OH radicals with gentamycin determined was 1.2·10⁹ dm³·mol⁻¹·s⁻¹. Upon^.OH attack a transient species with an absorption maximum at 270 nm is observed which decays by second-order kinetics within the solute concentration range of 3.2·10⁻⁵ to 1·10⁻³mol·dm⁻³. Transient species undergoes transformation to a permanent product absorbing between 260 and 340 nm with maximum absorption at 300 nm. Rate constant of the reaction of bimolecular decay of gentamycin radicals, k (Gen^.+Gen^.) was found to be ≈ 1.4·10⁷ dm³·mol⁻¹·s⁻¹.     

Studies of the reaction of the hydroxyl radical with the oxalate ion in an acidic aqueous solution by pulse radiolysis

The reaction of the · OH radical with the oxalate ion in an acidic aqueous solution was studied by pulse radiolysis. The rate constant for the reaction of formation of the radical HOOC-COO·(λ_max = 250 nm, ɛ = 1800 L mol⁻¹ cm⁻¹) is (5.0±0.5)·107 L mol⁻¹ s⁻¹. In the reaction with the hydrogen ion (k = 1.1·10⁷ L mol⁻¹ s⁻¹), the radical HOOC-COO· is transformed into a nonidentified radical designated arbitrarily as H⁺(HOOC-COO)· (λ_max = 260 nm, ɛ = 4000 L mol⁻¹ cm⁻¹). Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1165–1167, June, 2008.     

Transport mechanism of hydrogen through oxide film formed on zircaloy-4

The diffusion behavior of hydrogen in the oxide films of zircaloy-4 specimens containing different size of Zr(Fe,Cr)₂ precipitates was examined. In the case of the specimen containing fine precipitates, hydrogen diffused uniformly through the zirconium oxide phase. The diffusion coefficient was 2·10⁻²¹ m²·s⁻¹ at room temperature and 6·10⁻¹⁹ m²·s⁻¹ at 673 K. The transport rate of hydrogen in the oxide film of the specimen containing coarse precipitates was significantly higher than that of the specimen containing fine ones at both room temperature and 673 K.     

Degradation of 4-chlorophenol in aqueous solution by γ-radiation and ozone oxidation

The degradation of 4-chlorophenol (4-CP) by using gamma rays generated by a ⁶⁰Co source in the presence of O₃ was investigated. The radiolysis of 4-CP and the kinetics of 4-CP mineralization were analyzed based on the determination of total organic carbon (TOC). The influence of initial 4-CP concentration and the free radicals scavengers (such as NaHCO₃ and t-butanol) on the 4-CP degradation was also studied. The results showed that when the radiation rate was 336 Gy·min⁻¹, 4-chlorophenol at concentration of 10 mg·L⁻¹ could be completely degraded at the radiation dose of 2 kGy. The degradation of 4-chlorophenol could be described by a first-order reaction model, the rate constant of 4-CP degradation by combined ozonation and radiation was 0.1016 min⁻¹, which was 2.4 times higher than the sum of radiation (0.0294 min⁻¹) and ozonation (0.0137 min⁻¹). It revealed that the combination of radiation and ozonation resulted in synergistic effect, which can remarkably increase the degradation efficiency of 4-CP.     

Decay kinetics of benzophenone oxide in the liquid phase

The kinetics of self-termination of benzophenone oxide (BPO) in the liquid phase was studied by flash photolysis. The extinction coefficient of BPO (ε) was found to be virtually independent of the solvent nature, ε=(1.9±0.1)·10³ L mol⁻¹ cm⁻¹. The rate constant of the BPO self-temination increases from 1.8·10⁷ (MeCN) and 7.4·10⁷ (C₆H₆) to 1.5·10⁹ (n-decane) and 2.0·10⁹ L mol⁻¹ s⁻¹ (n-pentane) at 293±2 K. Solvation of BPO promotes a polar state of the molecule in MeCN and C₆H₆. In nonpolar hydrocarbons, a great contribution is made by the biradical structure resulting in an increase in the rate constant and a shift of the absorption maximum to the long-wave region (from 410 nm in MeCN to 425 nm inn-pentane). In solutions of benzene and acetonitrile, benzophenone oxide reacts with the parent diazo compound with a rate constant of (2–4)·10⁵ L mol⁻¹ s⁻¹ (293±2 K) along with the self-termination. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1329–1332, July, 1998.     

Neutral thallium clusters in aqueous solutions. Pulse radiolysis study

The formation of neutral Tl₂ (λ_max = 390 nm) and Tl₄ (λ_max = 360 nm) clusters in dilute aqueous solutions of Tl₂SO₄ containing formate ions was found by pulse radiolysis. The rate constants for the recombination of Tl⁰ atoms and Tl₂ clusters are equal to 1.5·10¹⁰ L mol⁻¹ s⁻¹ and 1.0·10¹⁰Lmol⁻¹ s⁻¹ (±30%), respectively, and the extinction coefficient of Tl₂ at 390 nm is −6.0·10³ L mol⁻¹ cm⁻¹ Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2367–2369, December, 1999.     

Hemoglobin-stabilized tetranitrosyl binuclear iron complex with pyridine-2-yl in aqueous solutions

The tetranitrosyl iron complex with pyridine-2-yl [Fe₂(SC₅H₄N)₂(NO)₄] (1) has higher NO-donating activity in 3% aqueous solutions of DMSO (pH 7.0, 25 °C) than the organic NO donor, viz., adduct of NO with diethylenetriamine (NO-adduct). The NO concentration was determined by the spectrophotometric method based on the formation of an NO complex with hemoglobin (Hb). The apparent first-order rate constants of the studied reactions are (6.15±0.6)·10⁻¹ s⁻¹ and (0.8±0.08)·10⁻¹ s⁻¹ for complex 1 and the NO-adduct, respectively, at an Hb concentration of 2·10⁻¹ mol L⁻¹ and the ratio [NO donor]/[Hb] = 10. The effect of Hb and [NO donor]/[Hb] ratio on the rate of NO generation from a solution of complex 1 was studied. For a fourfold decrease in the concentration of complex 1 the reaction rate constant decreases to 0.5·10⁻⁴ s⁻¹, whereas the fourfold increase in the Hb concentration results in the stabilization of complex 1. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 732–736, April, 2007.     

Sorption behavior of Sn(II) onto Haro river sand from aqueous acidic solutions

The sorption behavior of Sn(II) onto Haro river sand has been examined with respect to nature of electrolyte, agitation time, dosage of sorbent and concentration of sorbate. Maximum sorption (95.5%) has been achieved from 0.034M hydrochloric acid solution after equilibrating sorbate (2·10⁻⁵M) and sorbent (50 mg) for 120 minutes at aV/W ratio of 90 cm³·g⁻¹. The kinetic data have been subjected to Morris-Weber and Lagergren equations. The kinetics of sorption proceeds a two stage process consisting of a relatively slow initial uptake followed by a much rapid increase in the sorption. The rate constant of intraparticle transport, K_d, comes out to be 8.75·10⁻⁸ mol·g⁻¹·min^−1/2 and the first order rate constant for sorption is 0.0416 min⁻¹. The sorption data of Sn(II) onto Haro river sand followed Langmuir, Freundlich and Dubinin-Radushkevich (D-R) type isotherms. The Langmuir constant,Q, related to sorption capacity and,b, related to sorption energy are computed to be 10.6±1.1 μmol·g⁻¹ and 1123±137 dm³·mol⁻¹, respectively. The D-R isotherm yields the values ofC _m=348±151 μmol·g⁻¹ and β=−0.01044±0.0008 mol²·kJ⁻² and ofE=6.9±0.3 kJ·mol⁻¹. In all three isotherms correlation factor (γ) is ≥0.99. The influence of common anions and cations on the sorption has been investigated. Zn(II), Mg(II), oxalate, Pb(II), Mn(II) and tartrate reduce the sorption significantly whereas Fe(II) causes substantial increase in the sorption. It is essential that all ions causing a decrease in the sorption of Sn(II) must be absent from the sorptive solution otherwise low sorption yields would result.     

Kinetics of the radical reactions in pulse radiolyzed RHF — CO2(SF6)-O2-NO gaseous mixtures; RHF = CH3CH2F, CH3CHF2, CH3CF3, CH2FCF3

The kinetics of the peroxy radicals RHFO₂ reactions with NO has been studied by using pulse radiolysis and UV absorption spectroscopy. The rate constants of interaction of oxygen atoms with NO − k ₂ = 2.2±0.2·10⁻¹² cm³·s⁻¹ and NO₂ − k ₃ = 2.1±0.2·10⁻¹¹ cm³·s⁻¹ were found in agreement with the literature values. The bath gases (SF₆ or CO₂) have got minor effect on the rate constants of RHFO₂+NO→NO₂+prod. reactions; RHFO₂ = CH₃CH₂O₂, CH₃CHFO₂, CH₃CF₂O₂, CF₃CH₂O₂, CF₃CHFO₂. The obtained rate coefficients are in the scope of the literature values, although they are lower than those recommended in NIST database. The reasons are discussed.     

Coprecipitation as a means for the determination of zirconium traces by isotope dilution analysis in the presence of substoichiometric amounts of complexones

The possibility of using coprecipitation on Cu(OH)₂·nH₂O and Fe₂O₃·nH₂O precipitates to separate a part of zirconium unreacted with complexone in the presence of a 100-fold amount of impurities has been examined. The reaction between ethylenedia-minetetraacetic acid (EDTA) and zirconium 10⁻³−10⁻⁵ M has been used as substoichiometric reaction. A zirconium determination in the concentration range of 10⁻⁴−10⁻⁶ g/ml in artificial mixtures and steel samples has been developed using the systems of EDTA-Zr−Cu(OH)₂·nH₂O and EDTA−Zr−Fe₂O₃·nH₂O.     

Kinetics of the peroxy RFO2 radical formation in the RHF-O2-CO2 gaseous mixtures

The kinetic data on the molecular oxygen activity of CH₃CH^·, CH₃CF₂ ^· and CF₃CHF^· radicals are reported. In laboratory, these radicals were generated by pulsed (12 ns) electron beam interaction with the gaseous RHF-O₂-CO₂ mixtures containing large excess of carbon dioxide (RHF = CH₃CH₂F, CH₃CHF₂ or CH₂FCF₃). The transient product (O₃ or RFO₂ ^·) formation was monitored by the UV absorptions at 250 nm and the rate constants of Reactions (4) and (9) were obtained. The values of k ₉ diminished with increasing number of fluorine atoms in RHF molecule. For CH₃CH₂F and CH₃CHF₂ the k ₉’s were equal to (8.8–10.2)^·10⁻¹⁴cm^{3 ·}s⁻¹ and (7.3–8.4)^·10⁻¹⁴cm^{3 ·}s⁻¹, respectively, and seem to be determined for the first time. In the case of CH₂FCF₃ the obtained value of k _CF3CHF+O2 = 5.20±0.76^·10⁻¹⁴cm^{3 ·}s⁻¹ is much higher than the value published in the literature.⁴ The other determined rate constant data are comparable to the literature values.