International Journal of Radiation Applications and Instrumentation. Part C. Radiation Physics and Chemistry最新文献

Pulse radiolysis has been used to study kinetics of scavenging of hydrated electron (e^-_aq) by hexadecylpyridinium chloride, benzyl chloride and benzyl alcohol in aqueous micellar solutions of alkyltrimethylammonium halides.

The results corroborate our earlier finding [see the first part of this series by Szajdzińska-Piȩtek E., Gȩbicki J.L. and Kroh J. (1992) Radiat. Phys. Chem.39, 117] that reactivity of e^-_aq in cationic micellar solutions depends on the kind of micelle-bound acceptor. The effect seems to be related to the effectiveness of scavengers rather than to their different locations within aggregates.

The observed influence of micelle size and counterion substitution on e^-_aq scavenging is discussed in terms of inter- and intramicellar electron transfer, and partition of the solute between aggregates and aqueous phase.

Polymer hydrogels were obtained by radiation-induced copolymerization at -78°C of aqueous solutions of acrylic and methacrylic esters. The matrices were characterized by equilibrium water content measurements, by optical microscopy observations and by scanning electron microscopy analysis. Yeast cells were immobilized on these hydrogels and the ethanol productivity by batch fermentation was determined. Matrix hydrophilicity and porosity were found to deeply influence the adhesion of yeast cells and, hence, the ethanol productivity. The latter as well as other physico-chemical properties were also affected by the presence of a crosslinking agent added in small amounts to the polymerizing mixture.

Interactions of OH^· and Br_{$\text{2}\text{̇}$}$$ radicals with glutathione (GSH) have been studied in buffered neutral aqueous solutions using γ and pulse radiolysis. In steady state radiolysis, initial G values of GSH loss and formation of GSSG have been measured for GSH concentrations ranging between 5 x 10⁻⁵ and 5 x 10⁻³ mol dm⁻³. In pulse radiolysis experiments the absorption spectra and the kinetics of transients formed by the action of OH^· radicals have been determined.

It has been found that the bromide radical anion reacts with glutathione, producing quantitatively GSSG with a G value of 2.9×10⁻⁷ molJ⁻¹. It is not the same for OH^· radicals which show a non stoichiometric oxidation of thiol group of glutathione. The OH^·-induced oxidation of glutathione in neutral aqueous solution by pulse radiolysis has been found to produce not only the sulphur-centered radical (GS^· and GSSG∸) but at least one other alkyl radical.

Coprecipitated SiO₂-Al₂O₃ (Al₂O₃=33.2 mol%) and Li₂O-impregnated SiO₂-Al₂O₃ containing 1, 2.5 and 5 mol% Li₂O were prepared. The textural properties were determined by following the adsorption of nitrogen at 77K. The surface acidities were determined from pyridine adsorption at 423 K. The catalytic conversion of isopropanol on the catalyst prepared was carried out using the pulse microcatalytic technique.

The surface area decreased and the pore size increased upon irradiation with γ-rays (dose⩾ 30 M rad). The acidity decreased upon impregnation with Li₂O and/or irradiation with γ-rays.

Several types of organic scintillator were exposed to a ⁶⁰Co γ-ray source at a dose rate of 1.838 x 10⁻² Gy/s in order to study the radiation damage in the range 10³-4 x 10⁴ Gy of absorbed dose, both in air and in nitrogen environment. The effect of radiation damage was measured by the change in optical transmission and light output before and after the irradiation of each sample. A different degree of damage, related to the type of scintillator and to the radiation environment, was observed.

PVC was compressed into discs with a pressure of 0-0.88 GPa and then irradiated with 200 kGy at room temperature and liquid nitrogen temperature, the polymeric radicals formed were studied by EPR spectroscopy. The radical concentration and its decay with temperature and time were investigated. The number of radicals increased with increase in pressure and decrease in temperature. The radicals produced by irradiation at atmospheric pressure had shorter half-lives than those formed for the compressed samples, and showed an asymmetric pattern of alkylperoxyl radicals. In the case of compressed samples, the formation of peroxyl radicals was not appreciable probably due to lack of oxygen diffusion. In all the cases three different radicals were formed and their half-lives were determined.

The semiquinone radicals produced by one-electron reduction of 1-amino-4-hydroxy-9,10-anthraquinone and 1,4-diamino-9,10-anthraquinone have been studied in aqueous-organic mixed solvent using pulse radiolysis technique. Spectroscopic characteristics, kinetic characteristics of formation and decay, acid/base behaviour and redox characteristics of the semiquinones have been investigated and compared with those of some similar systems studied earlier. It has been shown that the variation of the disproportionation equilibria involving the reduced semiquinone radicals, the parent quinone and the fully reduced hydroquinone with pH of the solutions follow a similar trend as observed in the case of other dihydroxy quinones. Stability of the semiquinones over a broad pH range and their thermodynamic properties have been correlated.

The reaction of e^-_aq with ethylene trihiocarbonate in aqueous medium has been investigated employing pulse radiolysis technique. The bimolecular rate constant for the reaction has been obtained as 3×10¹⁰dm³mol⁻¹s⁻¹. A transient absorption spectrum, with λ_max at 315 nm, has been observed which is assigned to the neutral radical formed by the protonation of radical anion produced in the reaction of e^-_aq with ETTC. A similar absorption spectrum was also observed under the condition where the H atom instead of e^-_aq reacts with ETTC. The transient decayed by second-order kinetics with k₂=(9.1±1.0) ×10⁸ dm³ mol⁻¹ s⁻¹. The G(-ETTC) has been determined from ⁶⁰Co λ-radiolysis as 3.1.

The reactions of DPPH with Cl₂, NO₂ and F₂ were studied. In the para-phenyl position substituted diphenylpicrylhydrazines were formed. Besides this, the reaction of halogens led to products which were nitro-substituted in the para-phenyl position. Thus, it was shown that the reactions of halogens and halogen radicals with DPPH include a substitution at the picryl group of DPPH and its derivatives under liberation of NO₂.

By ESR in situ spectroscopy and computational analysis of spectra, nitro-, dinitro-, fluoro- and difluoro-diphenylpicrylhydrazyls were identified as transient intermediates. In the formation of these species nitrogen dioxide and fluorine act as oxidants for the corresponding substituted hydrazines.