International Journal for Radiation Physics and Chemistry最新文献

n-Pentane was irradiated in the solid phase at 77 K. Post-irradiation scavenging of radicals by dissolving at 110 K the irradiated pentane in a propane-oxygen mixture lowers the decanes and pentenes G-values to an extent of 40–60%. The principal experimental results are: (1) a radical G-value of 2·76; (2) a radicalar distribution of 30% in primary radicals and 70% in secondary radicals; (3) a rough dismutation-combination ratio of 2·1 at 120 K.

The reactions of tetraphenylphosphonium ion (Ar₄P⁺) with e_aq⁻, H atoms and OH radicals have been investigated. The absorption spectra of three transient species were obtained. Ar₄P· radicals formed by the reaction: Ar₄P⁺ + e_aq⁻ → Ar₄P· have a maximum absorption at 305 nm [ε₃₀₅ = (9400 ± 300) dm³ mol⁻¹ cm⁻¹] and decays by second-order kinetics with the rate constant 2k = (2·7 ±0·4) × 10⁹ dm³ mol⁻¹ s⁻¹. H atoms and OH radicals form transient adducts to the phenyl groups of the Ar₄P⁺ ion with the rate constants of (1·5 ± 0·3) × 10⁹ dm³ mol⁻¹ s⁻¹ and (3·0±0·3) × 10⁹ dm³ mol⁻¹ s⁻¹, respectively. Both adducts have broad absorption spectra at 300≈380 nm (λ_max = 340 nm) with the molar extinction coefficients ε₃₄₀ = 5400±300 dm³ mol⁻¹ cm⁻¹ for the H adduct and ε₃₄₀ = 3500±200 dm³ mol⁻¹ cm⁻¹ for the OH adduct.

In this paper our experiments on isothermal decay of thermoluminescence of the main peak of CaSO₄ : Dy phosphors at various temperatures and ⁶⁰Co γ doses are described. The decays are not monoexponential; however, as the shape of the decay curves at a same temperature is dose independent, first-order kinetics may be assumed. Consequently, the decay curves at 100 rad are broken down in exponential terms and for each term the decay constant and the related partial light sum are obtained. These results are interpreted, at first, by trying to associate with the peak a multilevel distribution of trap depths; however, the activation energies and the frequency factors for these levels are physically unacceptable. Subsequently, on the hypothesis of a continuous trap distribution, the decay curves are best fitted as a whole; in this way a frequency factor of 3 × 10¹² s⁻¹ and a trap distribution with an approximately gaussian main peak centred at about 1 > ṡ37 eV and three other minor peaks are obtained. To check the consistency of the results, a theoretical glow curve is synthesized and a single peak fairly similar to the experimental one emerges.

Almost all theoretical papers on the mechanism of radical reactions in the tracks of ionizing particles implicitly assume the independence of the radical distributions. In this paper the effect of correlations arising between the radical distributions in the course of the reaction process on its change in time and the product yields is studied. The problem has been formulated in terms of the joint probabilities of radical pairs according to a one-spur-one-radical model. It is found that the combination and recombination processes in real spurs must be more effective than prescribed by one-radical models assuming the independence of the distributions of the reacting particles. The results of those theories correspond with the results from our model only for local concentrations which are too low to be realistic. On the other hand, for the relative lowering of the molecular yield with increasing scavenger concentration this model gives the same deviations from the experiment for higher scavenger concentrations as other one-radical models.

A study of the radiolysis of monocrystalline, liquid and aqueous solutions of methane sulphonic acid is reported. E.S.R.-measurements on γ-irradiated single crystals show that two radicals ·CH₂SO₂(OH) and CH₃ŻSO₂(OH)⁻ are formed. Sulphonic acid-water mixtures were investigated by pulse radiolysis. A short-lived transient absorption with maximum at 450 nm is assigned to the radical ion CH₃ŻSO₂(OH)⁻ (ϵ = 1740 dm³ mol⁻¹ cm⁻¹). Two longer-lived transient absorptions at 263 and 347 nm in concentrated solution were shifted to 242 and 332 nm respectively with increasing water concentration.

The 242/263 nm absorption is ascribed to the ·CH₂SO₃⁻ radical and its protonated form and the 332/347 nm absorption to the CH₃SO₂· radical formed by the decomposition of the CH₃ŻSO₂(OH)⁻ radical ion. The interpretation of E.S.R. and optical spectra is based on the assumption of a hydrogen bonding structure of the sulphonic acid.

Various picosecond and nanosecond pulse radiolysis studies of excited states in alkane and erene liquids are described. In particular, the origin of the excited states is sought after. In alkanes ion neutralization gives rise to excited triplet states of solutes. Singlet energy transfer from excited alkanes to solutes gives rise to the excited singlet states of the solutes. In aromatic liquids both the excited singlet and triplet state of the solvent are observed, and energy transfer to solutes is readily established. The role of ion neutralization in the formation of excited states is proportionally less pronounced as the observed yield of ions is low. However, indirect experiments suggest that the ion neutralization reaction is too rapid for conventional observation, and even in arenes large yields of excited states are formed by ion neutralization.

The conditions determining the limits of applicability of the diffusion-drift model (DDM) of radiolysis of non-polar organic fluids containing additives of acceptors of charged particles have been obtained. The validity of the DDM for saturated hydrocarbons is associated with the localization of the electrons which move in the medium by thermally activated jumps from one localized state to another. It is shown that the use of the DDM in radiation-chemical kinetics is justified if the lenght of localization l (or the mean length of the free path Λ) of the electrons is small as compared with the characteristic dimension of the problem. For describing the death of ion pairs such a characteristic dimension is the mean initial distance between their components and for calculating the rate constants of the reactions of recombination and capture of the charges by an acceptor the radius of the absorbing sphere R. The corrections arising from calculation of these constants for the systems where l_L (or Λ) is greater than or comparable with R are evaluated.

Tryptophan and naphthalene in boric acid glass at 77 K give rise to a delayed fluorescence under U.V. excitation and to a photostimulated delayed fluorescence under visible light excitation of an irradiated sample. It is shown that these emissions are due to electron-cation recombination and that, beside the chemical trapping of electrons by protons which is the main process, a physical electron trapping occurs in this strongly acidic medium. This unexpected property is related to the inhomogeneous structure of boric acid glasses which plays an important role in the unique properties of this medium for photoionization studies of aromatic compounds.