International Journal for Radiation Physics and Chemistry最新文献

As difficulties are encountered with model theories in describing the nature of solvated electrons, it is suggested that possible non-model relations in the theory of solvated electrons be used. In the present work the results that follow from the sum rules, virial theorem and threshold formulae of the quantum theory of scattering are examined. In this way it is possible to establish relationships that can be used for determining some of the physical characteristics of solvated electrons directly from optical data.

Electron spin resonance studies of phosphorus compounds containing PH bonds, after exposure to ⁶⁰Co γ-rays, show that electron addition is followed by movement of hydrogen into the axial position of the resulting phosphoranyl radical. Subsequent thermally induced, irreversible, pseudo-rotations placed the hydrogen ligands in the equatorial position.

Electron loss was always accompanied by loss of the proton bonded to phosphorus, giving phosphoryl radicals. A range of other species were also detected, and their identities and reactivities are discussed.

1-Choloropropane has been irradiated in the presence of cyclohexene and the formation of hydrogen chloride and of products derived from cyclohexene has been studied as a function of the concentration of this additive. The irradiations, which were performed with accelerated electrons, were characterized by very high absorbed dose rates. Under such experimental conditions, transfer of excitation energy and radical addition to cyclohexene appear to be only of minor importance. The formation of products derived from cyclohexe is initiated predominantly by ion-molecule reactions between cyclohexene and the positive 1-chloropropane ions. The mechanisms of the subsequent reactions are discussed.

In this paper, we describe a new experimental method which is used to determine the effect of temperature on the mechanisms related to the detrapping of electrons trapped in a glass. The studied samples are organic vitreous solutions of an aromatic molecule (TMPD) inside a non-polar glass (3-MP or MCH). The intensity of the isothermal luminescence (ITL) following the photoionization of the sample at 77K is increased when applying thermal jumps ΔT≲2K (the rise time is ⋍s).

A general kinetical theory is used to explain the shapes of the luminescence curves perturbed by thermal jumps. It is shown that the experimental observations can be explained in terms of a slow diffusion of the trapped electrons towards a tunneling detrapping zone. When applying a thermal jump ΔT, the intensity of luminescence is multiplied by X such as: $\text{X =}\text{exp}\text{ΔT}\text{T}\text{E}\text{kT}\text{+ Y}\text{1+Y}$.

This relationship is in good agreement with experience. The thermal detrapping activation energy E and the tunnelling effect ratio Y can be determined through this formula. The shapes of the kinetic curves at T = 77K and T = 77·50K are compared in the case of 3-MP glassy samples (near the glass transition, T_g = 77K). It is concluded that there is a slow diffusion of trapped electrons (as it was already shown); the diffusion activation energy (E_d = 0·65eV) is found to be very close to viscosity activation energy (E = 0·65eV) as given by Willard. This last result seems to support the hypothesis according to which the diffusion of trapped electrons is the consequence of the diffusion of the trapping cavities (at T_g).

The e.p.r. method has been used to study the radical stages of low-temperature photolysis and radiolysis of polystyrene and to demonstrate the difference in them due to the photoconversion of the cyclohexadienyl radical. The authors have determined the quantum yield of the reaction of radical formation (ø ≅ 10⁻⁵) which weakly depends on the wavelength of the absorbed light at 230<λ<340 nm and the mean depth (l) at which radicals form (l≅9 ohms m for λ = 254 nm, i.e. in the region of inherent absorption of PS, and l ≅350 ohms m at λ≅300 nm). A shift is observed in the absorption band of polystyrene to the long-wave region owing to the secondary photoreactions of the cyclohexadienyl and peroxide radicals.

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.

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.

Previous observations on the spectral changes due to electrons in 1-propanol have been extended to 77 K. It is found that down to 118 K the decay in the I.R. and growth in the visible are first order and that from 118 to 313 K the rate constants fit the modified Arrhenius expression of Tamman and Hesse, as do the relaxation times obtained from dielectric dispersion measurements and the alcohol viscosity. These changes are considered to arise from molecular reorientation around the electrons. Below 118 K, the kinetics are no longer first order, the changes are much more extended in time and are also much faster than expected from an extrapolation of the observations at the higher temperatures. Electron loss, presumed due to ion recombination, also occurs. It is concluded that the mechanism responsible for the spectral shifts is different at these lower temperatures and that here thermal excitation from shallow traps and retrapping by deeper ones occurs.