International Journal for Radiation Physics and Chemistry最新文献

The reactivity of the oxide radical ion, O⁻, and the decay kinetics of the ozonide ion, O₃⁻, have been investigated in aqueous solutions at pH 12·8, in the presence of tetramethyl-, tetraethyl-, tetrapropyl- and tetrabutylammonium ions, O₂ and N₂O. Using pulse radiolysis to follow the O₃⁻ kinetics gives information on the competition of O₂ and R₄N⁺ for O⁻. Absolute rate constants for these reactions are: 3·0 × 10⁸ dm³ mol⁻¹ s⁻¹ for O⁻ + (CH₃)₄N⁺, 1·0 × 10⁹ dm³ mol⁻¹ s⁻¹ for O⁻ + (C₂H₅)₄N⁺, 1·3 × 10⁹ dm³ mol⁻¹ s⁻¹ for O⁻ + (C₃H₇)₄N⁺ and 2·2 × 10⁹ dm³ mol⁻¹ s⁻¹ for O⁻ + (C₄H₉)₄N⁺.

The decay of O₃⁻ occurs through the thermal dissociation reaction, O₃ ⇌ O₂ + O⁻, for which the absolute rate constant at 22°C was found to be 6·2 ± 1·2 × 10³ s⁻¹.

The absolute yield value G(H₂) = 1·36±0·07 for ethylene radiolysis was determined. Ethylene, unlike nitrous oxide, is convenient for dosimetry if small irradiation cells are used.

The kinetics of positive ion and electron scavengin gin certain n-alkanes, cycloalkanes, branched alkanes, aromatic hydrocarbons and in some polar compounds (ethers, dimethyl-formamide) have been investigated.

The non-homogeneous kinetic approach gives satisfactory agreement with experimental Results for n-hexane, cyclohexane, iso-octane and 2,3-dimethylbutane. Differences between positive ion and electron scavenging for ethers have been observed and ascribed to the complex structure of the corresponding positive ions. For benzene and dimethylformamide the homogeneous kinetic equation gives the best agreement with experimental results.

Characteristic parameters such as G_fi, G_gi, reactivity coefficients α, rate constant of ion scavenging k_s, geminate recombination parameters for several solvents λ, and the most probable distances of electron thermalization have been determined or calculated.

The effect of molecular structure on the ionic reactions has been discussed.

Fast kinetic spectrophotometry was used to study the absorption spectra of short-living intermediates produced by reactions of RCN molecules with H, e_aq⁻ and OH. The spectra were obtained on the microsecond time scale after an electron pulse from a Febetron 707 accelerator in aqueous solutions of the following compounds: hydrocyanic acid, acetonitrile, propionitrile, malononitrile and succinonitrile. It has been found that all intermediates absorb in the U.V. range (λ⩽300 nm) and disappear by fast bimolecular processes with decay rate constants of about 10⁹dm³mol⁻¹s⁻¹. In the presence of an efficient scavenger for hydroxyl radicals, the same transient spectra were registered in acid and neutral solutions suggesting that the protonations of e_aq⁻ adducts of these RCN molecules were complete within a submicrosecond time interval.

A partir des résultats concernant la radiolyse de divers systm̀es de solutés par les particules de recul de ${}^{10}\text{B}\text{(}\text{n}\text{, α)}{}^7\text{Li}$, le calcul des rendements radicalaires et moléculaires démontre l'existence de réactions se développant, en absence de bons capteurs, au voisinage immédiat de chaque trajectoire. Une hypothèse est proposée quant à l'origine de ces réactions: les produits moléculaires sortant du coeur des trajectoires pourraient réagir avec les produits radicalaires formés essentiellement dans une zone périphérique par les rayons δ qui dissiperaient ainsi environ 20% de l'énergie des particules α.

The electron bombardment of molecules generally gives rise to ions in more than one electronic state. The ion beam composition with respect to the electronic states can be determined by studying the attenuation of the beam as a function of the pressure of a suitable gas. In this way, the composition of B⁺, F⁺, C⁺, H₂O⁺ and H₃O⁺ ion beams was determined. The difference between the reactive behavior of the ion beam in the ground and the first excited state with simple targets such as molecular hydrogen and its stable isotopic variants and some of the factors which determine the amount of excited state produced were examined.

The influence of temperature, down to 87 K, on the formation of excited states in the pulse radiolysis of 10⁻³ mol dm⁻³ 9,10-diphenylanthracene in 3-methylpentane was investigated. Lowering the temperature decreases the yield of solute singlets and triplets produced during the pulse and extends the time scale of excited state formation up to milliseconds or even seconds. This effect is mainly due to slower ionic reactions at low temperature. The ionic processes are responsible for the formation of about 70% of the solute singlets and all the triplets in pulse-irradiated 10⁻³ mol dm⁻³ 9,10-diphenylanthracene in 3-methylpentane.

The authors have investigated the current of electrical conductivity I induced by a pulse of 2 × 10⁻⁷ s of high energy electrons in 3-methylpentane (3MP) over the temperature range 94–296 K. The determination of the drift mobility of the excess electron u is based on measurement of the amplitude of I in conditions in which the lifetime of the excess electron in 3MP τ ⪢ 2 × 10⁻⁷ s and the total number of free charges q generated in the course of one pulse. In liquid 3MP q was measured by integrating I and in solid 3MP by integrating the current of thermostimulated conductivity on heating the sample to melting point. At T = 296 K the value u = 0·22 cm² V⁻¹ s⁻¹ and agrees with the value obtained from measurements of the time of transit by the electron of the distance between electrodes d≈0·1 cm.

In the temperature interval from 94–296 K the value u monotonically changes from 10⁻⁸ to 0·22 cm² V⁻¹ s⁻¹. In the region of the melting point, the values of u in liquid and solid 3MP are much the same, whereas the activation energy changes from 0·14 to 0·4 eV on passing from liquid to solid 3MP. The activation energy of the mobility of the electron in solid 3MP is connected with the energy of the thermal release of the electron from the deepest structural traps.

Extrapolation of the function u(T) by the Arrhenius law with an activation energy of 0·4 eV gives the value u ≈ 10⁻¹⁵ cm² V⁻¹ s⁻¹ at 77 K which accords with the value obtained from measurement of the quasi-steady photo-conductivity and evaluation of the lifetime of the trapped electron in 3MP at 77 K.