International Journal for Radiation Physics and Chemistry最新文献

Several fundamental reactions have been investigated using nanosecond pulse radiolysis. The following reaction rate constants were measured: k(_{N2O⁻→N2+O⁻})>10⁸s⁻¹, k(_H⁺+O2⁻)= (5 ± 1) × 10¹⁰ dm³ mol⁻¹ s⁻¹. k(_{HO2→H⁺+O2⁻}) = (7 ± 2) × 10⁵ s⁻¹, k(_CO2⁻+O2) = (4.2 ± 0.4) × 10⁹ dm³ mol⁻¹ s⁻¹.

Scanning electron microscopy has been used to examine γ-irradiated purine and pyrimidine bases in dry powder form. Channelling is observed in some of the samples. Surface changes appear to be correlated with radiosensitivity as measured by other techniques.

The effect of ionizing radiation on high density poly (HD) and single (SC) crystals of polyethylene samples were investigated by DSC. For HD material the heat of fusion (ΔH_f) was found to drop by only ∼ 17% at about 700 Mrad of radiation dose with no detectable corresponding change in the melting temperature T_m. In contrast approximately 67% drop in ΔH_f and 18 K in T_m was observed for SC specimen. Such drastic differences in the melting behaviour were ascribed to greater sensitivity of the SC material to irradiation as far as effecting the crystal structure is concerned. Crosslinking taking place in the fold surface of the SC specimen (amorphous region) increases the strain energy at the fold and progressively affects the nearby crystal lattices. The amorphous region in HD material is different in morphology, and crosslinking taking place in that region does not affect the crystal structure substantially.

Dissociative electron attachment reaction to CH₃I, CH₃Cl and CH₃F in a 3-methylhexane glassy matrix was studied by determining the yield of trapped electrons and that of methyl radicals immediately after γ-irradiation at 77 K as a function of the scavenger concentration. The efficiency of conversion from the trapped electrons to the methyl radicals was also studied by photobleaching the trapped electrons. The results obtained are (1) the dissociative electron attachment occurs to CH₃F, for which the gas phase data indicate that the reaction is endothermic by 1·2 eV, during either the γ-irradiation or the photobleaching, and (2) CH₃F is relatively less efficient in scavenging photo-liberated electrons than in scavenging the electrons during the γ-irradiation, whereas CH₃I and CH₃Cl are efficient scavengers for both the electrons. The dependence of the yields of the trapped electrons and the methyl radicals is discussed in terms of the electron-tunneling mechanism and the epithermal electron-scavenging mechanism.

The dependence of H₂ yields on the concentration of certain solutes indicates that molecular hydrogen is formed via recombination of its precursors in spurs. The order of efficiency of solutes in decreasing the formation of H₂ does not correlate with the rate constants of their reactions with e_aq⁻ or H.

Due to their diffusive motion at energies ⩽10²eV and to their comparatively long lifetimes in the subvibrational energy range at the end of their tracks, positrons may form positronium by a reaction with (epi) thermal electrons. The order of the reactivity of solutes towards the precursors of positronium is the same as that towards precursors of the molecular hydrogen yield and is in agreement with the order of their relative rate constants towards the non-solvated electron.

It seems that the non-solvated electron takes part in the formation of positronium and of radiolytic H₂.

Exposure of aqueous alkaline glasses to ⁶⁰Co γ-rays followed by photobleaching to remove e_t⁻ resulted in E.S.R. spectra dominated by O_t^- and H·_t^-, but at ca. 110 K H·_t was lost and e_t⁻ reappeared.

Electron scavenging efficiencies have been measured at 77 and 4 K in ethylene glycol-water glass for the following scavengers which span a 250-fold range of scavenger efficiencies at 77 K: HCl, NaNO₃ and K₂CrO₄. The range of scavenging efficiencies decreases to 62 at 4 K with the largest relative change occurring for the less efficient scavengers. These results are suggested to be most consistent with a model in which scavenging occurs by tunneling from shallowly and deeply trapped electrons at 4 and 77 K, respectively.

The reaction of e_aq⁻ with halogenated aromatic compounds (fluoro-, chloro-, bromobenzene, and 2-, 3-, 4-chloro-aniline) was studied by conductometric pulse radiolysis and under steady-state conditions. It was established that in the pH range from 4 to 10 all e_aq⁻ are reacting with the compound in question by quantitative splitting of the halide anion (X⁻). Considering certain experimental factors G(X⁻)=2.7 was obtained by both methods for all investigated substances. This fact is in disagreement with previous observations on various halogenated compounds. However, it can be explained taking all possible reactions for each system into account.