International Journal for Radiation Physics and Chemistry最新文献

Short-lived free radicals formed in γ-irradiated methanol, ethanol and 2-propanol have been detected by E.S.R. combined with spin trapping method using 2,4,6-tri-t-buthylnitrosobenzene (BNB) as a spin trap. The observed spectra could be identified clearly by the help of deuterated alcohols. The hydrogen spin adduct, which had not been clearly identified in earlier works, was observed together with alkoxy radicals and other radicals. It was revealed that a part of the hydrogen adduct could come from proton transfer to the anion radical of BNB, which was produced by electron capture during irradiation. From the change of ^∗CH₂OH/CH₃O^∗ ratio with that of added spin trap concentration one may conclude that the methoxy radical and hydrogen atom are primary radicals in radiolysis of liquid phase methanol. This conclusion is also supported by both the change of the ratio with irradiation temperature and the isotope effect on the spin adduct yields.

Pulse radiolysis of adrenaline in acid aqueous solutions (pH 1–3) was carried out. The rate constants for the reactions of adrenaline with H and OH were determined: k(H + adr.) = (0·9±0·1) × 10⁹ dm³ mol⁻¹ s⁻¹; k(OH + adr.) = (1·65±0·15) × 10¹⁰ dm³ mol⁻¹ s⁻¹. The H-adduct of adrenaline has two λ_max, at 280 and 355 nm, with ϵ₂₈₀ = 420 m² mol⁻¹ and ϵ₃₅₅ = 390 m² mol⁻¹, which disappears according to a first order reaction, k₁ = 1·4 × 10³ s⁻¹. The spectra formed by OH attack was assigned to the corresponding benzoxy radical with absorption maxima at 285 and 365 nm and ϵ₂₈₅ = 620 m² mol⁻¹ and ϵ₃₆₅ = 105 m² mol⁻¹. Due to the overlapping of the intermediates, no decay kinetics could be obtained.

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.

An investigation into the formation and characterization of the transients arising from the reactions of hydroxyl radical with the complexes bis(ethylenediamine)platinum(II) perchlorate and chloride, chloro(diethylenetriamine)platinum(II) chloride and chloro(1,1,7,7-tetraethyldiethylenetriamine)platinum(II) chloride in aqueous media saturated with nitrous oxide has been carried out using the technique of pulse radiolysis. In general, the transients exhibit absorption bands with either a single, intense peak below 300 nm (ϵ ⪞ 400 m² mol⁻¹) or for the longer-lived species, two peaks of lesser intensity at about 350 and 500 nm. For the bis(ethylenediamine)-platinum(II) system, the transients are interrelated by acid-base reactions and in the presence of free chloride ion by substitution process. The disappearance of the longer-lived intermediate, which obeys second-order kinetics, does not lead to the formation of detectable amounts of ammonia (or free ethylenediamine). This feature in conjunction with other results indicates that the transients are not those arising from the degradation or loss of the co-ordinated amine ligand. Some of the intermediates exhibit reactivity towards either copper(II) perchlorate, an oxidant, or the reducing agent potassium ferrocyanide. The flash photolysis of trans-dichlorobis(ethylenediamine)platinum(IV) perchlorate has been used to generate and further characterize some of the transients encountered in the pulse radiolysis study. It is concluded that the intermediates are platinum(III) amine complex ions. For the Pt(III) species with absorption peaks below 300 nm, their structures are proposed to be distorted octahedra with substitutionally labile co-ordination sites. It is suggested that the products absorbing above 300 nm may be structurally different from those absorbing below 300 nm.

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.

Experiments on H atom scavenging by alkanethiols in γ-irradiated aqueous solutions have confirmed that the reaction products depend on thiol structure. The percentage of H abstraction decreases with increasing branching at the carbon atom α to sulfur while -SH abstraction simultaneously increases. Methyl and ethyl radicals appear to react only by H abstraction from the thiol group since the yields of methane and ethane are independent of thiol structure. There is no significant temperature dependence of the H₂ and H₂S yields over the range 0–50°C for aqueous solutions of cysteine and penicillamine.

Competition between CH and CC bond ruptures has been established and attributed largerly to ion-electron recombination.

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.

The reaction of OH radicals with aqueous tris(1,10-phenanthroline)iron(II) leads to the formation of an adduct, which exhibits a broad absorption band at rmpH = 6, λ_{max = 460 nm}, and ϵ₄₆₀ = 6700 (molar, decadic, 1 mol⁻¹ cm⁻¹). The rate of formation of the adduct is first order in complex concentration with a bimolecular rate constant $\text{k = (1 >}\text{s}\text{̇}\text{;05±0 >}\text{s}\text{̇}\text{;03)× 10}{}^{10}\text{1 mol}{}^{\mathrm{-1}}\text{s}{}^{\mathrm{-1}}$ independent of pH in the range pH 3–11. The adduct decays by mixed-order kinetics, but at 310 nm a second-order formation of a decay product can be directly observed.

The reaction of OH radicals with aqueous 1,10-phenanthroline leads also to the formation of an adduct which absorbs in the whole visible region with a maximum at 425 nm and ε₄₂₅ = 2612 (molar, decadic, 1 mol⁻¹ cm⁻¹) in neutral solution. The adduct exhibits a red shift in acidic and alkaline media. The formation is first order in 1,10-phenanthroline with a bimolecular rate constant $\text{k = (8 >}\text{s}\text{̇}\text{;6±0 >}\text{s}\text{̇}\text{;7)×10}{}^9\text{1 mol}{}^{\mathrm{-1}}\text{s}{}^{\mathrm{-}}$ at pH = 6; the rate of formation is pH dependent. The adduct decays according to second-order kinetics leading to the formation of a product that exhibits the presence of an additional functional group. A similar product, determined to have pK⋟4 > ṡ;2 and pK₂⋟8 > ṡ;1, has been isolated after γ-radiolysis of 1,10-phenanthroline.