International Journal for Radiation Physics and Chemistry最新文献

The fluorescence intensity of bicyclohexyl liquid excited both with β particles and with 184.9 nm light has been studied as a function of the concentration of perfluorocarbon electron scavengers. From this it has been possible to estimate (a) the fraction of all excited singlet states which derive from geminate ion pairs and (b) the probability (averaged over the spur size distribution) that a geminate ion pair will generate an excited singlet state on recombination. The latter value is compared with theoretical values and it is concluded that in bicyclohexyl the geminate electron does not spin-relax prior to recombination. Preliminary results for p-xylene are also presented and important differences between the saturated and aromatic hydrocarbon liquids are discussed.

Pulsed N.M.R. measurements of the proton spin-lattice, T₁, and spin-spin, T₂, relaxation times for γ-irradiated linear polydimethylsiloxane ($\text{M}$_w = 0.6 × 10⁴) as a function of dose up to 200 Mrad are reported. The dependences of T₁ and T₂ on dose are discussed in terms of the effects of the introduction of intermolecular crosslinks on the molecular motion. Above the gel point the spin-spin relaxation exhibits a double exponential decay characteristic of two-phase system. This behaviour is attributed to the heterogeneous phase separation of the material into gel and sol fractions. The value of T₂ for each phase provides information regarding the differing molecular mobilities of the gel and sol phases and their dependence on radiation dose. The sol fractions determined from the N.M.R. T₂ measurements are compared with those obtained using the conventional sol extraction technique and are shown to be reasonable quantitative agreement. The applicability of N.M.R. as a quantitative method for the determination of gel points and gel fractions is demonstrated and discussed.

Exposure of aqueous glasses containing carbonate enriched in ¹³CO₃²⁻ gave ^.OH and e_t⁻ as major primary products at 77 K, but ^.CO₂⁻ and CȮ₃⁻ features together with ¹³C satellite lines grew strongly on annealing above 77 K. Alkaline solutions gave mainly ^.O⁻ and e_t⁻, but on annealing a new radical, tentatively identified as CȮ₄³⁻, was detected. This had E.S.R. parameters comparable with those for ¹³CȮ₃⁻, but with a smaller anisotropy in both A(¹³C) and g. This species is thought to result from addition of ^.O⁻ to CO₃²⁻

Solutions is methanol (CD₃OD) gave mainly D₂ĊOD, e_t⁻, and ^.CO₂³⁻ radicals, but CȮ₃⁻ grew in strongly on annealing.

Neutral aqueous glasses containing formate ions gave HĊO and ĊO₂⁻ in addition to ^.OH radicals, together with a broad feature tentatively assigned to HĊO₂²⁻ or HĊO(OH)⁻ radical. These features were better defined in alkali glasses (HĊO₂²⁻) and in 6 mol dm⁻³ sulphuric acid glasses [HĊO(OH)⁻]. Features for ¹³CO₂⁻ were clearly resolved in the former, but in the acidic glasses a larger ¹³C hyperfine coupling suggested ¹³ĊO(OH). The formly radical was also detected in the scidic glasses but not in the alkaline media. The mechanisms of the reactions leading to these intermediates are discussed and compared with those for aqueous nitrite solutions.

The technique of pulse radiolysis has been used to study the effect of temperature on the solvated electron in 1-propanol. The spectrum of the solvated electron has been measured in the range 140–298 K. The wavelength at maximum absorption, λ_max, decreases with decreasing temperature (corresponding to an increase in the energy, E_max) but the spectral width at half height, $\text{ΔE}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$, changes little with temperature. At temperatures above ≈180 K, the formation of the solvated electron is complete at the end of the pulse and its spectrum shows no change in shape with time. Below ≈170 K, the absorption spectrum is time-dependent in both liquid and glassy phases, the changes being attributed to the solvation process. The reaction(s) leading to solvated electron formation following the pulse show an activation energy of 22±2 kJ mol⁻ and the solvated electron decays with an activation energy of 20±2 kJ mol⁻¹. The yield of solvated electrons decreases continuously with decreasing temperature in the range 298-77 K and, at all temperatures studied, is less than the total ionization yield measured by scavenging techniques.

The radical AsF₅⁻ is similar to PF₅⁻ but the central atom spin-density is higher. Crystals of KPF₆ containing traces of AsF₆⁻ give high yields of AsF₅⁻ on exposure to ${}^{60}\text{Co}\text{γ}$-rays. This efficient scavenger effect is explained in terms of the greater positive charge on arsenic.

The radiolysis of nitrilotriacetic acid (NTA) in neutral or alkaline solution, was studied in the presence and in the absence of dissolved oxygen. The radolytic yields of decomposition of NTA and formation of iminodiacetic acid(IDA) were determined; G(-NTA) was found to be equal to G(IDA). The formation of hydrogen peroxide and carbonyl compounds was also followed. The radiolysis was found to be initiated by hydrogen abstraction by both H and OH radicals with the formation of a dehydrogenated radical intermediate which ultimately stabilizes to give products. The radiolytic mechanism under different conditions has been discussed. From competition kinetic studies with sodium formate in neutral solution, the rate constant, k(OH + NTA), was found to be 3.0 x 10⁸ dm³ mol⁻¹s⁻¹.

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.