Radiation Physics and Chemistry (1977)最新文献

The use of pulse radiolysis to learn about processes which occur before the beginning of chemical times is discussed. Two examples, the distance distribution of positive and negative ions inn-hexane and the identity of the “dry electron” are discussed in detail. It is shown that the dry electron which reacts is not quasi-free, but instead must be associated with the solvent. Thus, the name “dry electron” is somewhat of a misnomer.

After electron-pulse irradiation of liquid cyclohexane and methylcyclohexane containing carbon tetrachloride as an electron scavenger, transient optical absorption bands were observed with peak wavelengths of about 500 nm. The bands are assigned to the corresponding alkane radical cations. Solute cation formation was studied in cyclohexane using solutes asn-decane,n-dodecane,n-hexadecane and benzene. It is shown that the solutes undergo electron transfer to cyclohexane radical cations. Charge-transfer rate constants were estimated and their observed correlation with the difference of the liquid-phase ionization potentials of solvent and solute, ΔE =I¹_C6H12 -I¹_S, is qualitatively compared with electron transfer theories.

In order to accelerate the process of omitting the labeling of the irradiated food, it is suggested to enact the hygienic safety standard of the irradiated food. It may be classified as three classes: (1) Its hygienic safety standard is similar to that of common food. (2) The maximum permissible quantities of harmful compounds induced by radiation must be controlled. (3) The quantity of unique radiolysis product may be determined.

We must put the stress on the prediction and detection of induced harmful radiolysis products such as peroxides, volatile basic nitrogen compounds and organic halides.

1-Hydroxy-1-methyl ethyl radicals produced in the irradiation of Na₃IrCl₆ solutions containing propanol-2 and acetone react very slowly with the IrCl^3-₆ anion (k of the order 100 M^-1 s^-1). The product of the reaction is a compound which reacts very efficiently with the radicals and thereby catalyses the formation of hydrogen. This compound is supposed to be an iridium hydride. No iridium is produced at small Na₃IrCl₆ concentrations and a maximum H₂ yield of 3.7 H₂/100 eV is observed at concentrations of IrCl^3-₆ between 2 and 5 times 10^-4 M. At higher concentrations, iridium metal starts to be formed. A faster formation of iridium occurs in solutions of Na₃IrCl₆(>10^-3 M) containing only propanol-2 as additive. In these solutions, the reduction of IrCl^3-₆ takes place thermally after initiation with λ radiation (some 10⁴ rads). The postirradiation effect is inhibited by O₂, N₂O, CH₃I, CH₂CHCN, H₂ and CO. A mechanism for the reduction of IrCl^3-₆ by propanol-2 is proposed, in which an Ir^I complex produced by radiation acts as the catalyst.

ITL spectra of γ-irradiated pure PMMA and PMMA matrices containing anthracene, pyrene, and naphthalene were studied at 77 K. Luminescence was found to be formed as a result of recombination of PMMA⁺ and aromatic cations with anionic species. The process occurs according to tunnelling mechanism.

The low-dose radiolysis of N₂-O₂ mixtures has been investigated at 101 kPa and 299 K. Measurement of the yield for NO and NO₂ as a function of the N₂ mole fraction has been analyzed to give a G(N) value of 7.3 ± 1.5 for the yield of N(⁴S) and N(²D,²P) atoms for the radiolysis of N₂. Computer simulation of the neutral N₂O₂ chemistry under radiolytic conditions showed that N atoms are predominately formed in a metastable state. Predissociation of N₂ electronic states in the 12 to 16 eV range is responsible for the production of metastable atomic N(²D) and N(²P) atoms.

The isothermal luminescence (ITL) from glassy polyethylene adipate (PEA) γ-irradiated at 77 K was observed over a long period of time, together with effect of the electron scavengers on it. The decay behavior of ITL is similar to that of polyethylene terephthalate or polycrystalline PEA obtained previously, so that the decay obeys the decay function I(t) = I₀/(1 + αt)^m. The detailed discussion on the parameters included in the decay function is given. Differences in the parameters between different materials or different physical states are found not to be very large, except the parameter I₀. Addition of biphenyl into PEA enhances considerably the intensity of ITL and causes the luminescence center to exchange from the ester cation into the biphenyl cation. In the biphenyl doped PEA, the possibility of the triplet-triplet energy transfer from the excited ester group to the biphenyl and the positive charge transfer from the ester cation to the biphenyl are shown.

The yields of the radiolytic products in air, N₂ and N₂O saturated aqueous solution of cyanide ion have been determined by combining the paper chromatographic method and carrier technique. The variations of the yields of the products in various systems have been investigated systematically by the scavenger method. The reaction kinetics of active species (OH, e^-_aq and H) with HCN and CN^- has been investigated. The G values of radiolytic products originating from different pathway of reactions were determined. The possibility of increasing the yields of amino acids has also been studied, and a method of increasing the G value of glycine has been found

p⁺-i-n⁺-diodes were irradiated by means of 10 ns-electron pulses with energies of 0.3 - 1 MeV. The induced current pulse was measured. The half times of growth and decay give information about electrical carrier life times and diffusion lengths.