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.

The effect of gamma radiation on the photoelectrochemical response of thermally grownn-type iron oxide has been studied; a dose-dependent decrease in the photocurrent was found. The data, discussed in terms of the Ga¨rtner theory, enable one to evaluate the width of the space-charge layer and the diffusion length of the minority charge carriers as a function of dose.

Water-vapour radiolysis under accelerated electrons in a one-pass flow system was investigated. The radiolysis parameters were changed over a wide range. Pure water vapour and its mixture with carbon monoxide were irradiated. The maximum radiation hydrogen yieldG_m = 8 in pure water vapour independent of dose rate was obtained at temperatures higher thanT_c. In mixtures of H₂O + CO at definite parameters the radical processes of water vapour decomposition transforms into a chain mechanism (the chain lengthv ≲ 200). The kinetics and the mechanisms of radical and chain processes of water vapour decomposition were considered.

The radiation facilities ofU´VVVR, Praha, the sources PERUN, RADEGAST, and GAMMACELL 220, their construction, exploitation capabilities, and dosimetric systems are described.

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.

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.

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.

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