Radiation Physics and Chemistry (1977)最新文献

Radiation degradation of short-cotton linters has been studied by using X-rays diffraction,an infrared spectrometer and a viscosimeter. Average molecular weight and crystallinity of short-cotton linters and the change of reducing sugar in ɜ-radiation degradation were examined. It was found that cellulosic saccharification in hydrolysis was enhanced with preirradiation of linters. This probably resulted from the radiation induced change of cellulosic structure. Sensitizers to promote radiation degradation effect were investigated. Carbon tetrachloride has been found to be effective.

The methods of technological dosimetry are discussed. The special attention is paid to the methods used in the U.S.S.R. The data on standard chemical and solid state dosimeters are presented. Some aspects on standardization of dosimeters in radiation processing are described. The information of high dose dosimeters which are lot produced in the U.S.S.R. is given. The examples of their application in radiation processing are presented.

A simple method utilizing a photochromic “intensity label” for monitoring electron-beam sources was evaluated. The labels exhibit a color change upon exposure to UV or e-beam radiation. A correlation was found between absorbed energy and Gardner Color Index at low electron-beam doses.

Investigations on the stratigraphic distribution of poly/methyl methacrylate/ in leather follow our earlier experiments on radiation grafting of vinyl monomers $\text{in situ}$.

Polymer distribution was determined for pigskins and cattlehides tanned with basic sulphates of chromium /III/. ¹⁴C-labelled methyl methacrylate was used in present experiments. Precision slicing technique was employed to cut consecutive slices parallel to the grain surface of the radiation modified leather. Quantitative analysis of polymer distribution in leather was based on radioactivity measurements. Each layer was burned in Oxymat apparatus and resulting ¹⁴CO₂ was analysed by liquid scintillation method.

On the basis of radioactivity measurements and visual observations with light microscope conclusion on desirable distribution of polymer was reached. In the midcorium part of leather polymer is evenly distributed and its content is much higher than for outer layers next to surface and flesh. Mechanism of relevant processes as well as formation and role played by peroxide compounds is discussed.

Carbon dioxide based gas mixtures, similar to those used as coolants in the Advanced Gas-cooled Nuclear Reactors, have been radiolyzed at the comparatively low dose rate of 3 Gy s^-1 using γ-radiation from a ⁶⁰Co source. The concentrations of certain C₄ and C₅ alkanes, ethanal and propanone, produced by radiolysis, have been determined under different conditions of temperature, pressure, gas composition, and surface area. Observations showed that these compounds were produced in concentrations of the order of 1/1000 of the methane concentration and that the production of these “trace organics” varied in a complex way with the experimental parameters. Mechanisms for the production of these organics have been proposed. Some unidentified products of radiolysis were observed and suggestions are made as to their nature.

An accurate and inexpensive spectrophotometric readout method is given for free radical dosimetry. The stable free radicals in irradiated alanine/glutamine powder, when dissolved in a solution containing ferrous ammonium sulphate and xylenol orange in 0.05 N H₂SO₄(FX), oxidize ferrous ions and the xylenol orange forms a complex with ferric ions produced in the solution. The absorbance of the complex is measured at 525 nm for alanine and at 540 nm for glutamine. The influence of various parameters, such as size of the container, weight of the powder dissolved, xylenol orange concentration, purity of distilled water, postirradiation stability and dose-rate dependence on the response of the dosimetric technique, has been investigated. It was found that the dosimetric response is independent of dose-rate. Alanine does not show any significant postirradiation fading. Irradiated glutamine powder is stable for about a month, the fading is less than 2% up to three months later, and it increases to only about 5% over a period of six months. The reproducibility of the method is better than ±2%, and it offers an alternative to ESR and lyoluminescence techniques for free radical dosimetry. A dose of 0.01 to 4 kGy can be measured with an alanine dosimeter and 0.1 to 100 kGy with a glutamine dosimeter. Empirical relationships between absorbance and dose are given.

The problem of delocalization of the energy initially absorbed by the medium is considered. We present a rigorous derivation of the formula for the delocalization due to the uncertainty principle for particles of arbitrary velocity. Using the value of the effective range of the electromagnetic field of a moving particle, we estimate the dimensions of the collective excitation area. We also discuss the possible radiation-chemical consequences of the initial delocalization of the energy absorbed by the medium.

Effect of gamma - irradiation ( 2.5–10 KGy ) on the flavour and flatulence causing oligosaccharides of broad bean were investigated. The method used for the cooked flavour analysis involved low temperature distillation. Gaschromatography was used to separate the flavour extracts into their various constituents. The major volatile free fatty acids isolated are C16, C18, C18:1, and C20. Identification of the major peaks from the non-acid fraction were carried out. Identified peaks were hydrocarbones, alcohols, ketones, aldehydes and phenoles. Most of the compounds found to increase with increase in radiation dose. On the other hand, sensory evaluation tests indicated no changes in broad bean flavour quality after irradiation. Sugars were also analysed by gas chromatographic method after TMS-ether derivation. Fructose, ∞ and β -glucose, sucrose, raffinose and stachyose were the major sugars present. The gas - forming oligosaccharides were found to decrease with increase in dose applied. On the other hand, other sugars found to increase with increase in radiation dose.

Samples of 19 different spices, milk powder, whole onions and frozen chicken were exposed to a Co-60 source with radiation doses up to 10⁴ Gy. The subsequent reaction of the irradiated foodstuffs in a luminol solution resulted in light emission (chemiluminescence). This effect can be used as an indicator of radiation treatment.