Radiation Physics and Chemistry (1977)最新文献

Using pulse radiolysis and coupled optical detection the pK_a of the HCO₃ radical is shown to lie between 7.0 and 8.2. The rate constant of self-recombination of CO^-₃ has a negative apparent activation energy which indicates a composite process.

An electron-attachment spectroscopy technique is described which enables the mean energy of electrons to be varied in the range 0.04–0.5 eV by means of a radiofrequency voltage superimposed on the d.c. voltage of an electron-capture detector. Plotting the electron-capture coefficients or the mean electron-capture cross sections against the mean electron energies for each compound yields a characteristic curve which may be helpful for the identification of unknown substances. An increase of the sensitivity and the specificity of the electron-capture detector is also possible. The dependence of the electron-capture coefficient on the mean electron energy for eight substances is discussed.

A laser-induced pressure-pulse apparatus (LIPP) for measuring charge-density and field-strength distributions in thick dielectric samples (some mm) with a spatial resolution of about 0.2 mm is described. First results on the charge-accumulation and storage processes in electron-irradiated polyethylene (PE), polypropylene (PP), and polymethylmethacrylate (PMMA) are presented.

In the past 3 yr much work has been done in the G.D.R. on food irradiation. The experiments have shown that this treatment gives favourable results in many products such as spices, onions, potatoes, chicken, animal feeds, fodder yeast, drugs and vaccines. Economic aspects of food irradiation require the effective use of an irradiation plant and cobalt-60. Therefore, a new multipurpose irradiation facility was developed, applicable as an onion irradiator with a capacity of about 15 ton/h and for the simultaneous irradiation of different products (spices, animal feed, chicken, etc.) in closed product ☐es with a size of 1.2 m x 1.0 m x 1.2 m. A microcomputer controls the transport of product ☐es around the gamma sources.

The compressive and bending strengths of a local tropical wood (Kapur-Dryobalanop sp.) were improved significantly by suitable impregnation of polymeric monomers (methylmethacrylate, methylmethacrylate—5% dioxane and vinyl acetate) inot the wood cellular structure and subsequent irradiation to form a wood-polymer composite. Statistical analysis revealed a linear relationship between increase in the strengths and the percentage of polymer impregnated. Fractographic analysis of the impact fractured surfaces under the scanning electron microscope showed the nature of the wood-polymer interface, which could account for the increase in the compressive and bending strengths.

Oxygen-free aqueous solutions of 0.05 mol dm^-3 malic acid (pH 2.4) were irradiated with ⁶⁰Co λ rays (0.1–92 kGy). Various small molecules were identified: CO, CO₂, CH₄, HCHO, CH₃CHO, (HCO)₂, CH₃COCHO, and CH₃COOH. With the exception of CO₂, they appear in small yields (G< 0.1) and represent minor radiolytic products. About 16 di-and polycarboxylic acids appear in irradiated solution, among them malonic and succinic acids being fairly abundant. Of particular importance is the efficient formation of dimers and trimers of malic acid. From the experimental data the value of k(e^-_aq + (HOOCCH₂CH(OH)COOH) was evaluated as ⩾3 × 10⁹ dm³ mol^-1 s^-1. Probable free-radical reactions leading to the formation of the radiolytic products are considered.

Research has demonstrated that irradiation is an effective means for reducing pathogens in sewage sludge to levels where sludge reuse in public areas meets criteria for protection of the public health. Complementary research has demonstrated the value of the irradiated sludge in both agronomic and animal science applications.

The benefits of sludge application to cropland are well documented. The irradiation process does not increase the extractability and plant uptake of a broad range of nutrients and heavy metals from sludge-amended soils. However, it does eliminate the hazards associated with pathogen contamination when applying sludge to agricultural land. Irradiated sludge has also been evaluated as a supplemental foodstuff for cattle and sheep. The data indicate that products derived from raw sewage may have a substantial nutritive value for ruminant animals.

Irradiation of sewage sludge is a practical means of sludge disinfection. Where a highly disinfected sludge is required, it should be considered as a viable sludge management alternative. Evaluation of sludge irradiation technology and its associated costs must be done with consideration of other sludge treatment processes to develop an acceptable sludge management system.

This paper looks at the various design concepts for the irradiation processing of food products, with particular emphasis on handling the products on pallets.

Pallets appear to offer the most attractive method for handling foods from many considerations. Products are transported on pallets. Warehouse space is commonly designed for pallet storage and, if products are already palletized before and after irradiation, then labour could be saved by irradiating on pallets. This is also an advantage for equipment operation since a larger carrier volume means lower operation speeds.

Different pallet irradiator design concepts are examined and their suitability for several applications are discussed. For example, low product holdup for fast turn around will be a consideration for those operating an irradiation “service” business; others may require a very large source where efficiency is the primary requirement and this will not be consistent with low holdup.

The radiation performance characteristics and processing costs of these machines are discussed.

The interaction of collagen and metalloproteins with radiation-generated radicals has been studied using spectrophotometric, chromatographic, and ESR techniques. The hydroxyl radical (·OH) reacted with and caused polymerization of acid soluble collagen. Similar reactions were also observed in a ferrimyoglobin and cytochrome C system. Insoluble collagen from bovine muscle subjected to radiation is followed by a first-order process for the decay of free radicals, depending on relative humidity of the system. When the samples were irradiated with 3 kGy at 25°C by a Cesium-137 Irradiator, the observed half life (hr) of free radicals in the samples decreased with increase of relative humidity RH: 31% > 69% > 100%. When collagen, previously kept dry or under 31% RH, was irradiated with 3 kGy at 77°K (-196°C), the decay of free radicals reached a plateau with annealing at -120°C or higher. The decay kept decreasing with annealing at -100°C or higher temperature when collagen maintained at 69 and 100% RH was used. It is concluded that the free radicals in moistened collagen from bovine muscle decreased at a higher rate than in dried collagen. This suggests that free radicals may persist for a longer period of time in irradiated dry proteins of food or animal feed than in foods of higher moisture extent.