The free radical species in polyacrylonitrile fibers induced by γ-radiation and their decay behaviors

Free radicals in vacuum, air and oxygen atmospheres were studied using electron spin resonance (ESR). Mainly two types of radicals, namely alkyl radicals and polyimine radicals, are formed in polyacrylonitrile (PAN) fibers after γ-ray irradiation. The G value of the radical formation was calculated to be 2.1 (number of radicals per 100 eV absorbed) in air at room temperature based on the ESR measurements. The radical stability and decay behaviors at room temperature and elevated temperatures were also investigated under different atmospheres. The alkyl radicals were found to be rather stable when stored in vacuum at room temperature, but they decayed via reaction with oxygen when stored in air. The alkyl radicals disappeared completely after a thermal treatment at 110 °C in vacuum, but only 15% of the polyimine radicals decayed; this indicates that polyimine radicals are more stable compared to the alkyl radicals due to their lower mobility.     

Systematic fabrication of chitosan nanoparticle by gamma irradiation

The present investigation is mainly focused on the systematic preparation of chitosan nanoparticle in the potential range 1–100 nm using γ-ray irradiation. The effect of irradiation conditions in terms of physical form of chitosan, i.e. flake, colloidal and acidic solution, and γ-ray dose was studied. The molecular weights of chitosan were 10, 25, and >1000 times reduced when irradiated with the γ-ray dose as high as 100 kGy in Chi-flake, Chi-colloid, and Chi-acid, respectively. The particle size reduced to 70 nm after being irradiated to only 10 kGy γ-rays and it showed a tendency to decrease when the γ-ray doses were increased. The γ-rays effectively induced the reduction of chitosan particle size to <100 nm with narrow size distribution. The effective size reduction was particularly observed in Chi-colloid. Heterogeneous chemical conjugation of deoxycholic acid onto 10 kGy irradiated Chi-colloid resulted in narrow particle size as small as 50 nm.     

Mineralization of aqueous phenolate solutions: A combination of irradiation treatment and wet oxidation

Wet oxidation (high-temperature, high-pressure oxidation of organic wastes in aqueous solution) and radiation technology were combined in γ-ray and electron beam induced oxidation of 4×10^?4–1×10^?2 mol dm^?3 Na-phenolate solutions in a wide O₂ concentration (1–20 bar pressure) and absorbed dose (0–50 kGy) range. Most experiments were made in stainless steel high pressure autoclave equipped with magnetic stirrer. The rate of oxidation was followed by chemical oxygen demand and total organic carbon content measurements. The rate was similar in γ-ray and pulsed electron beam irradiation and increased with O₂ concentration in the liquid.     

Preparation and properties of aminoxyl radicals having an aromatic core with long alkyl substituents

Series of monoradicals and biradicals having an aromatic core on one hand and long alkyl groups on the other hand have been prepared. It was found from their magnetic data that the biradical compounds having aromatic cores (azoxy, or azo) and long alkyl groups with TEMPO radicals at their ends showed fairly large antiferromagnetic interactions (J = −34, −39 K) being well expressed by ST model, while only weak antiferromagnetic interactions were observed in the corresponding PROXYL derivatives together with the corresponding monoradicals. The change of intermolecular magnetic interactions based on the structural change from trans- to cis-isomer by irradiation was found to be possible in a couple of azobenzene derivatives with an aminoxyl radical.     

Effect of high-dose irradiation on quality characteristics of ready-to-eat chicken breast

High-dose (higher than 30 kGy) irradiation has been used to sterilize specific-purposed foods for safe and long-term storage. The objective of this study was to investigate the effect of high-dose irradiation on the quality characteristics of ready-to-eat chicken breast in comparison with those of the low-dose irradiation. Ready-to-eat chicken breast was manufactured, vacuum-packaged, and irradiated at 0, 5, and 40 kGy. The populations of total aerobic bacteria were 4.75 and 2.26 Log CFU/g in the samples irradiated at 0 and 5 kGy, respectively. However, no viable cells were detected in the samples irradiated at 40 kGy. On day 10, bacteria were not detected in the samples irradiated at 40 kGy but the number of bacteria in the samples irradiated at 5 kGy was increased. The pH at day 0 was higher in the samples irradiated at 40 kGy than those at 0 and 5 kGy. The 2-thiobarbituric acid reactive substance (TBARS) values of the samples were not significantly different on day 0. However, on day 10, the TBARS value was significantly higher in the samples irradiated at 40 kGy than those at 0 and 5 kGy. There was no difference in the sensory scores of the samples, except for off-flavor, which was stronger in samples irradiated at 5 and 40 kGy than control. However, no difference in off-flavor between the irradiated ones was observed. After 10 days of storage, only the samples irradiated at 40 kGy showed higher off-flavor score. SPME-GC–MS analysis revealed that 5 kGy of irradiation produced 2-methylbutanal and 3-methylbutanal, which were not present in the control, whereas 40 kGy of irradiation produced hexane, heptane, pentanal, dimethly disulfide, heptanal, and nonanal, which were not detected in the control or the samples irradiated at 5 kGy. However, the amount of compounds such as allyl sulfide and diallyl disulfide decreased significantly in the samples irradiated at 5 kGy and 40 kGy.     

Radiation induced degradation of ketoprofen in dilute aqueous solution

The intermediates and final products of ketoprofen degradation were investigated in 0.4 mmol dm^?3 solution by pulse radiolysis and gamma radiolysis. For observation of final products UV?vis spectrophotometry and HPLC separation with diode array detection were used, and for identification MS was used. The reactions of ^?OH lead to hydroxycyclohexadienyl type radical intermediates, in their further reactions hydroxylated derivatives of ketoprofen form as final products. The hydrated electron is scavenged by the carbonyl oxygen and the electron adduct protonates to ketyl radical ^?OH is more effective in decomposing ketoprofen than hydrated electron. Chemical oxygen demand and total organic carbon content measurements on irradiated aerated solutions showed that using irradiation technology ketoprofen can be mineralised. The initial toxicity of the solution monitored by the Daphnia magna test steadily decreases with irradiation. Using 5 kGy dose no toxicity of the solution was detected with this test.     

Gamma ray induced changes on vibrational spectroscopic properties of strontium alumino-borosilicate glasses

The present investigation reports the effect of influence of aluminum ions on radiation damage of strontium borosilicate glasses studied by means of spectroscopic (viz., optical absorption (OA), infrared and Raman spectra). The composition of the glasses chosen for the study is 40SrO–xAl₂O₃–(15-x) B₂O₃–40SiO₂ (x = 5, 7.5, 10), all in mol%. The glasses were synthesized by conventional melt quenching method. Later, the samples were exposed to gamma (γ) radiation dose of strengths 10 kGy and 30 kGy with a dose rate of 1.5 Gy/s using ⁶⁰Co as radiation source. The infrared spectra (IR), Raman spectra and optical absorption (OA) spectra of the samples were recorded at ambient temperature before and after irradiation. The OA spectra of the pre-irradiated samples do not exhibit any absorption bands in the UV–vis regions and IR and Raman spectra exhibited conventional vibrational bands due to different borate, silicate AlO₄ and AlO₆ structural units. The OA spectra of post irradiated samples exhibited a broad absorption band in the wavelength region 600–750 nm; it is attributed to electron trapped color centers. The intensity of this peak is observed to increase with increase of the γ-ray dose. Considerable changes in the intensities of various bands in the IR and Raman spectra were also observed. The changes were explained based on structural modifications taking place in the glass network due to γ-ray irradiation and finally it is concluded that the glasses mixed with 10.0 mol% of Al₂O₃ are relatively more radiation resistant.     

Optical properties of a-Se90In10−x Snx chalcogenide thin films before and after gamma irradiation

Amorphous Se₉₀In_10?xSn_x (x=2, 4, 6, and 8) thin films of thickness 1000 Å were prepared on glass substrates by the thermal evaporation technique. Optical parameters of the films were investigated, in the wavelength range 400–700 nm, before and after irradiation by 4, 8, and 12 kGy doses of γ-ray. The optical absorption coefficient α for as-deposited and gamma irradiated films was calculated from the reflectance R and transmittance T measurements, which were recorded at room temperature. From the knowledge of α, at different wavelengths, the optical band gap E_g was calculated for all compositions of Se–In–Sn thin films before and after gamma irradiation. Results indicate that allowed indirect optical transition is predominated in as-deposited and irradiated films. Besides, it is found that the band gap decreases with increasing Sn concentration and this is attributed to the corresponding decrease in the average single bond energy of the films. The band gap, after irradiation at different doses of γ-ray, was found to decrease for all compositions of the studied films. This post-irradiation decrease in the band gap was interpreted in terms of a bond distribution model.     

Combined effect of γ-irradiation and bacterial-fermented dextrose on microbiological quality of refrigerated pork sausages

The objective of this study was to evaluate the effect of a concentrated fermented dextrose (FD), a natural antimicrobial product, combined with low dose γ-irradiation (1.5 kGy) on the microbiological quality of fresh pork sausages. Fresh pork sausages containing the FD (0.25%, 0.5% and 0.75%) were prepared in a meat pilot plant and were irradiated using a UC-15A irradiator equipped with a ⁶⁰Cobalt source. The γ-irradiation treatment alone was able to reduce the initial psychrophilic and mesophilic bacteria by more than 2 log CFU/g and kept the lactobacillus population under the detection limit (100 CFU/g). Results also showed that the FD alone was able to extend the shelf life of the sausages from 5 days up to 13 days. At day 13, the FD or irradiation alone showed 2 log CFU/g less mesophilic bacteria than the control. After combining FD and irradiation another reduction of the microbial count of 1 log CFU/g was observed. When combining the irradiation treatment with the FD results it showed a reduced growth rate of the psychrophilic and mesophilic bacteria compared to both treatments alone. This study demonstrated that FD with low dose gamma irradiation act in synergy to reduce the multiplication of the total bacterial flora in fresh sausages.     

Characterization of a power bipolar transistor as high-dose dosimeter for 1.9–2.2 MeV electron beams

Results of the characterization studies on a power bipolar transistor investigated as a possible radiation dosimeter under laboratory condition using electron beams of energies from 2.2 to 8.6 MeV and gamma rays from a ⁶⁰Co source and tested in industrial irradiation plants having high-activity ⁶⁰Co γ-source and high-energy, high-power electron beam have previously been reported. The present paper describes recent studies performed on this type of bipolar transistor irradiated with 1.9 and 2.2 MeV electron beams in the dose range 5–50 kGy. Dose response, post-irradiation heat treatment and stability, effects of temperature during irradiation in the range from –104 to +22 °C, dependence on temperature during reading in the range 20–50 °C, and the difference in response of the transistors irradiated from the plastic side and the copper side are reported. DLTS measurements performed on the irradiated devices to identify the recombination centres introduced by radiation and their dependence on dose and energy of the electron beam are also reported.     

Decomposition of 14C containing organic molecules released from radioactive waste by gamma-radiolysis under repository conditions

Decomposition of ¹⁴C containing organic molecules into an inorganic compound has been investigated by γ-ray irradiation experiments under simulated repository conditions for radioactive waste. Lower molecular weight organic acids, alcohols, and aldehydes leached from metallic waste are reacted with OH radicals to give carbonic acid. A decomposition efficiency that expresses consumption of OH radicals by decomposition reaction of organic molecules is proposed. Decomposition efficiency increases with increasing concentration of organic molecules (1×10⁻⁶–1×10⁻³ mol dm⁻³) and is not dependent on dose rate (10–1000 Gy h⁻¹). Observed dependence indicates that decomposition efficiency is determined by reaction probability of OH radicals with organic molecules.     

Analysis of electron spin resonance spectra of irradiated gingers: Organic radical components derived from carbohydrates

Electron spin resonance (ESR) spectral characterizations of gingers irradiated with electron beam were studied. Complex asymmetrical spectra (near g=2.005) with major spectral components (line width=2.4 mT) and minor signals (at 6 mT apart) were observed in irradiated gingers. The spectral intensity decreased considerably 30 days after irradiation, and continued to decrease steadily thereafter. The spectra simulated on the basis of characteristics of free radical components derived from carbohydrates in gingers are in good agreement with the observed spectra. Analysis showed that shortly after irradiation the major radical components of gingers were composed of radical species derived from amylose and cellulose, and the amylose radicals subsequently decreased considerably. At 30 days after irradiation, the major radical components of gingers were composed of radical species derived from cellulose, glucose, fructose or sucrose.     

Cotton fabric modification for imparting high water and oil repellency using perfluoroalkyl phosphate acrylate via γ-ray-induced grafting

The perfluoroalkyl phosphate acrylates were grafted onto a cotton fabric via γ-ray irradiation to improve the hydrophobic and oleophobic properties. The change in chemical structure of grafted cotton fabric was detected by the Fourier transform infrared spectroscopy and the X-ray photoelectron spectroscopy. The contact angles for water and sunflower oil were determined to be over 150° and 140°, respectively, after irradiated with a dose range of 471–5664 Gy. The flame retardancy of the fabric with a grafting ratio of over 13.0 wt% was improved, reaching to 24 compared with 18 of which before grafted, according to the limiting oxygen index measurement. The microstructure of the fabric before and after grafted was observed by the scanning electron microscope.     

The changes of fatty acid and amino acid compositions in sea bream (Sparus aurata) during irradiation process

Aqua cultured fish (sea bream) were irradiated by Cobalt-60 at commercial irradiation facility at dose of 2.5 and 5 kGy at 2–4 °C. The proximate composition, fatty acid and amino acid composition changes of irradiated aqua cultured sea bream (Sparus aurata) of Aegean Sea were investigated. Total saturated (28.01%) and total monounsaturated (28.42%) fatty acid contents of non-irradiated decreased content of 27.69–27.97% for 2.5 kGy irradiated groups and increased content of 28.33–28.56% for 5 kGy irradiated groups after irradiation process. Total polyunsaturated fatty acid content for irradiated samples was lower than that of non-irradiated samples. Aspartic acid, glutamic acid, serine, glycine, arginine, alanine, tyrosine, cystine, tryptophan, lysine and proline contents for 2.5 and 5 kGy irradiated sea bream are significantly different (p<0.05).     

Change in the enzymatic dual function of the peroxiredoxin protein by gamma irradiation

PP1084 protein was exposed to gamma irradiation ranging from 5 to 500 kGy. Native PAGE showed minor structural changes in PP1084 at 5 kGy, and major structural changes at >15 kGy. Size-exclusion chromatography (SEC) showed the formation of a new shoulder peak when the protein was irradiated with 15 and 30 kGy, and a double peak appeared at 100 kGy. The results of PAGE and SEC imply that PP1084 protein is degraded by gamma irradiation, with simultaneous oligomerization. PP1084 chaperone activity reached the highest level at 30 kGy of gamma irradiation, and then, decreased in a dose-dependent manner with increasing gamma irradiation. However, the peroxidase activity significantly decreased following exposure to all intensities of gamma irradiation. The improvement of chaperone activity using gamma irradiation might be promoted by the oligomeric structures containing covalently cross-linked amino acids. Consequently, PP1084 modification using gamma irradiation could elevate chaperone activity by about 3–4 folds compared to the non-irradiated protein.     

The origin of the radiobiological damage in cells stored in cryostatic conditions

The radiation induced free radical damage in Chinese hamster lung fibroblast V-79 cells stored in DMEM culture medium containing 10% DMSO has been investigated by matrix EPR spectroscopy in connection with the H₂O/DMSO binary phase diagram. A major part of the indirect effect is due to radicals from the DMSO·3H₂O phase in the freezing medium, which are released on warming in the temperature range between 130 K and 160 K, that is, far below the eutectic melting temperature (210 K). The radicals trapped in the DMSO·3H₂O phase react with oxygen above 160 K giving reactive oxygen species (ROS) of the type of peroxyl radicals. A lower limit yield of 10–15% was calculated for this conversion. Scavenging experiments with a stable nitroxyl radical (tempol) have demonstrated that part of the DMSO·3H₂O radicals escape by mutual recombination on melting and are therefore available for inducing indirect cell damage. The same experiments performed with pure frozen water have shown that OH radicals are not available for inducing cell damage. The EPR measurements performed on H₂O/DMSO frozen mixtures suggest that the radiation induced radical forming process does not change when passing to the low dose range below 1 Gy, in agreement with the linear model.     

Microstructural modifications in swift ion irradiated PET

Polyethylene terephthalte (PET) was irradiated with carbon (70 MeV) and copper (120 MeV) ions to analyze the induced modifications with respect to optical, structural and thermal properties. In the present investigation, the fluence for carbon irradiation was varied from 1×10¹¹ to 1×10¹⁴ ions cm⁻², while that for copper beam was kept in the range of 1×10¹¹ to 1×10¹³ ions cm⁻². UV–vis, FTIR, XRD and DSC techniques were utilized to study the induced changes. The analysis of UV–vis absorption studies reveals that there is decrease of optical energy gap up to 10% on carbon ion irradiation (at 1×10¹⁴ ions cm⁻²), whereas the copper beam (at 1×10¹³ ions cm⁻²) leads to a decrease of 49%. FTIR analysis indicated the formation of alkyne end groups along with the overall degradation of polymer with copper ion irradiation. X-ray diffraction analysis revealed that the semi-crystalline PET losses its crystallinity on swift ion irradiation. It was found that the carbon beam (1×10¹⁴ ions cm⁻²) decreased the crystallite size by 16% whereas this decrease is of 12% in case of the copper ion irradiated PET at 1×10¹³ ions cm⁻². The loss in crystallinity on irradiation has been supported by DSC thermograms.     

Dosimetric characteristics of different types of saccharides: An EPR and UV spectrometric study

The time stability and dose response of the free radicals produced in various types of “less-studied” mono- and disaccharides by γ-radiation is studied by EPR (Electron Paramagnetic Resonance) and UV spectrometry. The time evolution of the shape of the EPR spectra of irradiated saccharides is investigated from 5 min to 5 months after irradiation. The intensity of the stable EPR signal is studied as a function of the absorbed γ-dose in the range 0.5–20 kGy. Aqueous solutions of irradiated solid saccharides exhibit a UV absorption maximum in the range 250–290 nm. A linear dependency is found between the magnitude of the UV absorption maximum and the absorbed γ-dose. The time stability of the UV absorption maximum is also studied for every saccharide. The results are compared with those obtained for irradiated sucrose.     

Dielectric study of post-irradiation effects in gamma-irradiated polyethylenes

The post-irradiation dielectric behaviour of different polyethylenes (PEs) has been studied by means of dielectric loss (tan δ) analysis over the wide temperature (25–325 K) and frequency (1 kHz–1 MHz) ranges. For this reason, low density polyethylene (LDPE), linear low density polyethylene (LLDPE) and high density polyethylene (HDPE) samples were previously gamma irradiated in air to absorbed dose of 300 kGy. The irradiated samples were divided into two groups, and for the first one annealing treatment which can substantially reduce the concentration of free radicals were employed. For the second group, e.g. samples stored in air at room temperature after irradiation, post-irradiation evolution in free radical concentration, dielectric relaxation spectra and carbonyl content was investigated as a function of storage time, up to 90 days. Dielectric relaxation behaviour is related to differences in the initial structures of PEs (such as branching, crystallinity, etc.) and to the radiation-induced effects; carbonyl groups that were introduced by irradiation and/or delayed (post-irradiation) oxidation were regarded as tracer groups. Electron spin resonance (ESR), differential scanning calorimetry (DSC), infrared (IR) spectroscopy and gel measurements were used to determine the changes in free radical concentration, crystal fraction, oxidation and degree of network formation, respectively.     

Decomposition of p-nonylphenols in water and elimination of their estrogen activities by 60Co γ-ray irradiation

Concentration of p-nonylphenols (NPs) in water at 1 μmol dm⁻³ was decreased exponentially with absorbed dose when NPs were irradiated by ⁶⁰Co γ-rays. Two products having molecular weight of 236, presumably OH adducts of NPs, were detected by LC–MS analyses. The elimination of estrogen activity of aqueous NPs solution including such irradiation products at 5000 Gy (J kg⁻¹) was confirmed by the yeast two-hybrid assay. These results should expand the application of ionizing radiation to the treatment of NPs.