Exhaustive radiolysis of 11 mM aqueous benzene solutions: effect of added oxygen

The gamma radiolysis of aqueous benzene solutions was studied under various conditions (oxygenated, aerated and anoxic) to ascertain the role that oxygen plays in the destruction of benzene. For the oxygenated and aerated systems, phenol and biphenyl were the major quantified products. For the anoxic system, phenol was the sole quantified product. Benzene was initially consumed with approximately the same yield in each of the three systems; G(–benzene) was 0.49 μmol J^–1. Initial yields of phenol, G(phenol), were found to be 0.12, 0.060 and 0.030 μmol J^–1 for the oxygenated, aerated and anoxic systems, respectively. Biphenyl was initially formed with G=0.028 and 0.019 μmol J^–1 in the oxygenated and aerated systems, respectively. The percent conversion of benzene to CO₂ after an absorbed dose of 2500 kGy was 55.1%, 30.5% and 12.5%, respectively, for the oxygenated, aerated and anoxic systems. The last traces of benzene disappeared by a dose of ca. 60 kGy in all three systems. A mechanism was proposed for each system that depended upon the presence or absence of O₂. The total solution toxicity for each system was calculated by summing the individual toxicities of benzene and each quantified product. For the oxygenated and aerated systems, the total solution toxicity was found to go through a maximum at a dose of 22 kGy and then decrease to a value below that of the original solution. The total solution toxicity of the anoxic system was found to decrease from the onset of irradiation.     

The effect of 60Co (γ-ray) irradiation on the electrical characteristics of Au/SnO2/n-Si (MIS) structures

The effect of ⁶⁰Co (γ-ray) irradiation on the electrical properties of Au/SnO₂/n-Si (MIS) structures has been investigated using the capacitance–voltage (C–V) and conductance–voltage (G/ω−V) measurements in the frequency range 1 kHz to 1 MHz at room temperature. The MIS structures were exposed to γ-rays at a dose rate of 2.12 kGy/h in water and the range of total dose was 0–500 kGy. It was found that the C–V and G/ω−V curves were strongly influenced with both frequency and the presence of the dominant radiation-induced defects, and the series resistance was increased with increasing dose. Also, the radiation-induced threshold voltage shift (ΔV_T) strongly depended on radiation dose and frequency, and the density of interface states N_ss by Hill–Coleman method decreases with increasing radiation dose.     

Study on gamma and electron beam sterilization of third generation cephalosporins cefdinir and cefixime in solid state

The effect of gamma radiation from ⁶⁰Co source and 2 MeV e-beam was studied on two thermolabile cephalosporin antibiotics viz cefdinir and cefixime in solid state. The parameters studied to assess radiolytic degradation were loss of chemical and microbiological potency, change in optical rotation, electronic and vibrational absorption characteristics, thermal behavior and color modification. ESR spectroscopic study, HPLC related impurity profile, thermogram and Raman spectrum are applied in deducing the nature of radiolytic impurities and their formation hypotheses. Cefixime is radiation sensitive, whereas cefdinir has acceptable radiation resistance at 25 kGy dose. The nature of radiolytic related impurities and their concentrations indicates that the lactam ring is not highly susceptible to direct radiation attack, which otherwise is considered very sensitive to stress (thermal, chemical and photochemical).     

Radiolysis of pyridoxine (vitamin B6) in aqueous solution under different conditions

Aqueous solutions of pyridoxine (1 mM) without or with additive of K₃[Fe(CN)₆] (2.5 mM) were gamma-irradiated at different doses and dose rate of 2.16 kGy/h in the absence of air, in the presence of air or by their saturation with N₂O. The radiolytic products were analyzed with HPLC, mass spectrometry and UV spectroscopy. 2,4,5-Trihydroxymethyl-3-pyridinol, pyridoxal, isopyridoxal and 6-hydroxypyridoxine were formed by radiolysis in the absence of K₃[Fe(CN)₆], and their concentrations were much higher in samples saturated with N₂O. Pyridoxi-3,6-quinone was found by radiolysis under all the above-mentioned conditions but only in the presence of K₃[Fe(CN)₆]. Besides, the pyridoxal formation increased in the presence of this oxidizing agent. G values of pyridoxal formation and pyridoxine degradation were quantified. Some details of the radiolytic product formation were discussed.     

Oxidation of naringenin by gamma-radiation

The reaction of OH with naringenin (4′,5,7-trihydroxyflavanone) in the presence of air induced the formation of the hydroxylation product eriodictyol (3′,4′,5,7-tetrahydroxyflavanone). Its yield was dependent on pH. The initial degradation yield of naringenin was G_i(-Nar)=(2.5±0.2)×10⁻⁷ mol dm⁻³ J⁻¹. For the reaction with OH, a rate constant k (OH+naringenin)=(7.2±0.7)×10⁹ M⁻¹ s⁻¹ was determined. In the presence of N₂O and NaN₃/N₂O, no eriodyctiol was formed. Apigenin (4′,5,7-trihydroxyflavon) was detected as decay product of the naringenin phenoxyl radicals. In Ar-saturated solutions, naringenin exhibited a pronounced radiation resistance, G(-naringenin) ∼0.3×10⁻⁷ mol dm⁻³ J⁻¹.     

Irradiation effects on the C–V and G/ω–V characteristics of Sn/p-Si (MS) structures

In this paper, we have investigated the effects of ⁶⁰Co gamma (γ)-ray source on the electrical properties of Sn/p-Si metal–semiconductor (MS) structures using the capacitance–voltage (C–V) and conductance–voltage (G/ω–V) measurements before and after irradiation at room temperature. The MS structures were investigated in the frequency range 20–700 kHz irradiation effects on the electrical properties of Sn/p-Si MS structures before irradiation, and after irradiation, these structures were exposed to ⁶⁰Co γ-ray source irradiation with the dose rate of 2.12 kGy/h and the total dose range was 0–500 kGy at room temperature. It was found that the C–V and G/ω−V curves were strongly influenced with both frequency and the presence of the dominant radiation-induced defects, and the series resistance was increased with increase in dose. On the other hand, the interface state density (N_ss) as depended on radiation dose and frequency was determined from C–V and G/ω–V measurements, and the interface states densities decreased with increase in frequency and radiation dose.     

Radiation-induced degradation of aqueous 2,3-dihydroxynaphthalene

The degradation of aqueous 2,3-dihydroxynaphthaline (2,3-DHN) under the influence of γ-ray was investigated under various experimental conditions. Using 2.5×10⁻⁵ mol L⁻¹ 2,3-DHN in aerated media (pH=6–6.8) an initial degradation yield, G_i-(2,3-DHN)=0.32 was obtained, whereas in solutions saturated with N₂O the yield come to G_i-(2,3-DHN)=0.50.In airfree media the substrate decomposition was negligible. Possible reaction mechanisms are presented.Further, the rate constant, k(OH+2,3-DHN)=2.14×10¹⁰ L mol⁻¹ s⁻¹ was determined by competition reactions with PNDA.     

Pulse radiolysis of aqueous diphenyloxide

Pulse radiolysis of aqueous diphenyloxide (DPO) has been performed under various experimental conditions. The OH radicals react with DPO on various positions of the molecule with a rate constant, k=2.1×10¹⁰ l mol⁻¹ s⁻¹. The major reaction step appears to be a cleavage of the C–O bond of DPO resulting into C₆H₄OH (λ=285 nm) and C₆H₅O(λ=325 nm) radicals in addition to DPO–OH adducts. They disappear according to a second-order reaction. In the presence of air or in a gas mixture of N₂O:O₂=4:1 the DPO–OH adducts are scavenged by oxygen, resulting into peroxyl radicals, which are long-lived species. For the reaction of e_aq⁻ with DPO a rate constant, k=2×10¹⁰ l mol⁻¹ s⁻¹ was found.     

Effect of gamma radiation on the mechanical and barrier properties of HEMA grafted chitosan-based films

Chitosan films were prepared by dissolving 1% (w/v) chitosan powder in 2% (w/v) aqueous acetic acid solution. Chitosan films were prepared by solution casting. The values of puncture strength (PS), viscoelasticity coefficient and water vapor permeability (WVP) of the films were found to be 565 N/mm, 35%, and 3.30 g mm/m² day kPa, respectively. Chitosan solution was exposed to gamma irradiation (0.1–5 kGy) and it was revealed that PS values were reduced significantly (p≤0.05) after 1 kGy dose and it was not possible to form films after 5 kGy. Monomer, 2-hydroxyethyl methacrylate (HEMA) solution (0.1–1%, w/v) was incorporated into the chitosan solution and the formulation was exposed to gamma irradiation (0.3 kGy). A 0.1% (w/v) HEMA concentration at 0.3 kGy dose was found optimal-based on PS values for chitosan grafting. Then radiation dose (0.1–5 kGy) was optimized for HEMA grafting. The highest PS values (672 N/mm) were found at 0.7 kGy. The WVP of the grafted films improved significantly (p≤0.05) with the rise of radiation dose.     

About the OH yield in the radiolysis of an aqueous/H2O2 system. Its optimisation for water treatment

Unless the radiolytic reducing species are neutralised or converted into oxidising species, an EB remediation system cannot be considered a true Advanced Oxidation Processes (AOP). A water/H₂O₂ system irradiated by UVC mercury lamps constitutes a widely used OH production method. Employing H₂O₂ in radiolysis as well, an enhancement of the oxidative efficiency of an EB treatment can be obtained. Pulse radiolysis measurements of an aerated aqueous/H₂O₂/KSCN system have been systematically undertaken to assess the optimal H₂O₂ concentration. By linearly fitting a competition kinetics relationship, it is found that the scavengeable extra-yield of OH is ΔG(OH)=0.24 μmol J^?1 (R=0,9958), while the maximum experimental yield is measured G(OH)_max=(0.52±0.02) μmol J^?1 when [H₂O₂]=5–10 mM. Exceeding these concentrations the OH yield drops off.     

Microbial quality evaluation and effective decontamination of nutraceutically valued lotus seeds by electron beams and gamma irradiation

Lotus seeds are nutraceutically valued natural plant produce, which succumbs to microbial contamination, predominantly to toxigenic moulds. Results of the present study revealed seed coat portion to harbor higher proportion of microbial load, particularly fungi than cotyledon portion. Among the mycotoxins analyzed, aflatoxins (B₁, B₂, G₁ and G₂) were below detectable limits, while the seeds were devoid of Ochratoxin-A (OTA). Application of different doses of electron beam and gamma irradiation (0, 2.5, 5, 7.5, 10, 15 and 30 kGy) for decontamination purpose revealed significant dose-dependent decrease in the fungal contaminants (P<0.05). However, the contaminant yeasts could survive up to 10 kGy dose, which could be completely eliminated at 15 kGy. From the results obtained, a dose range between 10 and 15 kGy is recommended for complete decontamination, as these doses have also been shown earlier to have minimal effects on nutritional and functional properties of lotus seeds.     

Effect of radiation on disinfection and mechanical properties of Korean traditional paper,Hanji

Fumigants, including methyl bromide and ethylene oxide, are generally used for the preservation of the Korean cultural heritage, especially paper products like letters and books. However, the use of fumigants is banned because of their harmful effects on humans and the environment. Gamma irradiation is being considered as an alternative for the sterilization of insects and fungi in organic products. Therefore, the purpose of this study was to investigate the sterilization effects of radiation and its effect on the mechanical properties of the Korean traditional paper—Hanji. Treatment doses of 9 kGy and 8 kGy of gamma irradiation inactivated 5 log units of Aspergillus niger and Bacillus cereus spores inoculated on Hanji, respectively. The gamma irradiations up to an absorbed dose of 50 kGy resulted in no significant changes in the tensile strength, bursting strength, and appearance of Hanji. These results confirmed that radiation treatment disinfects the Korean traditional paper efficiently without changing its properties and that this treatment could be used to prevent the damage of Korean ancient archives by molds and fungi.     

Advanced oxidation of aromatic VOCs using a pilot system with electron beam–catalyst coupling

The decomposition of volatile organic compounds (VOCs) using a pilot system of electron beam (EB)–catalyst coupling was investigated. Two aromatic VOCs, toluene (1800 ppmC) and o-xylene (1500 ppmC), were irradiated with a dose range of 0–10 kGy at room temperature. The removal efficiencies for toluene and o-xylene were 92.4% and 94.5%, respectively, under a 10 kGy absorbed dose condition, which were higher than the results of 45.7% and 52.3% when EB-only was used, respectively. The CO₂ selectivity approached 100% for both toluene and o-xylene using the EB-catalyst coupling system, while the concentrations of O₃ formed were 0.02 ppm (toluene) and 0.003 ppm (o-xylene) at 10 kGy. The aerosol concentration was also measured as 43.2 μg/m³ (toluene) and 53.4 μg/m³ (o-xylene) at 10 kGy absorbed dose.     

Electron beam irradiation of fluoropolymers containing polyethers

A highly fluorinated monomer, 1,3-bis(1,1,1,3,3,3-hexafluoro-2-pentafluorophenyl methoxy-2-propyl)benzene (12F-FBE) was polymerized with some diphenols by polycondensation and then was electron beam irradiated between 100 and 1000 kGy to determine degradation radiochemistry yield (G_s) by gel permeation chromatography (GPC). The samples were characterized after irradiation by DSC, FTIR, and nuclear magnetic resonance (NMR). The fluoropolymers show apparent degradation in mechanical properties at 300 kGy, except 12F-FBE polymerized with biphenol and bisphenol A, when they did not show any apparent physical change up to 300 kGy; and continue to be flexible and transparent, with a radiochemical yield scission (G_s) of 0.75, 0.53, 0.88, and 0.38 for 12F-FBE/SDL aliphatic, 12F-FBE/biphenol, 12F-FBE/bisphenol A, and 12F-FBE/bisphenol O, respectively. The number average molecular weights for three of the polymers decrease upon 1000 kGy irradiation to 10% of their original values; however, the polymer from bisphenol A is much more stable and its M_n decreases to only 24% of original.     

Aflatoxins and ochratoxin a reduction in black and white pepper by gamma radiation

Irradiation is an important means of decontamination of food commodities, especially spices. The aim of the current study was to investigate the efficacy of gamma radiation (⁶⁰Co) for decontaminating ochratoxin A (OTA) and aflatoxins B₁ (AFB₁), B₂ (AFB₂), G₁ (AFG₁) and G₂ (AFG₂) residues in artificially contaminated black and white pepper samples. The moisture content of the pepper samples was set at 12% or 18%, and the applied gamma dose ranged from 5 to 30 kGy. Mycotoxin levels were determined by high-performance liquid chromatography (HPLC) after immunoaffinity column (IAC) chromatography. Both the gamma irradiation dose and moisture content showed significant effects (P<0.05) on mycotoxin reduction. The maximum toxin reductions, found at 18% moisture content and 30 kGy, were 55.2%, 50.6%, 39.2%, 47.7% and 42.9% for OTA, AFB1, AFB2, AFG1 and AFG2, respectively.     

Effect of gamma irradiation on microbial decontamination,and chemical and sensory characteristic of lycium fruit

Lycium fruit, popular traditional Chinese medicine and food supplement generally is ingested uncooked, was exposed to several doses of gamma irradiation (0–14 kGy) to evaluate decontamination efficiency, changes in chemical composition, and changes in sensory characteristic. In this study, lycium fruit specimens contained microbial counts of 3.1×10³–1.7×10⁵ CFU/g and 14 kGy was sufficient for microbial decontamination. Before irradiation, the main microbe isolated from lycium fruit was identified as a strain of yeast, Cryptococcus laurentii. After 10 kGy of irradiation, a Gram-positive spore-forming bacterium, Bacillus cereus, was the only survivor. The first 90% reduction (LD₉₀) of C. laurentii and B. cereus was approximately 0.6 and 6.5 kGy, respectively, the D₁₀ doses of C. laurentii and B. cereus was approximately 0.6 and 1.7 kGy, respectively. After 14 kGy irradiation, except the vitamin C content, other chemical composition (e.g., crude protein, β-carotene, riboflavin, fructose, etc.) and the sensory characteristic of lycium fruit specimens did not have significant changes. In conclusion, 14 kGy is the optimal decontamination dose for lycium fruit for retention of its sensory quality and extension of shelf life.     

Radiation-induced crosslinking of polyacrylonitrile fibers and the subsequent regulative effect on the preoxidation process

To investigate the radiation effect on polyacrylonitrile (PAN) fibers as well as on the preoxidation process, PAN fibers were irradiated by γ-rays at room temperature at 50–500 kGy in vacuum and then were thermally oxidized in air. Gel fraction determination indicated that γ irradiation led to the predominant crosslinking of PAN fibers, with G values (the number of event per 100 eV absorbed) of G(X)=0.28 and G(S)=0.16 for chain crosslinking and scission, respectively. It was found that irradiation caused a slight change in the crystal structure and tensile strength at low dose. Radiation led to a reduction of the onset temperature of cyclization reaction and moderated the exothermic behavior. The density of the PAN fibers after thermal oxidation was used to evaluate the preoxidation extent. It was proven that radiation could significantly accelerate the preoxidation process and consequently shortened the preoxidation time. Radiation crosslinking may have potential application in the production of PAN-based carbon fibers.     

Gamma radiation influence on technological characteristics of wheat flour

This study aimed at determining the influence of gamma radiation on technological characteristics of wheat (Triticum sativum) flour and physical properties of pan breads made with this flour. The bread formulation included wheat flour, water, milk, salt, sugar, yeast and butter. The α-amylase activity of wheat flour irradiated with 1, 3 and 9 kGy in a Gammacell 220 (AECL), one day, five days and one month after irradiation was evaluated. Deformation force, height and weight of breads prepared with the irradiated flour were also determined. The enzymatic activity increased—reduction of falling number time—as radiation dose increased, their values being 397 s (0 kGy), 388 s (1 kGy), 343 s (3 kGy) and 293 s (9 kGy) respectively, remaining almost constant over the period of one month. Pan breads prepared with irradiated wheat flour showed increased weight. Texture analysis showed that bread made of irradiated flour presented an increase in maximum deformation force. The results indicate that wheat flour ionizing radiation processing may confer increased enzymatic activity on bread making and depending on the irradiation dose, an increase in weight, height and deformation force parameters of pan breads made of it.     

Effect of combined radiation and NaOCl/ultrasonication on reduction of Bacillus cereus spores in rice

In this study, ionizing radiation in combination with sodium hypochlorite (NaOCl) and ultrasonication (US) was examined for its effectiveness in reducing Bacillus cereus F4810/72 spores in raw rice. We also evaluated whether the combined processing would produce synergistic effects compared to the individual treatments. The concentration of the initial B. cereus spore was approximately 2.9 log₁₀ CFU/g. After 0.1, 0.2 and 0.3 kGy irradiation treatment, spore populations were reduced by 1.3, 1.4 and 1.6 log₁₀ CFU/g, respectively. In the case of combined gamma irradiation and NaOCl/US treatment, the reduction was higher than those of each single treatment. The combined treatment of 0.1, 0.2 and 0.3 kGy and NaOCl (600–1000 ppm)/US (5–20 min) completely destroyed the spores in raw rice while the spores were not completely destroyed in the control treatment (0 kGy). These results indicated that it could be more effective to combine NaOCl with low dose gamma irradiation than high dose (concentration) of individual disinfection treatment to destroy B. cereus spores in food such as raw rice.     

The effects of ionizing irradiation on Salmonella inoculated on almonds and changes in sensory properties

The goal of this study was to test the efficacy of irradiation on destroying Salmonella on raw almonds and evaluating the resultant sensory changes in the almonds. Raw almonds inoculated with various strains of Salmonella were irradiated at 5 dose levels up to 3 kGy and the D value was determined. The strain SEPT30 was the most resistant strain with a D value of 1.25 kGy indicating that a 4 log CFU/g reduction would require a dose of 5.0 kGy. Irradiation at 2.98 and 5.25 kGy induced significant sensory changes in almond nuts as manifested by intensity of chemical/metallic/rancid flavor ranked by a trained panel. A consumer panel found that samples treated with 5.25 kGy irradiation rendered the almonds unacceptable. Thus, irradiation by itself is unlikely to be a feasible method to eliminate Salmonella from raw almonds.