EPR in non-doped irradiated polyacetylene

The influence of -irradiation on the paramagnetic properties of non-doped polyacetylene at low and high radiation doses has been studied and summarized. The dependence of the EPR spectra on the radiation dose in irradiated polyacetylene has been measured. No essential changes of the spin mobility as a consequence of irradiation were observed. Our measurements of spin concentration confirm the high resistivity of non-doped polyacetylene to radiation.     

Regularities in gas formation at γ-radiolysis of coals and petroleum residues

The regularities of H₂, CO, and CH₄ formation at -radiolysis of brown coals, hard coal, petroleum-bituminous rock, petroleum bitumen, tar, and petroleum residue have been studied at room temperature, absorbed radiation dose 30–2400 kGy, dose intensity 1.6–21.1 kGy/h. The radiation-chemical yields of these gases were found to constitute °G^r0.005–0.07 mol/100 eV for coals, and °G^r0.3–0.6 mol/100 eV for petroleum residues.     

On the radiation-induced polyaddition of bisperfluoroisopropenyl terephthalate with 1,4-dioxane

Radical polyaddition of bis(α-trifluoromethyl-β,β-difluorovinyl)terephthalate [CF₂C(CF₃)OCOC₆H₄COOC(CF₃)CF₂] (BFP) with 1,4-dioxane (DOX) afforded higher molecular weight polymers under γ-rays radiation from a source when compared to those yielded by benzoyl peroxide initiation. More detailed study on the radiation-induced polyaddition of BFP with DOX and optimization of the reaction conditions were carried out. It was necessary to irradiate with doses of 2000, 1500, and 750 kGy, to obtain quantitative conversion of BFP at the feed molar ratios DOX/BFP of 8.0, 16, and 32, respectively. Step-growth polymerization mechanism was suggested by the measurements of molecular weights of the polymers obtained with several irradiation doses. It was concluded that the molecular weight of the polymer could be controlled by the feed molar ratio of DOX/BFP and irradiation doses. The steep increase of molecular weight was observed at the feed molar ratio of DOX/BFP of 8.0 with the irradiation doses above 2000 kGy and the polymer with the weight-average molecular weight of 2.36×10⁴ was obtained with the dose of 3000 kGy. The reaction between polymers might take place after the quantitative conversion of BFP. Radiation-induced radical polyaddition mechanism of BFP with DOX was proposed.     

CPS K 843 Radiation-induced crosslinking: Effect on structure of polyethylene

Branched polyethylene irradiated (0–400 Mrad) with a Co⁶⁰ source at room temperature under vacuum was studied by density, wide- and small-angle X-ray scattering (WAXS and SAXS) measurements. The radiation effects on the structure of bulk, branched polyethylene are quite similar to those observed by others on single crystals or oriented preparations. These effects include changes in bulk density, crystallinity(w _c orv _c) and¯d ₁₀₀ and¯d ₂₀₀ spacings as a function of irradiation. A decrease in crystallinity is seen to begin at radiation dose 100 Mrad whereas lattice expansion indicating onset of an orthorhombic-hexagonal transition can begin as low as 10 Mrads. The decrease in crystallinity can be attributed to additional lattice distortions primarily introduced by the crosslinks occurring at the lateral grain boundaries, while lattice expansion can be associated with the same crosslinking mechanism which begins at the defects both within the crystals as well as those outside the crystals at the lateral grain boundaries. Strong evidence for a primary crosslinking-at-the-defects mechanism has also come from _c and _a data obtained in this study as a function of radiation dose. The same data have also led to an excellent correspondence between the measured density crystallinityv _c and the measured WAXS crystallinityw _c. Without consideration of the effects of crosslinks on _c and _a one would have obtained a divergence of the two crystallinities, especially at radiation doses greater than 100 Mrads.Dedicated Prof. Dr. R. Bonart on the occasion of his 60^th birthday     

Differential scanning calorimetric analysis of irradiated polytetrafluoroethylene films

Crystalline content of polytetrafluoroethylene (PTFE) can be substantially increased by electron beam irradiation. These changes as a function of radiation dose were examined in PTFE films by differential scanning calorimetry (DSC). Surprisingly small radiation doses (<0.002 Mrad) were found to cause a, fairly substantial increase (25%) in their heat of fusion. Variations in the heat of fusion and the peak melting temperature of PTFE films with radiation dose, in the range of 0.0017 to 16 Mrad, are examined.     

Mechanical properties of poly(vinyl methyl ether) hydrogels below and above their volume phase transition

The mechanical properties of radiation cross-linked poly(vinyl methyl ether) hydrogels below and above the volume phase transition (VPT) under isobar conditions were studied. The viscoelastic properties as a function of radiation dose, radiation source and polymer concentration at the state of irradiation were examined. Increased radiation doses led to higher cross-linking densities and higher moduli. Hydrogels irradiated with -rays were much harder than those obtained with electron beam irradiation at the same radiation dose. It was found that the modulus strongly increased by up to 1 order of magnitude at a temperature of the VPT of about 37 °C. In the collapsed state at temperatures well above the VPT a frequency dependence of the E() moduli in the range 0.1–22 Hz was detected, indicating viscoelastic behavior. To study the influence of solvent quality on the modulus of the hydrogels, rheological measurements were performed in water, 2-propanol and cyclohexane. A scaling exponent for the modulus according to de Gennes (G^2.25) was not found. Possible reasons for deviations (G^3.54) on poly(vinyl methyl ether) hydrogels were discussed in the context of deviations from ideal networks.     

Recycling of the used automotive lubricating oil by ionizing radiation process

The recycling process of the used mineral oils has been gaining a very important gap in the context of environmental protection. Among mineral oils from petroleum, the lubricating oils are not entirely consumed during their use; therefore, it is necessary to apply a treatment for recuperation seeking their reuse. Moreover, the environmental legislation of countries does not allow their discard in any type of soils, rivers, lakes, oceans or sewerage systems.The conventional treatment has shown certain difficulties in the recuperation process for used oils. The ionizing radiation process is renowned in the industrial effluents treatments due to its high efficiency in the degradation of organic compounds and in the removal of metals by the action of OH, H and e_aq radicals.In this work, used automotive lubricating oil was treated by the ionizing radiation process for metal removal and degradation of organic compounds. The samples were irradiated with 100 and 200 kGy irradiation doses. Determination of the elements Mg, Al, P, S, Cl, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Se, Mo, Nb, Cd, Sn, Ba, Bi and Pb, before and after the irradiation, was done by X-ray fluorescence technique and the organic profile was obtained by infrared spectroscopy.     

Advancements in accuracy of the alanine dosimetry system. Part 2. The influence of the irradiation temperature

Systematic measurements of the temperature coefficient for alanine electron paramagnetic resonance (EPR) response have been performed for irradiation in the temperature range (10–50)°C and in the absorbed dose range (1–100) kGy at the dose rate 9.5 kGy/h. During the ⁶⁰Co-ray irradiation, -l-alanine dosimeters were kept in a sealed aluminum holder that provided an effective heat exchange with the temperature-controlled environment. The time between the irradiation and signal measurements was standardized, and a reference sample fixed in the resonant cavity was used to correct the signals for small variations in the spectrometer sensitivity. The temperature coefficient for each dose was determined from approximately 30 experimental points processed by the weighted least-squares technique after the necessary statistical tests were done. The temperature coefficients thus determined were considerably lower than previously reported. The dose dependence of the temperature coefficient features a minimum at (20–30) kGy (about 0.135%/K) with higher values at 1 kGy (0.17%/K) and at 100 kGy ((0.175–0.19) %/K). With the exception of very high doses, no significant distinction was found between the temperature coefficients of Bruker and NIST dosimeters, which differ in shape and binder content.     

Parameter evaluation,kinetics, and energy consumption for Cr(VI) photocatalytic reduction under mild conditions

Photocatalytic reduction of hexavalent chromium, Cr(VI), ions in aqueous solutions was studied using remarkably low doses of commercial titania nanoparticles at conventional temperature range of 15–45 °C. A direct imposed irradiation photo-reactor, equipped with ultrasonic source was utilized. Design of experiments, correlating and process optimization were performed using central composite design of response surface methodology. Accordingly, a reduced quadratic expression was developed to predict the reduction efficiency as a function of involved parameters. Analysis of variance shows the agreement of the provided model with experimental data. At the found optimum conditions of titania concentration: 33.1 mg/L, pH: 2.50, temperature: 36 °C and reaction time: 120 min; 81 % efficiency was achieved for reduction of initial 5 mg/L of Cr(VI). The process revealed proceeding through parallel branches of photolysis and photocatalysis, and only UV irradiation was promising for reaction progress. Based on differential method of analysis, the relevant kinetic model, jointed with the Arrhenius equation, was introduced. Energy (electrical and thermal) consumption evaluations revealed that treatment at higher temperatures provides a significant cost reduction. Meantime, a criterion was proposed for a more valid assessment of photocatalytic processes.     

Effect of gamma-radiation on the Sn(II) content,radiochemical purity,in-vitro stability and biological distribution of some99mTc-labelled freeze dried kits

Gamma-irradiation can be used for the sterilization of some^99mTc-labelled freeze dried kits. In connection with this the effect of -radiation on Sn(II) content, radiochemical purity,in-vitro stability and biological distribution of some currently used^99mTc-labelled kits has been investigated. For irradiation the certain radiation sterilization doses (25 and 50 kGy) were used. A variable decrease of Sn(II) content was observed in all -irradiated kits. The losses are in the order of 10–25% compared with the Sn(II) content of original ones. The colour of the irradiated kits did not changed except DTPA which developed yellow colour after irradiation. For the irradiated and original kits nearly the same pH were found. The irradiated kits seemed to undergo partial decomposition or chemical alteration which led to some deviation of the biological distribution of them.     

Effect of60Co radiation on some chemical changes in potato starch pastes and gels

The effect of ionizing radiation /-⁶⁰Co/ on some chemical changes in potato starch pastes stored for 14 d at 4–5 °C and prepared from the starch irradiated in the range of doses 1.5–15 kGy has been studied. It was found that along with the increase in the doses used, the viscosity of pastes as well as the pH of solutions decreased. On the other hand, the increase in the concentration of reducing sugars was observed. The retrogradation of pastes was found to be inhibited by increasing doses of radiation pointing out that ionizing radiation has a favourable effect on their stability during the time of storage.     

Alteration of yeast activity by gamma radiation

Yeast is an important component in microbe based industrial technologies. Due to the techno-economic reasons, the fermentation technique has acquired renewed interest. The effect of -radiation on the fermentation reaction has been investigated. The studies show that exposure of the fermentation mixture to -radiation at 5 kGy enhance alcohol production, whereas irradiation at higher doses, viz., 10 kGy and 25 kGy caused a considerable reduction in the alcohol yield. Therefore, low dose irradiation of fermentation mixtures can be applied for increasing the alcohol production by about 25%.     

The effects of gamma rays upon monohydrated and anhydrous asparagine: a DSC study in sealed pans

Non-irradiated and gamma irradiated monohydrated (l Asn·H₂O) and anhydrous (l Asn) asparagines, in solid state, were studied by means of DSC. The samples were irradiated at room temperature with gamma radiations using a ¹³⁷Cs source. The exposure doses ranged between 1 and 10 kGy. All samples were scanned in sealed pans, from room temperature to a temperature beyond the melting point. The DSC scans of l Asn·H₂O samples in sealed crucibles revealed the presence of two dehydration processes and one of decomposition and only decomposition in the case of l Asn. The influence of gamma irradiation consisted in decreasing the enthalpy of dehydration and of decomposition. A decomposition mechanism is proposed.     

Radiolysis of aqueous-ethanolic solution of tryptophan

The effect of ethanol on radiation stability of tryptophan during -irradiation of its aqueous solutions was investigated. In comparison with radiation losses of tryptophan irradiated in pure water, the losses in aqueous-ethanolic solutions are considerably higher and they increase with increasing ethanol concentration. Basic radiation products of tryptophan formed on irradiation of its aqueous-ethanolic solutions in consequence of the reaction of tryptophan with acetaldehyde as the main product of radiolysis of ethanol were followed by paper electrophoresis.     

Blends of normal high density and ultra-high molecular weight polyethylene, γ irradiated at a low dose

The kinetics of a nonisothermal crystallization and melting of irradiated with dose of 6 Mrad blends of an ultra-high molecular-weight polyethylene (UHMWPE) and a high-density polyethylene with normal molecular weight (NMWPE) is investigated by means of DSC. The blends have been prepared at temperature below the flow temperature of UHMWPE: The enthalpies of melting of the polyethylenes increase, while those of their blends decrease after irradiation. The enthalpies of crystallization of the pure polyethylenes are higher, while those of their blends almost do not change or are a bit higher after irradiation. The rates of a nonisothermal crystallization and melting of the polyethylenes increase, while those of the polyethylenes in the blends decrease after irradiation. Thermomechanical measurements under constant load in wide-temperature interval of irradiated polyethylenes and their blends have been made. A high-elastic plateau in viscous-liquid state is established on the thermomechanical curves of UHMWPE, and the blends with high content of UHMWPE. On the basis of results obtained assumptions have been made about the processes taking place in the blends under the action of irradiation, as well as about the character of the mutual influence between the components in the process of irradiation.     

Influence of electron beam pre-irradiation on the thermal behaviors of polyacrylonitrile

Thermal treatment of polyacrylonitrile pre-irradiated by electron beam was performed to investigate the radiation effects on thermally activated reactions. Thermal properties were characterized by differential scanning calorimetry and thermogravimetric analyses. Pre-irradiation lowers the onset temperature of reactions and alleviated the heat evolution process. Char yields (800 °C) of polyacrylonitrile increase significantly with increasing irradiation dose. FTIR was used to monitor the thermal reaction. The results reveal that the thermal reactions can be regulated by pre-irradiation dose. FTIR and UV-visible absorption spectra of pre-irradiation polyacrylonitrile illustrate the formation of -HCN-NCH- conjugation across the polymeric chains as a function of dose, which could improve the thermal behaviors of polyacrylonitrile.     

Structural aspects of the radiation modification of the dielectric properties of polyolefins

The effects of crystallization conditions and supermolecular structure on the processes of radical formation and changes in the dielectric (tan; ) and strength (E _st) properties of LDPE, HDPE, and PP under exposure to -radiation were studied. It was found that polyolefin specimens with a high crystallinity exhibited an enhanced electric strength, radiation stability, and a high yield of quasi-stable radicals at 293 K. It was assumed that a possible mechanism of the electric strengthening of PE and PP by their radiation modification (at radiation doses of 30–50 and to 5–6 Mrad, respectively) consists in a reaction of the type R^· + e^– R^–, the capture of trapped electrons by quasi-stable radicals.__________Translated from Khimiya Vysokikh Energii, Vol. 39, No. 3, 2005, pp. 176–182.Original Russian Text Copyright © 2005 by Magerramov, Dashdamirov.     

A comparative pulse radiolysis study on DNA's of various molecular masses under anoxic and salt-free conditions,based on conductivity measurements

OH radical attack on various molecular mass DNA molecules in aqueous solutions in O₂-free, N₂O-saturated solutions at room temperature and with lower doses have been studied. The two phenomena, resulting in a negative and a positive conductivity build-up under a short electron pulse (0.4–1 s), are discussed in the light of their dependence on the pH, dose rate, concentration and temperature. The positive conductivity build-up observed at lower concentrations of DNA and higher doses is attributed to a degradation process resulting in ssb formation and liberation of counter ions, whereas the negative conductivity build-up at the higher concentrations of DNA and relatively lower doses is attributed to an intermolecular reaction, resulting in cross-links and condensation of the counter ions. The dependence of the applied potential (20–100 V) on the rate constant and conductivity build-up for both processes are shown.     

Study of effects of γ-irradiation on Tuffak polycarbonate track detector by TG

Effects induced by r-irradiation in the dose range of 0–10 Mrad on Tuffak polycarbonate track detector films have been studied by thermogravimetry (TG). The samples were irradiated with ⁶⁰Co r-rays for doses of 3, 5 and 10 Mrad. The TG studies indicate that unirradiated and the r-irradiated samples degrade in two steps. The kinetics of the two steps of degradation was also evaluated from the TG curves. Irradiation enhances the degradation rate and the effect increases further with increasing radiation dose. The activation energy values calculated for all the steps decrease on irradiation. A linear relationship observed between the decrease in activation energy and the dose received by the sample suggests the possibility of the use of Tuffak polycarbonate detector as r dosimeter.The authors are thankful to Dr. V. K. Manchanda, Head, Radiochemistry Division, BARC for his encouragement and support during this work.     

Structure of single-molecule single crystals of isotactic polystyrene and their radiation resistance

The structure of single-molecule single crystals of isotactic polystyrene (i-PS) was investigated by electron diffraction (ED). The nanoscale single-molecule single crystals were found to be more resistant to electron irradiation when compared to the larger crystals of many molecules, as indicated by both observation of ED and high-resolution electron microscopy with increasing radiation dose. It is proposed that since the single-molecule single crystals are very small, the secondary electrons escape more frequently from the crystal so that the radiation damage is reduced. Lattice imaging was achieved at room temperature in the case of single-molecule single crystals because of their stability to electron irradiation. Published 1998 John Wiley & Sons, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

J Polym Sci B: Polym Phys 36 : 105–112, 1998