辐照剂量率对明胶自由基和性能的影响

为探讨剂量率对明胶分子辐照分解的影响机理,采用电子自旋共振(ESR)、凝胶渗透色谱(GPC)等检测技术分析明胶经剂量率为60、480Gy/min 60 Co以及剂量率为12 000Gy/min加速器辐照0~32kGy剂量后,自由基特征、明胶性能与剂量率的关系。结果表明,未辐照明胶ESR信号微弱,三种辐照方式处理后的明胶均呈现相似的ESR双峰特征;相同吸收剂量下,明胶自由基信号强度由大到小依次为60Gy/min 60 Co辐照明胶、480Gy/min 60 Co辐照明胶和12 000Gy/min加速器辐照明胶;60 Co辐照后自由基信号强度(y)与剂量(x)的线性关系为y=26.983x2+1 641.8x-205.69;辐照明胶特性黏度、平均相对分子质量、凝胶强度和断裂伸长率由高到低依次为480Gy/min 60 Co辐照明胶、12 000Gy/min加速器辐照明胶和60Gy/min 60 Co辐照明胶。可见,高剂量率辐照可能减少明胶中有效长寿命自由基的含量,从而抑制明胶辐照灭菌中性能的劣变。     

Spectroscopic analysis and mechanical properties of electron beam irradiated polypropylene/epoxidized natural rubber (PP/ENR) polymer blends

Polymer blends based on different ratios of polypropylene (PP) and epoxidized natural rubber (ENR) were prepared by melt extrusion into sheets. The PP/ENR blends were exposed to various dose of accelerated electrons. The formation of free radicals during and after electron beam irradiation was illustrated by electron spin resonance (ESR). Also, the effect of electron beam irradiation on the mechanical and structural morphology was investigated by stress-strain behavior and scanning electron microscope (SEM). The ESR spectra indicated the formation of alkyl and allyl radicals during electron beam irradiation and peroxyl radicals during the post effect. The rate of radical decay was found to be second-order kinetics. The improvement in mechanical properties and structural morphology was confirmed to be due to the effect of electron beam irradiation.     

Physical and chemical response of 145 MeV Ne ion irradiated polymethylmethacrylate (PMMA) polymer

Characterization of ion induced modifications in the physical, chemical and structural properties of polymethylmethacrylate (PMMA) polymer induced by 145 MeV Ne⁶⁺ ions has been carried out by FTIR, UV-Visible, Differential scanning calorimetry (DSC) and X-ray diffraction. Heavy ion irradiation was carried out under a vacuum of ∼10⁻⁶ torr at Variable Energy Cyclotron Centre, Kolkata, India using a low beam current (∼15 nA). Ion fluences of 10¹⁰, 10¹¹, 10¹², 10¹³ ions/cm² were used. The optical band gap (E_g), calculated from the absorption edge of the UV-Vis spectra of these films in 200-800 nm region varied from 2.167 eV to 1.512 eV for virgin and irradiated samples. In FTIR spectra appreciable changes have been observed after irradiation, indicating the molecular fragmentation, cross-linking, formation of unsaturated groups and free radicals. DSC thermograms give information about the thermal stability and type of thermal reactions (exothermic/endothermic) on the application of heat to the polymer. XRD analyses show slight shift of peak position and significant changes in peak intensity. XRD results show a decrease of ∼4.12% in crystallite size of irradiated sample at the higher fluence of 10¹² ions/cm².     

Properties of radicals created by γ-ray irradiation of silk fabrics

The properties of radicals from γ-ray irradiated silk fabrics were studied by electron spin resonance method (ESR). The ESR spectra of silk fabrics irradiated in N2 showed a doublet at room temperature. The doublet became a singlet at g=2.0057 after placing the sample in air for 24 hours. This can be explained by formation of peroxide radicals. The radical concentration of the irradiated silk fabric and the decay rate of radicals are significantly affected by irradiation conditions, which include the absorbed dose, atmosphere, and water content of the silk fabric samples. However, no dose rate effect on the radical concentration was observed. The results are of help in our practice of property modification of silk products by radiation graft copolymerization.     

Measurements of free radical in vitamin E-doped ultra-high molecular weight polyethylene: Dependence on materials processing and irradiation environments

Ultra-high molecular weight polyethylene (UHMWPE), doped with vitamin E (α-tocopherol (α-T)), was irradiated with gamma rays in nitrogen (N₂) or air, and the resulting free radicals were detected in air using an electron spin resonance (ESR) technique. Two groups of samples were investigated. In one group, samples were prepared from blends of α-T (20 wt%) and UHMWPE powder (PPE-α-T) and, in the other, from compression molded blocks (CMPE-α-T). The CMPE-α-T blocks contained 0% (control), 0.5%, 1.0%, 10.0%, 15.0%, 20.0% and 25.0% α-T by weight.When irradiation was performed in air, the ESR spectrum of powder samples showed the presence of only vitamin E radical (tocopheroxyl, α-T-O), and there was no detectable signal due to PE radicals (alkyl/allyl). Most likely, all PE radicals were quenched by vitamin E during irradiation in air. However, when irradiation was performed in N₂, composite ESR spectra showed the presence of both PE and α-T-O radicals. Compared to the control (PPE, 0% α-T) PE radicals in PPE-20% α-T were found to be significantly reduced or quenched by α-T. The presence of α-T in powder samples, however, did not affect the long-term (71 days in this study) oxidation behavior of the PE radicals.Compression molded samples, with and without α-T, produced identical ESR spectra irrespective of their irradiation environment N₂ or air. However, radical concentration, measured immediately after irradiation, was found to be an order of magnitude less in CMPE-α-T than in the control (CMPE-0% α-T). They also evidenced identical structural changes in the respective ESR spectra during subsequent oxidation for 24 days in open air. These observations suggest that α-T can effectively quench a significant fraction of PE radicals during irradiation, but has no measurable effect on subsequent reactions. No significant difference was found in the ESR spectra of samples containing different α-T concentration.     

稳定剂对PVC辐射变色性能影响的研究

采用^60Coγ射线对聚氯乙烯（Polyvinyl chloride,PVC）／稳定剂复合体系进行辐照。研究了不同稳定剂对PVC辐射变色．陛能的影响;并采用紫外光谱仪（Ultraviolet spectrometer,UV）和傅立叶变换红外光谱仪（Fouriertransform infrared spectrometer,FT—IR）对其结构进行了表征。结果表明,硬脂酸钙（Calcium stearate,CaSt）,硬脂酸锌（Zinc stearate,ZnSt）复合稳定剂、环氧大豆油、亚磷酸酯和光稳定剂的加入可提高PVC耐辐射变色性能。亚磷酸酯的加入可提高PVC的耐辐射氧化性能。在相同吸收剂量下,添加硬脂酸钙／硬脂酸锌复合稳定剂的PVC具有优异的耐辐射变色性能。在吸收剂量为30kGy时,CaSt：Znst为4：1的PVC黄变指数变化率为8．3％。PVC经辐照后主要形成3至4个共轭双键的不饱和酮或共轭烯烃结构。     

Irradiation/temperature synergy effects on degradation and ageing of chlorosulphonated polyethylene

Chlorosulphonated polyethylene (CSPE) irradiated with 2.5 MeV β particles has been studied by means of FTIR spectroscopy. The effects of dose rate, temperature and atmosphere on molecular changes were investigated. The main modifications were loss of sulphonyl chloride groups, formation of trans-vinylene groups and in the presence of oxygen formation of oxidation products. Results were discussed in terms of interspur and intraspur reactions.     

Some characteristics of radiolysis under the influence of a pulsed beam of fast electrons

The purpose of this paper is to study the main characteristics of radiolysis associated with the use of electron pulse accelerators. On the basis of a typical mechanism of the chemical reactions of free radicals formed under the influence of a pulsed fast electron beam, the mean stationary concentration of free radicals [R]_st is calculated as a function of the duty factor q of the electron current pulses. The calculation is carried out for various powers, corresponding to various rates of formation of the free radicals, various current pulse widths, and various free radical loss constants for reactions of the first and second orders. Graphs of [R]_st as a function of q are presented.Translated from Atomnaya Énergiya, Vol. 17, No. 5, pp. 393–400, November, 1964     

High dose radiolysis of aqueous solutions of chloromethanes: Importance in the storage of radioactive organic wastes

The radiolysis of aqueous solutions of chloromethanes (dichloromethane, CH₂Cl₂; chloroform, CHCl₃; and carbon tetrachloride, CCl₄) was performed with γ-rays to doses sufficient to completely decompose the solute in order to estimate the effects of radiation on the long-term storage of mixed waste in enclosed containers. One of the main relevant products was the inorganic chloride anion, which increased in concentration with increasing radiation dose due to the reactions of radiolytic decomposition products of water with the chloromethane. The pH of the solutions was observed to decrease with irradiation due to the formation of H₃O⁺ as the counter ion to Cl⁻, i.e. the main radiolytic decomposition product is hydrochloric acid. Polymer formation was observed in aerated solutions as a precipitate while deaerated solutions exhibited a slight turbidity.     

Recovery behavior in neutron irradiated β-sic

Reaction sintered β-SiC specimens were neutron-irradiated in the fast breeder reactors, JOYO, Rapsodie and Phenix, at temperatures around 430 to 550°C to a fluence from 4.0 × 10²³to 1.0 × 10²⁷ n/m² (E > 0.1 MeV). A change in the specimen length was accurately measured using a conventional micrometer after isochronal annealing at high temperatures. The specimens irradiated to a neutron fluence of about 10²⁵ n/m² showed a larger dimensional change on anneals than those irradiated to a fluence of 10²⁶ n/m². A change in lattice parameters by annealing was also measured. It showed that the temperature dependence is nearby identical to that of the macroscopic length change. The transmission electron microscopic study of the neutron-irradiated β-SiC specimens showed the formation of irradiation induced defects, considered to be dislocation loops. An increase in the neutron fluence resulted in the growth of the dislocation loops. The dislocation loops in strongly irradiated β-SiC interacted with each other, forming the heavily disturbed dislocation structure. The effect of the neutron fluence on the microstructure and dimendional change was discussed.     

ESR signals from silk fabrics irradiated by UV -rays

ESR studies were done on UV-ray irradiated silk fabric samples at room temperature. Different types of UV lamps were used and similar ESR signals were observed. The results indicate that UV-rays can produce free radicals for graft-copolymerization of monomer onto silk fibers without external additives or co additives, Also, radicals in silk fabrics irradiated by UV-rays are purer than that irradiated by γ-rays. The study suggests that UV-lights may be a better tool to improve properties of silk fabrics by grafting monomers onto the polymer chains.     

Hydrogen production in gamma radiolysis of the mixture of mordenite and seawater

Hydrogen production by γ-radiolysis of the mixture of mordenite, a zeolite mineral, and seawater was studied in order to provide basic points of view for the influences of zeolite minerals, of the salts in seawater, and of rise in temperature on the hydrogen production by the radiolysis of water. These influences are required to be considered in the evaluation of the hydrogen production from residual water in the waste zeolite adsorbents generated in Fukushima Dai-ichi Nuclear Power Station. As the influence of the mordenite, an additional production of hydrogen besides the hydrogen production by the radiolysis of water was observed. The additional hydrogen can be interpreted as the hydrogen production induced by the absorbed energy of the mordenite at the yield of 2.3×10^?8 mol/J. The influence of the salts was observed as increase of the hydrogen production. The influence of the salts can be attributed to the reactions of bromide and chloride ions inhibiting the reaction of hydrogen with hydroxyl radical. The influence of the rise in temperature was not significantly observed up to 60°C in the mixture with seawater. The results show that the additional production of hydrogen due to the mordenite had little temperature dependence.     

Effect of ion irradiation on the M-Nitroaniline single crystals

In this report, the modifications in the structural, optical, mechanical, electrical and nonlinear properties of 70 MeV Li³⁺ and 100 MeV Ag⁷⁺ ion irradiated M-Nitroaniline single crystals are studied. The irradiation induced defect structures at the crystal surface which becomes more prominent at higher irradiation fluences, leading to the enhancement in the optical absorption behaviour and the nonlinear property of the irradiated crystals. The mechanism leading to the enhanced nonlinearity and the blue shift of the irradiated M-NA crystals has been discussed.     

Synthesis of nanodimensional TiO2 thin films using energetic ion beam

Nanophases of TiO₂ are achieved by irradiating polycrystalline thin films of TiO₂ by 100 MeV Au ion beam at varying fluence. The surface morphology of pristine and irradiated films is studied by atomic force microscopy (AFM). Phase of the film before and after irradiation is identified by glancing angle X-ray diffraction (GAXRD). The blue shift observed in UV-vis absorption edge of the irradiated films indicates nanostructure formation. Electron spin resonance (ESR) studies are carried out to identify defects created by the irradiation. The nanocrystallisation induced by SHI irradiation in polycrystalline thin films is studied.     

On the impact of reactive solutes on radiation induced oxidative dissolution of UO2

The impact of 2-propanol (100 mM), NaCl (0.1 - 2 M) and Fe(II)(aq) (10 μM) on the radiation induced oxidative dissolution of UO₂ is investigated experimentally by γ-irradiating a UO₂ pellet immersed in aqueous solution containing 10 mM together with one of the studied solutes and measure the U(VI) concentration in solution as a function of irradiation time. The solution was saturated with one of the following gases; Air, N₂O, inert gas (N₂ or Ar) in order to vary the experimental conditions and/or avoid the influence of oxygen. The results show that, in the presence of oxygen, 2 M chloride decrease the rate of UO₂ dissolution whereas the dissolution rate increases somewhat in the presence of 100 mM 2-propanol. Under oxygen-free conditions both 2 M chloride, 100 mM 2-propanol and 10 μM Fe(II)(aq) decrease the rate of UO₂ dissolution. The trends in dissolution rates were reproduced by calculations based on previously determined rate constants for UO₂ oxidation and oxidant concentrations obtained from numerical simulation of radiolysis in the corresponding homogeneous systems (taking reactions between the different solutes and the products of water radiolysis as well as changes in oxygen solubility into account). However, the results indicate that we cannot fully account for the G-values in 2 M chloride solution or all reactions involving Cl⁻ in the aqueous phase. This calls for further studies of the chloride system.     

Development of function-graded proton exchange membrane for PEFC using heavy ion beam irradiation

The graded energy deposition of heavy ion beam irradiation to polymeric materials was utilized to synthesize a novel proton exchange membrane (PEM) with the graded density of sulfonic acid groups toward the thickness direction. Stacked Poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) films were irradiated by Xe⁵⁴⁺ ion beam with the energy of 6 MeV/u under a vacuum condition. The induced trapped radicals by the irradiation were measured by electron spin resonance (ESR) spectroscopy. Irradiated films were grafted with styrene monomer and then sulfonated. X-ray photo-electron spectroscopy (XPS) spectra showed that the densities of sulfonic acid groups were controlled for injection “Surface” and transmit “Back” sides of the fabricated PEM. The membrane electrode assembly (MEA) fabricated by the function-graded PEM showed improved fuel cell performance in terms of voltage stability. It was expected that the function-graded PEM could control the graded concentration of sulfonic acid groups in PEM.     

Mechanical properties of cubic zirconia irradiated with swift heavy ions

The modifications of the mechanical properties of cubic (yttria-stabilized) zirconia induced by swift heavy ion irradiation are investigated. Polycrystalline pellets were irradiated at room temperature with 940 MeV Pb ions at the GANIL accelerator in Caen at fluences ranging from 5 × 10¹¹ to 4 × 10¹³ cm⁻². The microhardness and the fracture toughness of irradiated YSZ were studied by Vickers micro-indentation. Although YSZ is damaged by irradiation, an increase of the microhardness and fracture toughness with increasing ion fluence is observed. A strengthening of YSZ, associated with residual compressive stresses induced in the surface layer by irradiation, explain these results.     

聚乙烯的辐射致色及机理研究

为了探求聚乙烯（PE）辐射致色的主要原因,用测色色差计测定了高密度聚乙烯（HDPE）和低密度聚乙烯（LDPE）在不同剂量辐照时及其在辐照后黄度的变化,并用ESR谱仪和紫外可见光谱仪测定了辐照时自由基、共轭双键的生成,辐照后存放时自由基的衰减和共轭双键的变化。结果表明,HDPE比LDPE更容易辐射致色,经不同剂量辐照后的PE的黄度均随存放时间增加而降低,最后趋于稳定。辐照时自由基的生成以及辐照后存放时自由基的衰减规律和PE黄度的变化非常相似,但辐照时共轭双键的生成以及辐照后的变化与PE黄度的变化不同,PE的辐射致色主要是由生成的陷落自由基引起的。     

电子自旋共振技术鉴别辐照茶叶

研究黄山毛峰和祁门红茶经Co-60γ射线辐照诱导的电子自旋共振(Electron spin resonance,ESR)波谱特征,以及吸收剂量、贮藏时间与茶叶中自由基ESR信号强度的关系,考察利用ESR技术鉴别辐照茶叶的可行性。结果显示,低吸收剂量能显著增加茶叶中ESR信号强度(p0.01);茶叶中自由基的信号强度随吸收剂量呈多项式关系增长,与贮藏时间呈乘幂函数关系下降;在常温贮藏70 d后,信号强度逐渐稳定,但依然显著高于未辐照样品的信号强度(p0.01),据此表明,使用ESR法可以鉴别辐照与非辐照的茶叶。