Abstract
Upstream of the efficiency of proton or carbon ion beams in cancer therapy, and to optimize hadrontherapy results, we analysed the chemistry of Fricke solutions in track-end of 64-MeV ...protons and 1.14-GeV carbon ions. An original optical setup is designed to determine the primary track-segment yields along the last millimetres of the ion track with a sub-millimetre resolution. The Fe
3+
-yield falls in the Bragg peak to (4.9 ± 0.4) × 10
–7
mol/J and 1.9 × 10
–7
mol/J, under protons and carbon ions respectively. Beyond the Bragg peak, a yield recovery is observed over 1 mm for proton beams. It is attributed to the intermediate-LET of protons in this region where their energy decreases and energy distribution becomes broader, in relation with the longitudinal straggling of the beam. Consequently to this LET decrease in the distal part of the Bragg peak, Fe
3+
-yield increases. For the first time, this signature is highlighted at the chemical level under proton irradiation. Nevertheless, this phenomenon is not identified for carbon ion beams since their straggling is lower. It would need a greater spatial resolution to be observed.
To evaluate the influence of specific parameters, i.e. energy sink concentration and excitons and/or radical migration, on the mechanisms underlying the formation of double bonds in aliphatic ...polymers, materials with energy sinks in the chain were synthesized. By following the radiation-induced modifications in ethylene/styrene random copolymers, as a function of the styrene content and of the irradiation temperature, we were able to understand the formation mechanisms of trans-vinylenes, trans-trans-dienes, allyl radicals and vinyls. The irradiation temperature allows the discrimination between energy transfers (at 11 K and at room temperature, RT) and of radical migration (at RT). Irradiations were performed using swift heavy ions, and we could show that track overlapping has also an influence on the studied chemical group concentrations. For instance, trans-vinylenes are influenced by excitation transfer and radical migration: their formation decreases in presence of styrene aromatic rings, whatever the dose range and the irradiation temperature. On the opposite, vinyls are formed only at high ionizing density and are not influenced by excitation transfer; however, their concentration is influenced by radical migration.
•Ethylene/styrene copolymers were irradiated at 11 K and room temperature.•Double bonds formation mechanism was studied.•Energy and radical migration was evaluated as a function of the double bond nature.•Track overlapping effect on double bonds formation was evaluated.
Display omitted
•Dual borohydrido Nd/Mg dialkyl catalysts polymerize butadiene with good efficiency.•Highly 1,4-trans selectivity is observed.•Up to 16.9% styrene can be incorporated in the ...poly(1,4-trans) butadiene backbone.
The combination of a neodymium borohydride, Nd(BH4)3(THF)3 (1) or Cp*Nd(BH4)2(THF)x (2), with MgnBuEt (BEM), affords an efficient and highly selective (up to 96.7% 1,4-trans) catalyst for butadiene polymerization. In the presence of excesses of Mg co-catalyst, polymer chain transfer takes place between neodymium and magnesium, and significant amounts of 1,2-units are observed. When considered for butadiene-styrene statistical copolymerization, the catalytic system based on 2 showed a good ability to produce poly(1,4-trans-butadiene)-co-styrene), with strong impact of the Mg/Nd ratio on the yield and on the copolymer microstructure, including the percentage of inserted styrene (up to 16.9mol%). Whatever the co-monomers concentration the polybutadiene backbone remained 1,4-trans. The precise microstructure of the polymers and copolymers was thoroughly analyzed by means of high resolution NMR spectroscopy (900MHz) and MALDI-ToF spectrometry.
Gamma radiolysis of ion exchange resins (IER) is widely studied since the sixties, as a function of different parameters (resin type, dose, atmosphere, water content …). However, to our knowledge, ...there are very few data concerning hydrogen emission from anionic and cationic resins irradiated at high Linear Energy Transfers (LET). In the present work, we focus on the influence of hydration on hydrogen emission, in anionic and cationic resins irradiated under inert atmosphere using Swift Heavy Ions (SHI) and gamma irradiations. The radiation chemical yield of molecular hydrogen is nonlinear with water content for both resins. The molecular hydrogen production depends first on the water form in IER (free or linked) and second on the solubility of degradation products. Three steps have been observed: at lower water content where G(H2) is stable, at 50%, G(H2) increases due to reactions between water radiolytic species and the resin functional groups and at high water content, G(H2) decreases probably due to its accumulation in water and its consumption by hydroxyl radicals in the supernatant.
•In ion exchange resins submitted to ionizing radiation, hydrogen production evolves as function of water content and form.•A linear energy transfer effect on radiolytic hydrogen production is revealed in cationic and anionic exchange resins.•Radiolytic degradation mechanisms of cationic avec anionic exchange resins are proposed
Organic molecules are part of the Long-Lived Intermediate-Level Waste (LL-ILW) packages. These packages are planned to be delivered at the French deep geological repository, consequently their ...degradation has to be thoroughly understood in order to support the safety studies. In a first period, these organic molecules, which include polymers, are radio-oxidized because of their close proximity with radionuclides. In a second period, water will diffuse inside the site up to the packages, leading to the alkaline hydrolysis of the radio-oxidized polymers. The objective of this study is to evaluate the parameters having a major influence on these radio-oxidized polyolefins hydrolysis at high pH. Aliphatic polymers are chosen because of their relative importance, in quantity, in the French LL-ILW packages.
In this work, we have first radio-oxidized aliphatic polymers in conditions that are representative of their ageing in the first period of the LL-ILW packages: we have employed different doses up to 10 MGy, different emitters - or their equivalent -, i.e. γ-rays and swift heavy ions (SHI) irradiation to model α-rays. To model the second period of ageing of these LL-ILW packages, we have hydrolyzed under alkaline conditions and under inert atmosphere these radio-oxidized polymers.
We have evaluated the influence of the materials’ composition (the resin chemical structure, presence of charges and fillers) and of the irradiation conditions (irradiation type, linear energy transfer (LET) and dose). We observed that hydrolysis is influenced not only by the molecular structure of the polymer, but also by the presence of inorganic fillers and organic additives. The hydrolysis increases with increasing dose and increasing LET for SHI. The most penalizing conditions were encountered under low LET ionizing rays. This is related to the higher oxidation level induced under γ-rays: the higher the oxidation rate, the higher the polyolefins sensitivity to alkaline hydrolysis.
•The sensitivity of irradiated polyolefins to alkaline hydrolysis has been evaluated.•Degradation increases with increasing LET and increasing dose.•Degradation decreases in presence of additives.•Most penalizing conditions are encountered using low LET ionizing rays.•The higher the oxidation rate, the higher the polyolefins sensitivity to hydrolysis.
This work reports the effect of very high doses, up to 10MGy, on the H2 emission from high density polyethylene (HDPE) irradiated with gamma rays and ion beams, in the presence of oxygen. This was ...obtained through a two-step procedure. First, HDPE films were pre-aged, at different doses, using either gamma rays or ion beams. In the second step, the pre-aged samples were irradiated in closed glass ampoules for gas quantification, using the same beam type as for pre-ageing.
The hydrogen emission rate decreases when dose increases for both gamma rays and ion beams. However, the decreasing rate appears higher under gamma rays than under ion beam irradiations and this is assigned to a lesser oxidation level under the latter. Herein, we show the effectiveness of the radiation-induced defects scavenging effect under oxidative atmosphere, under low and high excitation densities.
•Polyethylene is radio-oxidized, using gamma rays and ions beams.•H2 emission rate is determined as function of dose and irradiation type.•H2 emission rate is observed to decrease when dose increases.•H2 decrease is attributed to energy and radical transfers to oxidized defects.
This article is aimed at studying the evolution of H2 release as well as radiation-induced defects in polyethylene (PE), as a function of the irradiation dose under anoxic conditions. We analyze the ...influence of the energy transfers and trapping toward radiation-induced defects on the evolution of the radiation chemical yields with dose. One key objective herein is to quantify the contribution of these transfers toward trans-vinylene (TV) on H2 emission. For this purpose, pure PE was irradiated in a large dose domain and H2 emission was compared to that in predoped PEs containing chemically inserted TV groups irradiated at low doses. In parallel, evolutions of the concentrations of the TV groups and minor defects (vinyl and trans–trans-diene) as a function of dose were considered. Moreover, measuring simultaneously H2 and unsaturated groups had allowed inferring the cross-linking evolution with dose. With this methodology, we have succeeded in quantifying the efficiency of TVs and cross-links as energy traps and, using simple models, in fully describing the evolution of all of the radiation chemical yields. Besides, irradiations were performed using either low linear energy transfer irradiations (electron beams, γ rays) or ion beams, with the objective to assess the influence of the high ionization and excitation densities induced by the latter on PE ageing and energy transfer processes.
With the aim of understanding the radiation effects of alpha particles on polymers, this paper analyses the role of the heterogeneity of energy deposition, at the nanometric scale, on the ...radiation-induced oxidation of an ethylene-propylene-diene elastomer based on 1,4 hexadiene (EPDMh). This polymer was irradiated with 20Ne, at various Linear Energy Transfer (LET), in the presence of oxygen. Macromolecular defects such as carbonyls, alkenes and alkynes were monitored on-line, using Fourier Transform Infrared Spectroscopy (FTIR), and their evolution as a function of both LET and irradiation dose were studied.
Carbonyl group consists of various chemical functions which absorption bands overlap one another in a limited spectral area. The different components were extracted by curve fitting, allowing monitoring the specific evolution of each of these chemical functions as a function of the irradiation conditions. Among carbonyl containing functions, the creation of ketone groups is the most important.
LET influences the alkene radiation chemical yield at initial dose and, apart from trans-vinylene, it also influences the dose evolution of their concentration. Conversely, LET has no significant influence on the total carbonyl concentration.
Atactic glassy polystyrene (PS) has been irradiated in anoxic conditions by electron and ion beams. The induced modifications were followed, in situ, by Fourier transform infrared spectroscopy ...(FTIR). In-film modifications and hydrocarbon gas release were followed. In-situ measurements allowed one to avoid any spurious oxidation of the films after irradiation and also permitted studying in detail the evolution with dose of the FTIR spectra. The data were quantitatively analyzed, and we present a complete analysis of the effects of the Linear Energy Transfer (LET) on the radiation chemical yields of several radiation-induced modifications (alkynes, allenes, alkenes, benzene, and disubstituted benzenes). For a better understanding of the LET effects, the in-film modifications are compared to H2 release data from the literature and to our measurements of hydrocarbon gaseous molecule yields obtained by us. The overall destruction yield becomes very significant at high LET, and the radiation sensitivity of this aromatic polymer merges with typical values of aliphatic polymers: the radiation resistance conferred at low LET to polystyrene by the phenyl side groups is lost at high LET. This loss of radiation resistance equally affects the aromatic and aliphatic moieties. Monosubstituted alkynes are created above a LET threshold, whereas the other radiation-induced modifications are observed in the whole LET range. Several observations indicate that the phenyl ring is broken at high LET. Comparison of the alkyne yield in PS, polyethylene, and polycarbonate as well as the formation of nitrile bonds in poly(vinylpyridine-co-styrene) are consistent with a cleavage of the phenyl ring as the prominent source of alkynes. As the competing damage mechanisms do not have the same LET evolution, the relative importance of a specific modification on the global damage depends on LET. Some (benzene and disubstituted benzenes) dominate at low LET, while others (in-film alkyne and acetylene release) dominate at high LET.
PDF
