Search results for "RADIATION"

Separation of lanthanides and actinides using magnetic silica particles bearing covalently attached tetra-CMPO-calix[4]arenes

2004

Calix[4]arene tetraethers in the cone conformation bearing four –NH–CO–CH2–P(O)Ph2 (= CMPO) residues on their wide rim and one, two or four ω-amino alkyl residues of various lengths at the narrow rim were synthesized. Reaction with dichlorotriazinyl (DCT) functionalized magnetic particles led to complete coverage of the available surface by covalently linked CMPO-calix[4]arenes in all cases. Magnetically assisted removal of Eu(III) and Am(III) from acidic solutions was distinctly more efficient with these particles in comparison to analogous particles bearing the same amount of analogous single-chain CMPO-functions. The best result, an increase of the extraction efficiency by a factor of 14…

Relaxation of electron-hole pairs and scintillation mechanism in alkali halide crystals

1997

Abstract The mechanism of the ionizing radiation energy transfer from host lattice to luminescence centers is discussed taking into account the results of the recent experimental investigations of electron-hole pair relaxation in alkali iodide crystals. The high scintillation yield in CsI-Tl, CsI-Na and partially in Nal-Tl crystals is explained by the process of the motion and capture of a one-center self-trapped exciton by impurity ions.

Thermal, Pressure and Light Induced Spin Transition in the Two-Dimensional Coordination Polymer [Fe(pmd)2[Cu(CN)2]2]

2008

[EN] A complete structural, calorimetric, and magnetic characterisation of the 2D coordination spin crossover polymer {Fe(pmd)(2)[Cu(CN)(2)](2)} is reported. The crystal structure has been investigated below room temperature at 180 K and 90 K, and at 30 K after irradiating the sample at low temperature with green light ( lambda = 532 nm). The volume cell contraction through the thermal spin transition is only 18 angstrom(3) which is lower than the usually observed value of around 25-30 angstrom(3) while the average Fe-N bond distances decrease by the typical value of about 0.19 angstrom. The structural data of the irradiated state indicate that the high spin state is well induced since the …

Irradiation of low density and high density polyethylenes in presence of carbon dioxide in subcritical and supercritical conditions

1998

Abstract The grafting of carboxylated and oxygenated functions on low density and high density polyethylenes is carried out by gamma irradiation in the presence of carbon dioxide. Both crosslinking and grafting of oxidised groups occur. The extent of these molecular modifications depends on the physical conditions of the gas phase and on the nature of the polymer matrix.

1975

The formation and the behaviour of radiation induced free radicals in poly[1-(tert-butoxy carbonylthio)ethylene] (2) and in a statistical copolymer 4 from O-tert-butyl S-vinyl thiocarbonate (1) with N-vinylpyrrolidone (1:1) was studied, using ESR spectroscopy. After γ-irradiation at 77 K, tert-butyl radicals and other species were detected in the polymers. The yield for the homopolymer was evaluated to be Gtert-butyl = 0.18. Investigations on the behaviour of radicals with an annealing procedure revealed, that at first the tert-butyl radicals disappear with increasing temperature and that a further warming up leads to a concentration rise of this radical species. A radical cation localized …

Gamma radiation of EVA-AA/MMA swollen systems to obtain mechanically improved blends

2002

In this work a "new" way to obtain "compatibilised" blends of rubber-glassy thermoplastic components is presented. Polyethylen-vinyl acetate acrylic acid terpolymer is swollen by methylmetacrylate and the system is irradiated through gamma rays in order to induce polymerisation of the monomer. Solubility and dynamic mechanical tests indicate the formation of a two phase system, even though in presence of strong interactions between the two components. Mechanical tensile behaviour is that of a ductile material with appreciable modulus values.

Thermal properties of e-beam cured epoxy/thermoplastic matrices for advanced composite materials

2007

The aim of this work is to investigate the possibility to improve the thermal behaviour of epoxy based systems, cured by ionizing radiation, in order to produce matrices for advanced carbon fibres composites. Blends of two epoxy monomers, difunctional and trifunctional, have been polymerized by e-beam irradiation and the dynamic mechanical thermal properties have been investigated. The increase of the concentration of the trifunctional epoxy monomer in the blend causes a marked increase of the Tg, but strongly decreases the reactivity. Subsequently, blends of the same epoxy monomers with a high Tg thermoplastic toughening agent have been considered and their reactivity and the thermal prope…

Characterization of ultra-high-molecular-weight polyethylene (UHMWPE) modified by ion implantation

2004

Abstract Surface modification of ultra high molecular weight polyethylene (UHMWPE) is induced by ion implantation of different ions at 300 keV energy. The aim of this work was the chemical, physical and mechanical characterization of the modified material in order to know deep inside about the effect of the ion beam upon the polymer. The irradiated surfaces are investigated by Raman spectroscopy, infrared absorption and micro-hardness analysis, scanning electron microscopy. Pin on disc measurements valuated the wear of the UHMWPE against a stainless steel probe; wear resistance increases of about 76% after the ion implantation. This result can be attributed to the ion bombardment inducing a…

Studies on electron-beam irradiation and plastic deformation of medical-grade ultra-high molecular weight polyethylene

2011

Abstract Separated and combined electron-beam irradiation and plastic deformation effects on the structures of ultra-high molecular weight polyethylene (UHMWPE) were studied. It was found that the concentration of carbonyl (ketones, esters and peresters), hydroxyl and vinyl groups increases with the growing dose of adsorbed electrons. It also tends to exhibit a slight increase in the melting point and crystallinity of the samples. A mechanical stress in the polymer was found to accelerate radiation-induced degradation. It was concluded that each of the factors studied (i.e. electron beam sterilization and plastic deformation) had a different impact on the polymer structure. The change in th…

Effects of gamma-irradiation on the alpha-tocopherol and fatty acids content of raw unpeeled almond kernels (Prunus dulcis)

2014

Abstract The present study evaluated fatty acid composition and α-tocopherol content of almond as a function of irradiation dose in order to determine dose levels causing minimal undesirable changes to almonds. Raw unpeeled almonds variety Tuono ( Prunus dulcis (Mill.) D. A. Webb) were irradiated using 60 Co source at dose of 0.5, 1.5, 3, 6, 8 and 10 kGy. Both control and irradiated samples were kept frozen and immediately analyzed. The data obtained showed no change in fatty acid compositions up to a dose of 10 kGy; on the contrary, a general trend observed is that increasing the dose of irradiation resulted in the decrease of α-tocopherol content. The study has shown that irradiation is a…