Search results for "γ irradiation"
showing 7 items of 7 documents
Gamma ray induced 11.8 mT ESR doublet in natural silica
1998
Abstract We report electron spin resonance (ESR) measurements in natural and synthetic vitreous SiO2 samples irradiated by γ rays. An 11.8 mT doublet, asymmetrically centered on the resonance line of the E′ center, was detected only in natural samples. The intensity of this doublet as a function of γ exposure tends to saturate for doses as low as 0.2 Mrad and is not related to the growth kinetics of the E′ centers. Photoluminescence (PL) measurements on the same samples have shown that two emissions at 3.15 and 4.26 eV bleach with the same kinetics as does the 11.8 mT doublet on increasing the γ ray dose. We tentatively suggest the presence of a conversion mechanism, activated by γ irradiat…
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…
Macro-oriented network of liquid-crystalline polyesters: crosslinking induced by g-irradiation and thermally activated reaction.
2000
Abstract The synthesis of a macro-oriented network from liquid-crystalline polymers, bearing pendant groups with unsaturations, is reported. Virgin polymers are processable to obtain oriented samples, e.g. fibres, which may be crosslinked through thermal activation and/or exposure to γ-radiation. The liquid-crystalline state is “frozen” and the macroscopic anisotropy is preserved even at high temperatures. Compared to virgin fibres, irradiated samples show an enhancement of tensile performances, thus indicating that the main effect of irradiation is crosslinking without significant degradation phenomena.
Microgels of polyaspartamide and poly(ethylene glycol) derivatives obtained by γ-irradiation
2002
Abstract The copolymer PHG based on α , β -poly( N -2-hydroxyethyl)- dl -aspartamide (PHEA) functionalized with glycidyl methacrylate has been exposed in aqueous solution to a γ -ray source at different irradiation doses (2, 2.5 and 3.5 kGy), alone or in combination with poly(ethylene glycol)dimethacrylate (PEGDMA) or poly(ethylene glycol)diacrylate (PEGDA). The irradiation produces microgel systems that have been characterized by viscosity measurements. Lyophilization of microgels gives rise to samples able to swell instantaneously in water whereas their treatment with acetone produces swellable microparticles that have been characterized.
Room Temperature Instability of E′γ Centers Induced by γ Irradiation in Amorphous SiO2
2008
We study by optical absorption measurements the stability of E'(gamma) centers induced in amorphous silica at room temperature by gamma irradiation up to 79 kGy. A significant portion of the defects spontaneously decay after the end of irradiation, thus allowing the partial recovery of the transparency loss initially induced by irradiation. The decay kinetics observed after gamma irradiation with a 0.6 kGy dose closely resembles that measured after exposure to 2000 pulses of pulsed ultraviolet (4.7 eV) laser light of 40 mJ/cm(2) energy density per pulse. In this regime, annealing is ascribed to the reaction of the induced E'(gamma) centers with diffusing H(2) of radiolytic origin. At higher…
Absorption band at 7.6 eV induced by γ-irradiation in silica glasses
2001
Optical absorption of defects induced by γ-irradiation in both natural and synthetic silica is experimentally investigated in the vacuum-ultraviolet (UV) range. Our results show that γ-rays, in a dose range of 1000 Mrad, induce an absorption band centered at 7.6 eV, the so-called E band, whose growth kinetics is not related to γ-activated precursors but to defects of the glassy matrix directly induced via the breaking of Si–O bonds occurring under γ-irradiation. Moreover, we observe that γ-rays do not bleach the E band present in some silica samples before irradiation, so ruling out that the associated defects can be precursors of the paramagnetic E′ centers, also induced by γ-irradiation.
The Effects of Admixtures on Resistance to Radiation of Lithium Niobate Crystals
2015
The studies of optical absorption and transmission of crystalline lithium niobate compounds modified by rare-earth and alkali-earth elements: LiNbO3: Y (0.46 wt %), LiNbO3: Y (0.32 wt %), Mg (0.24 wt %), LiNbO3: Mg (0.27 wt %), LiNbO3: Gd (0.004, 0.04, 0.26, and 0.43 wt %), and ostensibly pure LiNbO3 is reported. The features of absorption and transmission are examined with respect to the dosage of γ-irradiation, the annealing temperature, and the type and concentration of modifying admixtures. The features revealed in different ways of bleaching γ-irradiated and annealed in vacuum ostensibly pure lithium niobate crystals are used to refine the mechanisms of developing electron and point de…