Search results for "IRRADIATION"
showing 10 items of 1012 documents
Gamma rays induced synthesis of graphene oxide/gold nanoparticle composites: structural and photothermal study
2022
Gamma irradiation provides an alternative pathway to conventional gold nanoparticle synthesis because it is simple, fast, and economical. Here, we employed gamma irradiation at low doses (1–20 kGy) to obtain gold nanoparticles (Au NPs) anchored onto graphene oxide (GO) sheets. GO was selected as a suitable platform for the nucleation and growth of Au NPs because of its large surface area and good dispersibility in water due to the presence of polar oxygen-containing functional groups in its structure. Gamma irradiation at all the applied doses led to the reduction of chloroauric acid and the formation of evenly distributed Au NPs at the GO surface, simultaneously causing the reduction of GO…
Origin of the visible absorption in radiation-resistant optical fibers
2013
In this work we investigated the point defects at the origin of the degradation of radiation-tolerant optical fibers used in the visible part of the spectrum for plasma diagnostics in radiation environments. For this aim, the effects of γ -ray irradiation up to the dose of 10 MGy(SiO2) and post-irradiation thermal annealing at 550◦C were studied for a Fluorinedoped fiber. An absorption peaking around 2 eV is mainly responsible for the measured radiation-induced losses, its origin being currently debated in the literature. On the basis of the unchanging shape of this band with the radiation dose, its correlation with the 1.9 eV photoluminescent band and the thermal treatment results we assig…
Thermally and optically stimulated radiative processes in LiBaF3 crystals
2004
Abstract In LiBaF3 crystals both valence–core transitions (5.4– 6.5 eV ) and so-called self-trapped exciton luminescence (about 4.3 eV ) are important for practical application. Here, we present a study of 4.3 eV luminescence under photo- and thermostimulation after X-irradiation of undoped LiBaF3 crystals at various temperatures. Optically stimulated luminescence as a result of electron recombination with both self-trapped holes and holes localized at some defects, were observed after X-irradiation below 130 K and that of electron recombination with defect-localized holes was observed after X-irradiation above 130 K . The spectra of thermo-stimulated luminescence (TSL) contain a broad band…
centers induced by γ irradiation in sol–gel synthesized oxygen deficient amorphous silicon dioxide
2007
The effects of room temperature γ-ray irradiation up to a dose of ∼1300 kGy are investigated by Electron paramagnetic resonance (EPR) measurements in amorphous silicon dioxide (a-SiO2) produced by a sol-gel synthesis method that introduces O{triple bond, long}Si{single bond}Si{triple bond, long}O oxygen deficiency. We have found that exposure to radiation generates the Eγ′ center with the same spectral features found in high purity commercial a-SiO2. The maximum concentration of defects induced in this sol-gel material indicates that its resistance to radiation is comparable to that of synthetic fused a-SiO2. The concentration of Eγ′ center increases with irradiation, featuring a sublinear …
Luminescence processes induced by UV radiation in A1N nanotips and nanorods
2008
Abstract The processes of the UV radiation induced photoluminescence, thermoluminescence and optically stimulated luminescence in the AlN nanotips and nanorods are studied in comparison with those in the AlN ceramics. The emission spectra of the UV radiation induced luminescence processes in the AlN nanostructures are similar to those of AlN ceramics, presumably originating from recombination processes with participation of the oxygen-related centres. In the nanostructures the luminescence processes occur mainly through the excitation of the host lattice, probably due to the smaller content of the randomly distributed defects in the lattice. The observed small mutual differences in the lumi…
A Preliminary Estimation of the Direct Ultraviolet Spectral Irradiance in Valencia (Spain): Comparison with Measured Values
2000
UVSPEC and SMARTS2 models have been used to estimate the UV spectral irradiance values in Valencia, Spain, and the results of these estimations have been compared with experimental measurements of direct irradiance at normal incidence obtained using an Optronic OL 754 in the 300-400 nm range. The relative RMSD and MBD parameters have been used to estimate the deviations of the modelled values with respect to the experimental values. The results indicate that the deviations are smaller when the SMARTS2 model is used with the appropriate aerosol coefficients.
Irradiation detection of herbal ingredients used in plant food supplements by Electron Spin Resonance on samples pre-treated with alcoholic extraction
2020
Abstract This study aimed to verify the applicability of the EN 1787 method for the detection of irradiation in herbal ingredients used in Plant Food Supplements (PFSs). In matrices such as herbs and spices the main limit of the method is the presence of intrinsic radicals responsible for spurious signals leading to complex ESR spectra. To overcome this limit, before ESR measurement a treatment with alcohol has been proposed (Delincee and Soika, 2002; Ahn et al., 2012, 2014). As reported in the literature, this treatment is expected to reduce/eliminate the confounding signals so that the samples may be correctly classified. In this study the efficacy of the pre-treatment was tested on raw h…
Photosensibilisierte Oxidation von Lysozym bei Verschiedenen Wellenlängen
1974
The photooxidation of lysozyme in the presence of methylene blue, riboflavine, and bengal rose at differentpH values and wavelengths was studied. Monochromatic irradiation at shorter wavelengths (345 and 365 nm) is - in contrast to visible light - characterized by higher energy yields and lower oxygen consumption. This behavior suggests that the mechanism of photooxidation depends on the wavelength. The specific destruction of amino acid residues is also wavelength-dependent. Using visible light of 448 and 621 nm for riboflavine and methylene blue, respectively, we have confirmed the selective destruction of histidine and tryptophan atpH 7,0. The energy yield for the destruction of tryptoph…
Controlled release of tyrosol and ferulic acid encapsulated in chitosan–gelatin films after electron beam irradiation
2016
Abstract This work deals with the study of the release kinetics of antioxidants (ferulic acid and tyrosol) incorporated into chitosan–gelatin edible films after irradiation processes. The aim was to determine the influence of electron beam irradiation (at 60 kGy) on the retention of antioxidants in the film, their release in water (pH=7) at 25 °C, in relation with the barrier and mechanical properties of biopolymer films. The film preparation process coupled to the irradiation induced a loss of about 20% of tyrosol but did not affect the ferulic acid content. However, 27% of the ferulic acid remained entrapped in the biopolymer network during the release experiments whereas all tyrosol was …
Recombinant human erythropoietin increases the radiosensitivity of xenografted human tumours in anaemic nude mice
2001
Purpose: The effect of recombinant human erythropoietin (Epo) on the radiosensitivity of human tumour xenografts growing in anaemic nude mice was studied. Methods and materials: Anaemia was induced by total body irradiation (TBI) of mice prior to tumour transplantation. The development of anaemia was prevented by Epo (1000 U/kg s.c.) given 3 times weekly starting 2 weeks prior to TBI (5 Gy). Epo treatment did not influence the growth rate of the tumours, which were transplanted into the subcutis of the hind leg of mice. Thirteen days after TBI (tumour volume of approx. 40 mm3), a single-dose irradiation (12 Gy) of the tumour was performed resulting in a growth delay with subsequent regrowth…