Results 1 - 9 of 9
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[en] In the present work Ce3+-doped germanate glasses containing Gd2O3 and BaO or La2O3 were developed. The UV and VIS transmission spectra of these glasses were measured before and after irradiation at doses ranging between 3 and 277 Gy. The radiation induced absorption coefficient μ was calculated on the basis of the measured transmission spectra. From these results the cerium ions doping turns out to be effective in improving the radiation hardness of glasses with respect to their undoped matrices
[en] Highlights: • 5wt% and 7.5wt% rice proteins aqueous solutions were submitted to gamma radiation. • Protein structure was studied by UV–VIS spectra and luminescence emission spectra. • New products were formed as a result of radiation induced oxidation of Tyr and Trp. • FRET occurs in two different donor-acceptor systems. • pH value of RP solutions changes as a function of absorbed doses. - Abstract: The use of proteins as natural biopolymers are sensibly increasing in several application fields such as food industry, packaging and environment protection. In particular, rice proteins (RP) present good nutritional, hypoallergenic and healthful properties very interesting for human consumption. Since ionizing radiation can be successfully applied on protein containing systems involved in different industrial processes, this work aims to determine the effect of gamma radiation on 5 wt%–7.5 wt% RP aqueous solutions in a wide range of absorbed doses up to around 40 kGy. The changes of RP secondary and tertiary structures and their chemical composition were followed by UV–VIS absorbance spectroscopy, luminescence analysis and pH measurements. The experimental data showed the occurrence of the unfolding of RP chains with the increase of the absorbed dose and the formation of new molecules, due to the reaction among tryptophane and tyrosine amino acids and the radical species induced by gamma radiation. The results are also confirmed by the modification of the pH values measured for the irradiated solutions.
[en] Full text: Spatial high resolution dosimetry is very important in all areas of radiation therapy and, in particular, whenever narrow photon beams are required for Stereotactic Radiotherapy (SRT) and small field segments are used for Intensity Modulated Radiotherapy (IMRT). The available detectors are often too large with respect to the beam size considered, which is characterized by high dose gradients and lack of charged particle equilibrium. An ideal solution is represented by single crystal diamond detectors, which are small solid state devices, radiation hard, tissue equivalent and capable of real time response. In the present work, synthetic CVD single crystal diamond dosimeters (SCD), fabricated at Rome 'Tor Vergata' University Laboratories, have been characterized. The devices consist of a p-type/intrinsic/metal layered structure. They have been analyzed in terms of reproducibility, linearity, depth dose distributions, energy, dose rate and field size dependence by using 6 and 10 MV Bremsstrahlung x-ray beams, produced by a CLINAC DHX Varian accelerator and the gamma irradiation facility CALLIOPE. The gamma Calliope plant is a pool-type irradiation facility equipped with the 60Co γ-source in a high-volume (7 x 6 x 3.9m3). Maximum dose rate is 9400 Gy/h. The measurements have been compared with a calibrated ionization chamber and a Fricke dosimeter. The SCD's response is shown to be linearly correlated with the ionization chamber output over the whole dose range explored. Reproducibility, energy and dose rate dependency lower than 1% were observed. A depth dose distribution and irradiation field dependence in agreement with those obtained by reference dosimeters within 2% of accuracy were demonstrated as well. The results of this study are very encouraging about the suitability of SCD for clinical dosimetry with photon beams. (author)
[en] We investigated Czochralski-grown YAG:Pr single crystal as a potential novel scintillator. Optical characteristics including photoluminescence, radioluminescence, scintillation decay, radiation damage and thermoluminescence were measured. Their dependence on the dopant concentration was studied. The radiation damage results show that with increasing concentration of Pr the radiation damage reduces. Thermoluminescence above room temperature shows the dominant glow curve peak around 250 C. Comparing to YAG:Ce scintillator an advantage of YAG:Pr is its much faster scintillation decay (16-17 ns at room temperature) and an absence of slow components in the decay. Therefore YAG:Pr appears as potentially interesting scintillator material. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
[en] Optical properties and irradiation resistance of heavy metal oxide tellurite glasses in the TeO2-PbO-Bi2O3-B2O3 system doped with different ions are investigated. The results indicate that the matrix glass has a moderate UV cut-off edges at about 386 nm wavelength. The UV cut-off positions are obviously shifted to red by the addition of Ce4+. The introduction of Cr3+, Ce4+ and Ni2+ into the matrix glass exerts positive influences on irradiation resistance of glasses and cerium plays the most pronounced role. Such phenomena are mainly attributed to the variable valences of these cations. (copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
[en] The effect of copper ion doping on the γ-ray irradiation resistance of Mn2+ and Pr3+ doped phosphate glasses has been studied. UV–visible transmission spectra and photoluminescence spectra have been measured before and after γ-irradiation to characterize the radiation-induced defects. The electron paramagnetic resonance spectra of the irradiated samples with, and without Cu ions have been compared to show the ability of Cu ions to suppress the generation of radiation-induced color centers. The differential transmission spectra and the radiation-induced absorption coefficients have also been calculated for discussion of the observed phenomena. The much improved γ-irradiation resistance of Mn2+ and Pr3+ doped phosphate glasses has been demonstrated through CuO co-doping
[en] Gamma-ray (γ-ray) sensitivity has been studied in Ag-doped and/or AgI-modified Ge–Ga–S glasses. The sensitivity is controllable in terms of silver presence. Compared to the silver-free sample, the AgI-modified glass shows greater sensitivity to γ-ray irradiation regarding larger change in the transmission spectra (ΔT), whereas improved resistance to γ-ray irradiation occurs in the silver-doped AgI-modified glass with only 1 mol% silver metal being intentionally added.
[en] In the present work, photochromism of WO_3–P_2O_5 glass under gamma-ray irradiation was reported. As-prepared glass samples with different WO_3 content are all optically transparent in the visible wavelength range thanks to the addition of a small amount of oxidizing couple Sb_2O_3–NaNO_3. The photochromic properties are identified by transmission spectra of the glasses before and after irradiation. The results show that the irradiation induced darkening results from the reduction of W"6"+ to W"5"+ or W"4"+. The existence of WO_6 clusters in glasses of high WO_3 content is proved by XPS, which is the main reason for the obvious photochromic effects. The WO_3–P_2O_5 glass is a promising candidate in gamma-ray sensitive detector.
[en] The present work is focused on the γ-radiation induced polymerization of ethyl methacrylate (EMA) and methyl acrylate (MA) monomers mixture to obtain a co-polymer with specific features. The effect of the irradiation parameters (radiation absorbed dose, dose rate) and of the environmental atmosphere on the features of the final products was investigated. Attenuated Total Reflectance - Fourier Transform Infrared Spectroscopy (ATR-FTIR) and Nuclear Magnetic Resonance high-resolution analyses of hydrogen and carbon nuclei (1H and 13C NMR) were applied to follow the γ-induced modifications by monitoring the co-polymerization process and allowed the irradiation parameters optimization. Diffusion-Ordered NMR (DOSY-NMR) data were used to evaluate the co-polymers polydispersity and polymerization degree. Since the last parameter is strongly influenced by the γ radiation and environmental conditions, a comparison among samples prepared and irradiated in air and under nitrogen atmosphere was carried out. In presence of oxygen, higher radiation was required to obtain a full solid co-polymer since a partial amount of energy released to the samples was involved in competitive processes, i.e. oxygen-containing free radicals formation and primary radicals recombination. Irrespectively to the environmental atmosphere, more homogeneous samples in term of polymerization degree dispersion was achieved at lower dose rates. At radiation absorbed doses higher than those needed for the formation of the co-polymer, while in case of samples irradiated in air heavy depolymerization was verified, a sensible increase of the samples stability was attained if the irradiation was performed under nitrogen atmosphere. - Highlights: • EMA/MA co-polymer was successfully obtained by γ-induced polymerization. • Solvent-free EMA/MA monomers mixture was used as starting material. • Irradiation parameters and environmental atmosphere influence the final co-polymer. • More stable co-polymers were produced under nitrogen atmosphere.