Search results for "Radiation"
showing 10 items of 5298 documents
Improvement of the wettability and dissolution of fenofibrate compacts by plasma treatment
2011
Abstract The goal of this study was to investigate the effect of plasma treatment on the wettability and dissolution of fenofibrate compacts. Contact angle measurements and intrinsic dissolution rate studies of untreated and plasma-treated fenofibrate compacts were conducted. The contact angle data clearly show that the wettability of the tablet surface increased with the duration of plasma treatment. Analyses of stability revealed that the surfaces which were plasma-treated for more than 1 min regained some degree of hydrophobicity after storage in air. Since their hydrophobic recovery finally reached the level observed with 1 min plasma-treated fenofibrate compacts it was deduced that per…
Ion diffusion-controlled processes in fluoride crystals
2001
Ionic and ion diffusion-controlled thermally stimulated relaxation (TSR) processes in CaF 2 , BaF 2 and LiBaF 3 crystals (X-ray irradiated at 290 K) have been investigated by means of ionic conductivity and the correlated ionic thermally stimulated depolarisation current (TSDC), and radiation-induced optical absorption band thermal bleaching techniques at 290-650 K. It was found that under a DC field fluorides store large ionic space-charge. In CaF 2 , BaF 2 and LiBaF 3 , by using the ionic TSDC technique we were able to detect a series of the interstitial anion and/or anion vacancy delocalisation stages in the extrinsic ionic conductivity region. At least 4-6 wide and overlapping ionic TSD…
Irradiation effects on the absorption edge of silica glass
2007
Abstract Vacuum ultraviolet absorption experiments were carried out on a variety of specimens of amorphous silica β-irradiated at different doses from ∼103 to 5 × 106 kGy. Changes in the width of the absorption (Urbach) edge were investigated. These changes strongly depend on the kind of silica considered: in particular the Urbach energy of silica of industrial manufacture increases in the irradiated samples, whereas in sol–gel silica it is poorly influenced by the irradiation. The fictive temperature of the different materials before and after irradiation was also monitored. The changes of the Urbach energy and of the fictive temperature are tentatively discussed considering the disorder d…
Interpretation of absorption edges by resonant electronic spectroscopy: experiment and theory
2004
Abstract Resonant electronic spectroscopy consists in measuring a non-radiative decay process (Auger or autoionization process) excited with photon energies around an absorption edge. The resonant spectra carry information both on the nature of the electronic transitions near the absorption edge by scanning the very first empty orbitals above the Fermi level (through the absorption process), and, on the other hand, on the atomic electronic configuration through the lineshape of the observed decay process. In this paper, after a quick review of the pioneering works in this field, we show that resonant measurements and their theoretical modeling can be used to precisely interpret complex abso…
Luminescence and ultraviolet excitation spectroscopy of SrI2 and SrI2:Eu2+
2013
Abstract We report measurements of luminescence and its ultraviolet excitation spectra in SrI2 and SrI2:Eu2+ at temperatures of 10 and 300 K. Attention is focused on determining the exciton energy and its temperature shift from features of the excitation spectra and limits placed by absorption spectroscopy on a 120 μm thin crystal, on observation of a broadened Eu emission band attributed to trace Eu associated with oxygen in nominally undoped crystals, and on adding observations concerning the 3.4 eV band at low temperature attributed by Pustovarov et al. to the self-trapped exciton.
Luminescence and transient absorption in ZnWO4 and ZnWO4–Fe crystals
2001
Abstract The transient absorption spectra and relaxation kinetics under pulse electron beam excitation in ZnWO 4 and ZnWO 4 –Fe, as well as luminescence spectra and decay kinetics, were studied. It is shown that a fraction of transient absorption is due to luminescence center excited state. The energy transfer from intrinsic excitations to the defect or impurity states is not efficient. The role of Fe-impurities in the decay process is discussed.
Optical, infrared and electron-microscopy studies of metallic clusters in layered crystals
2007
Abstract An influence of ( Cd i ) n metallic clusters on the optical absorption and phonon spectra of CdI 2 crystals was studied. Metallic clusters of spherical shape were formed during the growth of non-stoichiometric crystals. Radii of clusters are in range from 10 to 500 nm according to scanning electron microscopy (SEM) data. The density of clusters was estimated from fractal dimension calculations. The fractal dimension of ( Cd i ) n clusters has been found to be varied from 1.488 to 1.793. In the framework of Mie theory the spectral and size dependencies of extinction coefficients were calculated. From the experimentally obtained spectra it is evident that the metallic clusters are re…
Thermostimulated recombination processes in LiBaF3 crystals
2004
Abstract The creation of radiation defects in LiBaF 3 crystals at 10 K and the processes of their thermostimulated recombination are investigated. The methods of optical absorption, thermal bleaching of color centers, thermostimulated luminescence and fractional glow technique are used. The radiation defects anneal in a multi-stage process accompanied with thermo-luminescence at 20, 46, 105, 130, 170, 210 and 270 K . Differences in the optical absorption spectra measured before and after the TSL peaks are obtained and recombination parameters are determined. The TSL peak at 20 K arises from the delocalization of H-centers. The presence of two TSL peaks related to V K -centers at 105 and 130…
Accuracy of 210Pb dating in two annually laminated lake sediments with high Cs background
1997
Abstract A low-background gamma ray spectroscopy system has been used for nondestructive determination of 210Pb, 226Ra, 134Cs and 137Cs in lake sediment samples. Two Finnish sediment cores with high 137Cs activity originating from the Chernobyl accident have been analysed and dated using 210Pb. The accuracy of the 210Pb dating method was checked by varve counting of replicate samples. In one lake the 210Pb method gave similar dating results as varves, but in the other lake significant differences were detected. It was found that a high Cs concentration significantly impairs the accuracy of the 210Pb activity measurement. However, tha reliability of the dating result depends mostly on the co…
Charge transfer in the novel donor-acceptor complexes tetra- and hexamethoxypyrene with tetracyanoquinodimethane studied by HAXPES
2012
Abstract The effect of charge transfer (CT) in complexes of the donors tetra - and hexamethoxyprene ( TMP and HMP ) with the classical acceptor tetracyanoquinodimethane ( TCNQ ) was studied using hard X-ray photoemission (HAXPES). Microcrystals of the complex were grown via vapour diffusion from donor–acceptor mixtures. The bulk sensitivity of HAXPES at a photon energy of 6 keV completely eliminates the problem of surface contamination for such delicate organic materials grown from solution. The donor molecules were produced using a novel synthesis route functionalizing polycyclic aromatic hydrocarbons at their periphery. For comparison, spectra were also taken from thin-film samples of the…