Search results for "RADIATION"

Coupled theoretical and experimental studies for the radiation hardening of silica-based optical fibers

2014

International audience; We applied theoretical and experimental spectroscopy tools to ad hoc silica-based "canonical" samples to characterize the influence of several dopants and of some drawing process parameters on their radiation sensitivities. We present in this paper, the recent advances and results occurring from our coupled approach. On the experimental side, we studied the doping influence on the response of optical fibers and showed that changing the drawing parameters has a negligible influence on the fiber response in the case of specialty fibers. We focus mainly on the ${rm SiE}^prime$ defect that is observed through Electron Paramagnetic Resonance (EPR) measurements in all cano…

Indium surfactant effect on AlN/GaN heterostructures grown by metal-organic vapor-phase epitaxy: Applications to intersubband transitions

2006

We report on a dramatic improvement of the optical and structural properties of AlN/GaN multiple quantum wells (MQWs) grown by metal-organic vapor-phase epitaxy using indium as a surfactant. This improvement is observed using photoluminescence as well as x-ray diffraction. Atomic force microscopy shows different surface morphologies between samples grown with and without In. This is ascribed to a modified relaxation mechanism induced by different surface kinetics. These improved MQWs exhibit intersubband absorption at short wavelength (2 mu m). The absorption linewidth is as low as 65 meV and the absorption coefficient is increased by 85%.

GaP/TiO2 Composite Photocatalyst for CO2 Reduction in Gas-Solid Regime under Simulated Solar Light Irradiation

2014

Search for Neutrino‐induced Cascades from Gamma‐Ray Bursts with AMANDA

2007

Using the neutrino telescope AMANDA-II, we have conducted two analyses searching for neutrino-induced cascades from gamma-ray bursts. No evidence of astrophysical neutrinos was found, and limits are presented for several models. We also present neutrino effective areas which allow the calculation of limits for any neutrino production model. The first analysis looked for a statistical excess of events within a sliding window of 1 or 100 seconds (for short and long burst classes, respectively) during the years 2001-2003. The resulting upper limit on the diffuse flux normalization times E^2 for the Waxman-Bahcall model at 1 PeV is 1.6 x 10^-6 GeV cm^-2 s^-1 sr^-1 (a factor of 120 above the the…

Estimation of the emission temperature of an electrodeless discharge lamp and determination of the oscillator strength for the I(2P3/2) 183.038 nm re…

2001

Abstract The 183.038 nm resonance absorption transition of I( 2 P 3/2 ) has been studied using a flash photolysis set-up for gas-phase chemistry and a radio frequency powered electrodeless discharge lamp filled with iodine. The dependence of self-absorption and self-reversal on iodine partial pressure in the discharge volume was measured. The optimum iodine partial pressure, with self-absorption minimized and acceptable intensity, is determined to be approximately 2.5×10 −3 mbar. A method is described to estimate the temperature of the emitting atoms using direct measurements of relative absorption at different absorber concentrations. This yields an emission temperature of 923±50 K. Using …

Hydro-MRT mit schnellen Sequenzen bei Morbus Crohn: Vergleich mit der fraktionierten Magen-Darm-Passage

2008

PURPOSE To compare the value of hydro-MRI with that of barium studies in patients with Crohn's disease. MATERIALS AND METHODS After an oral bowel opacification using 1000 ml of a 2.5% mannitol solution, axial and coronal breath-hold sequences (T2W HASTE +/- FS, contrast-enhanced T1W FLASH FS) were acquired in 46 patients with Crohn's disease at 1.0 T. The findings of hydro-MRI were compared with those of barium studies. RESULTS In the stomach and the small bowel, hydro-MRI and barium studies demonstrated similar numbers of Crohn's involvements (39 vs. 36); in the colon, hydro-MRI showed clearly more affections (23 vs. 10). Hydro-MRI showed 12.7 cm of inflamed bowel per patient, on average (…

Study of optical and magneto processes in Rb atomic vapor layer of nanometric thickness

2012

Using a narrow-band resonant fluorescence spectra from a nano-cell with a thickness of L= [lambda]/2, and VSOP resonances formed at a thickness L =[lambda] ([lambda] is the wavelength of the resonant radiation), for the first time it was experimentally investigated the behaviour of the frequency and intensity (transition probabilities) of the atomic hyperfine structure transitions between the 85Rb, 87Rb, D1 and D2 lines Zeeman sublevels in external magnetic fields in range 5 - 7000G. The behaviour of tens of previously unstudied atomic transitions was analyzed and it is demonstrated that the intensities of these lines can both greatly increase, and decrease (tenfold). For the first time it …

Properties and generation by irradiation of germanium point defects in Ge-doped silica

2012

Ge doped amorphous silicon dioxide (Ge doped silica) has attracted the attention of researchers for more than 50 years. This material is used in many different technological fields from electronics, to telecommunication, to optics. In particular, it is widely used for the production of optical fibers and linear and nonlinear optical devices. The optical fibers, which allow to transmit optical signals with high speed avoiding interferences, are constituted by two regions with different refractive index values: core (inner part) and cladding (external part). To increase the refractive index of the core with respect to that of cladding, Ge doping of silica is commonly used. Moreover, in the Ge…

EPR investigations of polymeric and H2O2 -modified C3N4 -based photocatalysts

2019

The C3N4 -based nanopowders prepared by thermal condensation of melamine (MCN) with subsequent thermal etching (MCN-TE) and H2O2 -treatment were investigated by Q- and X-band EPR spectroscopy in dark and upon in situ UVA or visible-light exposure. Lorentzian signal at g = 2.003, more pronounced in the case of the thermally etched material, dominates EPR spectra of MCN and MCN-TE. More complex spectra were found for H2O2 -treated photocatalysts revealing the presence of signals attributed to the radicals produced via H2O2 interaction with C/N sites in the C3N4 polymeric network. The X-band spectra monitored upon in situ irradiation of the C3N4 -based photocatalysts evidenced the intensity gr…

UV laser induced photolysis of glycolic acid isolated in argon matrices

2021

The photochemistry of matrix-isolated glycolic acid, induced by UV light, was studied by FTIR spectroscopy and B3LYPD3/6-311++G(3df,3pd) calculations. Several decomposition pathways were found to take place upon 212 nm and 226 nm wavelengths irradiation. A number of complexes formed between photoproducts were identified, among them those of formaldehyde with water, carbon monoxide and carbon dioxide as well as the H2O-CO complexes. The structure and spectroscopic assignment of the photoproducts were made comparing the experimental results with the theoretical predictions and available literature data. The observed formation of different complexes indicates various pathways for their formati…