Search results for "IRRADIATION"

Experimental evidence for two different precursors of Eγ′ centers in silica

2004

Abstract Electron paramagnetic resonance measurements of concentration and line shape of E γ ′ centers induced by γ ray irradiation are presented for natural and synthetic commercial silica with different OH contents. Synthetic materials with OH content >200 ppm by weight show one line shape for all investigated doses. In contrast, the other materials show a different line shape at low irradiation doses. Differences are also observed in the concentration growth of the E γ ′ centers in synthetic wet materials and in the other materials. The results are interpreted as evidence of two E γ ′ centers distinguishable by their line shape and having different precursors.

Electric field induced alignment-orientation conversion in diatomic molecules: analysis and observation for NaK

1999

This article reports the observation of the molecular fluorescence circularity under irradiation with linearly polarised light. This alignment-orientation conversion phenomenon arises as a result of partial transformation from alignment of the ensemble of 1 P state molecular angular momenta into their orientation under the effect of non-linear dc Stark effect. Circularity rate up to 0.12 was observed in D 1 P! X 1 S fluorescence of 23 Na 39 K molecules in agreement with the theoretically predicted value.

Photocatalytic and Catalytic Reactions in Gas–Solid and in Liquid–Solid Systems

2019

Abstract Heterogeneous photocatalytic and thermal-catalytic reactions are here presented focusing the differences and similarities between the two processes. When possible, the comparison was made for the same chemical reaction in the presence of an inorganic material playing the role of both catalyst or/and photocatalyst. Several examples are presented where a catalytic reaction can occur at milder experimental conditions and, particularly, at lower temperature when the system is also irradiated by UV and/or visible light. The differences in mechanistic aspects, conversions, and selectivities between catalytic and photocatalytic reactions will be also considered because these occurrences a…

The use of X-ray-induced and thermostimulated visible and UV luminescence for understanding X-ray poling of silica glasses

2007

In this paper, we studied the X-ray-induced visible and UV luminescence (XRL) during X-ray irradiation, afterglow (after X-ray was switched off) and thermostimulated luminescence (TSL). Comparisons were performed between with and without applying an electric field of 1.5 kV/mm on the sample. The typical TSL curve for X-ray-irradiated samples present two peaks centered at 90 and 280 °C. The relative intensity of these two peaks is X-ray dose dependent. An external electric field enhances the XRL, but has no effect on the afterglow. The TSL and afterglow spectra are identical with one peak at 3.25 eV, whereas XRL spectrum displays an additional peak at 4.25 eV. A model of electron exchange be…

Time-resolved luminescence and induced absorption in PbWO4

1997

Abstract Luminescence and short-lived induced absorption are studied for two undoped PbWO4 crystals. Luminescence decay at LNT is delayed relative to irradiation pulse. The delay observed is either due to reabsorption of luminescence or due to creation of luminescence center excited states via energy or/and charge transfer after irradiation pulse. Short-lived absorption is observed within 1.1–3.6 eV spectral region at LNT as well as at RT. It is proposed that the short-lived absorption band peaking at ~ 3.5 eV is intrinsic.

Formation of HXeO in a xenon matrix: Indirect evidence of production, trapping, and mobility of XeO (1 1Σ+) in solid Xe

2004

IR spectroscopy, laser induced fluorescence (LIF), and thermoluminescence (TL) measurements have been combined to monitor trapping, thermal mobility, and reactions of oxygen atoms in solid xenon. HXeO and O(3) have been used as IR active species that probe the reactions of oxygen atoms. N(2)O and H(2)O have been used as precursors for oxygen atoms by photolysis at 193 nm. Upon annealing of matrices after photolysis, ozone forms at two different temperatures: at 18-24 K from close O ...O(2) pairs and at approximately 27 K due to global mobility of oxygen atoms. HXeO forms at approximately 30 K reliably at higher temperature than ozone. Both LIF and TL show activation of oxygen atoms around 3…

1974

The formation and behaviour of radiation-induced free radicals in statistical copolymers of ethoxyvinylthiomethane (1a) with N-vinylpyrrolidone (2) (1:2,5) and of ethylthiovinylthiomethane (1b) with 2 (1:3,5) has been studied using electron spin resonance spectroscopy. After a γ-irradiation of the copolymers at 77K Cα-radicals in the vinylpyrrolidone moieties could be detected. Investigations on the behaviour of these radicals with an annealing procedure revealed that only in the copolymer (3b) with the dithioacetal group a transfer reaction of hydrogen atoms to the Cα-radicals in the vinylpyrrolidone moieties occurs. This process may be regarded as a repair mechanism. Es wurde die Bildung …

Focused microwave-assisted Soxhlet extraction: An expeditive approach for the isolation of lipids from sausage products

2003

A prototype of extractor based on the conventional Soxhlet principles but assisted in the cartridge zone by focused microwaves is proposed for accelerating the extraction of lipids from sausage products. The extraction process has been optimised using a multivariate design involving the main variables influencing the performance of the prototype (namely, irradiation power P, irradiation time T and number of cycles C). Under the optimum working conditions (P=160 W, T=10 s and C=14), the extraction of lipids from different Spanish sausage products is complete in 45 min. The extracts thus obtained have been compared with those provided by conventional Soxhlet extraction for 8 h by development …

Evaluation of extraction alternatives for Fourier transform infrared spectrometric determination of oil and greases in water

1997

Abstract Liquid-liquid extraction (LLE), solid phase extraction (SPE) and microwave-assisted extraction are evaluated for Fourier transform infrared (FTIR) spectrometric determination of oil and grease in polluted waters. A fast microwave-assisted quantitative procedure is proposed for the total extraction of oil and grease into CCl 4 from water samples, with an irradiation time of 1 min at an exit power of 520 W using closed PTFE vessels. The FTIR quantification of oil and grease is carried out by the measurement of the area under the absorbance spectra in the range between 3058 and 2780 cm −1 , with a baseline established between 3200 and 2700 cm −1 . The analytical features of the propos…

Anticancer platinum agents and light

2019

Abstract Since the discovery of cisplatin, light activation has been employed as a strategy to switch and improve the anticancer effects of platinum compounds. This contribution highlights some of the most representative discoveries obtained in the field of platinum-based photochemotherapy over the years.