Search results for "IRRADIATION"
showing 10 items of 1012 documents
Ion diffusion-controlled thermally stimulated processes in x-ray irradiated halide crystals
2003
The ionic and ion diffusion-controlled thermally stimulated relaxation (TSR) processes in CaF2, BaF2, LiBaF3 and KBr crystals were investigated above 290 K by means of the ionic conductivity, ionic thermally stimulated depolarisation current (TSDC) and thermal bleaching techniques. Under a DC field the halide crystals store large ionic space charge. We were able to detect in CaF2, BaF2, LiBaF3 and KBr in the extrinsic ionic conductivity region a series of the ionic defect (the interstitial anion and/or anion vacancies - in fluorides; the cation vacancies - in KBr) release stages: 3-6 wide and overlapping ionic TSDC peaks. The correlated data of the ionic TSDC and the F band thermal show tha…
UV and vacuum-UV properties of ge related centers in gamma irradiated silica
2002
Photochemical inhomogeneity in the reduction process of the optical activity related to Ge oxygen deficient point defects in silica, characterized by an absorption band centered at 5.15 v eV and two emission bands centered at 3.2 v eV and 4.3 v eV, have been investigated. We have made a comparative study of the stationary and time dependent photoluminescence under excitation in the UV (5 v eV) and in the vacuum-UV (7.4 v eV) ranges in natural silica samples with native and with n -irradiation bleached optical activity. Our measurements evidence that the same spectral features are observed in the native and in the irradiated samples, but for an intensity reduction in the irradiated ones. Mor…
Radiation induced defects in SiO 2
2002
The main luminescent centers in SiO 2 films are the red luminescence R (650 v nm; 1.85 v eV) of the non-bridging oxygen hole center (NBOHC) and the twofold-coordinated (divalent) silicon with a blue B (460 v nm; 2.7 v eV) and a UV band (285 v nm; 4.4 v eV). Especially the latter ones are produced under irradiation, but from existing precursors assumed as silicon related oxygen deficient centers (SiODC). Therefore, in order to prove these models we compare a direct oxygen implantation with a direct silicon implantation into SiO 2 layers. The main result is: implanting oxygen increases the red band R but does not affect the blue band B. Silicon surplus increases the amplitude of the blue (B) …
Changes in the thermoelectric response of vitreous carbon due to the irradiation by γ-rays
2014
In order to study variations in the thermoelectric properties, some commercial glassy carbon samples were subjected to a sequence of steps consisting of a combination of irradiation with γ-rays produced by radioisotopes 60Co, and hydrogen adsorption when the samples were put in an over pressured atmosphere of this gas. With this procedure it was possible to observe that the irradiation decreases the electrical conductivity of glassy carbon samples and the hydrogenation changes the sign of Seebeck coefficient. The material initially is an n-type semiconductor, but with hydrogenation changes to p-type semiconductor. X-ray diffraction analysis showed that the hydrogenated vitreous carbon is mo…
Optical properties of oxygen-deficiency related centers in amorphous SiO 2 investigated by synchrotron radiation
2002
We report an investigation of the photoluminescence activity at 4.4 v eV in g -irradiated silica under UV and vacuum-UV excitation by synchrotron radiation. Our results evidence two iso-energetic contributions which can be related to two oxygen-deficient centers variants: ODC(I) and ODC(II). The first, excited within the 7.6 v eV absorption, is detected only at low temperature and has a lifetime of about 2 v ns. The second exhibits two excitation maxima peaked at 5.0 and 6.8 v eV, its amplitude decreases by a factor 2 on increasing the temperature whereas its lifetime has a value of about 4 v ns. These features give new insights on the excitation pathway of the 4.4 v eV emission involving t…
Behaviour of neutron irradiated beryllium during temperature excursions up to and beyond its melting temperature
2015
Abstract Beryllium pebble behaviour has been studied regarding the accidental operation conditions of tritium breeding blanket of fusion reactors. Structure evolution, oxidation and thermal properties have been compared for nonirradiated and neutron irradiated beryllium pebbles during thermal treatment in a temperature range from ambient temperature to 1600 K. For neutron irradiated pebbles tritium release process was studied. Methods of temperature programmed tritium desorption (TPD) in combination with thermogravimetry (TG) and temperature differential analysis (TDA), scanning electron microscopy (SEM) in combination with Energy Dispersive X-ray analysis (EDX) have been used. It was found…
ESR dosimeter material properties of phenols compound exposed to radiotherapeutic electron beams
2017
Abstract There is a need for a sensitive dosimeter using Electron Spin Resonance spectroscopy for use in medical applications, since non-destructive read-out and dose archival could be achieved with this method. This work reports a systematic ESR investigation of IRGANOX ® 1076 exposed to clinical electron beams produced by a LINAC used for radiation therapy treatments. Recently, dosimetric features of this material were investigated for irradiation with 6 0Co γ -photons and neutrons in both pellet and film shape and have been found promising thanks to their high efficiency of radiation-matter energy transfer and radical stability at room temperature. Here the analysis of the dosimetric fea…
Time resolved photoluminescence associated with non-bridging oxygen hole centers in irradiated silica
2008
Abstract We report time resolved photoluminescence spectra of irradiated silica under excitation with a laser tunable in the visible and UV range. The investigated samples exhibit the emission band at 1.9 eV associated with non-bridging oxygen hole centers, whose spectral and kinetics properties do not depend on the kind of irradiation (γ, β and neutrons). The 1.9 eV luminescence decay follows a multi-exponential curve with a characteristic lifetime that increases from 8.9 μs to 10.4 μs on increasing the emission energy. This dependence accounts for the blue-shift of the emission band during its decay and is interpreted as due to the inhomogeneous properties of silica leading to a distribut…
ESR response of phenol compounds for dosimetry of gamma photon beams
2014
Abstract In the present paper we investigate the features of IRGANOX® 1076 phenols as a material for electron spin resonance (ESR) dosimetry. We experimentally analyzed the ESR response of pellets of IRGANOX® 1076 phenols irradiated with 60Co photons. The best experimental parameters (modulation amplitude and microwave power) for dosimetric applications have been obtained. The dependence of ESR signal as function of γ dose is found to be linear in the dose range studied (12–60 Gy) and the lowest measurable dose is found to be of the order of 1 Gy. The signal after irradiation is very stable in the first thirty days. From the point of view of the tissue equivalence, these materials have mass…
ESR response of watch glasses to proton beams
2010
In this paper we have analyzed the electron spin resonance (ESR) signal of watch glasses irradiated with %60 MeV proton beams in the dose range between 1 and 105 Gy. The composition of samples expressed in oxides weight percentages has been obtained carrying out X-ray fluorescence spectrometry (XRF) mea- surements. The ESR signal has been studied in terms of its dependence on microwave power and modulation field in order to choose the optimal recording parameters. The dependence of the radioinduced signal on the exposure dose has been investigated. A numerical procedure aimed at improving the sensitivity in the low dose range has been developed.