Search results for "Instrumentation"
showing 10 items of 4914 documents
Electron paramagnetic resonance of doped and undoped BaFBr detected by recombination luminescence
1998
Abstract The recombination processes in the X-ray storage phosphor BaFBr:Eu2+ was investigated by measuring the microwave-induced changes in the recombination luminescence in a (high) magnetic field. Besides the resonances of the F(Br−) centre, of the VK(Br−2) centre and of the Eu2+ ground state we observed a line of a hitherto unknown hole centre. The maximum of the luminescence band in which the VK(Br−2) centre could be detected was about 400 nm. The resonance of the unknown hole centre belongs to a luminescence band peaking at about 350 nm.
Crystal structure determination of 1-pentanol from low-temperature powder diffraction data by Patterson search methods
2005
5 pages.-- PACS: 61.66.Hq; 61.50.Lt
Photo- and thermostimulated processes in α-Al2O3
1995
Abstract We reported on the recombination processes determined by the release of electrons from defects connected with the dosimetric 430 K thermostimulated luminescence (TSL) peak as well as with the 260 K TSL peak. These TSL peaks appear in thermochemically reduced α-Al 2 O 3 crystals containing hydrogen and emission of these TSL peaks corresponds to luminescence of the F-center. The X-ray exposure or UV excitation in the absorption band of F-centers at 6.0 eV of reduced α-Al 2 O 3 crystals doped with acceptor impurities results in the appearance of a broad anisotropic complex absorption band in the spectral region 2.5–3.5 eV and in the appearance of a predominant TSL peak at 430 K. Above…
Tl-related radiation defects in CsI:Tl
2004
Abstract Angular dependencies of the EPR spectra detected via the magnetic circular dichroism of the optical absorption (MCDA-EPR) observed in the MCDA bands at 355, 411, 425, 442, 465, 536, and 815 nm of γ- or X-irradiated CsI:Tl crystals have been investigated. The MCDA-EPR spectrum at B || [1 0 0] consists of two quartets of intense lines. The spectrum could be satisfactorily explained taking into account hyperfine (hf) interactions of unpaired electron with S= 1 2 with three Tl nuclei I ( 205 Tl , 203 Tl )= 1 2 . Therefore we propose as a model a Tl-trimer centre. The hf interactions along a [1 0 0] direction with two equivalent Tl and one single Tl were observed. As a centre model we p…
Self-trapped holes and recombination luminescence in LiBaF3 crystals
2001
Abstract We investigated electron paramagnetic resonance (EPR) angular dependencies, recombination afterglow and thermostimulated luminescence of undoped LiBaF3 crystals, X-irradiated at low temperatures. EPR parameters of the F2− molecule oriented along the [1 1 0] direction have been obtained. Based on the value of the g-shift Δg=g⊥−gII=0.02, characteristic for the VK-centres in similar perovskites, we propose that we indeed observed the VK-centres, not the H-centres. X-irradiation below 170 K results in creation of a long-time temperature-independent afterglow due to the tunnelling recombination between close electron and hole centres. The F-type electron centres and the VK as well as pr…
Dosimetry in mixed gamma–neutron radiation fields and energy compensation filters for CaF2:Tm TL detectors
2008
Abstract Strong fields of thermal and epithermal neutrons as used for Boron Neutron Capture Therapy (BNCT) show a relatively small gamma dose. However, for accurate dose estimation, both the neutron as well as the gamma component has to be considered. Different approaches have been studied with various thermoluminescence detectors (TLDs). As a result, CaF2:Tm detectors (TLD-300) are attributed to be most insensitive to thermal neutrons but not tissue-equivalent. In this paper we focus on the measurement of the gamma dose with TLD-300 in mixed irradiation fields. To overcome the disadvantage of being not tissue-equivalent, a study on energy compensation filters was performed. The paper compr…
EPR of molybdenum-related defect in CdWO4 crystal
1998
Abstract EPR spectra of a molybdenum-related structure defect have been observed at a temperature of 20 K in CdWO 4 scintillator crystal, being as-grown “blue-coloured”. Mo 95 and Mo 97 isotope superhyperfine ( shf ) splittings have been resolved. Further splittings in EPR spectra have been interpreted as arising from shf interactions with W nuclea. In the present model of the defect, the unpaired spin is localised in the Cd-site position and molybdenum replaces one of the neighbouring W atoms.
The energy transfer to the luminescence centers in PbWO4
1998
Abstract The luminescence spectra, rise and decay kinetics and the yield of luminescence in undoped PbWO 4 crystals were studied after pulsed electron beam irradiation. The luminescence intensity rise observed after irradiation pulse showed two mechanisms—excitonic relaxation and electron–hole recombination—were involved in the formation of the excited states of the blue luminescence centers. It is proposed that the excited states of WO 3 and WO 2− 4 luminescence centers were formed from some intermediate metastable state.
Advanced trap spectroscopy using the glow rate technique based on bleaching of color centers
2001
Abstract The glow rate technique (GRT) is the extension of the known heating rate method to the full glow curve. The GRT like the fractional glow technique (FGT) offers a procedure for evaluation of the mean activation energy as a function of temperature in the case of arbitrary thermostimulated relaxation kinetics represented by trap distribution function. The experimental procedure involves at least two subsequent measurements of thermostimulated recombination kinetics at different heating rates. The extension of the GRT to the direct measurements of thermostimulated bleaching of the radiation-induced color centers is presented. The experimental procedure involves measurements of the deca…
Exposure of -alanine and -ammonium tartrate ESR dosimeters to thermal neutrons: Experiments and Monte Carlo simulations
2008
Abstract Electron spin resonance solid state dosimetry with alanine and ammonium tartrate pellets is a valuable tool in both medical and industrial applications when dealing with photon and charged particle beams. Its use in neutron beams is limited by the low nuclear cross section values of atoms in the pellets. Addition of boron (10B) or gadolinium ( Gd 2 O 3 ) , known to have high neutron capture cross sections, has been proposed to improve neutron sensitivity. In this paper we present the results of an experimental study concerning neutron sensitivity vs. gadolinium concentration in dosimeter mixtures, with the aim of optimizing mixture composition and maximizing the electron spin resol…