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Positron Lifetime Spectroscopy (positron + lifetime_spectroscopy)
Selected AbstractsPositron annihilation study of recrystallization behaviour in Zr2.5%Nb alloyPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 11 2009S. Mulki Abstract In CANDU reactors Zr 2.5%Nb alloy is used as pressure tube material due to low neutron absorption cross section, a high resistance to corrosion in water, high strength and good creep resistance. The two phase alloy consists of ,-fcc and ,-bcc. The recrystallization behavior of Zr2.5Nb strongly depends on morphology and distribution of second phase. In this study, the material was deformed to 60% and then was recrystallized in , + , region for different duration (i.e. 2 minutes to 14 days at 700 °C). The recrystallized microstructure was characterized by Orientation Imaging Microscopy (OIM). The evolution of microstructure was examined by Positron Lifetime Spectroscopy and Doppler Broadening measurement for each heat treated samples. Results from positron annihilation studies and other microstructural examination have been used to rationalize the recrystallization aspects, defects and ,-phase distribution. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] A comparative study of transformation of micellar structures in CTAB and TTAB binary systems using Positron Lifetime SpectroscopyPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 11 2009R. Yadav Abstract The micellar structures of cetyl-tri-methyl ammonium bromide (CTAB) and its homologues have been investigated employing several conventional techniques. However, due to lack of sensitivity inherent in these techniques and the perturbation introduced by the probe, the detailed structures of the aggregates in the so-called single phase regions of these systems are far from being fully understood. Positron has been found to be a useful non-destructive probe for investigating micellar structures in surfactant systems [1-3] The present study is an effort to get a better insight into the micellar structures and their transformations in CTAB and TTAB aqueous binary systems Positron lifetime spectroscopy has been employed to study these systems covering a wide range of surfactant concentrations. A comparative study of the results obtained for the two surfactant systems have been discussed in this paper. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Positron Annihilation Lifetimes in Cucurbiturils: Evidence of Internal Inclusion of Gold in CB[7]CHEMPHYSCHEM, Issue 5 2009Pedro Montes-Navajas Abstract Positron lifetime spectroscopy serves to determine the void volumes of cucurbituril (CB) capsules, which are not amenable to standard gas adsorption methods. In the case of the host,guest complex Au§CB[7], it also provides evidence of the inclusion of gold nanoparticles in the CB cavity (see space-filling model; Au golden, C gray, H cyan, N blue, O red). Positron annihilation lifetime (PAL) measurements are carried out to determine the cavity dimensions of hydrated and dehydrated cucurbiturils (CB[n]; n=5,6,7,8). In the case of hydrated samples, the dimensions of the cavity are unrelated to the number of glycoluril units of the CB, whereas for dehydrated samples the cavity dimensions measured by PAL follow the expected order, although the experimental values obtained by PAL are significantly smaller than the dimensions of each CB determined by crystallography. For a host,guest complex in which colloidal gold nanoparticles are assumed to be included inside CB[7], a significant reduction of the cavity size is measured. This represents an experimental evidence of the inclusion of gold inside CB[7], which complements previous high-resolution transmission electron microscopy (TEM) images. [source] Positron annihilation spectroscopy using high-energy photonsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 2 2010Maik Butterling Abstract The superconducting electron accelerator ELBE (Electron Linac with high Brilliance and low Emittance) at the Research Centre Dresden-Rossendorf (Germany) serves as a high-intensity bremsstrahlung photon-source delivering a pulsed beam (26,MHz) with very short bunches (<5,ps). The photons are being converted into positrons by means of pair production inside the target material thus forming an intense positron source. The accelerator machine pulse is used as time reference allowing positron lifetime spectroscopy. We performed positron annihilation spectroscopy by pair production in different sample materials and used coincidence techniques to reduce the background due to scattered photons significantly in order resulting in spectra of extraordinary high quality. [source] Positron source based on the 48V isotope dedicated to positron lifetime spectroscopyPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 11 2009Jerzy Dryzek Abstract In the paper we consider application of the 48V isotope as a source in the positron lifetime spectroscopy. The isotope was produced in the 48Ti(p,n)48V reaction using 15 MeV proton beam. As a target the natural titanium thin plate was used. The measurements using the typical positron lifetime spectrometer have shown the usefulness of the source obtained for this application. Due to its properties, the source may be used for measurements of positron annihilation characteristics in high temperature or aggressive environments. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] A study of dye molecule diffusion in human hair using positron lifetime spectroscopyPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 11 2009M. N. Chandrashekara Abstract The diffusion behavior of a commercial permanent liquid hair dye in human hair has been investigated using Positron Annihilation Lifetime Spectroscopy (PALS) and gravimetric sorption method. The o-Ps lifetime parameters ,3 and I3 decrease rapidly during the first 60 minutes of sorption time. This is understood in terms of dye molecules filling the free volume cavities in hair. The sorption results suggest that the dye molecule diffusion is essentially a Fickian process. In the latter part of the sorption, where positron parameters remain almost constant, mass increase might be due to surface adhesion. These two stages of sorption are well separated by the positron technique. The study shows that the free volume theory and positron technique, widely used in polymer research, may expediently be used to understand hair properties, more importantly diffusion of dye molecules. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Order-disorder transitions in self-assembled polymers: A positron annihilation studyPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 11 2009Ramasubbu Ramani Abstract We report here the first results of order-disorder transition (ODT) in a self-assembled comb-like polymer-amphiphile supramolecular system as identified from the change in positron lifetime parameters. We have used poly(4-vinyl pyridine) hydrogen bonded with 3-pentadecyl phenol, which upon heating showed a stepwise reduction in o -Ps intensity at the ODT from lamellar self-assembled state to the disordered state. The ODT temperature was confirmed by differential scanning calorimetry and small angle X-ray scattering. The free volume "holes" in this polymer-amphiphile system are proposed to be near the chain ends of the polymer backbones. We suggest that positron lifetime spectroscopy can serve as a technique to identify ODTs in self-assembled lamellar structured supramolecular systems. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Application of fast-digitizer card Acqiris DP-240 in positron lifetime spectroscopyPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 11 2009Martin Petriska Abstract Based on the available knowledge base in positron annihilation measurements, new software for digital positron lifetime spectrometry has been designed within the frame of joint activity between STU Bratislava and JRC Petten. The tests of the new positron digital-life time setup have been carried out. Detectors with BaF2 scintillators and fast-dynode outputs were chosen for such studies. As the digitiser unit, the card Acqiris DP240 was fully tested. Originally, start and stop timing signals were sampled to digital waveforms separately at a rate of 1 GS/s in 8 bit resolution. However, due to limited quality of collected waveforms which significantly affected post-processing of data, the joined delayed channel mode with 2 GS/s sampling rate was applied for further studies. The full setup was benchmarked by a series of calibration measurements of two high purity materials, specifically Si and Ni. The inter-comparison of conventional analogue- and digital-based processing are discussed in detail. Further, the optimisation of main parameters for waveform-processing are analysed too. Such a new approach in the digital life-time spectroscopy will help to improve the resolution of existing methodology which might enhance the capabilities of this technique for further applications, especially in materials science. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Positron annihilation characteristics in UO2: for lattice and vacancy defects induced by electron irradiationPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2007M.-F. Barthe Abstract In this work both 22Na based positron lifetime spectroscopy (PALS) and slow positron beam based Doppler annihilation-ray broadening spectrometry (SPBDB) have been used to characterize respectively the bulk and the first micron under the surface of sintered UO2 disks that have been polished and annealed at high temperature (1700 °C/24 h/ArH2). Results show the presence of negative ions that are tentatively identified to negatively charged oxygen atoms located in interstitial sites. The positron annihilation characteristics in the UO2 lattice have been determined and are equal to SL(UO2) = 0.371(5), WL(UO2) = 0.078(7), ,L(UO2) = 169 ± 1 ps. Such disks have been irradiated at room temperature with electrons and , particles at different fluences. After irradiation SPBDB and PALS measurements show the formation of U-related vacancy defects after a 2.5 MeV electrons irradiation whereas no defects are detected for an irradiation at 1 MeV. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Digital positron lifetime spectroscopy: present status and outlookPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2007F. Be Abstract This contribution summarizes achievements in instrumentation for positron lifetime measurements with emphasis on digital spectrometric systems. A significant part of the data presented are based on a long-term exploitation of a conventional positron lifetime spectrometer developed at Charles University in early 90s, on bench-mark testing measurements with this spectrometer working temporarily in conjunction with a pair of 8-bit, 4 GS/s digitizers and on analogous measurements with a recently assembled digital positron lifetime spectrometer. In addition, results from testing experiments with microchannel plate photomultipliers are briefly reported. Further development of positron lifetime technique is discussed. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||