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[en] This is with reference to Mater. Sci. Eng. B 234 (2017) 28–39, the journal publication entitled “Positron annihilation spectroscopy and photoluminescence investigation of LaOF:Tb3+ nanophosphor fabricated via ultrasound assisted sonochemical route”. The doi link of the publication is https://doi.org/10.1016/j.mseb.2017.07.001 which was published on October 2017. It is to be informed to all the readers and the journal officials that there has been inadvertent mistake in the authors list of this publication by leaving two important authors name who contributed significantly for the PALS and CDBS discussions. Hence in the authors list two important author names and their affiliations were included. Further, there is a change in one of the sentence of acknowledgement as noted below: K. Hareesh received an Australian Endeavour and India Council Postdoctoral Research Fellowship. The Australian Research Council and the University of Western Australia partially supported the research.” is to be included instead of “Authors thanks to Prof. J.F. Williams and Dr. K. Hareesh of University of Western Australia, Perth WA-6009, Australia for recording PALS and CDBS data. The authors would like to apologise for any inconvenience caused.
[en] Highlights: • Ordered mesoporous polymers (OMPs) were hydrothermally synthesized at high temperatures. • Ordered mesopores was constructed from self assembly of copolymer template with resol. • OMPs contain abundant sub-nano level structures such as free volumes, unopened nanopores. • Sub-nano level structures of OMPs were investigated by positron annihilation technique. • Positron annihilation act as useful technique for optimization of synthetic conditions of OMPs. - Abstract: We report here a high temperature directed, self-assembly to the synthesis of ordered mesoporous organic polymers (OMPs) with different nanopore sizes and BET surface areas. The synthesized OMPs have large BET surface areas (219–512 m2/g), ordered mesopores, and adjustable pore volumes (0.20–0.48 cm3/g). Their rules of sub-nano level structures such as free volumes, unopened nanopores and electronic environment in the synthesized OMP materials were systematically investigated by using positron annihilation lifetime spectroscopy, which acts as an important technique for investigating microstructures of ordered mesoporous organic polymers and optimization of synthetic conditions of porous organic polymers.
[en] A method for forming a continuous flux of monochromatic positrons with a controlled time of arrival at the target, independent of the start time in a limited start time interval, is suggested. Such an ordered positron flux (OPF) allows one to construct an experimental setup for studies of solid matter structure by positron annihilation spectroscopy (PAS) in its most efficient version — the Positron Annihilation Lifetime Spectroscopy (PALS). Simultaneously, by varying the potential of the target, one can control the energy of the positrons on the target and, accordingly, the depth of their penetration into the sample under study, measuring the distribution of defects in depth with high resolution.
[ru]Предлагается метод формирования непрерывного потока монохроматических позитронов с контролируемым временем прихода на мишень, не зависящим от момента времени старта в ограниченном интервале времени. Такой упорядоченный поток позитронов позволяет создать экспериментальную установку для исследования структуры твердого тела методом позитронной аннигиляционной спектроскопии (ПАС) в его наиболее эффективном варианте — измерении времени жизни позитрона в исследуемом веществе. Одновременно, варьируя ускоряющий потенциал мишени, можно изменять энергию позитронов на мишени и контролируемо изменять глубину их проникновения в исследуемый образец. Таким образом, можно измерять с высоким разрешением распределение дефектов по глубине.
[en] This report describes the automation implemented in the low temperature Positron Annihilation Spectroscopy system. Temperature programmer and controller is interfaced to PC through an IEEE-488.2 add-on card. Through this data can be read and written to the temperature controller and it can be handled remotely. The PC (Pentium, win XP) also houses the PCI based MCA card (8K FAST Com Tec, P7882). Software was developed to communicate with the temperature controller and control the function of MCA. This help in uninterrupted data acquisition at different time segments by automatically varying temperature at its preset value with better precision. (author)
[en] In this work we investigated vacancies in maghemite and Zn substituted maghemite (γ-Fe2−yZn3y/2O3, y=0.0, 0.11, 0.24, 0.36, 0.50 and 0.66) nanoparticles using coincidence Doppler broadening and positron annihilation lifetime spectroscopy. Coincidence Doppler broadening spectroscopy (CDBS) measurements showed that the positrons annihilated in cation vacancies that surrounded by oxygen anions. Also, the CDBS showed that in pure maghemite and in the y=0.11 samples the vacancies are in octahedral and tetrahedral sites, respectively. For other samples they are distributed in both octahedral and tetrahedral sites. The positron annihilation lifetime spectroscopy (PALS) measurements confirmed the results of the CDBS measurements and also exhibited that the number of vacancies in y=0.36 sample is less than the other samples. This is attributed to Zn substituted magnetite phase in this sample as well as Zn substituted maghemite phase. - Highlights: • The cation vacancy distribution of maghemite is obtained with PLSA. • The effect of Zn substitution in maghemite nanoparticles on variation of cation vacancies distribution is investigated. • There exists an extra phase of Zn substituted with magnetite and with maghemite which decreases the vacancy concentration of the y=0.36 sample.
[en] The Nuclear Imaging Detector Development group at the Department of Physics, University of Regina is developing Canada's first positron emission tomography (PET) system for plant physiological function studies. In its current configuration the system consists of four detectors heads, each with active area of 48x48 mm2. In a typical arrangement the four detectors are grouped in two pairs of opposing heads for detecting coincident events from positron annihilation, however the system geometry, data acquisition and image reconstruction are flexible and can be easily reconfigured on-demand to accommodate other scanner configurations. The detector pairs can be scanned along the vertical axis allowing to image plants up to 50 cm tall, while the plant within the Field of View (FOV) of the scanner can be rotated on a precision controlled motorized platform to provide a complete 3D coverage of the plant. Current development and characterization of the plant PET system will be presented. (author)
[en] Positron annihilation lifetime spectroscopy (PALS) was applied to study the annealing of radiation-induced defects in polycrystalline tungsten (W) irradiated with 21.6 MeV protons at 100 °C up to a fluence of 5 × 1015 p/cm2. Three components were observed in the measured spectra: short-lifetime of 100–120 ps (positron annihilation in the defect-free W lattice), medium-lifetime of ∼190–330 ps (annihilation at mono-vacancies and small vacancy cluster containing ∼ 2–4 vacancies) and long-lifetime of ∼500 ps (annihilation in large vacancy clusters containing more than 10 vacancies). The irradiation of W with protons at 100 °C, primary, led to the formation of mono-vacancies, self-interstitial defects were created as well but migrated towards sinks during the irradiation. Onset of vacancy diffusion in W starts already at 200 °C before defect recovery stage III. After annealing at ∼400 °C, a sharp drop in the intensity of the positron medium-life component together with a simultaneous increase in positron lifetime from ∼220 to ∼280 ps is observed, and a long-life component appears. This indicates migration and annealing of vacancies and their agglomeration in large vacancy clusters. After annealing at 500–700C, the intensity of long-life component increases indicating the growth of large vacancy clusters but at 900 °C they anneal completely as the mean lifetime recovers nearly to the value measured in the un-irradiated material.
[en] Room temperature photoconductivity measurements have been carried out on various as-grown SrTiO3 single crystals provided from different suppliers. We observed an increase in the conductivity of samples based on photon energy and photon intensity. While low energy photons decreased the conductivity, photons with energy close to the band gap of SrTiO3 enhanced the conductivity. No persistent photoconductivity was observed in these samples. Defects play the main role in inducing the photoconductivity. Positron annihilation lifetime spectroscopy and digital coincidence Doppler broadening spectroscopy were used to investigate the presence and nature of defects in the photoconductive samples. The measurements revealed high concentration of defects and the dependence of photoconductivity on defect concentration under 365 and 400 nm illumination. (paper)
[en] The results and possibilities of the samples surfaces research by the Doppler method of positron annihilation spectroscopy (PAS) for a monochromatic beam of positrons at the LEPTA facility are presented in this paper. Method with high-resolution sensitivity to defects like vacancies and dislocations allows scanning of the surface and near-surface sample layers to a depth of several micrometers by the method of Doppler broadening of annihilation lines. The opportunities for the development of a PAS method based on the measurement of the positron lifetime in the sample irradiated by ordered flow of positrons from the injector of accelerator complex LEPTA at JINR are discussed.