First Stages of Nano-Crystallization of Amorphous Fe75.5Cu1Si12.5B8 Studied by the Positron Annihilation Lifetime Technique

1993 ◽  
Vol 321 ◽  
Author(s):  
A. J. Kruk ◽  
H. Schut ◽  
J. Sietsma ◽  
A. Van Veen
Keyword(s):  
Positron Annihilation ◽  
Crystallization Process ◽  
Positron Lifetime ◽  
Early Stage ◽  
Average Density ◽  
Crystalline Material ◽  
Positron Annihilation Lifetime ◽  
Resistivity Measurements ◽  
Nano Crystalline ◽  
Crystallisation Process

ABSTRACTThe first stages of the nano-crystallization process of amorphous Fe75.5Cu1Nb3Si12.5B8 into a nano-crystalline structure are investigated by the positron annihilation lifetime technique. Samples have been isothermally annealed at 643 K for times varying between 600 and 105 seconds. The positron lifetime spectra have been analyzed allowing for three lifetimes. The shortest and the longest lifetime, τ1 = 150 ± 2 ps and τ3 = 1500–2000 ps respectively, are attributed to annihilation of positrons in the amorphous phase and to the formation and annihilation of ortho-positronium at the surface of the stacked foils and did not change significantly upon the annealing. The intermediate positron lifetime τ2 increased from 324 ps to 387 ps. The intensity of this component increased from 5 to 15%. Comparison with resistivity measurements indicates that the change of this lifetime component occurs at an early stage in the crystallisation process, i.e. when the fraction of crystalline material is on the order of 10−3. The increase of τ2 is attributed to positrons annihilating in a region with lower average density surrounding the small crystallite.

Preliminary Positron Lifetime Results on Free Volumes in Cyclodextrins

2010 ◽  
Vol 666 ◽  
pp. 99-102 ◽  
Author(s):  
Maria Fatima Ferreira Marques ◽  
A.M.G. Moreira Da Silva ◽  
P.M. Gordo ◽  
Z. Kajcsos
Keyword(s):  
Positron Annihilation ◽  
Free Volume ◽  
Positron Lifetime ◽  
Positron Annihilation Lifetime Spectroscopy ◽  
Positron Source ◽  
Lifetime Component ◽  
Positron Annihilation Lifetime ◽  
Long Lifetime

Positron annihilation lifetime spectroscopy was used to study the free-volume parameters in various pure -, - and -cyclodextrins samples and, in the case of β-cyclodextrin, with inclusion of S-carvone and thymoquinone. The results clearly indicate the presence of long lifetime components related to Ps-formation. The data show that the addition of S-carvone to β-cyclodextrin results in a decrease of o-Ps lifetime that we ascribe to a reduction of free volume holes from 81.8 to 63.7 Å3. The long lifetime component disappears when thymoquinone is added to -cyclodextrin, indicating this substance acts as an o-Ps quencher. For all samples studied, a decrease in the long lifetime component values was observed with increasing source in situ time, a result that might be attributed to the irradiation of the sample by the 22Na positron source.

Positron Annihilation in Carbon Nanotubes

2008 ◽  
Vol 607 ◽  
pp. 198-200 ◽  
Author(s):  
Wei Feng Guo ◽  
Xiang Lei Chen ◽  
Huai Jiang Du ◽  
Hui Min Weng ◽  
Bang Jiao Ye
Keyword(s):  
Carbon Nanotubes ◽  
Positron Annihilation ◽  
Positron Lifetime ◽  
External Surface ◽  
Single Component ◽  
Positron Annihilation Lifetime

Positron annihilation lifetime spectra have been measured in carbon nanotubes being pressed as a function of pressure up to 1536MPa. In addition, positron lifetime experiments for carbon nanotubes in vacuum, nitrogen and air have been performed respectively. Lifetimes have been obtained using LIFETIME program. The results display a single-component positron annihilation lifetime. Positron lifetime for carbon nanotubes decreases as the pressure increases, but lifetime is basically consistent after the pressure of 960MPa. Positron annihilation lifetime for carbon nanotubes in air is the shortest whereas the lifetime in vacuum the longest. We conclude that a positron annihilates with an electron on the external surface of carbon nanotubes.

scholarly journals POSITRON LIFETIME MEASUREMENTS IN NATURAL RUBBER WITH DIFFERENT FILLERS

2013 ◽  
Vol 22 ◽  
pp. 112-117 ◽  
Author(s):  
A. MANDAL ◽  
S. MUKHERJEE ◽  
S. PAN ◽  
A. SENGUPTA
Keyword(s):  
Natural Rubber ◽  
Positron Annihilation ◽  
Free Volume ◽  
Positron Lifetime ◽  
Amorphous Region ◽  
Filler Concentration ◽  
Lifetime Measurements ◽  
Positron Annihilation Lifetime

Positron annihilation lifetime spectra (PLAS) have been measured for natural rubber polymer with different fillers (Titenium dioxide, Nanosilica and Nanoclay) as a function of filler concentration to investigate how these fillers affect the microstructure of free volume of natural rubber. The lifetime spectra is analyzed by using LT9.0 and the longest lived component(τo-Ps) is attributed to the pick- off annihilation of o-Ps in free volume sites, available mostly in the amorphous region of polymer. On the basis of the τo-Ps values the radii of the free volume holes (Rh) are calculated. The PALS results show that o-Ps lifetime as well as the size of free volume decreases with the increase of filler concentration.

Recent Progress on the Positron Annihilation Experiments on Irradiated Ferritic/Martensitic Steels Containing Helium

2021 ◽  
Vol 1024 ◽  
pp. 1-12
Author(s):  
Vladimir Krsjak
Keyword(s):  
Radiation Damage ◽  
Positron Annihilation ◽  
Neutron Irradiation ◽  
Early Stage ◽  
High Sensitivity ◽  
Positron Annihilation Spectroscopy ◽  
Martensitic Steels ◽  
Positron Annihilation Lifetime ◽  
Induced Defects

The well-known and often acceptable radiation tolerance of ferritic/martensitic (f/m) steels can be severely diminished when neutron irradiation is accompanied by the production of helium. The presence of helium in the irradiated materials changes the kinetics of the nucleation, recombination, and clustering of the radiation-induced defects. High production rates of helium may lead to a non-negligible volumetric bubble swelling at relatively low temperatures. Extrapolation of the knowledge gained from neutron irradiation experiments to fusion or spallation environments is additionally complicated due to the unknown and comprehensive effects of dpa rate, temperature, the presence of sinks in the crystal lattice and others. To improve the understanding of the microstructure and irradiation parameters effects, close attention must be paid to the early stages of the radiation damage. It is expected that the pre-existing vacancy-type defects, attributed to lattice distortion at the grain/subgrain boundaries and oxide-matrix interfaces, are effective sinks for primary defects and helium, i.e. they control the formation and growth of helium-vacancy agglomerations. This early-stage radiation damage, however, cannot be captured by conventional transmission electron microscopy, and thus other experimental techniques are called for. One of the most perspective experimental approaches to investigate small vacancy-type defects, with a high sensitivity to confined helium, is to utilize positron annihilation spectroscopy (PAS). In particular, two spectroscopy techniques, positron annihilation lifetime spectroscopy (PALS) and Doppler broadening spectroscopy (DBS) of the annihilation line, can be beneficially used for the characterization of helium-vacancy clusters. This paper reviews the recent positron annihilation spectroscopy characterization of various irradiation experiments involving helium. Mainly two types of irradiation experiments are addressed, helium implantation and spallation neutron source irradiation experiments. Discussion is aimed at the potential of PAS in the early-stage formation of helium bubbles and the investigation of the effects of irradiation parameters in defect production and accumulation.

Positron Lifetime Annihilation Study of Porous Composites and Silicas Synthesized Using Polymer Templates

2017 ◽  
Vol 373 ◽  
pp. 280-283
Author(s):  
Marek Gorgol ◽  
Agnieszka Kierys ◽  
Radosław Zaleski
Keyword(s):  
Composite Materials ◽  
Porous Structure ◽  
Positron Annihilation ◽  
Positron Lifetime ◽  
Polymer Chains ◽  
Positron Annihilation Lifetime ◽  
Hydrophobic Polymers ◽  
Polymer Templates ◽  
Chemical Character ◽  
Porous Composites

The porous structure of polymer-silica composites, based on three polymer templates, which differ in a porosity and hydrophobicity, was examined using positron annihilation lifetime spectroscopy. Additionally, the investigation of silicas obtained after removal of polymers during calcination of composite materials, was performed. In composites based on hydrophobic polymers, silica condensates only in larger free volumes, while SiO2 deeply penetrates spaces between polymer chains, when the template is polar. Moreover, the structure of the silica gel, obtained after polymer removal, depends on chemical character of the template, rather than its porosity.

Positron Lifetime Studies of Polyaniline Conducting Polymers

1995 ◽  
Vol 413 ◽  
Author(s):  
C. M. Huang ◽  
J. Liu ◽  
T. C. Sandreczki ◽  
Y. C. Jean
Keyword(s):  
Positron Annihilation ◽  
Room Temperature ◽  
Positron Lifetime ◽  
The Other ◽  
Chemical Compositions ◽  
Lifetime Measurements ◽  
Positron Annihilation Lifetime ◽  
Positron Lifetimes ◽  
Lifetime Studies ◽  
Made In

ABSTRACTPositron annihilation lifetime measurements are made in a series of polyaniline polymers with different chemical compositions and protonation ratios at room temperature. Two positron lifetimes are observed in these materials: one is assigned to annihilation in the bulk and the other to voids created due to protonation. A relationship between conductivities and positron annihilation probabilities is found.

Examination of Neutron-Irradiated Pressure-Vessel Steel Using Positron Annihilation Lifetime Spectrosopy

1998 ◽  
Vol 540 ◽  
Author(s):  
Stephen E. Cumblidge ◽  
Arthur T. Motta ◽  
Gary L. Catchen
Keyword(s):  
Positron Annihilation ◽  
Pressure Vessel ◽  
Positron Lifetime ◽  
Pressure Vessel Steel ◽  
Vessel Steel ◽  
Positron Annihilation Lifetime ◽  
Annealing Temperatures ◽  
Neutron Damage ◽  
Reactor Temperature ◽  
Positron Lifetimes

AbstractOn a variety of pressure-vessel (PV) steels, we have observed changes in the average positron lifetime with increasing (near end-of-life) neutron fluences. Samples were irradiated at reactor-temperature and subjected to post-irradiation annealing, and they were examined using positron annihilation lifetime spectroscopy (PALS). The measured average positron lifetimes in high-temperature (2900 C-300° C) irradiated PV steels decrease with increasing neutron damage up to fluences of 8.5×1018 cm−2 and increase again at higher fluences. Annealing of high-fluence, 300° C irradiated ASTM A508 PV steel samples produces an initial decrease in average positron lifetimes with increasing annealing temperatures of up to 400° C, followed by an increase in average positron lifetime with higher annealing temperatures, when samples were annealed in successive 24-hour steps. A sample of weld steel, irradiated to 2.2×1019 cm−2 at 290° C, shows similar behavior in which the minimum lifetime occurs at ≈ 450° C. These trends are similar to those seen in previous studies performed on VVER and other ferritic steels.

Positron Annihilation in Thermally Treated Co-Zr-V Metallic Glasses

2010 ◽  
Vol 666 ◽  
pp. 58-61
Author(s):  
Ewa Dryzek ◽  
Jacek Jaworski ◽  
Eric Fleury ◽  
Andrzej Budziak
Keyword(s):  
Heat Treatment ◽  
Magnetic Properties ◽  
Chemical Composition ◽  
Positron Annihilation ◽  
Metallic Glasses ◽  
Annealing Temperature ◽  
Positron Lifetime ◽  
Positron Annihilation Lifetime Spectroscopy ◽  
Positron Annihilation Lifetime ◽  
Microstructure Changes

Positron annihilation lifetime spectroscopy (PALS) has been applied to study if the microstructure changes in Co80Zr10V10 and Co65Zr10V25 metallic glasses after heat treatment. Samples in as-quenched state were isothermally annealed at chosen temperatures in the temperature range 100°C - 580°C for 1 hour. In spite of differences of chemical composition and magnetic properties the obtained dependencies of positron lifetime on annealing temperature do not differ significantly for lower temperatures. The higher increase of positron lifetime for Co65Zr10V25 than that for Co80Zr10V10 indicates differences in crystallization in the two metallic glasses studied.

scholarly journals Determining the positron lifetime of a material using Positron Annihilation Lifetime Spectroscopy

2019 ◽  
Vol 25 ◽  
pp. 245
Author(s):  
K. Triantou ◽  
K. Mergia ◽  
I. E. Stamatelatos ◽  
G. Apostolopoulos ◽  
S. Messoloras
Keyword(s):  
Positron Annihilation ◽  
Positron Lifetime ◽  
Positron Annihilation Lifetime Spectroscopy ◽  
Positron Annihilation Lifetime

N/A

A New Version of LT Program for Positron Lifetime Spectra Analysis

2010 ◽  
Vol 666 ◽  
pp. 138-141 ◽  
Author(s):  
Dawid Giebel ◽  
Jerzy Kansy
Keyword(s):  
User Interface ◽  
Positron Annihilation ◽  
Programming Language ◽  
Operating Systems ◽  
Positron Lifetime ◽  
Spectra Analysis ◽  
Positron Annihilation Lifetime ◽  
Modern Programming Language

LT 10 is a new version of LT program designed to analysis of Positron Annihilation Lifetime Spectra (PALS). The new program is equipped with a new user interface and other features unavailable in its previous versions. It has been created again in a modern programming language and is now compatible with the latest operating systems.

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