Positron annihilation studies on coordination compounds. 1. Investigation of positron lifetime and angular correlation of annihilation .gamma. photons on the mixed complexes of bis(dimethylglyoximato)cobalt(III) with unidentate ligands

1977 ◽  
Vol 81 (14) ◽  
pp. 1424-1427 ◽  
Author(s):  
K. Burger ◽  
B. Levay ◽  
A. Vertes ◽  
C. Varhelyi
Keyword(s):  
Positron Annihilation ◽  
Angular Correlation ◽  
Coordination Compounds ◽  
Positron Lifetime ◽  
Mixed Complexes

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.

Positron Annihilation with Core Electrons in the Noble Metals

1974 ◽  
Vol 52 (4) ◽  
pp. 336-339 ◽  
Author(s):  
E. H. Becker ◽  
A. G. Gould ◽  
E. M. D. Senicki ◽  
B. G. Hogg
Keyword(s):  
Simple Model ◽  
Fermi Surface ◽  
Single Crystals ◽  
Positron Annihilation ◽  
Angular Correlation ◽  
Noble Metals ◽  
Correlation Data ◽  
Core Electrons

Experimental angular correlation curves for identically oriented single crystals of copper, silver, and gold have been obtained using "a point geometry" apparatus. The differences between these angular correlation data are compared to the differences predicted using a simple model of the Fermi surface combined with calculations of the theoretical core distributions.

Investigation of Polymer Relaxation after Deformation by Positron Annihilation

1992 ◽  
Vol 247 ◽  
Author(s):  
Sergey A. Tishin ◽  
Mihail I. Tsapovestsky ◽  
Vladimir A. Tishin ◽  
Vladimir N. Kestelman
Keyword(s):  
Positron Annihilation ◽  
Angular Correlation ◽  
Life Time ◽  
Slow Relaxation ◽  
Dielectric Losses ◽  
Free Film ◽  
Axial Tension ◽  
Polymer Relaxation ◽  
Sample Density ◽  
Nonmonotonic Change

ABSTRACTThe relaxation of polyimid films after the axial tension has been investigated by measuring life-time of positrons and angular correlation of annihilation photons. The nonmonotonic change of mean life-time while relaxing the free film has been found. Two range of changes of positron-sensitive properties can be seen: “rapid” relaxation for 4–5 hours (characterized by reducing life-time of short-lived component) and “slow” relaxation (characterized by reducing the intensity of long-lived component). The results of this investigation have been compared with those of measuring of sample density and dielectric losses. The possible explanations and the- changes of mechanizms of relaxation with the conditions of deformation and “the rest” of polymers are analyzed.

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.

Angular Correlation of Positron Annihilation Radiation from Single Crystals of Vanadium-Deuterium Alloys

1979 ◽  
Vol 46 (2) ◽  
pp. 481-487 ◽  
Author(s):  
Masayuki Hasegawa ◽  
Shu-ichi Koike ◽  
Makoto Hirabayashi ◽  
Hajime Asano ◽  
Toshiharu Suzuki
Keyword(s):  
Single Crystals ◽  
Positron Annihilation ◽  
Angular Correlation ◽  
Annihilation Radiation

Positron Lifetime Calculation for Plastic Deformed Nanocrystalline Copper

2017 ◽  
Vol 373 ◽  
pp. 31-34
Author(s):  
Kai Zhou ◽  
Ting Zhang
Keyword(s):  
Positron Annihilation ◽  
Deformation Mechanism ◽  
Positron Lifetime ◽  
Experimental Information ◽  
Point Of View ◽  
Nanocrystalline Copper ◽  
Mean Grain Size ◽  
Positron Lifetimes ◽  
Boundary Deformation

Positron lifetime calculation has been performed on a computer-generated nanocrystalline copper with a mean grain size of 9.1 nm during its deformation. For the undeformed and deformed nanocrystalline copper, calculated positron lifetimes are around 157 ps which come from the positron annihilation in the free volume in grain boundaries. Due to the grain-boundary deformation mechanism, no vacancies or vacancy clusters will be induced in grains during the plastic deformation of the nanocrystalline copper, which is different to the deformation of the conventional polycrystal. From this point of view, in-situ positron annihilation measurements can provide important experimental information on the deformation mechanism of nanocrystalline metals.

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