Defect and Dislocation Density Parameters of 5251 Al Alloy Using Positron Annihilation Lifetime Technique

2012 ◽  
Vol 332 ◽  
pp. 17-25 ◽  
Author(s):  
M.A. Abdel-Rahman ◽  
M. Elsayed ◽  
Ahmed G. Attallah ◽  
A.A. Ibrahim ◽  
Emad A. Badawi
Keyword(s):  
Cross Section ◽  
Positron Lifetime ◽  
Defect Density ◽  
Theoretical Calculations ◽  
Linear Increase ◽  
Trapping Efficiency ◽  
Al Alloy ◽  
Trapping Rate ◽  
Lifetime Measurements ◽  
Positron Annihilation Lifetime

The result of positron lifetime measurements of a defected 5251 Al alloy is reported. Positron lifetime is measured as a function of the thickness reduction of the sample which shows a nearly linear increase and then becomes constant; which can be considered to be a reason for the defect movement saturation. The trapping rate, trapping efficiency, trapping cross-section, defect concentration and defect density of positrons are also measured for the sample concerned. The behaviors of these parameters are matched with theoretical calculations. Data are analyzed using the PATFIT88 computer program.

Positron Lifetime Studies of Defect Structures in Bal-xKxBiO3

1990 ◽  
Vol 209 ◽  
Author(s):  
J.C. O'Brien ◽  
R.H. Howell ◽  
H.B. Radousky ◽  
P.A. Sterne ◽  
D.G. Hinks ◽  
...  
Keyword(s):  
Normal State ◽  
Room Temperature ◽  
Positron Lifetime ◽  
Theoretical Calculations ◽  
Defect Structures ◽  
Cryogenic Temperatures ◽  
Aging Effects ◽  
Temperature Dependent ◽  
Lifetime Measurements ◽  
Lifetime Studies

ABSTRACTTemperature-dependent positron lifetime experiments have been performed from room temperature to cryogenic temperatures on Ba1−xKxBiO3. for x=0.4 and 0.5. From the temperature dependence of the positron lifetime in the normal state, we observe a clear signature of competition between separate defect populations to trap the positron. Theoretical calculations of lifetimes of free or trapped positrons have been performed on Ba1−xKxBiO3, to help identify these defects. Lifetime measurements separated by long times have been performed and evidence of aging effects in the sample defect populations is seen in these materials.

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.

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.

Point Defect Study in Fe72Al28 Alloy as a Function of Thermal Treatment by Positron Lifetime Spectroscopy

2010 ◽  
Vol 666 ◽  
pp. 50-53 ◽  
Author(s):  
Jerzy Kansy ◽  
Aneta Hanc ◽  
Magdalena Jabłońska ◽  
E. Bernstock-Kopaczyńska ◽  
Dawid Giebel
Keyword(s):  
Positron Lifetime ◽  
Vacancy Concentration ◽  
Theoretical Calculations ◽  
Cast State ◽  
Slow Cooling ◽  
Positron Annihilation Lifetime ◽  
Trapping Model ◽  
Positron Lifetime Spectroscopy ◽  
Rate Of Cooling ◽  
Nearest Neighborhood

The defect structure of Fe28Al samples is examined with the Positron Annihilation Lifetime Spectroscopy. The studies are carried out for samples in as-cast state and after heat treatments: annealing for 24 hours at 900°C (or 1050°C) and either slow cooling with furnace or quenching to oil. The PALS spectra are analyzed using two-state trapping model. Only one type of defects is detected. The positron lifetime in these defects (V) suggests that they are quenched-in Fe-monovacancies (VFe). The vacancy concentration strongly depends on the rate of cooling. Besides, V also depends slightly on the rate of cooling of the material. This fact suggests, according to the predictions of latest theoretical calculations, that V is sensitive to the atomic configuration in the nearest neighborhood of VFe, which give hope to estimate the degree of atomic ordering in alloys by the PALS technique.

STUDY OF TRAPPING RATE AND DEFECT DENSITY IN AlSi11.35Mg0.23 BY POSITRON ANNIHILATION TECHNIQUE

2004 ◽  
Vol 11 (04n05) ◽  
pp. 427-432 ◽  
Author(s):  
M. A. ABDEL-RAHMAN ◽  
M. S. ABDALLAH ◽  
EMAD A. BADAWI
Keyword(s):  
Positron Annihilation ◽  
Defect Density ◽  
Defect Concentration ◽  
Thickness Reduction ◽  
Trapping Rate ◽  
Positron Annihilation Lifetime ◽  
Maximum Value ◽  
Mean Lifetime ◽  
The Mean

The measurements of Positron Annihilation Lifetime Technique (PALT) have been performed on AlSi 11.35 Mg 0.23 Alloys. It has been shown that positrons can become trapped at imperfect locations in solids and their mean lifetime can be influenced by changes in the concentration of such defects. No change has been observed in the mean lifetime values at the saturation of defect concentration. The trapping rates of positrons can be determined for thickness reduction up to 11% for dislocation. The concentration of defect (ρ') range varies from 8.65×1015 to 2.35×1018 cm -3 up to the maximum value of strain (ε) 0.23.

XUV Absorption Spectra of Carbon Ions

1988 ◽  
Vol 102 ◽  
pp. 71-73
Author(s):  
E. Jannitti ◽  
P. Nicolosi ◽  
G. Tondello
Keyword(s):  
Absorption Spectra ◽  
Cross Section ◽  
Theoretical Calculations ◽  
Photoionization Cross Section ◽  
Carbon Ions

AbstractThe photoabsorption spectra of the carbon ions have been obtained by using two laser-produced plasmas. The photoionization cross-section of the CV has been absolutely measured and the value at threshold, σ=(4.7±0.5) × 10−19cm2, as well as its behaviour at higher energies agrees quite well with the theoretical calculations.

Seeking the Good Fitting Procedure of PALS Polymer Spectra

2008 ◽  
Vol 607 ◽  
pp. 64-66
Author(s):  
Nicolas Laforest ◽  
Jérémie De Baerdemaeker ◽  
Corine Bas ◽  
Charles Dauwe
Keyword(s):  
Experimental Data ◽  
Low Temperature ◽  
Positron Annihilation ◽  
Physical Meaning ◽  
Lifetime Measurements ◽  
Positron Annihilation Lifetime ◽  
Fitting Procedure ◽  
Fitting Procedures ◽  
Blob Model

Positron annihilation lifetime measurements on polymethylmethacrylate (PMMA) at low temperature were performed. Different discrete fitting procedures have been used to analyze the experimental data. It shows that the extracted parameters depend strongly on the fitting procedure. The physical meaning of the results is discussed. The blob model seems to give the best annihilation parameters.

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.

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