Positron Lifetime Studies of Polyaniline Conducting Polymers

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.

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Positron Lifetime Studies of Defect Structures in Bal-xKxBiO3

MRS Proceedings ◽

10.1557/proc-209-877 ◽

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.

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POSITRON LIFETIME MEASUREMENTS IN NATURAL RUBBER WITH DIFFERENT FILLERS

International Journal of Modern Physics Conference Series ◽

10.1142/s2010194513009999 ◽

2013 ◽

Vol 22 ◽

pp. 112-117 ◽

Cited By ~ 1

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.

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

MRS Proceedings ◽

10.1557/proc-540-471 ◽

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.

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Positron annihilation measurements in high energy alpha irradiated undoped indium antimonide

International Journal of Modern Physics B ◽

10.1142/s0217979214502105 ◽

2014 ◽

Vol 28 (30) ◽

pp. 1450210 ◽

Cited By ~ 1

Author(s):

Sandip Pan ◽

Arunava Mandal ◽

Subrata Mukherjee ◽

Achintya Kumar Saha ◽

Anirban Roychowdhury ◽

...

Keyword(s):

Positron Annihilation ◽

Temperature Region ◽

Indium Antimonide ◽

Line Shape ◽

Room Temperature ◽

Positron Lifetime ◽

High Energy ◽

Isochronal Annealing ◽

Positron Annihilation Lifetime ◽

Lifetime Analysis

Positron annihilation lifetime spectroscopy and Doppler broadening annihilation line-shape measurements were carried out in 40 MeV alpha-irradiated undoped InSb. After irradiation the sample was subjected to an isochronal annealing over temperature region of 25°C–400°C with annealing time of 30 min at each set temperature. After each annealing the positron measurements were carried out at room temperature. Formation of radiation induced defects and their recovery with annealing temperature were investigated. A three component positron lifetime analysis was undertaken to observe the trapping of positrons in the sample after irradiation and during annealing. The average positron lifetime value τ avg = 313 ps at room temperature after irradiation indicated the presence of defects and the high value of τ2 at room temperature suggested that the probable defects were divacancies. A two stage recovery of defects was observed during post irradiation isochronal annealing over the temperature region 25°C–400°C. The variations in line-shape parameter (S) and defect specific parameter (R) during annealing in the temperature region 25°C–400°C resembled the behavior of τ avg indicating the migration of vacancies, formation of vacancy clusters and the disappearance of defects between 300°C to 400°C.

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Positron Annihilation Lifetime Spectroscopy in the study of defects in materials

HNPS Proceedings ◽

10.12681/hnps.1872 ◽

2019 ◽

Vol 24 ◽

pp. 235

Author(s):

K. Triantou ◽

K. Mergia ◽

I. E. Stamatelatos

Keyword(s):

Positron Annihilation ◽

Electron Density ◽

Positron Lifetime ◽

Positron Annihilation Lifetime Spectroscopy ◽

Vacancy Defects ◽

Positron Annihilation Lifetime ◽

Defect Site ◽

Experimental Apparatus ◽

Valuable Method ◽

Positron Lifetimes

The Positron Annihilation Lifetime Spectroscopy (PALS) is a valuable method for the study of the open volume defects in materials. The reduced electron density at the vacant/defect site increases the positron lifetime, and positron lifetime increases as the size of defect increases. In the current paper the experimental apparatus for the measurement of the positron lifetime in materials is described and the spectra from W and Cd specimens are analyzed. The presence of dislocations and vacancy defects is found, since the positron lifetimes of specimens are higher than the defect-free (bulk) values.

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Seeking the Good Fitting Procedure of PALS Polymer Spectra

Materials Science Forum ◽

10.4028/www.scientific.net/msf.607.64 ◽

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.

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

MRS Proceedings ◽

10.1557/proc-321-245 ◽

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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Preliminary Positron Lifetime Results on Free Volumes in Cyclodextrins

Materials Science Forum ◽

10.4028/www.scientific.net/msf.666.99 ◽

2010 ◽

Vol 666 ◽

pp. 99-102 ◽

Cited By ~ 3

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.

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Positron Annihilation Lifetime Measurements in Collagen Biopolymer

MRS Proceedings ◽

10.1557/proc-530-33 ◽

1998 ◽

Vol 530 ◽

Cited By ~ 1

Author(s):

S. Siles ◽

G. Moya ◽

X.H. Li ◽

J. Kansy ◽

P. Moser

Keyword(s):

Positron Annihilation ◽

Amorphous Region ◽

Positron Annihilation Spectroscopy ◽

Lifetime Data ◽

Spectroscopy Technique ◽

Lifetime Measurements ◽

Lifetime Distributions ◽

Positron Annihilation Lifetime ◽

Coincidence System ◽

Three Components

AbstractLifetime measurement in Positron Annihilation Spectroscopy (PAS) is applied to the study of free-volume collagen characteristics as a function of concentration. The lifetimes of positrons were obtained by a conventional fast-fast coincidence system. All lifetime data are fitted in three components by using the computer program POSITRON FIT and resolved. For each concentration, lifetime distributions were analyzed in order to obtain the different components, thus we have observed three components of which a long component τ3. This long lived component can be associated with a pick-off annihilation of ortho-positronium (o-Ps) trapped in free volumes of amorphous region. This investigation shows the potential of the positron annihilation spectroscopy technique in the study of biopolymer microstructures.

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