Positron annihilation in 60Co irradiated alkali halides

1978 ◽  
Vol 56 (12) ◽  
pp. 1527-1530 ◽  
Author(s):  
S. Dannefaer ◽  
D. P. Kerr ◽  
G. W. Dean ◽  
B. G. Hogg
Keyword(s):  
Experimental Data ◽  
Positron Annihilation ◽  
Momentum Distribution ◽  
Positron Lifetime ◽  
Alkali Halides ◽  
Systematic Investigation ◽  
Theoretical Treatment ◽  
Doppler Broadening ◽  
Lifetime Component ◽  
Gamma Irradiated

A systematic investigation of 17 gamma-irradiated alkali halides using positron lifetime and Doppler broadening techniques has been performed. For eight of the alkali halides (NaCl, NaBr, KCl, KBr, KI, RbCl, RbBr, and RbI), a new lifetime with values between 1.0 and 1.3 ns is attributed to positrons trapped in F centres. Despite large F centre concentrations in LiF, LiCl, LiBr, and NaF, no such lifetime component is observed in these samples. Doppler broadening measurements show that in nearly all cases the momentum distribution becomes narrower upon irradiation. The experimental data are discussed in view of a recent theoretical treatment of the positron – F centre problem.

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.

Ni-Substitution Induced Inversion in ZnFe2O4 Seen by Positron Annihilation

2012 ◽  
Vol 733 ◽  
pp. 219-223 ◽  
Author(s):  
P.M.G. Nambissan ◽  
O. Mondal ◽  
C. Chakrabarty ◽  
M. Pal
Keyword(s):  
Positron Annihilation ◽  
Spinel Structure ◽  
Positron Lifetime ◽  
Drastic Change ◽  
Doppler Broadening ◽  
Positron Trapping ◽  
Normal Spinel ◽  
Ni Substitution ◽  
Positron Lifetimes ◽  
Coincidence Doppler Broadening

We report in this work about the inversion of the spinel structure of ZnFe2O4induced by the substitution of Zn2+by Ni2+ions. Positron lifetimes were measured in Zn1-xNixFe2O4with different concentrations (x) of doped Ni2+ions and a drastic change across x = 0.4 – 0.6 was observed, which is attributed to this transformation. The interchange of positions of the cations on doping leaves a fraction of them unoccupied and these vacancies act as positron trapping centres. Since Ni2+is smaller in size than Zn2+, defects due to non-stoichiometry are less in NiFe2O4than in ZnFe2O4. The increase in positron lifetime implies the trapping of positrons being shifted from A- to B-sites and is an indication of the transformation from inverse to normal spinel configuration. Coincidence Doppler broadening measurements supported these findings.

Investigation of Defects Accumulation in the Process of Hydrogen Sorption and Desorption

2015 ◽  
Vol 1085 ◽  
pp. 328-334 ◽  
Author(s):  
Andrey M. Lider ◽  
Olga V. Husaeva ◽  
Yuriy S. Bordulev ◽  
Roman S. Laptev ◽  
Viktor N. Kudiiarov
Keyword(s):  
Positron Annihilation ◽  
Gas Phase ◽  
Defect Structure ◽  
Positron Lifetime ◽  
Pure Titanium ◽  
Structure Study ◽  
Hydrogen Sorption ◽  
Doppler Broadening ◽  
Commercially Pure Titanium ◽  
Commercially Pure

This paper is devoted to the defect structure study of commercially pure titanium after hydrogen sorption-desorption cycles by means of positron lifetime (PL) and Doppler broadening spectrometry. Material was loaded with hydrogen from the gas phase till the concentration of hydrogen reached the value of 0.05 wt.% for each cycle. The essential changes in the positron annihilation characteristics of the sample are occurred after the each stage of treatment.

Positron annihilation in mordenite zeolite

2021 ◽  
Vol 6 (1) ◽  
pp. 50-55
Author(s):  
Hoa Lang Trinh ◽  
Van Tao Chau ◽  
Hoang Lam Le ◽  
Quoc Dung Tran
Keyword(s):  
Experimental Data ◽  
Positron Annihilation ◽  
Dft Calculation ◽  
Positron Lifetime ◽  
Theoretical Study ◽  
Material Structure ◽  
Accuracy Analysis ◽  
Complicated Structure ◽  
Theoretical Results ◽  
Selection Of

The theoretical study of the positron annihilation in complex material such as zeolite is greatly significant to support and increase the accuracy analysis of the material structure from the experimental data of the positron annihilation. The mordenite zeolite is a big and complicated structure consisting of channels and cavities. The analysis of the mordenite structure is studied by the PALS so depending on the selection of the positron lifetime components of the positron annihilation spectra fitting methods. Therefore, these positron life times in on TO4, Na, Ca, K, Fe, H2O and the rings which form the channels and cavities are sophisticatedly studied by the DFT calculation using Ab-initio. The mordenite and modified mordenite zeolite structures are precisely analyzed, and the physical behaviors of the positron in these are more understood by these theoretical results.

Positron Annihilation in Teflon and Polyethylene

1974 ◽  
Vol 52 (11) ◽  
pp. 935-939 ◽  
Author(s):  
Donald P. Kerr
Keyword(s):  
Angular Distribution ◽  
Positron Annihilation ◽  
Angular Correlation ◽  
Gamma Rays ◽  
Momentum Distribution ◽  
Angular Distributions ◽  
Distribution Data ◽  
Lifetime Component ◽  
Considerable Uncertainty ◽  
Correlation Data

Both the time spectra and the angular distributions of the annihilation gamma rays have been measured for positrons annihilating in Teflon and polyethylene in an attempt to clarify which annihilation mechanisms account for the various lifetimes in these materials. Some authors have suggested that, in addition to the longest lifetime component, one of the shorter lived components also arises from the pickoff annihilation of orthopositronium. If this were the case, substantially more positronium would be formed than is indicated by the intensity of the longest lived component alone, and should be detectable through a measurement of the intensity of the low momentum portion of the momentum distribution obtained from the angular correlation data. In the present work, four lifetimes are apparent in the time spectra although there is considerable uncertainty in resolving the two shortest components. The angular distribution data, in both cases, yielded a low momentum component whose intensity indicates that only the longest lifetime component arises from pickoff annihilation of orthopositronium. The three shorter lifetime components are discussed.

Positron Annihilation Studies on La1-xSrxMnO3 Manganites

2017 ◽  
Vol 373 ◽  
pp. 201-204
Author(s):  
Yu Yang Huang ◽  
Yan Meng ◽  
Wen Hua Huang ◽  
Shou Lei Xu ◽  
Ding Kang Xiong ◽  
...  
Keyword(s):  
Curie Temperature ◽  
Positron Annihilation ◽  
Electron Density ◽  
Exchange Coupling ◽  
Positron Lifetime ◽  
Double Exchange ◽  
Ferromagnetic Coupling ◽  
Doppler Broadening ◽  
Doppler Broadening Spectra ◽  
Coincidence Doppler Broadening

Positron lifetime and coincidence Doppler broadening spectra of La1-xSrxMnO3 and LaMnO3 manganites were measured. The effects of Sr contents on the microdefects of La1-xSrxMnO3 were investigated by means of positron lifetime results. The signals of 3d electrons of La1-xSrxMnO3 were extracted from the coincidence Doppler broadening spectra. The results show that the electron density of La1-xSrxMnO3 is larger than that of LaMnO3. The open volume of the defect in La1-xSrxMnO3 increases with the Sr contents. The signals of 3d electrons of ferromagnetic La1-xSrxMnO3 is larger than that of antiferromagnetic LaMnO3, and it reaches the maximum at x=0.33, that is, the signals of 3d electrons of the La0.67Sr0.33MnO3 is the highest in all testing samples, which corresponds to a lowest resistivity and a higher Curie temperature of the manganite. The influence of 3d electrons on the ferromagnetic double-exchange coupling and anti-ferromagnetic coupling of La1-xSrxMnO3 were discussed.

Doppler Broadening Measurement of Positron Annihilation in Alkali Halides

1978 ◽  
Vol 44 (1) ◽  
pp. 204-210 ◽  
Author(s):  
Yasukazu Yoshizawa ◽  
Kiyoshi Shizuma ◽  
Toshiaki Fujita ◽  
Masato Nishi
Keyword(s):  
Positron Annihilation ◽  
Alkali Halides ◽  
Doppler Broadening

Hydrogen interaction with oxidized Si(111) probed with positrons

1989 ◽  
Vol 67 (8) ◽  
pp. 818-820 ◽  
Author(s):  
K. G. Lynn ◽  
Bent Nielsen ◽  
D. O. Welch
Keyword(s):  
Positron Annihilation ◽  
Momentum Distribution ◽  
Electron Pair ◽  
Positron Beam ◽  
Thermally Grown Oxide ◽  
Doppler Broadening ◽  
Hydrogen Binding ◽  
Hydrogen Interaction ◽  
Hydrogen Exposure ◽  
Variable Energy

A variable-energy positron beam was utilized to study the interface action of hydrogen with Si(111) covered by an ultrahigh-vacuum thermally grown oxide of 2–3 nm thickness. It was observed that positrons implanted at shallow depth (<100 nm) after diffusion are trapped either at the interface between the oxide and the Si or in the oxide. The positron-annihilation characteristics of these trapped positrons are found to be very sensitive to hydrogen exposure. The momentum distribution of the annihilating positron–electron pair, as observed in the Doppler broadening of the annihilation line, broadens considerably after exposure to hydrogen. The effect recovers after annealing at [Formula: see text], suggesting a hydrogen binding at the interface of ~3 ± 0.3 eV.

An Investigation of Point Defects in NiAl Using Positron Annihilation Techniques

1998 ◽  
Vol 552 ◽  
Author(s):  
Werner Puff ◽  
Bernd Logar ◽  
Adam G. Balogh
Keyword(s):  
Positron Annihilation ◽  
Point Defects ◽  
Proton Irradiation ◽  
Positron Lifetime ◽  
Composition Range ◽  
Isochronal Annealing ◽  
Doppler Broadening ◽  
Positron Lifetime Spectroscopy ◽  
Induced Defects

ABSTRACTVacancy-like defects in NiAl in the composition range 47 at.-% < CNi < 53 at.-% are investigated by means of positron lifetime spectroscopy and Doppler-broadening measurements. The observed lifetimes in the annealed samples confirm that defects are quenched-in during the production of the samples. Isochronal annealing of samples quenched at 1600°C and after proton irradiation show that the induced defects are quite different.

Study of Gamma Irradiation Effect on Unplasticized PVC by Positron Annihilation

2017 ◽  
Vol 373 ◽  
pp. 274-279
Author(s):  
Bao Yi Wang ◽  
Jing Yang ◽  
Xing Zhong Cao ◽  
Long Wei ◽  
Run Sheng Yu
Keyword(s):  
Gamma Irradiation ◽  
Positron Annihilation ◽  
Reference Sample ◽  
Irradiation Effect ◽  
Doppler Broadening ◽  
Carbonyl Groups ◽  
Positron Annihilation Lifetime ◽  
Ratio Curve ◽  
Gamma Irradiated ◽  
Coincidence Doppler Broadening

Positron annihilation technique is used to study the gamma irradiation effect on unplasticized PVC (UPVC). Positron annihilation lifetime spectroscopy (PALS) results show that both the o-Ps lifetime and intensity decrease with the increase of gamma irradiation dose. By comparing Coincidence Doppler Broadening (CDB) results of four typical polymers using different reference sample, it is confirmed that CDB ratio curve can truthfully reflect the momentum difference of electrons which positrons annihilate with. The CDB results of gamma-irradiated UPVC using non-irradiated UPVC rather than commonly chosen LDPE as a reference sample show obvious oxygen peak, together with FTIR results, verify the appearance of carbonyl groups around the free volume.

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