Vacancy-Solute Binding Energies in Aluminum by Positron Annihilation

Resonant Positron Annihilation on Molecules

Materials Science Forum ◽

10.4028/www.scientific.net/msf.607.9 ◽

2008 ◽

Vol 607 ◽

pp. 9-16 ◽

Cited By ~ 1

Author(s):

J.A. Young ◽

C.M. Surko

Keyword(s):

Positron Annihilation ◽

Binding Energies ◽

Current Understanding ◽

Positronium Atom ◽

Feshbach Resonances ◽

Positron Energy ◽

Incident Positron

At incident positron energies below the threshold for positronium atom formation, there are many cases in which annihilation rates for molecules are far in excess of that possible on the basis of simple two-body collisions. We now understand that this phenomenon is due to positron attachment to molecules mediated by vibrational Feshbach resonances. The attachment enhances greatly the overlap of the positron with molecular electrons and hence increases the probability of annihilation. Furthermore, measurements of the annihilation spectra as a function of incident positron energy provide a means of measuring positron-molecule binding energies. In this paper we present an overview of our current understanding of this process, highlighting key results and discussing outstanding issues that remain to be explained.

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Calculation of Positron Binding Energies and Electron–Positron Annihilation Rates for Atomic Systems with the Reduced Explicitly Correlated Hartree–Fock Method in the Nuclear–Electronic Orbital Framework

The Journal of Physical Chemistry A ◽

10.1021/acs.jpca.6b10124 ◽

2017 ◽

Vol 121 (2) ◽

pp. 515-522 ◽

Cited By ~ 7

Author(s):

Kurt R. Brorsen ◽

Michael V. Pak ◽

Sharon Hammes-Schiffer

Keyword(s):

Positron Annihilation ◽

Binding Energies ◽

Atomic Systems ◽

Hartree Fock ◽

Electron Positron Annihilation ◽

Electron Positron ◽

Explicitly Correlated

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Influence of geometry on positron binding to molecules

Journal of Physics B Atomic Molecular and Optical Physics ◽

10.1088/1361-6455/ac3e78 ◽

2021 ◽

Author(s):

J R Danielson ◽

Soumen Ghosh ◽

clifford surko

Keyword(s):

Dipole Moment ◽

Binding Energy ◽

Positron Annihilation ◽

Significant Role ◽

Dipole Moments ◽

Molecular Size ◽

Molecular Geometry ◽

Binding Energies ◽

Molecular Polarizability ◽

Global Parameters

Abstract Annihilation studies have established that positrons bind to most molecules. They also provide measurements of the positron-molecule binding energies, which are found to vary widely and depend upon molecular size and composition. Trends of binding energy with global parameters such as molecular polarizability and dipole moment have been discussed previously. In this paper, the dependence of binding energy on molecular geometry is investigated by studying resonant positron annihilation on selected pairs of isomers. It is found that molecular geometry can play a significant role in determining the binding energies even for isomers with very similar polarizabilities and dipole moments. The possible origins of this dependence are discussed.

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Ageing Characteristics of Al-Mg-(Ge,Si)-Cu Alloys

Materials Science Forum ◽

10.4028/www.scientific.net/msf.794-796.971 ◽

2014 ◽

Vol 794-796 ◽

pp. 971-976 ◽

Cited By ~ 2

Author(s):

Meng Liu ◽

Calin Daniel Marioara ◽

Randi Holmestad ◽

John Banhart

Keyword(s):

Positron Annihilation ◽

Positron Lifetime ◽

Binding Energies ◽

Natural Ageing ◽

Atomic Size ◽

Initial Formation ◽

Positron Annihilation Lifetime ◽

Cu Alloys ◽

Initial Decrease

In order to elucidate some of the differences between Al-Mg-Si and Al-Mg-Ge alloys and the role of Cu, a series of Al-Mg-Ge, Al-Mg-Si and Al-Mg-Ge-Si alloys, some of them containing Cu, are investigated by positron annihilation lifetime spectroscopy during natural ageing. Al-Mg-Ge alloys show qualitatively the same evolution of positron lifetime τ1Cwith time as Al-Mg-Si alloys, namely an initial decrease, followed by a re-increase, after which τ1Cdrops to an equilibrium value. However, for alloys with equal Mg contents, Ge gives rise to a notably slower ageing kinetics than Si, pointing at effects of atomic size or solute-vacancy binding energies. Adding Cu to both Al-Mg-Ge and Al-Mg-Si alloys slows down the initial formation of clusters but promotes their further growth.

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Investigation of Helium Behavior in RAFM Steel by Positron Annihilation Doppler Broadening and Thermal Desorption Spectroscopy

Materials ◽

10.3390/ma11091523 ◽

2018 ◽

Vol 11 (9) ◽

pp. 1523

Author(s):

Zhenyu Shen ◽

Liping Guo ◽

Weiping Zhang ◽

Shuoxue Jin ◽

Xingzhong Cao ◽

...

Keyword(s):

Positron Annihilation ◽

Thermal Desorption ◽

Thermal Desorption Spectroscopy ◽

Binding Energies ◽

Doppler Broadening ◽

Martensitic Steels ◽

Helium Bubbles ◽

Different Temperatures ◽

Higher Temperature ◽

Rafm Steel

The behavior of helium in reduced-activation ferritic/martensitic steels was investigated systematically with positron annihilation Doppler broadening measurement and thermal desorption spectroscopy. Specimens were irradiated with helium ions with different energies to various fluences at different temperatures. A threshold fluence was observed above which the rate of formation and growth of helium bubbles dramatically increased. Irradiation at higher temperature could suppress the formation and growth of HenVm clusters with low binding energies and enhance that of helium bubbles and HenVm clusters with high binding energies. Different changes of S parameters were observed in various depth after the irradiation temperature was increased from 523 K to 723 K. Irradiation of 18 keV-He+ enhanced the growth of HenVm clusters and helium bubbles compared with 100 keV-He+ irradiation. A possible mechanism is discussed.

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