Positron bound states in alkali halides

Bussolati, C.; Dupasquier, A.; Zappa, L.

doi:10.1007/bf02711095

Cited by 57 publications

(11 citation statements)

References 7 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…More vacancy defects were formed in product MgO due to the removal of H 2 O and crystal type change during decomposition. In early performed [38,39], similar longlived τ 2 ≈0.4~0.6 ns with an intensity I 2 =50% have been detected in alkali halides, which was explained as being attributed to major processes (Ⅰ) annihilation from a complex compound (e + -anion) and (Ⅱ) annihilation with vacancy A-centers (crystal defects). In the present case, the second lifetime components τ 2 of Mg(OH) 2 and MgO are attributed to positrons annihilating in the intersections of several interfaces or some vacancy clusters in grain boundary areas.…”

Section: Analysis Of Positron Annihilation Lifetime Spectramentioning

confidence: 68%

Characterizations of the thermal decomposition of nano-magnesium hydroxide by positron annihilation lifetime spectroscopy

et al. 2017

View full text Add to dashboard Cite

The thermal decomposition behavior of magnesium hydroxide (Mg(OH) 2 ) nanopowders was investigated by positron annihilation lifetime spectroscopy (PALS), X-ray diffraction (XRD), thermogravimetric and differential scanning calorimetry (TG-DSC) analysis, high-resolution transmission electron microscopy (HRTEM) and scanning electron microscopy (SEM). It was indicated that the microstructural changes started from 300 C were earlier than the phase transformation from hexagonal Mg(OH )2 nanopowders to face-centered cubic MgO occurred at about 380 C during decomposition process. The variation of positron annihilation parameters revealed the production of new vacancy defects and the aggregation of vacancy clusters in grain boundary areas and microvoids between particles due to the removal of H 2 O and rearrangement of interface atoms. A positron trapping model was proposed to help further understand the changes of microstructure and interfacial defects during Mg(OH) 2 thermal decomposition.

show abstract

Section: Analysis Of Positron Annihilation Lifetime Spectramentioning

confidence: 68%

Characterizations of the thermal decomposition of nano-magnesium hydroxide by positron annihilation lifetime spectroscopy

et al. 2017

View full text Add to dashboard Cite

show abstract

“…Using ( 5 ) and (6) The K-dependent lifetimes and intensities used in (a), (7), and (8) were obtained from the experimental data by extrapolation to the phase transition temperature…”

Section: From (3) One Easily Getsmentioning

confidence: 99%

“…A determination of the crystallinity during the lifetime measurements was not possible. Nevertheless, to get quantitative informations, we evaluated (a), (7), and (8) using K as a parameter. The results of these calculations are summarized in Fig.…”

Section: From (3) One Easily Getsmentioning

confidence: 99%

Investigations on the phase transition of PTFE at the melting point by positron annihilation

Kindl

Sormann

1981

Phys. Stat. Sol. (a)

View full text Add to dashboard Cite

Positron lifetime spectra of the semi-crystalline polymer PTFE between +220 and +420 "C are measured and decomposed into four terms. These are physically interpreted, especially based on their behaviour a t the phase transition temperature of +327 "C. The longest-lived, strongly temperature-dependent component is associated with the ortho-positronium (0-ps) pickoff decay in amorphous and crystalline regions. A simple model calculation for the phase transition yields a higher lifetime and formation probability of 0-Ps in the amorphous phase. In contrast, the third component does not show such a marked temperature trend. The second component is assigned to the free positron annihilation. The shortest-lived component consists of two parts: (i) the parapositronium (p-Ps) part and (ii) a second short-lived component probably due to the annihilation of a n [e+, F-] bound state. Positronen-LebensdauerspeUren des semikristallinen Polymers PTFE werden zwischen +220 und +420 "C gemeseen und in vier Terme aufgelost. Diese werden vor allem auf Grund ihres Verhaltens beim Phasenubergang bei +327 "C physikalisch interpretiert. Die langlebigste, stark temperaturabhiingige Komponente wird dem Ortho-Positronium (0-ps)-pickoff-Zerfall in amorphen und kristallinen Bereichen zugeschrieben. Eine einfache Modellrechnung fiir den Phasenubergang ergibt eine hohere Lebensdauer und Bildungswahrscheinlichkeit des 0-Ps in der amorphen Phase. I m Gegensatz dazu zeigt die dritte Komponente keine so ausgepriigte Temperaturabhiingigkeit. Die zweite Komponente wird der Annihilation der freien Positronen zugeordnet. Die kurzlebigste Komponente besteht &us zwei Anteilen: (i) dem Para-Positronium (p-Ps)-Anteil und (ii) einem weiteren kurzlebigen Beitrag, der wahrscheinlich einem gebundenen Zustand [e+, F-] zuzuordnen ist.

show abstract

“…The polarization effect in PsCl has been treated in several one-particle model potential calculations to various degrees of accuracy [18][19][20][21]. The most recent of these calculations gives a binding energy of 1.40 eV [21].…”

mentioning

confidence: 99%

Binding energy of positronium chloride: A quantum Monte Carlo calculation

1992

View full text Add to dashboard Cite

The binding energy of positronium chloride is calculated using a model potential for the ten core electrons and the quantum Monte Carlo method for the eight valence electrons and the positron. The result is 1.91 ±0.16 eV. Except for three-and four-particle systems, this is the first accurate calculation of the binding energy of a compound containing a positron. PACS numbers: 36.10.Dr, 14.60.Cd, 31.20.Di, 82.55.+e Compounds containing a positron in addition to electrons and nuclei are important in several areas: surface studies, ceramic and doped Cw superconductors, radiation chemistry, many-body quantum mechanics, voids in polymers and molecular crystals, mass spectrometry (especially of biologically significant compounds), etc. [ll. In spite of their importance, our knowledge of their binding energies is extremely sparse. No direct measurements have been reported, although very recent progress has been made [2]. Except for the present work, accurate quantum mechanical calculations have been applied only to two-, three-, and four-particle systems. Positronium chloride (PsCl) is an atom consisting of a chlorine atom combined with a positronium atom. It is stable compared to separated CI and Ps atoms. Its ACAR (angular correlation of annihilation radiation) spectrum has been observed in aqueous solutions of chloride ions [3-5], graphite-intercalated chloride compounds [6,7], and chloride-doped polyacetylene [8]. The observed ACAR curves agree closely with that calculated from the Hartree-Fock wave function for gaseous PsCl [9] (although adding waters of hydration to the calculation degrades the agreement somewhat [10]). None of this experimental work gives an indication of the magnitude of the binding energy-just its sign. An assertion has been made that the PAL (positron annihilation lifetime) spectrum of chlorine gas and of argon-chlorine gas mixtures gives the Ps-Cl bond strength as 2.0 ±0.5 eV [11]. Experimental evidence supporting this assertion was not given [11,12]. Theoretical evidence that PsCl is bound was provided in 1953 by Simons, who calculated a positronic orbital in the fixed field of a chloride ion represented by a HartreeFock wave function [13]. Simons' calculated Ps-Cl bond energy was 0.59 eV, which is a lower bound. This calculation was repeated some years later with a more modern chloride wave function, with similar results [14]. Cade and Farazdel added full self-consistency, which increased the calculated bond energy slightly to 0.73 eV [15,16]. These calculations omit two important sources of stability for the system: polarization and correlation. The first is a long-range effect and can be adequately treated in a very simple way by including a polarization potential term in the Hartree-Fock equation for the positron.Correlation is a short-range effect and is much more difficult to treat by conventional quantum mechanical techniques. The purely electronic correlation energy amounts to about 20 eV [17]. The PsCl binding energies quoted in this paragraph are compromised because they rest on the...

show abstract

Positron bound states in alkali halides

Cited by 57 publications

References 7 publications

Characterizations of the thermal decomposition of nano-magnesium hydroxide by positron annihilation lifetime spectroscopy

Characterizations of the thermal decomposition of nano-magnesium hydroxide by positron annihilation lifetime spectroscopy

Investigations on the phase transition of PTFE at the melting point by positron annihilation

Binding energy of positronium chloride: A quantum Monte Carlo calculation

Contact Info

Product

Resources

About