Positronium Fraction and Positron Life Time at Ni(110) and Ge(110) Surfaces

Shrivastava, Sharad; Gupta, Varsha

doi:10.12693/aphyspola.79.853

Cited by 3 publications

(2 citation statements)

References 10 publications

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“…Such a spectrum showing 100% Ps formation, however, is demanding to be obtained experimentally and cannot easily be verified. On contrary, a theoretical calculation [27] even finds a saturating upper limit of 90 % for the Ps emission from Ge(110) at high temperatures.…”

Section: Introductionmentioning

confidence: 90%

Absolute fraction of emitted Ps determined by GEANT4 supported analysis of gamma spectra

Rienäcker,

Gigl,

Nebbia

et al. 2020

Preprint

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The fraction of positronium (Ps) emitted from a surface of a germanium single crystal at high temperature is usually assumed to approach unity at zero positron implantation energy. In the experiment, however, the determination of the absolute Ps fraction is not straight forward since recording a reference spectrum with 100 % Ps formation remains demanding. We use GEANT4simulated detector responses to 2γ-and 3γ radiation sources mimicking positron and Ps annihilation inside the (coincidence) Doppler-broadening spectrometer at NEPOMUC, FRM II, in order to derive a reliable value for the Ps fraction re-emitted from a Ge(100)-target heated close to its melting point. Analysis of the measured spectra by fitting the simulated spectra shows an absolute value of 74 ±4 % maximum Ps formation, contradicting the 100 %-assumption.

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Section: Introductionmentioning

confidence: 90%

Absolute fraction of emitted Ps determined by GEANT4 supported analysis of gamma spectra

Rienäcker,

Gigl,

Nebbia

et al. 2020

Preprint

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“…(7) for N(t). The fraction of positronium formation at the surface of the semiconductor has been obtained employing the relation where αs = αe+ -I-αST+αso +αsP+αsv-sv Equation (19) can be used to calculate the fraction of positronium formation in semiconductors.…”

Section: Calculation Of Positronium Fractionmentioning

confidence: 99%

Fraction of Positronium Formation at Semiconductor Surface

Shrivastava

Upadhyay

1999

Acta Phys. Pol. A

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The fraction of positronium formation (fps) has been calculated in Ge(110), Ge(111), Si(110) and Si(111) surfaces by solving the diffusion equation for positrons in semiconductors and by setting up the rate equation to describe the processes that are supposed to occur when a thermalised positron encounters the surface including the trapping of positrons in neutral and negative vacancies. Certain parameters used in the evaluation of fp s , e.g., the bulk annihilation rate (As), the positron diffusion length (L+), the diffusion coefficient (D+) and the implantation profile parameter (A), have been taken from the experiments. The calculated values of fps as a function of incident positron energy and temperature in Ge(110) and Si(111) have been compared with the experimental results. It has been found that in general the calculated results are in good agreement with the experimental ones. The calculation also confirms that the trapping rate of positrons into negative vacancy has a T -112 dependence with respect to the temperature.

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