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

TL;DR

This study uses GEANT4 simulations and gamma spectra analysis to accurately determine the positronium emission fraction from a germanium surface, revealing it is about 72%, not 100% as previously assumed.

Contribution

It introduces a GEANT4-supported spectral analysis method to reliably measure the absolute positronium emission fraction from germanium surfaces.

Findings

Positronium emission fraction is approximately 72% from heated germanium.

The commonly assumed 100% Ps formation at zero implantation energy is incorrect.

Simulation-based spectral fitting provides a reliable measurement approach.

Abstract

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 GEANT4-simulated detector responses to $2\gamma$ and $3\gamma$ 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 reemitted 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 $(72\,\pm{4})\,\%$ maximum Ps formation, contradicting the $100\,\%$ assumption.