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Probing Positron Cooling in Noble Gases via Annihilation γ Spectra
1Centre for Theoretical Atomic, Molecular and Optical Physics, School of Mathematics and Physics, Queen's University Belfast, Belfast BT7 1NN, Northern Ireland, United Kingdom.
Physical Review Letters
|December 9, 2017
Summary
Positron annihilation gamma spectra in noble gases reveal details of positron cooling. Gamma spectra and shape parameters offer a new way to study this process, complementing existing methods.
Area of Science:
- Atomic and Molecular Physics
- Quantum Many-Body Theory
- Plasma Physics
Background:
- Positron annihilation spectroscopy is a powerful tool for material science.
- Understanding positron cooling in gases is crucial for various applications.
- Previous studies have focused on positron lifetime spectroscopy.
Purpose of the Study:
- To calculate gamma spectra for positron annihilation in noble gases.
- To investigate the time-varying gamma spectra during positron cooling.
- To explore the sensitivity of gamma spectra to positron momentum evolution.
Main Methods:
- Utilizing many-body theory to compute gamma spectra.
- Incorporating time-evolving positron-momentum distributions.
- Analyzing S-bar and W-bar shape parameters of the gamma spectra.
Main Results:
- Calculated gamma spectra for positron annihilation in noble gases up to the positronium-formation threshold.
- Determined time-varying gamma spectra during positron cooling.
- Observed that gamma spectra and shape parameters are sensitive to positron momentum distribution evolution.
Conclusions:
- Gamma spectra analysis provides a complementary method to positron lifetime spectroscopy for studying positron cooling.
- The sensitivity of spectral shape parameters offers new insights into the dynamics of positron cooling.
- This approach enhances our understanding of fundamental positron-atom interactions.
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