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Near-Threshold Ionization of Argon by Positron Impact
T J Babij1, J R Machacek1, D J Murtagh1
1Plasma Research Laboratory, Research School of Physics and Engineering, Australian National University, Canberra ACT 2601, Australia.
Physical Review Letters
|March 31, 2018
Summary
Positron impact ionization of Argon (Ar) was measured near the ionization threshold. Results show similar threshold behavior to electron impact ionization, challenging existing theories.
Area of Science:
- Atomic and Molecular Physics
- Quantum Mechanics
- Plasma Physics
Background:
- Understanding atomic ionization is crucial for plasma physics and materials science.
- Positron-atom collisions offer unique insights into ionization mechanisms.
- Existing theories, like Wannier theory, predict specific threshold behaviors.
Purpose of the Study:
- To measure the direct single-ionization cross section of Argon (Ar) by positron impact.
- To compare experimental data with semiclassical calculations and theoretical predictions.
- To investigate the threshold behavior of positron impact ionization.
Main Methods:
- Experimental measurement of the direct single-ionization cross section for Argon by positron impact.
- Comparison of experimental results with semiclassical calculations.
- Analysis of the power law variation in the threshold region.
Main Results:
- The direct single-ionization cross section for Ar by positron impact was measured above the first ionization threshold.
- Experimental results showed a smaller exponent than predicted by most previous extensions of Wannier theory.
- No significant difference in threshold behavior was observed between positron and electron impact ionization.
Conclusions:
- The experimental findings challenge current extensions of Wannier theory for positron impact ionization.
- The observed similarity between positron and electron impact ionization suggests a common underlying mechanism.
- Further theoretical work is needed to explain the discrepancy and the observed threshold behavior.
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