Abstract
The single ionization cross sections for He and by positron impact have been measured in the first few eV above threshold and found to exhibit a different energy dependence from the corresponding electron results. If the data, between 1 and 3 eV above threshold, are fitted by a power law, exponents of and are obtained for He and , respectively. This agrees qualitatively with extensions of the Wannier theory in that the exponent is larger than for electron impact. The quantitative disagreement with the predicted value of 2.65 might indicate that the range of validity of this theory is smaller than expected.
- Received 6 November 1995
DOI:https://doi.org/10.1103/PhysRevLett.77.1250
©1996 American Physical Society