Near-Threshold Ionization of He andH2by Positron Impact

P. Ashley, J. Moxom, G. Laricchia
1996 Physical Review Letters  
The single ionization cross sections for He and H 2 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 1.99 6 0.19 and 1.70 6 0.11 are obtained for He and H 2 , respectively. This agrees qualitatively with extensions of the Wannier theory in that the exponent is larger than for electron impact.
more » ... or 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. [S0031-9007(96)
doi:10.1103/physrevlett.77.1250 pmid:10063029 fatcat:mtcdeqo2tze7rmopo34hr3ky7u