Double differential cross sections for electron ejection from helium by fast protons

Abstract

Measurements of the angular and energy distributions of electrons ejected from helium atoms by protons with energies between 20 and 100 keV are presented in tabular and graphical form. The electron energy range is between 5 and 100 eV and the angular range is between 0 and 100°. The distributions have been converted to double differential cross sections by normalisation against other published data. An analysis of the accuracy of the results is presented.AINSE fellow 1982-84; now with TRIUMF (Tri-University Meson Facility), Vancouver, Canada.

Energy distributions for ionization in ion-atom collisions

“…For energies larger than 15 eV our calculation follows a path close to the experimental results, and below that energy there is a slope change in experimental data measured by Gibson [25] and Schulz [8], which is also seen in this work. In the data of reference [26] does not appear the structure close to 27 eV since the measurements were done at electron emission angles above 10 • .…”

Electron production in proton collisions with atoms and molecules: energy distributions

“…This problem is not discussed by any of the researchers using gas-beam targets except Gibson and Reid and may be a source of significant error. In this regard, we mention the systematic differences in the measured angular dependence of doubly-differential cross sections between Gibson and Reid and other workers (see, specifically, Reid, 1986, andCheng et al, 1989b). It appears that the poorly characterized shape of the effusive gas target in Gibson and Reid's "fountain" spectrometer allows a significant angular dependence of (nlfl),f that was not accounted for in the analysis.…”

Dynamics of Antimatter-Atom Collisions

“…(Such a difference cannot be explained by energy loss resulting from charge transfer to the continuum; the total cross section associated with this mechanism is far too small. 13,22 ) Further calculations by us indicate that do/dE for protons lies above and is roughly parallel to that for antiprotons for 75 £E < 500 keV. At energies E ;S 75 keV, electron capture maintains the dominance of the energy loss per collision for protons, while the p ionization cross section is decreasing rapidly.…”

“…New experimental evidence suggests that these large-angle data may, in fact, be high by an amount which would account for the discrepancy with our theory. 22 The p results diverge dramatically from those for protons; the angular differential cross sections differ by over an order of magnitude at both small and large scattering angles. The reason for these differences is easily understood classically; receding positive projectiles will tend to pull electrons out with them to small angles, whereas negative projectiles will repel ejected electrons to larger angles.…”