Abstract
We have extended the measurements ofK-andL-shell ionization cross sections by electron impact into the ultra relativistic energy region, 0.9≦E≦2.0 GeV, in order to search for a saturation of the cross section. This phenomenon, which is due to the polarization of the target medium, is called density effect. It is predicted to occur at several hundred MeV impact energy and preferentially for lowZ target elements. Theoretical calculations are presented, based on the one-photon-exchange approximation. The absolute measurements of theK-andL-shell cross sections for Ni(K), Cu(K), Ag(K, L) and Au(L) performed at the 2.5 GeV electron synchrotron of the Bonn University, however, exhibit that the cross sections show no saturation but are still increasing. Furthermore, from theK X-ray yields, obtained at 0.9 and 2.0 GeV by bombarding the lowZ elements S, Ca, Mn, Ni and Ge, we obtain for the corresponding cross section ratio σ K (2GeV)/σ K (0.9GeV)=1.08±0.01 on the average. TheK X-ray yield of a composite Ca — Mn target amounts to
. All three results are in disagreement with theory. This severe discrepancy is discussed but the origin for it is not yet understood.
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Work supported by Deutsche Forschungsgemeinschaft
We are grateful to Prof. P. Manakos and Prof. G. Sauermann for many stimulating discussions. The help provided by Prof. G. Knop, Dr. D. Husmann and Prof. W. von Witsch and the excellent working conditions that we encountered at Bonn is highly appreciated. Finally, we also thank the GSI and Dr. H. Folger for preparing some of the targets that have been used.
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Genz, H., Brendel, C., Eschwey, P. et al. Search for the density effect in inner-shell lonization by ultra relativistic electron impact. Z Physik A 305, 9–19 (1982). https://doi.org/10.1007/BF01415072
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DOI: https://doi.org/10.1007/BF01415072