We have performed experimental and theoretical studies of double ionization of helium by 6 MeV proton impact using a recently developed tool, four-particle Dalitz plots [Schulz et al., J. Phys. B 22, 3091 (2007)] which enable the representation of multiple differential cross sections as a function of all four fragments in a single spectrum without loss of any part of the total cross section. As a result, the relative importance of the various interactions between the fragments can be studied in great detail. Comparisons of experimental data with theoretical first-order calculations and simulations for the higher-order (TS-2) process show that elastic scattering between the heavy particles is surprisingly strong. For a large fraction of collision events, the final-state electron momenta are small compared to the momenta of the heavy particles. Our results suggest that an uncorrelated double ionization mechanism, involving two independent interactions of the projectile with both electrons, is significantly more important than previously expected for such fast collisions.




German Research Association
National Science Foundation (U.S.)

Keywords and Phrases

Charged particles; Electrons; Flow interactions; Helium; Inert gases; Ion bombardment; Ionization; Nuclear physics; Radioactivity; (e ,3e) process; American Physical Society (APS); collision events; Differential cross section (FDCS); Double ionization (DI); Experimental data; first orders; Heavy particles; Higher order; Ion impact; Proton impact; Relative importance; Total cross section (TSC); Uncorrelated

International Standard Serial Number (ISSN)


Document Type

Article - Journal

Document Version

Final Version

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© 2008 American Physical Society (APS), All rights reserved.

Publication Date

01 Jun 2008

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Physics Commons