title
SIMILARITIES BETWEEN ION-IMPACT AND PHOTO-DOUBLE IONISATION OF HELIUM
AT SMALL MOMENTUM TRANSFERS
authors
B. Bapat, R. Moshammer, S. Keller, W. Schmitt, A. Cassimi, L. Adoui,
H. Kollmus, R. D\"orner, Th. Weber, K. Khayyat, R. Mann, J. P. Grandin,
J. Ullrich
affiliations
Fakult\"at f\"ur Physik, Universit\"at Freiburg, 
79104 Freiburg, Germany
Institut f\"ur Theoretische Physik, Universit\"at Frankfurt, 
60054 Frankfurt, Germany
Centre Interdisciplinaire Recherche avec les Ions Lourds, 
14040 Caen, France
Institut f\"ur Kernphysik, Universit\"at Frankfurt, 
60486 Frankfurt,Germany
Gesellschaft f\"ur Schwerionenforschung, 
64291 Darmstadt, Germany
summary
Double ionisation of helium by the impact of 100 MeV/u C$^{6+}$ ions
has been studied in a kinematically complete experiment. For small 
momentum transfers, the electron angular distribution shows a 
pattern similar to that in photoionisation. Calculations in the Born
approximation plus shake-off using a Hartree-Fock ground state 
wavefunction agree well with the oberved distributions if the 
interaction between the outgoing electrons is accounted for.