Ionization of stabilized helium atoms by proton and antiproton impacts

The classical trajectory Monte Carlo method is applied to the calculation of single- and double-ionization cross sections of helium atoms by proton and antiproton impacts. The classical helium atom is stabilized by the introduction of the Heisenberg core potentials that prevent autoionization of classical two-electron atoms under the constraint of the uncertainty principle. The ratio of the double- to single-ionization cross sections is larger for antiproton impact than for proton impact in agreement with measurements, though the difference is slightly smaller than the experimental findings. It is important to generate the initial distribution microcanonically taking all the possible configurations into account. Exclusive use of the circular orbits fails to account for the dependence on the projectile charge. The Bohr helium model without the stabilization is too fragile to be used for collision problems of charged particles even at high energies