Collisional mechanisms for single and double ionization of He by protons and antiprotons
Classical trajectory Monte Carlo calculations have been used to elucidate the collision mechanisms responsible for the differences in the single- and double-ionization cross sections of He atoms by protons and antiprotons in the energy range from 250 to 1000 keV. The calculations employed the Bohr helium-atom model which includes the 1/r/sub 12/ electron-electron interaction. The unexpected large observed difference (Andersen et al., Phys. Rev. Lett. 57, 2149 (1986)) in the ratio R of double to single ionization for proton and antiproton collisions is reproduced by the calculations. The calculations indicate that the antiproton double-ionization cross section is larger than that for protons because of two effects. The first effect is that the antiproton can push one electron into the other from larger impact parameters than for protons which must be between the nucleus and the first electron in order to pull it into a trajectory which collides with the second electron. The most important effect, however, is that at small impact parameters the antiproton screens the helium nucleus causing a Coulomb explosion while the proton increases the binding of the two electrons. The calculations also show a component of the difference in the ratio R at low energies (Eless than or equal to500 keV) is due to the single-ionization cross sections with protons predicted to have a larger cross section than antiprotons (36% difference at 250 keV).
- Research Organization:
- Department of Physics and Laboratory for Atomic and Molecular Research, University of Missouri-Rolla, Rolla, Missouri
- OSTI ID:
- 6404729
- Journal Information:
- Phys. Rev. A; (United States), Vol. 36:3
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
HELIUM
ION-ATOM COLLISIONS
HYDROGEN IONS 1 PLUS
ANTIPROTONS
BOHR THEORY
CROSS SECTIONS
IONIZATION
KEV RANGE 100-1000
MONTE CARLO METHOD
ANTIBARYONS
ANTIMATTER
ANTINUCLEI
ANTINUCLEONS
ANTIPARTICLES
ATOM COLLISIONS
BARYONS
CATIONS
CHARGED PARTICLES
COLLISIONS
ELEMENTARY PARTICLES
ELEMENTS
ENERGY RANGE
FERMIONS
FLUIDS
GASES
HADRONS
HYDROGEN IONS
ION COLLISIONS
IONS
KEV RANGE
NONMETALS
NUCLEI
NUCLEONS
RARE GASES
640304* - Atomic
Molecular & Chemical Physics- Collision Phenomena