The ionization of helium by neutral helium atoms

Abstract A method is described for investigating the ionization produced in helium by collisions between quasi-stationary atoms—that is, atoms possessing only therm al velocities—and a beam of neutral helium atoms with kinetic energy less than 100 eV. Ionization is shown to begin when the kinetic energy of the bombarding atoms is twice as great as the minimum kinetic energy which electrons m ust possess in order to ionize helium.