Total Ionization in Argon by Heavy Ions of Energies 8 to 100 keV

The total ionization produced by ions stopped in argon gas has been measured in the energy range 8-100 keV. The experimental method employed an ion accelerator and a cylindrical ionization chamber with a differentially pumped open window. The following ions were studied: hydrogen, helium, carbon, nitrogen, oxygen, and argon. The average energy loss per ion pair ($W$ value) was found to be dependent on both the velocity and mass of the incident ions at low ion velocities. The $W$ value, in electron volts per ion pair, ranges from 26.8 for 50-keV protons to 90.9 for 25-keV argon ions.