The Emission of Secondary Electrons Under High Energy Positive Ion Bombardment

The yield of secondary electrons from metallic surfaces produced by high energy positive ions has been measured for the energy range 43 to 426 kv. Cold targets of Mo, Pb, Al and Cu were bombarded by protons, $\mathrm{H}_2^{}{}_{}{}^{+}$ ions and ${\mathrm{He}}^{+}$ ions. For protons the yield decreased from approximately 4 at low energies to approximately 2 at high energies. For $\mathrm{H}_2^{}{}_{}{}^{+}$ ions the yields were more nearly constant with energy and about equal to 6. No great dependence of the yield on the kind of metal used was detected. The yield of secondaries from Mo under ${\mathrm{He}}^{+}$ bombardment was approximately 13 and varied very slowly with the energy. The great majority of the secondaries had energies less than 30 volts in all cases. The electrostatic generator and associated high voltage apparatus is of a type which has been described before. However, several new features in the design and operation are described in detail here. The proton source is of the low voltage, capillary type and delivers 50 μa of focused ions of which approximately 50 percent are protons. This arc has been in operation for a year without replacement.