Capture of Argon K -Shell Electrons by 2.5- to 12-MeV Protons

Using coincidence techniques, we have measured the cross section for capture of electrons from the K shell of argon atoms by protons in the energy range from 2.5 to 12 MeV. Of the total cross section for electron capture, the contribution of capture from the argon K shell increases with proton energy from 0.5% at 2.5 MeV to 47% at 12 MeV. The contribution of electron capture to the total argon K-shell tonization cross section decreases from 0.4% at 2.5 MeV to less than 0.1% at 12 MeV.