Energy Dependence of Multiple Inner-Shell Ionization of A1 by Alpha-Particle Bombardment

The excitation of states in A1 with single $K$-plus multiple $L$-shell vacancies formed by collisions with 0.4-3.0-MeV helium ions is studied by observing the x-ray decay associated with filling of the $K$-shell vacancy. The observed $K$ x rays come from initial states with one $K$-shell and 0, 1, 2, and 3 $L$-shell vacancies. The absolute cross section for each of these transitions is determined and compared to a calculation using multiple Coulomb ionization. An important result of this experiment is the observation that the ratio of double to single ionization exhibits a maximum at a bombarding energy near the maximum for $L$-shell ionization.