Characteristic K X-ray production in heavy ion-atom collisions in solids

Some of the factors influencing the characteristic K X-ray yields which result from heavy (Z1 approximately 35) ion bombardment of similar atomic number targets (Z2) are reported. All targets are in the form of narrow, shallow distributions implanted into solid hosts. At the beam energies used, viz. 2 to 4 MeV, K-vacancy production is presumed to arise from a collision sequence, the first producing a projectile L-shell vacancy in a projectile-host atom encounter and the second, a projectile-target atom encounter, transferring the L-vacancy via transient MO orbitals to the K-shell of one of the heavy collision partners. Evidence for a two-step process is presented. First, Kr K X-ray excitation functions measured for Kr++ bombardment of Si(Kr) and Be(Kr) targets are identical in shape. The different magnitudes are attributed to different efficiencies for Kr 2p-shell ionization in Kr-Si and Kr-Be collisions. Second, systematic variation of the host material for fixed (Z1, Z2) demonstrates clearly the role of level matching effects between the projectile-2p and host-1s energy levels in creating projectile 2p-vacancies. (Auth.)