Charge state and incident energy dependence of K X-ray emission as a function of target thickness for 50–165 MeV Cu ions incident on 11–250 μg/cm 2 Cu

Abstract

Thin self-supporting Cu targets in 11–250 μg/cm 2 thickness were bombarded with 50–165 MeV Cu q i + ions (7 ⩽ q i ⩽ 24) to investigate the target thickness dependence of inner shell vacancy production processes in the symmetric collision of Cu + Cu. Doppler-shifted projectile K X-rays were discriminated from the target K X-rays, and the projectile and target K X-ray yields were separately measured as a function of target thickness. The K X-ray yields emitted from the projectile and the target Cu atoms are strongly dependent on the projectile initial charge state and target thickness for all the investigated collision systems of Cu q i + + Cu. From the observed K X-ray yields, K-shell vacancy production cross sections averaged over the target thickness t of projectile σ KV and target σ ∗ KV were separately derived taking into account the fluorescence yield that can be estimated from the K α X-ray energy shift. When the values of σ KV and σ ∗ KV are extrapolated to zero foil thickness, the K shell vacancy formed in the collision has been found to be equally shared between projectile and target in a single collision. With the increase of penetration depth, however, the values of σ ∗ KV are greater than those of σ KV presumably due to electron transfer of a target K electron to the projectile K vacancy. the evolution process of projectile excited states as a function of target thickness and the resulting variation of projectile and target K X-ray emissions are discussed.