Measurement of heavy ion induced x-ray production cross sections in metallic targets at MeV energies

Abstract

Experimental X-ray production cross sections (i.e. probability of X-ray generation in a target by an incoming MeV ion) are useful not only for fundamental ion beam – matter interaction studies, but also for the development of new ion beam materials analysis techniques such as Heavy Ion Particle Induced X-ray Emission (HI-PIXE) spectroscopy. Unfortunately, while theoretical predictions of X-ray production cross sections due to light (Z<6) projectile ions are generally in good agreement with experiment, this is not the same for heavier projectiles. Experimental studies show that heavy ions induce higher X-ray yields in targets compared to light ions of the same velocity, which implies higher sensitivity for Heavy Ion PIXE. There is therefore a need for substantial experimental data to improve theoretical models. This dissertation presents measurements carried out at the iThemba Laboratory for Accelerator Based Sciences (LABS) to determine X-ray production cross sections in Vanadium (V), Zirconium (Zr) and Tin (Sn) metal oxide films due to carbon and chlorine MeV ion beams at an ion velocity range of 0.1-1.0 MeV/u. The measured cross sections are compared to predictions by the modified Plane Wave Born Approximation (PWBA) and the ECPSSR theory that takes into account; the energy loss (E) of the projectile due to Coulomb deflection (C) by the target atom, and the perturbed-stationary state (PSS) and relativistic nature (R) of the target atoms’ inner shell. The observed agreements and discrepancies between experiment and theory are discussed in terms of the atomic ionization mechanisms for each projectile-target collision.