Stopping force of 0.1 me v/u - 0.5 me v/u ions in thin metallic foils time of flight spectrometry

Abstract

The work presented here is aimed at determining the stopping force of heavy ions in pure metallic foils using time of flight spectrometry and comparing the data obtained from experiments with data obtained from predictive stopping force models (SRIM, DPASS and CasP). This is done to improve the predictive accuracy of heavy ion stopping in matter by the stopping force models. The experimental data obtained from this work will be added to the relevant database for the improvement of predictive stopping force models, due to the lack of data of heavy ion stopping in matter. This work describes energy loss measurements, which were done using the tandem accelerator at iThemba LABS TAMS on the ERDA (Elastic Recoil Detection Analysis) beam line, of heavy ions (silicon, oxygen, titanium and copper) through (cobalt, platinum and palladium) thin foils using a Time of Flight – Energy spectrometer (ToF-E). In addition to energy loss measurements, depth profiling of the thin metallic foils was also carried out at iThemba LABS TAMS using RBS technique. Energy loss measurements, together with thickness measurements from RBS technique, were used to determine the stopping force of the different ion-target combinations. The use of the thick scatter target makes it possible to produce recoil ions of different species which are poly-energetic and the ToF-E, which is responsible for energy loss measurements, can separate the recoil ions by mass. The combination of these two apparatus makes it possible to measure the energy loss of different recoil ions across a wide range of energies with only one experimental run. The results presented in this work show a comparison of experimental stopping force and stopping force obtained from predictive models with ion energies between 0.1 MeV/u – 0.4 MeV/u. The results show, with some exceptions, that there is an agreement with stopping force trends between the experimental data and theoretical data with a variation in energy, although there is are discrepancies in the stopping force predictions. The discrepancies in stopping force can be attributed largely to ion-atom interactions which are not accounted for in the predictive models.