Acceleration limitations to ion beam analysis

Energy spread of ion beams is an important limitation of nuclear reaction analysis. While in single-stage electrostatic accelerators ion source or high voltage instabilities predominate, tandem type machines exhibit the stripping process as an additional and rather complex source of energy broadening. We have investigated the energy widths of the ions H-1 and N-15 for resonance reactions and He-4 from a 3 MV tandem accelerator operated with a gas stripping column. Major differences between the final energy spread of injected atomic and molecular negative ions have been observed. Molecular break-up and energy-loss straggling may easily amount to a few keV(1), whereas the contribution by high voltage ripple is negligible in most cases. The results will be discussed in view of their impact on different analytical techniques for high-resolution analysis of thin solid films.