Energy spread of ion beams passing a gas stripper

Since the energy spread of accelerated particle beams is not well known for tandem-type machines, we have measured current-energy distributions for a variety of ion beams delivered by our 3 MV tandem at varying stripper gas pressure. The energy widths of light ions produced from injected negatively charged atoms, such as H"- and He"-, are mainly due to the accelerating voltage ripple, whereas for heavier ions, such as C"- and F"-, energy straggling in the stripper gas dominates. In case of injected negatively charged molecules, such as NH_2"- and CN"-, Coulomb explosion in the gas stripper produces satellite peaks on both sides of the unshifted central line. These deviations from Gaussian line shape complicate precise line-shape analyses, as, for example, required in nuclear reaction Doppler spectrometry of vibrational states in target materials. The most relevant charge-exchange processes in the stripper gas are discussed in some detail. (orig.)Available from TIB Hannover: RO 6920(1997,6) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman