A crossed-beam technique previously developed and used in this laboratory for studies of ionisation and electron capture in H+-He and He2+-He collisions down to 64 keV amu-' and 50 keV amu-l has been adapted to extend measurements down to 9 keV amu-' and 6 keV amu-' respectively. The method, which incorporates time-of-flight spectroscopy together with electron-ion and ion-ion coincidence counting of the collision products, provides high precision cross sections for individual collision channels. Some serious discrepancies are obtained with previous cross sections for single ionisation measured by Afrosimov er a2 and the important role of transfer ionisation at low energies is confirmed. The need for better theoretical descriptions of low-energy ionisation is demonstrated.
A pulsed crossed-beam technique incorporating time-of-flight spectroscopy which was recently developed in this laboratory has been applied to measurements of the cross sections for single and double ionisation of helium. Measurements over the unusually wide energy range from near threshold to 10 000 eV provide valuable checks on previous measurements based on different experimental approaches and an assessment of the range of validity of a number of theoretical predictions.
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