Mutual neutralization cross sections for He+/H- and Li+/D- have been measured by a merged beam technique for centre of mass energies between 0.6 and 300 eV. The results are in good agreement with previous inclined and merged beam measurements and with recent theory, all of which only covered energy ranges above 30 eV. At interaction speeds greater than about 3*105 m s-1 results for H+/H-, He+/H-, Li+/H- and Li+/D- all converge.

A merged beam apparatus is described that has been developed to study mutual neutralization. Initially, it has been used to measure cross sections for H+/H- neutralization for centre-of-mass energies between 3 and 500 eV. The results are in excellent agreement with those of Szucs et al. (1984), which covered the range from 5 to 2000 eV, and with inclined beam measurements of Peart et al in the overlapping range of energies from 30 to 500 eV. There is also good accord with a variety of recent theoretical results, notably those by Sidis et al. (1983) Fussen and Kubach (1986) and Shingal and Bransden.

A merged beam apparatus has been used to measure cross sections for O+/O- and N+/O- mutual neutralization for centre-of-mass energies between 1 and 600 eV. The results are in good agreement with inclined beam measurements of Peart et al. (1989) in the overlapping range of energies above 33 eV but they are incompatible with results of earlier merged beam experiments performed elsewhere.

A merged-beam apparatus has been used to measure cross sections for H + 2 /D − mutual neutralization for centre-of-mass energies between 3 and 460 eV. Different ion sources and gas mixtures were used to vary the vibrational state population of the H + 2 ions and the cross section appears to be insensitive to the initial vibrational state. The measurements differ significantly from the results of a recent calculation but, at interaction speeds greater than about 2.5 × 10 5 m s −1 , converge with results for the atomic ion pairs

A detector has been developed that has an efficiency greater than 95% for a variety of ions that strike it with energies of more than a few keV, The efficiency is constant over the large entrance aperture (2.5 cm diameter) and for particle fluxes up to 4*104 s-1. An important feature is the ability to identify correlated pairs of particles that arrive as little as 30 ns apart, even in the presence of large, uncorrelated backgrounds.