The ionization afterglow techniques involve the production of electron-ion pairs in a gas by a short pulse of high energy nuclear radiation, 20 to 30 MeV electrons in this case. The electron density and electron-atom collision frequency are measured by passing through the dilute plasma formed a microwave signal, whose amplitude and phase shift are measured with a microwave detector in a bridge configuration. An X-band microwave cavity and a 300 Mc cavity have also been utilized to perform measurements with higher sensitivity at lower pressures. The results from these experiments include determinations of electron attachment and electron-ion recombination co-efficients as well as momentum and energy transfer cross sections. In common with other afterglow techniques, the measurements usually refer to a thermally averaged electron energy spectrum. Some specific examples from studies of momentum and energy transfer, as well as electron-ion recombination in nitrogen, are presented.

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