Steady-state impedance and electron distribution in a 63Ni electron-capture detector

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Journal of Chromatography A





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This study seeks to extend an earlier measurement of the initial (i.e. β-generated) charge distribution in a simulated, parallel-plate electron-capture detector, to the steady state, i.e. to the distribution that prevails when the rates of charge generation and destruction have become equal in the absence of an electric field. Such measurement have important implications for the validity of the "stirred reactor" concept, for the simulation of electron-capture process, and for the validation of mechanistic experiments that rely on the heterogeneity of the plasma. Measurements based on the ratio of electrical impedance over a variable interelectrode distance in the reversed and regular field directions of different pulse regimes show that the initial, steep plasma gradient relaxes only slightly when the system approaches steady state. This result is confirmed by measurement of the maximum collectable charge at different electrode gaps and pulse intervals. There does occur a relaxation of the plasma density, but it is minor and less than expected from a second-order recombination rate. Although the accuracy of these results is limited by a variety of instrumental factors, it is clear from a comparison of measurements done at initial, intermediate and steady states that the the electron-capture detector plasma remains heterogeneous under both d.c. and pulse drive conditions. © 1987.