Experimental determination of the primary and secondary ionisation coefficients in krypton and xenon

The primary ionisation coefficient alpha of Kr and Xe has been evaluated from measurements of the spatial growth of ionisation currents between plane-parallel gold electrodes for the respective ranges 40<E/n<250 Td and 60<E/n<400 Td. Deviations from Kruithof's values are found, especially at the lower of range E/n. In the same gases the secondary ionisation coefficient gamma has been determined from measurements of the breakdown voltage. It has been clearly established that gamma depends on the electrode separation and a qualitative explanation is proposed.