MEASUREMENTS OF ELECTRON-IMPACT IONIZATION CROSS SECTIONS OF
      ARGON, KRYPTON, AND XENON BY COMPARISON WITH PHOTOIONIZATION


   A.A. Sorokin$^\ast$, L.A. Shmaenok$^\ast$, S.V. Bobashev$^\ast$, M.
                   Richter$^\sharp$, G. Ulm$^\sharp$


  $^\ast$Ioffe Physico-Technical Institute, Politekhnicheskaya 26, St.
                       Petersburg 194021, Russia
  $^\sharp$Physikalisch-Technische Bundesanstalt, Abbestr. 2-12, 10587
                             Berlin, Germany

A new method recently developed is applied to measure ratios of total
cross sections for electron-impact
ionization and photoionization in Ar, Kr, and Xe with a relative
uncertainty as low as 1.3%. Using our
measured cross-section ratios and well-known photoionization cross
sections, we deduce absolute total
electron-impact ionization cross sections of Ar, Kr, and Xe with
unparalleled low relative uncertainty of 2%.