Compton Double Ionization of Helium in the Region of the Cross-Section Maximum

The ratio of double-to-single ionization in helium by Compton scattering has been measured in the 8{endash}28thinspthinspkeV x-ray energy range. The ratio attains a maximum value of 1.6{percent} near 13thinspthinspkeV before descending towards the high-energy asymptotic region. The reported results resolve the discrepancies among previously published theoretical and experimental work in this energy range. The present data are most closely approximated by the results of the many-body perturbation theory calculation of Bergstrom {ital et al.}thinspthinsp[Phys.thinspthinspRev.thinspthinspA {bold 51}, 3044 (1995)]. {copyright} {ital 1999} {ital The American Physical Society}