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Abstract:
We have measured the Compton double-to-single ionization ratio of helium using an ion time-of-flight spectrometer along with monochromatized synchrotron radiation of 57 keV. This photon energy is high and probes the Compton ionization alone, since the photoionization makes only a negligible contribution to the total cross section. Comparing our result, which is (1.25±0.3)%, with theoretical calculations and measurements at lower energies shows that this energy is most likely still not high enough to confirm the value of the asymptotic high-energy limit experimentally.
