We report the first measurement of the ratio of double-to-single photoionization of helium well above the double-ionization threshold. Using a time-of-flight technique, we find He++/He+=1.6±0.3% at hν=2.8 keV. This value lies between calculations by Amusia (2.3%) and by Samson, who predicts 1.2% by analogy with electron-impact ionization cross sections of singly charged ions. Good agreement is obtained with older shake calculations of Byron and Joachain, and of Åberg, who predict 1.7%.
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Copyright American Physical Society, used with permission
Levin, J. C.,
Lindle, D. W.,
Miller, R. D.,
Berrah Mansour, N.,
Berry, H. G.,
Sellin, I. A.
Measurement of the Ratio of Double-to-Single Photoionization of Helium at 2.8 keV Using Synchrotron Radiation.
Physical Review Letters, 67(8),
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