Electron Shake-Off Resulting fromK-Shell Ionization in Neon Measured as a Function of Photoelectron Velocity

The relative abundances of the differently charged ions that result from photoionization in the $K$ shell of neon were measured with a specially designed mass spectrometer. Results were obtained as a function of the x-ray energy from 17.5 to 0.93 keV using characteristic lines from a variety of targets. The charge spectrum resulting from 1.5-keV x rays is as follows: ${\mathrm{Ne}}^{1+}$ 5.7±0.6%, ${\mathrm{Ne}}^{2+}$ 70.2±0.5%, ${\mathrm{Ne}}^{3+}$ 20.8+0.3%, ${\mathrm{Ne}}^{4+}$ 3.0±0.2%, ${\mathrm{Ne}}^{5+}$ 0.28±0.07%. At higher energies the spectrum, with the exception of charge 1, remains essentially the same. At lower energies, however, the relative abundances for ions of charges greater than 2 begin to drop at about 500 eV above the $K$ edge of neon. From these data and from previous data on the extent of double electron emission in the $\mathrm{KLL}$ Auger process, the extent of electron shake-off arising from photoionization has been evaluated. Specifically, it was found that when the photoelectron leaves the $K$ shell of neon with a velocity more than 1.5×${10}^9$ cm/sec there is a 16% probability for a single electron shake-off, which agrees well with calculations based on the sudden approximation. Simplified calculations on multiple electron ejection were also shown to be in agreement with the observed abundances of the more highly charged ions. Direct collision and electron correlation are discussed as other possible sources for extra electron emission and the data are used to set upper limits to these contributions.