Relationship between the ratios of double to single ionization of helium by photons and charged particles

Double Ionization of He by Fast Protons at Large Energy Transfer

“…At low energy transfer (DE , 2 keV), R͑DE͒ lies near 2%, in good agreement with the predictions for photoionization [14][15][16][17][18] (since photons are annihilated in photoionization, DE is simply the incident photon energy). The same value of R͑DE͒ for charged particle impact and photoionization is expected within the validity of the Bethe-Born approximation [25,30,31]. However, with increasing DE, R͑DE͒ starts deviating downwards from that for photoionization at the energy transfer region where previous measurements end.…”

“…For collisions where first order perturbation approximation is valid, the ratio R͑DE͒ as a function of energy transfer ͑DE͒ is predicted to be the same for both Compton scattering and charged particles at large DE [29]. At smaller energy transfer ("small" in this work still requires the ejected electron to be fast), both Compton scattering and charged particle scattering are related to photoionization in first order [30,31].…”

“…For collisions where first order perturbation approximation is valid, the ratio R͑DE͒ as a function of energy transfer ͑DE͒ is predicted to be the same for both Compton scattering and charged particles at large DE [29]. At smaller energy transfer ("small" in this work still requires the ejected electron to be fast), both Compton scattering and charged particle scattering are related to photoionization in first order [30,31].In this Letter, we report the first direct measurement of R͑DE͒ in fast proton-He collision. Here the energy transfer DE was measured directly and completely by measuring the energy loss of protons after the collision, whereas previously DE was either calculated by assuming binary kinematics between protons and electrons [26] or measured at one particular electron emission angle [27,28].…”

“…On the theoretical side, the subject has drawn renewed interest [2,[29][30][31] very recently, partially driven by the flurry of new experiments at synchrotron light sources [10 -12,19], and theoretical calculations for photoionization and Compton scattering [13][14][15][16][17][18][20][21][22][23]. Although a higher ratio close to that for photoionization was observed for charged particles when fast electrons were isolated [26][27][28], the difference between charged particle scattering and photoionization still remains.…”

Ionization of Helium in the Attosecond Equivalent Light Pulse of 1 GeV/NucleonU92+Projectiles

“…Several recent theoretical publications have been devoted to come to a detailed understanding of this equiva-lence [8][9][10][11]. Charged particle induced dipole transitions at a specific energy loss DE P of the projectile have been related to the absorption of a photon with an energy of E g DE P .…”