Strong asymmetry of the electron-loss-to-continuum cusp of multielectron ${\mathrm{U}}^{28+}$ projectiles in near-relativistic collisions with gaseous targets

The process of electron-loss to the continuum (ELC) has been studied for the collision systems ${\mathrm{U}}^{28+}+{\mathrm{H}}_2$ at a collision energy of 50 MeV/u, ${\mathrm{U}}^{28+}+{\mathrm{N}}_2$ at 30 MeV/u, and ${\mathrm{U}}^{28+}+\mathrm{Xe}$ at 50 MeV/u. The energy distributions of cusp electrons emitted at an angle of $0^{\circ }$ with respect to the projectile beam were measured using a magnetic forward-angle electron spectrometer. For these collision systems far from equilibrium charge state, a significantly asymmetric cusp shape is observed. The experimental results are compared to calculations based on first-order perturbation theory, which predict an almost symmetric cusp shape. Some possible reasons for this discrepancy are discussed.

Figure 1

Energy distribution of electrons observed within an angle of ${\vartheta }_e=0^{\circ }–2.4^{\circ }$ with respect to the projectile beam in collisions of ${\mathrm{U}}^{28+}$ ions with gaseous targets. The experimental data (dots) were normalized to theory (lines). The contributions of the individual subshells of ${\mathrm{U}}^{28+}$ are shown. The lines labeled “rest” contain the contributions from the shells $1s^2, 2s^2, 2p^6, 3s^2, 3p^6$, and $4s^2$.