Projectile electron loss and capture in MeV/u collisions of U28+ with H2, N2 and Ar

Electron capture and loss cross sections for U 28+ colliding with H 2 , N 2 and Ar were measured at 3.5 and 6.5 MeV/u. These data were used to benchmark n -body calculations using the classical trajectory Monte Carlo method. The n -body calculations include electrons on both nuclear centres and all electron–electron and electron–nuclear interactions between each centre. For the U 28+ ion, 36 electrons were incorporated in the calculations (4s 2 4p 6 4d 10 4f 14 5s 2 5p 2 ), while for the H, N and Ar targets all electrons were used except those for the K-shell of Ar, leading to 39-, 45- and 54-body calculations, respectively. Projectile electron loss was predicted for U 28+ at energies from 2 to 150 MeV/u. Only for the H-target did the projectile electron loss cross section decrease approximately as E −1 . The heavier targets exhibited slower energy dependences, contrary to the E −1 prediction of one-electron theories. Moreover, the collisional interactions are quite strong with an average of 1.64 and 2.88 electrons removed from the U 28+ ion at 10 MeV/u in each collision with N and Ar, respectively. These data and calculations were used to assess the vacuum requirements for the SIS-100 synchrotron ring under construction at GSI-Darmstadt. For the residual gases expected to be in the ring, the U 28+ lifetime was found to be essentially constant as a function of projectile energy, leading to very stringent vacuum requirements.