Energy dependence of the metastable fraction in B3+(1s(2) S-1,1s2S S-3) beams produced in collisions with thin-foil and gas targets - art. no. 052702

The fraction of metastable ions in B3+ (1s(2) S-1.1s2s S-3) beams produced in collisions with thin-foil and.-as targets has been measured as a functio n of the incident energy in the range of 0.85-9 MeV. This was done by compa ring the electron yield of doubly excited states formed in the collision of B3+ with hydrogen and helium targets. Significant differences were observe d in the energy dependence of the metastable fraction between production in foil and gas targets. It was shown that the production of 1s2s S-3 metasta ble ions in a foil yields a constant fraction over the investigated energy range, unlike the fraction of metastable 1s2s S-3 ions produced in collisio ns with gas targets. which strongly depends on the incident beam energy. A theoretical study of the processes contributing to the formation of the S-3 metastable ions in collisions with foil and gas has been made. K-vacancy p roduction in the ion-beam stripping process has been identified as a domina nt mechanism and used to explain the observed difference in the energy depe ndence of the metastable fraction between production in collisions with gas and foil targets. A model is proposed for the calculation of the metastabl e fraction for He-like beams.