Recoil separator ERNA: ion beam purification

For improved measurements of the key astrophysical reaction C-12(alpha, gam ma)O-16 in inverse kinematics, a recoil separator ERNA is developed to dete ct directly the O-16 recoils with nearly 100% efficiency. Since the C-12 pr ojectiles and the O-16 recoils have essentially the same momentum and since the C-12 ion beam emerging from an accelerator usually passes through a mo mentum filter, a sufficient absence of an O-16 beam contaminant in the C-12 ion beam is of utmost importance for ERNA. In the present work, a Wien fil ter together with a Delta E - E telescope are used to investigate the beam contaminants accompanying a momentum-filtered C-12 ion beam and to measure the level of ion beam purification achievable with the Wien filter. (C) 199 9 Elsevier Science B.V. All rights reserved.