Beam-foil lifetime measurements for Ga II and Ga III using a field-emission ion source

A brief description is given of the modifications to a 2-MV Van de Graaff accelerator that are required to incorporate a field-emission ion source. The source is used to obtain a 1-μA beam of Ga+ ions. Lifetime measurements using the beam-foil technique are reported for the 4s5s1S, 4s4p1P, 4s4d1D, 4s5d1D, 4p21D, 4s5s3S, 4p23p, and 4s4d3D terms of Ga II and for the 5s2S, 4p2P, 4d2D, and 5f2F terms of Ga III. A detailed discussion is given of the cascading problem in the case of the Ga II resonance transition at 1414 Å.