Francium sources at Laboratori Nazionali di Legnaro: Design and performance

A facility for the production of radioactive francium is operating at the laboratories of the Istituto Nazionale di Fisica Nucleare INFN in Legnaro, Italy. The goal is to collect a cold sample of radioactive atoms in a magneto-optical trap for studies in atomic, nuclear, and particle physics. Production of francium is achieved via the fusion-evaporation reaction 197Au(18O, kn)215-kFr generated by a 100-MeV 18O6+ beam on a thick gold target. The production target is heated to 1200 K and kept at a potential of +3 kV to enhance Fr diffusion and surface desorption. Average production rates are 0.7 x 106 ions / s for 210Fr with a primary beam flux of 1012 particles / s, with peaks of 2 x 106 ions / s. Details are given on the design and construction of the production targets and on the measurements that characterize their performance.