A CYCLOTRON AS A POWERFUL TOOL FOR MASS MEASUREMENTS OF EXOTIC NUCLEI

An original method using the second cyclotron of GANIL as a high resol ution mass spectrometer was recently developed to measure the masses o f exotic nuclei, This direct time of flight technique has been success fully used with A = 100 isobars in the vicinity of Sn-100, produced vi a the fusion-evaporation reaction Cr-50 + Ni-58 at 255 MeV. The second ary ions were simultaneously accelerated and detected inside the cyclo tron close to the extraction radius, using a silicon detector telescop e mounted on a radially movable probe. The cyclotron was first tuned, using this detection system, with the Cr-50(11+) primary beam degraded to the same velocity as the A = 100 secondary ions, This very critica l and quire tricky preliminary tuning procedure, as well as the mass d etermination procedure, which are common to ail the experiments using this method, are presented and discussed.