Direct mass measurements of 100Sn and magic nuclei near the N=Z line

The masses of nuclei far from stability are of particular interest in nuclear structure studies, and many methods of varying precision have been developed to undertake their measurement. A direct time of flight technique in conjunction with the SPEG spectrometer at GANIL has been extended to the mass measurement of proton-rich nuclei near N = Z line in the mass region A ≅ 60-80 known to provide input for astrophysical modelling of the rp-process and information relevant to the nuclear structure in a region of high deformation. The radioactive beams were produced via the fragmentation of a 78Kr beam on a natNi target, using the new SISSI device. A purification method based on the stripping of the secondary ions was successfully used for the first time, and the masses of 70Se and 71Se were measured. In order to improve the mass resolution for heavier nuclei, another method using the second cyclotron of GANIL (CSS2) as a high resolution spectrometer has been developed. An experiment aimed at measuring the masses of A 100 isobars in the vicinity of the doubly magic nucleus 100Sn was successfully performed, using this original technique. Secondary ions of 100Ag, 100Cd, 100In and 100Sn produced via fusion-evaporation reaction 50Cr + 58Ni and simultaneously accelerated in the CSS2 cyclotron. The mass of 100Cd and, for the first time, the masses of 100Sn were determined directly with respect to the reference mass of 100Ag. These results have been compared to various theoretical predictions and open the discussion on considerations of spin-isospin symmetry. (author)