MASS MEASUREMENT OF THE DOUBLY-MAGIC NUCLEUS SN-100

The mass of the doubly-magic nucleus Sn-100 was measured using the sec ond cyclotron of GANIL as a high resolution mass spectrometer. The fus ion-evaporation reaction Cr-50 + Ni-58 was used to produce the A = 100 secondary ions at 5.3 MeV/nucleon incident energy. Ions of Ag-100, Cd -100, In-100 and Sn-100 were produced and accelerated simultaneously a nd the masses of the three latter isobars were measured with respect t o the abundantly produced Ag-100. The total observed yield of accelera ted Sn-100 ions was about 10 counts. The known mass of Cd-100 was very well reproduced and the masses of In-100 and Sn-100 were determined f or the first time with precisions of 3 x 10(-6) and 10(-5) respectivel y. Our results do agree well with recent shell model calculations but disagree from extrapolations by systematics.