Hyperfine structure, spin, and isotope shift measurements have been performed on " "Rb and """"" Rb .The Rb nuclei have been produced either by spallation of Nb or by fission of U by a 600 MeV proton beam. They have been separated in mass before being transformed into a thermal atomic beam which interacts at a right angle with the light from a c.w. tunable dye laser. The charge radii changes deduced from the isotope shifts exhibit shell effects at N = 50 and deformations at N = 60, which are discussed. NUCLEAR STRUCTURERb,~~~~~R bm. Measured hyperfine constants A(5s Sg/2), A(5P P3/2), B(5P P3/2); spins, isotope shifts. Deduced p, , Qs, 6 (r ). High resolution laser spectroscopy on thermal atomic beams.

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The extended radius of a halo nuclide is very sensitive to the minute binding energy of its valence nucleons. The binding energy of 11Li has been measured with high precision by using the radio-frequency spectrometer MISTRAL at CERN's ISOLDE facility. The new two-neutron separation energy of 378+/-5 keV is 25% higher than the previously accepted value with an uncertainty 5 times smaller.