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An ion beam cooler and buncher has beendeveloped for the manipulation of radioactive ion beams. The gas-lled linear radiofrequency ion trap system is installed at the Penning trap mass spectrometer ISOLTRAP at ISOLDE/CERN. Its purpose is to accumulate the 60-keV continuous ISOLDE ion beam with high e ciency and to convert it into low-energy low-emittance ion pulses. The e ciency was found to exceed 10 % in agreement with simulations. A more than 10-fold reduction of the ISOLDE beam emittance can beachieved. The system has beenused successfully for rst on-line experiments. Its principle, setup and performance will be discussed.

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Isotope shifts in dielectronic recombination spectra were studied for Li-like A Nd 57+ ions with A=142 and A=150. From the displacement of resonance positions energy shifts δE 142,150 (2s − 2p 1/2 ) = 40.2(3)(6) meV ((stat)(sys)) and δE 142,150 (2s − 2p 3/2 ) = 42.3(12)(20) meV of 2s − 2p j transitions were deduced. An evaluation of these values within a full QED treatment yields a change in the mean-square charge radius of 142,150 δ r 2 = -1.36(1)(3) fm 2 . The approach is conceptually new and combines the advantage of a simple atomic structure with high sensitivity to nuclear size.

High-precision mass and charge radius measurements on ;{17-22}Ne, including the proton-halo candidate 17Ne, have been performed with Penning trap mass spectrometry and collinear laser spectroscopy. The 17Ne mass uncertainty is improved by factor 50, and the charge radii of ;{17-19}Ne are determined for the first time. The fermionic molecular dynamics model explains the pronounced changes in the ground-state structure. It attributes the large charge radius of 17Ne to an extended proton configuration with an s;{2} component of about 40%. In 18Ne the smaller radius is due to a significantly smaller s;{2} component. The radii increase again for ;{19-22}Ne due to cluster admixtures.