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Targetry developments for the third generation of Radioactive Ion Beams facilities

Final Activity Report Summary - TARGDEV (Targetry developments for the third generation of Radioactive Ion Beams facilities)

The project objective was the definition of at least two prospective electrolytic targets, the characterisation of their release properties and the implementation of the method for a practical on-line application to new beams.

After an extensive research it became clear that, because of their diffusion properties, electrolytic targets were best suited for facilities implementing projectile fragmentation, i.e. not ISOLDE. Promising results obtained by the new materials with low work functions as negative ionisers led to many off and on-line tests. In order to keep up with previous delays and to meet the scientific demand for negative beams, it was decided to concentrate on the development of the aforementioned ionisers. The effort was worthwhile: during an on-line run in November 2006 we recorded the best yields ever of 38Cl and 39Cl at ISOLDE. Good yields were also obtained for 40, 41Cl and 71, 73, 75, 76, 77Br, though the employed target did not allow larger intensities.

A new application of low work function materials was therefore developed, i.e. the high-temperature radially trapping cavities for resonant laser ion sources. These cavities were usually made of W or Ta, thus leading to unwanted contaminants produced by surface ionisation. Low work function material could dramatically reduce the ionisation of contaminants, either alkali or alkaline-earth. The negative ionisers were successfully tested during laser ionisation of gallium in collaboration with a research group from the University of Mainz. The results were outstanding. While keeping the same efficiency as in the W cavity, the negative ionisers ensured a suppression factor larger than 1 000 for alkali tracers.

Finally, we studied the diffusion behaviour of 18F into several prospective target materials with grain size down to nanometres, e.g. Al2O3, Al2TiO5, SiC, MgO.