First ECR-Ionized Noble Gas Radioisotopes at ISOLDE

The production of light noble gas radioisotopes with high ionization potentials has been hampered by modest ionization efficiencies for standard plasma ion-sources. However, the decay losses are minimal as the lingering time of light noble gases within plasma ion-sources is negligible when compared to its diffusion out of the target material. Previous singly charged ECRIS have shown a higher efficiency but also a lingering time of the order of 1 s and a total weight that prevents remote handling by the ISOLDE robot. The compact MINIMONO efficiently addressed the lingering time and weight issues. In addition, the MINIMONO maintained the high off-line ionization efficiency for light noble gases. This paper describes a standard ISOLDE target unit equipped with a MINIMONO ion-source and the first tests. The ion-source has been tested off-line and equipped with a CaO target for on-line tests. Valuable information was gained about high current (100-500 muA) transport through the ISOLDE mass separators designed for <10 muA. The yields and release curves (merged diffusion and effusion lingering time) of several light gaseous elements produced via irradiation by 1.4 GeV protons of the CaO target (thickness of 4.6 g/cm2) are presented and compared with those obtained under similar condition with a plasma ion-source. This paper is a longer version of a contribution to Radioactive Nuclear Beams 6, Argonne National Laboratory, Illinois, USA, Sept 22-26, 2003. To be published in Nucl. Phys. A.