High-temperature carbide targets for fast on-line mass separation of alkali and noble gas elements

Targets of vanadium, lanthanum and uranium carbides kept at temperatures around 20000C have been used at the ISOLDE on-line separator at the CERN 600 MeV Synchro-cyclotron for production at Ar, Xe, Rb, Cs and Fr isotopes. The target materials are prepared either by sintering finely divided powders or by impregnation of graphite cloth with the respective target elements. Isotopic production yields peak at 108-109 atoms/s, and the distribution of time delays between production and measurement extended well below 1 s. The measured delay is treated in the framework of simple diffusion theory and a relation between observed and decay-loss-corrected yields has been derived. Approximate formation cross-sections have been deduced and compared with empirical systematics. In the course of the development work the following new nuclides were identified: 32Ar(Tsub(1/2) approximately 75 ms), 46Ar(9+-1 s), 201Fr(48+-15 ms) 202Fr(0.35+-0.02 s) and 230Fr(19+-1 s). (Auth.)