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 2000 °C have been used at the ISOLDE on-line isotope separator at the CERN 600 MeV Synchro-cyclotron for production of 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 10 8 –10 9 atoms/s, and the distribution of time delays between production and measurement extend 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: 32 Ar( T ½ ∼ 75 ms), 46 Ar(9 ± 1 s), 201 Fr(48 ± 15 ms), 202 Fr(0.35 ± 0.02 s) and 230 Fr(19 ± 1 s).