The 205T1 experiment

205Tl has been previously proposed as a geological detector for solar neutrinos, making use of the reaction 205Tl(ν,e−)205Pb with a neutrino threshold of only ≂43 keV. We report on an experiment performed to study the feasibility of detecting radioactive 205Pb nuclei (T1/2=15 million years) at very low concentrations using the recently developed technique of accelerator mass spectrometry. Empolying the high‐energy ion beams of good quality from the UNILAC heavy‐ion accelerator at the GSI Darmstadt, we are able to demonstrate a suppression of neighbouring isotopes to better than 1 in 1016 and of neighbouring elements to about 1 in 103. While these results are very encouraging, the minimum number of atoms detectable is still severely limited by the efficiency of producing mulitply‐charged ions from present ion sources. Future improvements in ion‐source performance are briefly discussed.