If it is separated from its uranium decay products a second time, this protactinium will decay to equally pure uranium 233 over the next few months. With careful attention to the relevant ...

from the thorium energy blog, using thorium as the fertile material and U-233 as the fissile material has a secret advantage in the “proliferation” department–the inevitable formation of uranium-232.

As discoverers of eka-tantalum’s longest-lived isotope, Meitner and Hahn named this new element protactinium. They had isolated protactinium 231, a member of the uranium 235 decay chain. In 1938, they ...