${}^{233}\text{U}$ is produced by

Uranium-233 (${}^{233}\text{U}$) is a fissile isotope of uranium that is bred from thorium-232 (${}^{232}\text{Th}$) as part of the thorium fuel cycle. When ${}^{232}\text{Th}$ captures a neutron, it becomes ${}^{233}\text{Th}$, which then beta decays via protactinium-233 (${}^{233}\text{Pa}$) into ${}^{233}\text{U}$.