Th233

Th-233, or thorium-233, is a radioactive isotope of thorium with mass number 233. It is not naturally abundant and is produced in nuclear reactors by neutron capture on Th-232. Th-233 has a half-life of about 22.3 minutes and decays by beta minus emission to protactinium-233 (Pa-233).

Pa-233 decays by beta minus emission with a half-life of about 27 days to uranium-233 (U-233), which is fissile and has a half-life of 159,200 years. This decay sequence makes Th-233 an intermediate in the thorium fuel cycle, where Th-232 is bred toward U-233 for use as reactor fuel.

Production and use: In the thorium fuel cycle, Th-232 captures a neutron to become Th-233, which rapidly becomes Pa-233 and then U-233. Uranium-233 can be used as reactor fuel or for research; Th-233 is typically produced transiently in irradiation facilities during fuel-cycle operations and is not usually stored as a long-term material.

Occurrence and safety: Th-233 is not present in significant natural concentrations. Handling requires radiological safety measures. The isotope emits beta radiation during its decay to Pa-233, and its progeny (notably U-233) contribute additional hazards. Shielding, containment, and regulatory controls are standard for materials involved in the thorium fuel cycle.