Protactinium233

Protactinium-233 (Pa-233) is a radioactive isotope of the element protactinium (atomic number 91) with a mass number of 233. It has 142 neutrons and is not found in nature in any significant quantity. Pa-233 is produced in nuclear systems that process thorium: thorium-232 captures a neutron to become thorium-233, which beta decays to protactinium-233, and subsequently Pa-233 beta decays to uranium-233.

Nuclear properties of Pa-233 include a half-life of about 27 days. It decays predominantly by beta emission to uranium-233, which is a fissile material of interest for nuclear fuel cycles. The decay chain makes Pa-233 an intermediate nuclide in the thorium-232–uranium-233 breeding pathway used in some reactor designs and research facilities.

Production and applications are mainly industrial and scientific. In reactor environments, Pa-233 serves as a transient intermediate in the production of U-233 for potential use as nuclear fuel. Because of its radioactivity, handling Pa-233 requires appropriate shielding and containment, and protocols seek to minimize exposure and environmental release. The isotope’s relatively short half-life means it is short-lived compared with some other actinides, influencing processing timing in thorium-cycle operations.

Safety and regulation considerations emphasize strict control of all actinide species, including Pa-233, due to radiological and chemical hazards. Pa-233 itself raises radiological concerns during production and decay to U-233, which is fissile and subject to additional regulatory oversight.

See also: protactinium, uranium-233, thorium fuel cycle.