Pa233

Protactinium-233, denoted Pa-233, is a radioactive isotope of protactinium (atomic number 91) with a mass number of 233. It is a synthetic nuclide that appears briefly in the thorium fuel cycle and in certain irradiation experiments. As an isotope of actinide elements, its chemical behavior is similar to other protactinium isotopes, but Pa-233 itself is short-lived and highly radioactive.

In a typical thorium-based reactor process, thorium-232 captures a neutron to become thorium-233, which has a short half-life of about 22 minutes and rapidly beta decays to Pa-233. Pa-233 then beta decays to uranium-233 (U-233) with a half-life of roughly 27 days. This stepwise decay sequence makes Pa-233 an intermediate in the production of U-233, a fissile material used in the thorium fuel cycle.

Decay and radioactivity: The primary decay mode of Pa-233 is beta minus decay to U-233. The short-lived Th-233 and the longer-lived Pa-233 together drive the buildup of U-233, which has a much longer half-life of about 159,200 years and is the key fissile nuclide in certain reactor designs and experimental fuel cycles.

Applications and significance: Pa-233 is mainly of interest as a transient intermediate in the production of U-233 for use as reactor fuel in thorium-based systems. Its study aids understanding of actinide chemistry and reactor physics, especially in reprocessing and fuel-cycle analysis.

Safety: Pa-233 is highly radioactive and requires appropriate shielding, handling controls, and remote equipment in any practical work or processing environment.