uranium232

Uranium-232 (U-232) is a radioactive isotope of uranium with 92 protons and 140 neutrons, giving a mass number of 232. It is not encountered in appreciable natural concentrations.

Production and occurrence: U-232 is produced as a byproduct during neutron irradiation in nuclear reactors, particularly in the thorium fuel cycle and in reprocessing of irradiated fuel. It can arise when U-231 or Pa-231 captures neutrons and subsequently decays, and as a contaminant in reactor-produced uranium or thorium products. Its presence in uranium materials is typically trace and the measurement of U-232 can be used for attribution.

Decay properties: U-232 decays by alpha emission to thorium-228 with a half-life of about 68.9 years. Through successive alpha and beta decays in its chain, a series of short-lived daughters including Ra-228, Th-228, Ra-224, Rn-220, Pb-212, Bi-212, and Tl-208 are produced, ending at stable Pb-208. The decay chain emits multiple gamma rays, notably a strong line at 2.615 MeV from Tl-208, making U-232 contamination relatively easy to detect by gamma spectroscopy. The high gamma emission imposes stringent shielding and handling requirements.

Significance: U-232 behaves as a radiological fingerprint in nuclear forensics and safeguards; its presence can reveal origin or processing history of uranium materials. It also poses a practical concern in the use of uranium for weapons or fuel, since external gamma radiation from U-232 and its daughters complicates processing and storage.