Polonium is a chemical element with symbol Po and atomic number 84. A rare and highly radioactive metal with no stable isotopes, polonium is chemically similar to selenium and tellurium, though it also shows resemblances to its horizontal neighbors thallium, lead, and bismuth due to its metallic character. Due to the short half-life of all its isotopes, its natural occurrence is limited to tiny traces of the fleeting polonium-210 (with a half-life of 138 days) in uranium ores, as it is the penultimate daughter of natural uranium-238. Though slightly longer-lived isotopes exist, they are much more difficult to produce. Today, polonium is more often produced in milligram quantities by the neutron irradiation of bismuth. Due to its intense radioactivity, which results in radiolysis of chemica