1881.

Research has led to the discovery of the heaviest element yet known to science.

The new element, Governmentium (Gv), has one neutron, 25 assistant neutrons, 88 deputy neutrons, and 198 assistant deputy neutrons, giving it an atomic mass of 312.
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Governmentium has a normal half-life of 2-6 years. It does not decay, but undergoes a reorganization in which a portion of the assistant neutrons and deputy neutrons exchange places.
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Science reveals heaviest element ever discovered (via @aabram)