93
Neptunium
Atomic Number93
Atomic Mass237 u
CategoryActinide
State at Room TempSolid
Year Discovered1940
About Neptunium
The first element beyond uranium ever created, named for the next planet out, following the uranium naming sequence. Made at Berkeley by neutron bombardment. Its 2 million year half-life makes it the longest lived transuranic element. Present in spent nuclear fuel, it can be reprocessed into weapons material, so it is carefully tracked. Also used in neutron detection instruments.
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