It was the summer of 1936 when Ernest Lawrence, the inventor of the atom-smashing cyclotron, received a visit from Emilio Segrè, a scientific colleague from Italy. Dr Lawrence was happy to oblige; as far as he was concerned the stuff Segrè sought was mere radioactive trash. He sealed some scraps of the foil in an envelope and mailed it to Segrè's lab in Sicily. Unbeknownst to Lawrence, Segrè was on a surreptitious scientific errand. Elements with 42 and 44 protons--42molybdenum and 44ruthenium respectively--had been isolated decades earlier, but element 43 was yet to be seen.