Martin David Kamen, (1913–2002), a Canadian-born American biochemist who discovered carbon-14, the radioactive isotope of carbon used to trace biochemical pathways and mechanisms and to date archeological and anthropological objects. He also carried out extensive research in photosynthesis. Kamen used the isotope oxygen-18 to trace the chemical's role in the process, confirming that that the oxygen created during photosynthesis comes only from the water molecules. Unfortunately, much of his energy at this time was diverted to non-scientific matters; a successful but protracted libel suit against the Chicago Tribune, which falsely accused him of being a communist, as well as a successful, 7-year battle to recover his passport, which had been rescinded by the U.S. government.

Further Reading
Martin Kamen, Who Discovered Carbon-14, Wins Fermi Award (U. S. Department of Energy, Lawrence Berkeley National Laboratory)
The Enrico Fermi Award - Martin D. Kamen, 1995 (U. S. Department of Energy, Office of Science)

Martin David Kamen, (1913–2002), a Canadian-born American biochemist who discovered carbon-14, the radioactive isotope of carbon used to trace biochemical pathways and mechanisms and to date archeological and anthropological objects. He also carried out extensive research in photosynthesis. Kamen used the isotope oxygen-18 to trace the chemical's role in the process, confirming that that the oxygen created during photosynthesis comes only from the water molecules. Unfortunately, much of his energy at this time was diverted to non-scientific matters; a successful but protracted libel suit against the Chicago Tribune, which falsely accused him of being a communist, as well as a successful, 7-year battle to recover his passport, which had been rescinded by the U.S. government.

Further Reading
Martin Kamen, Who Discovered Carbon-14, Wins Fermi Award (U. S. Department of Energy, Lawrence Berkeley National Laboratory)
The Enrico Fermi Award - Martin D. Kamen, 1995 (U. S. Department of Energy, Office of Science)