“[When we created plutonium], we almost made a … terrible mistake, because we thought we’d reached the very top of the periodic table, that nobody would ever go higher than atomic number 94. So we thought we should name it “extremium” or “ultimum,” you know, the ultimate. [Now they’re up to element 112.] Think of how foolish we would [feel now] if we had given such a name.”

Before Dr. Glenn Seaborg and his colleagues at the University of California began experimenting back in 1940, uranium was the heaviest element in the periodic table. By bombarding uranium with atomic particles in a particle accelerator, Dr. Seaborg was able to create a new element, one not found in nature. Its nucleus contained 94 protons and so it was given the atomic number 94. Dr. Seaborg proposed that they name the new element plutonium, after the planet Pluto. In 1951, Dr. Seaborg was awarded the Nobel prize in chemistry for his codiscovery of plutonium and other so-called “transuranium” (meaning “beyond uranium”) elements that followed.

Plutonium is a radioactive element, which means it emits particles from its nucleus, producing energy in the process. This “miracle” element was soon being used to produce nuclear energy as well as nuclear weapons. While working on the top-secret Manhattan Project, Dr. Seaborg himself helped synthesize the plutonium needed to make the two bombs that effectively ended World War II—the ones that were dropped on the Japanese cities of Hiroshima and Nagasaki in 1945. But Dr. Seaborg saw productive uses for atomic energy as well. “During the Manhattan Project, I had helped create the most destructive manmade force ever known. But I was convinced that the atom had even greater potential for peaceful uses.” Today, nuclear power produces about 17% of the world’s electricity. In addition, many of the radioactive isotopes Dr. Seaborg helped develop are used in modern medicine to combat the growth of cancerous tumors.