Chemists, Run!

Creating new heavy elements is a scientific tour de force that gets harder and harder as the easier possibilities are knocked off the list. When Chemist Paul R. Fields of the Argonne National Laboratory got into the game last year, all the elements above uranium (No. 92 and nature's heaviest) through element No. 101 (mendelevium) had already been synthesized.*He knew that the next candidate, element No. 102, would be the toughest yet. Last week, in a joint release of Argonne, Britain's Harwell laboratory and Sweden's Nobel Institute for Physics, a U.S.-British-Swedish team sparked by Fields reported the creation of element 102. Their method involved footwork as well as physics.

Overstuffed Atom. Fields and his colleague Arnold Friedman decided that the best bet would be to bombard curium with carbon ions in a cyclotron. This would be quite a trick; curium, element No. 96, is itself synthetic and intensely radioactive. If any of it were fattened into element 102, the fragile, overstuffed atoms would predictably disintegrate in a few minutes.

Fields and Friedman interested British Chemist John Milsted, who wangled some time on the Stockholm cyclotron, the only one in operation capable of projecting a sufficiently intense beam of carbon ions. Milsted also undertook the tricky job of making curium into a thin film, and sandwiching it between aluminum foil to form a suitable target. The apparatus was arranged so that any atoms of element 102 formed would be knocked out of the target and would stick to a "catcher foil," a bit of plastic film.

Juggler Technique. Element 102 disintegrated so fast that a major problem was to prove that it had been created at all. The scientists developed a technique that would have done credit to a team of Japanese jugglers. After the curium had been bombarded for about 20 minutes, the Swedes shut down the cyclotron. As the concrete shield opened, a group of scientists, wearing gloves and dust masks against radioactivity, dashed into the cyclotron chamber. One snatched the target from the machine, another took it apart and passed it to a third, who extracted the catcher foil. The fastest runner, generally Swedish Chemist Lennart Holm, then dashed 100 yards to a waiting elevator.

Upstairs the foil went into an apparatus that measured alpha particles from the disintegrating atoms. With practice, the scientists cut the total elapsed time to 1 1/2 minutes, and enough of the newly created atoms remained to produce alpha particles. The scientists had their proof when these particles turned out to have almost exactly the energy that physical theory had predicted. Next, the plastic foil was burned away, the invisible residue dissolved in hydrochloric acid, and the acid then poured through a column filled with material that has varying attraction for different chemical elements. When alpha particles were found coming from the place in the column predicted for element 102, the scientists could be sure that they had succeeded.

They did not create much of it--only about 50 atoms or one billion-trillionth of an ounce. "Hardly a commercial quantity," said Chemist Fields. Asked why he and his friends went to such trouble, he said with a happy smile: "Well, discovery of a new element is considered a big thing in some circles."

* The number of protons in the nucleus determines the number of a chemical element. Hydrogen has one proton; uranium has 92. For each proton, each atom has one electron. The number and pattern of the electrons, which are arranged in shells around the nucleus, control the element's chemical properties. If the outer shell is complete, with room for no more electrons, the element is a "noble" gas (helium, neon, argon, krypton, xenon and radon) that forms no chemical compounds. A single electron in the outermost shell makes the element a highly reactive alkali metal (lithium, sodium, potassium, rubidium and cesium). In 1869 Russian Chemist Dmitri Mendeleeff noted these relationships of the elements, and, without knowing anything of electrons, arranged the elements by properties in the theoretical Mendeleeff Periodic Table, which has proved basically correct.

By 1925 almost all spaces in the table had been filled with elements found in nature. The four remaining blanks (Nos. 43, 61, 85 and 87) belonged to elements whose atoms are so unstable (radioactive) that, if any once existed in nature, they have long since disappeared. With the development of nuclear physics, the blanks were filled with elements created artificially. This left only the transuranic (heavier than uranium) elements for scientists to use as tests of their skill.

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