Element 112 debuts in fusion of lead, zinc.

Researchers have added a chemical element to the periodic table.

So far unnamed, this new atom has a nucleus consisting of 112 protons and 165 neutrons, giving it an atomic mass of 277. It's the heaviest nucleus yet created in the laboratory.

The detection of a single nucleus of element 112 is the latest in a series of discoveries at GSI, the center for heavy ion studies in Darmstadt, Germany. In late 1994, a GSI team produced elements 110 and 111 (SN: 1/7/95, p. 5).

This sequence of experiments brings nuclear physicists tantalizingly close to creating element 114. Theorists have long predicted that a combination of 114 protons and about 184 neutrons would be more long-lived than other superheavy atoms in the periodic table. Uranium, with atomic number 92, is the heaviest naturally occurring element.

Sigurd Hofmann of GSI and his collaborators announced their discovery of element 112 last week in a paper submitted to Zeitschrift fur Physik A.

The researchers made element 112 by accelerating zinc ions to high energies, then slamming them into a lead target. Very rarely, when a zinc ion had just the right energy, it would fuse with a lead nucleus to create a new element.

Collecting data for several weeks earlier this year, the GSI group ended up detecting a single nucleus of element 112. It decayed after less than a millisecond by emitting an alpha particle, which consists of two protons and two neutrons, to create an iso tope of element 110 with an atomic mass of 273.

That isotope, in turn, decayed by emitting an alpha particle to form a new isotope of element 108, and so on.

The pattern of the isotope lifetimes helps establish that nuclei with about 162 neutrons hold together more strongly than nuclei with a smaller or larger number of neutrons (SN: 9/24/94, p. 206). Theories of nuclear structure assume that neutrons and prot ons are arranged in layers, or shells, and predict that certain numbers of these particles lead to particularly stable configurations.

Recent calculations suggest that a narrow "peninsula" of relatively stable isotopes, including element 112, may link the known superheavy elements to the putative "island" of stability at atomic number 114, says Yuri A. Lazarev of the Joint Institute for Nuclear Research in Dubna, Russia. He and his coworkers have confirmed this picture in recent experiments that produced the heaviest known isotopes of elements 104, 106, 108, and 110.

At GSI, researchers are now preparing experiments involving even heavier projectiles than zinc to produce elements 113 and 114. The results may answer questions about the maximum size and weight that atomic nuclei can attain-a fundamental issue in underst anding the structure of matter in the universe.