Element 112 debuts in fusion of lead and 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 is 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.

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 to create an isotope 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 life-times helps establish that nuclei with about 162 neutrons hold together more strongly than nuclei with a smaller or larger number of neutrons.  Theories of nuclear structure assume that neutrons and protons are arranged in layers, or shells, and predict that certain numbers of these particles lead to particularly stable configurations.

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 understanding the structure of matter in universe.

(Science News, vol. 149:134; March 2, 1996)

Questions:
1.	If scientists were to produce element 114 by firing high-energy zinc ions into another element, what element should they use as the target?
2.	If scientists were to use lead as the target, what element should they use for the high-energy projectile ions?