Transuranium Element

Following is a brief sketch of each of the transuranium elements. The chemical properties of these elements have in most cases been determined by nuclear chemists using incredibly ingenious experiments, often working with one atom at a time, and with radioisotopes that last only a few minutes. We will omit the chemical properties of these elements, however, because they are not available in sufficient quantities to be used in any practical chemical way; only their nuclear properties are important.

Neptunium (93)—Named after the planet Neptune, the next planet "in line" after Uranus, for which uranium (92) was named. Discovered in 1940 by McMillan and Abelson at the Radiation Laboratory of University of California, Berkeley (now called the Lawrence Radiation Laboratory), as a product of the radioactive decay of uranium after it was bombarded with neutrons. The neutrons produced uranium-239 from the "ordinary" uranium-238. The resulting uranium-239 has a half-life of 23.5 minutes, changing itself into to neptunium-239, which has a half-life of 2.35 days. Trace amounts of neptunium actually occur on Earth, because it is continually being formed in uranium ores by the small numbers of ever-present neutrons.

Plutonium (94)—First found in 1940 by Seaborg, McMillan, Kennedy, and Wahl at Berkeley as a secondary product of the radioactive decay of neutron-bombarded uranium. The most important isotope of plutonium is plutonium-239, which has a half-life of 24,390 years. It is produced in large quantities from the neutron bombardment of uranium-238 while ordinary nuclear power reactors are operating. When the reactor fuel is reprocessed, the plutonium can be recovered. This fact is of critical strategic importance because plutonium-239 is the major ingredient in nuclear weapons.

Americium (95)—Named after the Americas because europium, its just-above neighbor in the periodic table, had been named after Europe. Found by Seaborg, James, Morgan, and Ghiorso in 1944 in neutron-irradiated plutonium during the Manhattan Project (the atomic bomb project) in Chicago in 1944.

Curium (96)—Named after Marie Curie, the discoverer of the elements radium and polonium and the world's first nuclear chemist, and her husband, physicist Pierre Curie. First identified by Seaborg, James, and Ghiorso in 1944 after bombarding plutonium-239 with helium nuclei in a cyclotron.

Berkelium (97)—Named after Berkeley, California. Discovered in 1949 by Thompson, Ghiorso, and Seaborg by bombarding a few milligrams of americium-241 with helium ions. By 1962 the first visible quantity of berkelium had been produced. It weighed three billionths of a gram.

Einsteinium (99)—Named after Albert Einstein. Discovered by Ghiorso and his coworkers at Berkeley in the debris from the world's first large thermonuclear (hydrogen bomb) explosion, in the Pacific Ocean in 1952. About a hundredth of a microgram of einsteinium was separated out of the bomb products.

Fermium (100)—Named after physicist Enrico Fermi. Isolated in 1952 from the debris of a thermonuclear explosion in the Pacific by Ghiorso, working with scientists from Berkeley, the Argonne National Laboratory, and the Oak Ridge National Laboratory. Also produced by a group at the Nobel Institute in Stockholm by bombarding uranium with oxygen ions in a heavy ion accelerator, a kind of cyclotron.

Mendelevium (101)—Named after Dmitri Mendeleev, originator of the periodic table. Made by Ghiorso, Harvey, Choppin, Thompson, and Seaborg at Berkeley in 1955 by bombarding einsteinium-253 with helium ions. The discovery was based on the detection of only 17 atoms.

Nobelium (102)—Named after Alfred Nobel, Swedish discoverer of dynamite and founder of the Nobel prizes. Produced and positively identified in 1958 by Ghiorso, Sikkeland, Walton, and Seaborg at Berkeley, by bombarding curium with carbon ions. It was also produced, but not clearly identified as element 102, by a group of American, British, and Swedish scientists in 1957 at the Nobel Institute of Physics in Stockholm. IUPAC hastily named the element for the Swedish workers. The Berkeley chemists eventually agreed to the Swedish name, but not to the Swedes' credit for discovery. Ironically, in 1992 the International Unions of Pure and Applied Chemistry and of Pure and Applied Physics (IUPAC and IUPAP) credited the discovery of nobelium to a group of Russian scientists at the Joint Institute for Nuclear Research at Dubna, near Moscow.

Lawrencium (103)—Named for Ernest O. Lawrence, inventor of the cyclotron. Produced in 1961 by Ghiorso, Sikkeland, Larsh, and Latimer at Berkeley by bombarding californium with boron ions.

Elements 104 to 110—The identities of the true discoverers of these elements are tangled in an assortment of very difficult experiments performed by different groups of scientists at the American Lawrence Radiation Laboratory in Berkeley, the German Gesellschaft für Schwerionenforschung (Institute for Heavy-Ion Research) in Darmstadt, the Russian Joint Institute for Nuclear Research in Dubna, and the Swedish Nobel Institute of Physics in Stockholm.