Dubnium is an artificially produced radioactive element with 105 protons—that is, with an atomic number of 105. Scientists have discovered many isotopes of dubnium. Different isotopes of an element have the same number of protons but different numbers of neutrons. The most stable isotope of dubnium has an atomic mass number (total number of protons and neutrons) of 262. This isotope has a half-life of 34 seconds—that is, due to radioactive decay, only half the atoms in a sample of isotope 262 would still be atoms of that isotope after 34 seconds.
The chemical symbol for the element is Db. Chemists classify dubnium in in the transactinide element group among the transuranium elements. For information on the position of dubnium on the periodic table, see the article Periodic table.
In 1968, scientists at the Joint Institute for Nuclear Research in Dubna, near Moscow, claimed that they had been the first to produce the element. Dubna was then part of the Soviet Union and is now in Russia. In 1970 and 1971, the scientists presented additional claims. They had bombarded americium, whose atomic number is 95, with neon, whose atomic number is 10. In 1970, researchers at the Lawrence Radiation Laboratory (now Lawrence Berkeley National Laboratory) in Berkeley, California, made a rival claim. The Berkeley researchers had bombarded californium, whose atomic number is 98, with nitrogen, which has an atomic number of 7.
In 1986, the International Union of Pure and Applied Chemistry (IUPAC) and the International Union of Pure and Applied Physics formed a working group to review the histories of the elements with atomic numbers from 101 to 109. The group concluded that the 1970 Berkeley claim and the 1971 Dubna claim were equally convincing. In 1993, IUPAC accepted the group’s recommendation that the discovery of the element be shared by the institutions. Disagreements about what to name the element delayed an official naming until 1997, however.
Dubnium is named after the Dubna laboratory. Before being named, dubnium had commonly been referred to as element 105.
