Bohrium is an artificially produced radioactive element with 107 protons—that is, with an atomic number of 107. Scientists have discovered several isotopes of bohrium. Different isotopes of an element have the same number of protons but different numbers of neutrons. The most stable isotope of bohrium has an atomic mass number (total number of protons and neutrons) of 264. This isotope has a half-life of 0.44 second—that is, due to radioactive decay, only half the atoms in a sample of isotope 264 would still be atoms of that isotope after 0.44 second.
Bohrium is named after Danish physicist Niels Bohr , who made many contributions to the study of the atomic nucleus. The chemical symbol for bohrium is Bh. Chemists classify bohrium in the transactinide element group among the transuranium elements . For information on the position of bohrium on the periodic table, see the article Periodic table .
In 1976, scientists at the Joint Institute for Nuclear Research in Dubna, near Moscow, first announced the production of the element. Dubna was then part of the Soviet Union and is now in Russia. In 1981, a group at the Heavy Ion Research Center in Darmstadt, West Germany (now part of Germany), made a rival claim. The scientists at Darmstadt had bombarded bismuth, whose atomic number is 83, with chromium, which has an atomic number of 24. The Darmstadt work, unlike that of the Soviets, provided definitive evidence of the atomic number and atomic mass of the element.
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. IUPAC is the recognized authority in crediting the discovery of elements and assigning names to them. In 1993, IUPAC accepted the working group’s conclusion that the Germans deserved credit for the discovery of the element. Disagreements about what to name the element delayed an official naming until 1997, however. Before being named, bohrium had commonly been referred to as element 107.
