Dubnium (Db). Diagram of the nuclear composition and electron configuration of an atom of dubnium-268 (atomic number: 105), the most stable isotope of this radioactive element. The nucleus consists of 105 protons (red) and 163 neutrons (yellow). 105 electrons (white) bind to the nucleus, successively occupying available electron shells (rings). Dubnium, named for where it was first synthesised in 1970, is a transactinide and transition metal in group 5, period 7, and the d-block of the periodic table. Dubnium-268 has a half-life of 29 hours, its nucleus stabilising by electron capture to form rutherfordium-268.