Rutherfordium (Rf). Diagram of the nuclear composition and electron configuration of an atom of rutherfordium-263 (atomic number: 104), the most stable isotope of this radioactive element. The nucleus consists of 104 protons (red) and 159 neutrons (yellow). 104 electrons (white) bind to the nucleus, successively occupying available electron shells (rings). Named after Ernest Rutherford and first synthesised in 1968, it is a transactinide and transition metal in group 4, period 7, and the d-block of the periodic table. Rutherfordium-263 has a half-life of 15 minutes, its nucleus emitting an alpha particle to form nobelium-259.