Isotopes of rutherfordium

Rutherfordium (Rf) is a synthetic element, and thus a standard atomic mass cannot be given. Like all synthetic elements, it has no stable isotopes. The first isotope to be synthesized was either ²⁵⁹Rf in 1966 or ²⁵⁷Rf in 1969. There are 16 known radioisotopes from ²⁵³Rf to ²⁷⁰Rf (3 of which, ²⁶⁶Rf, ²⁶⁸Rf, and ²⁷⁰Rf are unconfirmed) and 4 isomers. The longest-lived isotope is ²⁶⁷Rf with an estimated half-life of 5 hours. The longest directly measured half-life is ²⁶³Rf at 11 minutes, and the longest-lived isomer is ^261mRf with a half-life of 81 seconds.

Super-heavy elements such as rutherfordium are produced by bombarding lighter elements in particle accelerators that induces fusion reactions. Whereas most of the isotopes of rutherfordium can be synthesized directly this way, some heavier ones have only been observed as decay products of elements with higher atomic numbers.

Depending on the energies involved, the former are separated into "hot" and "cold". In hot fusion reactions, very light, high-energy projectiles are accelerated toward very heavy targets (actinides), giving rise to compound nuclei at high excitation energy (~40–50 MeV) that may either fission or evaporate several (3 to 5) neutrons. In cold fusion reactions, the produced fused nuclei have a relatively low excitation energy (~10–20 MeV), which decreases the probability that these products will undergo fission reactions. As the fused nuclei cool to the ground state, they require emission of only one or two neutrons, and thus, allows for the generation of more neutron-rich products. The latter is a distinct concept from that of where nuclear fusion claimed to be achieved at room temperature conditions (see cold fusion).

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