Isotopes of rutherfordium

Rutherfordium (104Rf) is a synthetic element, and thus a standard atomic weight 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 a half-life of 2.5 hours, and the longest-lived isomer is 261mRf with a half-life of 81 seconds. Rutherfordium (104Rf) is a synthetic element, and thus a standard atomic weight 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 a half-life of 2.5 hours, 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). The synthesis of rutherfordium was first attempted in 1964 by the team at Dubna using the hot fusion reaction of neon-22 projectiles with plutonium-242 targets: The first study produced evidence for a spontaneous fission with a 0.3 second half-life and another one at 8 seconds. While the former observation was eventually retracted, the latter eventually became associated with the 259Rf isotope. In 1966, the Soviet team repeated the experiment using a chemical study of volatile chloride products. They identified a volatile chloride with eka-hafnium properties that decayed fast through spontaneous fission. This gave strong evidence for the formation of RfCl4, and although a half-life was not accurately measured, later evidence suggested that the product was most likely 259Rf. The team repeated the experiment several times over the next few years, and in 1971, they revised the spontaneous fission half-life for the isotope at 4.5 seconds. In 1969, researchers at the University of California led by Albert Ghiorso, tried to confirm the original results reported at Dubna. In a reaction of curium-248 with oxygen-16, they were unable to confirm the result of the Soviet team, but managed to observe the spontaneous fission of 260Rf with a very short half-life of 10–30 ms: In 1970, the American team also studied the same reaction with oxygen-18 and identified 261Rf with a half-life of 65 seconds (later refined to 75 seconds). Later experiments at the Lawrence Berkeley National Laboratory in California also revealed the formation of a short-lived isomer of 262Rf (which undergoes spontaneous fission with a half-life of 47 ms), and spontaneous fission activities with long lifetimes tentatively assigned to 263Rf. The reaction of californium-249 with carbon-13 was also investigated by the Ghiorso team, which indicated the formation of the short-lived 258Rf (which undergoes spontaneous fission in 11 ms): In trying to confirm these results by using carbon-12 instead, they also observed the first alpha decays from 257Rf.