Lutetium is the name of element 71. Under some classification schemes, it is considered the last lanthanide. In other schemes, it is classed as a Group 3 element, and the lanthanides are considered to end with Yb. It is considered a lanthanide in classification systems which place La in group 3 and the lanthanides between Group 3 and Group 4, but is considered a Group 3 element in systems which regard La through Yb as lying between Group 2 and Group 3. In either case, it has the characteristic lanthanide preference for the +3 oxidation state.
Lutetium has been spelled "lutecium", however that spelling is falling out of use.
NUCLEAR PROPERTIES
Thirty-six isotopes of Lu have been observed, out of a total of 86 total isotopes predicted between 233Lu to 148Lu. In addition, 42 isomers have been observed, Heavy isotopes, 178Lu and heavier, decay by beta emission with half-lives which peak at 28.4 min in 178Lu and decline to near 0.001 sec at the neutron dripline. Light isotopes, 173Lu and below, decay in ways that reduce positive nuclear charge. Positive beta decay (positron emission or electron capture) is observed in all isotopes from 173Lu down to 150Lu. Alpha decay is also observed in 160Lu to 153Lu, a consequence of neutron shell closure at N = 82. The lightest isotopes, 152Lu and down, decay by proton or beta-delayed proton emission.
Lutetium's most significant isotopes are found in the band 177Lu to 174Lu. 175Lu is the element's only effectively stable isotope and the other three are peculiar. 174Lu decays by positron emission with a 3.31 year half-life; and also has an isomer, 174m1Lu, with a 0.4 yr half-life. 177Lu's ground state decays by beta emission with a 6.65 day half-life - but an isomer, 177m3Lu has a 160.44 day half-life. That isomer has a decay energy Q(b) = 0.50 MeV and spin of 23/2-. There is plenty of energy for fast beta decay, but decay is inhibited by the difficulty of shedding so much spin. Finally, there is 176Lu, which is unusual in to two ways. First, its half-life is 3.85E10 yr, and extraordinarily long half-life for a beta-decaying species. Second, while its ground state decays only by negative beta emission, it has a 3.66 hr isomer which has both beta decay (branch ratio = 0.9915) and electron capture branches (BR = 0.0095). and 177Lu are relatively short-lived, but 176Lu has a half-life 3.85E10 years. Its decay energy is 107 keV, so this nuclide's long half-life is due to its high spin, which suppresses ordinary beta-decay.