nobelium (nōbēˈlēəm) [key], artificially produced radioactive chemical element; symbol No; at. no. 102; mass no. of most stable isotope 259; m.p. 827°C; b.p. and density unknown; valence +2, +3. It is a metal of the actinide series in Group 3 of the periodic table. Nobelium was the 10th transuranium element to be discovered. It was first produced and detected in Apr., 1958, by Albert Ghiorso, Torbjørn Sikkeland, John R. Walton, and Glenn T. Seaborg at the Univ. of California at Berkeley; they used a heavy-ion linear accelerator to bombard a mixture of curium-244 and curium-246 with carbon-12 ions, producing nobelium-254 (half-life 55 sec). The name of the element was originally suggested by scientists at the Nobel Institute of Physics, who in 1957 reported synthesis of an isotope of the element; although the name was adopted, it was later shown that the element could not have the properties they reported. Thirteen isotopes, all of which are radioactive, are known; the most stable, nobelium-259, has a 58-min half-life.