A silvery-gray radioactive metal, the first synthetically produced element, having 14 isotopes with masses ranging from 92 to 105 and half-lives up to 4.2 × 106 years. It is used as a tracer and to eliminate corrosion in steel. Atomic number 43; melting point 2,200°C; specific gravity 11.50; valence 0, 2, 4, 5, 6, 7. See Table at element.
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.