Definition of "rubidium" [ru•bid•i•um]

• A soft silvery-white metallic element of the alkali group that ignites spontaneously in air and reacts violently with water, used in photocells and in the manufacture of vacuum tubes. Atomic number 37; atomic weight 85.47; melting point 38.89°C; boiling point 688°C; specific gravity (solid) 1.532; valence 1, 2, 3, 4. See Table at element. (noun)

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.

• "Following the very spectacular demonstrations of BEC in rubidium and sodium by the JILA and MIT groups, the field has developed explosively and over 20 groups are now conducting BEC experiments."
• "This suggestion has been of great service in spectrum analysis, and as applied by Bunsen, Kirchoff, and others, has led to the discovery of several new elements, such as rubidium and thallium, as well as increasing our knowledge of the heavenly bodies."
• "The scientific basis of this method is described in detail in Brent Dalrymple’s book The Age of the Earth, and depends upon the known and very long half-lives by which three radioactive chemical elements steadily decay and transform into different, stable elements: uranium slowly becomes lead, potassium slowly becomes argon, and the more exotic strontium becomes the rare element called rubidium."