from The American Heritage® Dictionary of the English Language, 4th Edition

  • n. The most common isotope of uranium, having mass number 238 and half-life 4.46 × 109 years, nonfissionable but irradiated with neutrons to produce fissionable plutonium 239.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • n. the commonest isotope of uranium; it is not fissionable but when irradiated with neutrons it produces fissionable plutonium 239


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