uranium 238

noun

Definition of uranium 238 

: an isotope of uranium of mass number 238 that is the most stable uranium isotope, that constitutes over 99 percent of natural uranium, that is not fissile but can be used to produce a fissile isotope of plutonium, and that has a half-life of 4.5 billion years

First Known Use of uranium 238

1942, in the meaning defined above

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The first known use of uranium 238 was in 1942

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