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FISSILE MATERIAL
Material containing a bignumber of easily fissionable nuclei which giveoffmultipleneutrons in the fission process. Normal importance is that if a sufficiently bigamount of fissilematerial is put together, a fissionchainreaction can occur. Sometimes used synonymously with fissionable material, i.e., material that can be fissioned (though often under restricted circumstances, such as only with thermal (slow) neutrons). A more restricted importance use of fissilematerial limits the concept to those materials which can be fissioned by neutrons of all energies (fast & slow).
Examples include Uranium-235 and Plutonium-239.