To make fuel for electricity-generating reactors, uranium is enriched to less than 5 percent of the isotope U-235.

为将燃料做成电能反应堆，铀被浓缩至U-235同位素含量5%以下。

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The device's primary source of neutron radiation was the radioactive element californium, but the stream of neutrons produced by the californium was multiplied by passing it through a lattice of highly enriched uranium U-235, whose nuclear fission released additional neutrons.

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