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Precursor in plutonium-238 production

An important use of Np is as a precursor in plutonium-238 production, where it is irradiated with neutrons to form Pu, an alpha emitter for radioisotope thermal generators for spacecraft and military applications. Np will capture a neutron to form Np and beta decay with a half-life of just over two days to Pu.

Pu also exists in sizable quantities in spent nuclear fuel but would have to be separated from other isotopes of plutonium. Irradiating neptunium-237 with electron beams, provoking bremsstrahlung, also produces quite pure samples of the isotope plutonium-236, useful as a tracer to determine plutonium concentration in the environment.