Neptunium (Np). Diagram of the nuclear composition and electron configuration of an atom of neptunium-239 (atomic number: 93), a trace isotope of this element. The nucleus consists of 93 protons (red) and 146 neutrons (blue). Neptunium is an actinide and transuranic element in period 7, and the f-block of the periodic table. Actinides are soft radioactive metals. Neptunium-239 was produced by neutron bombardment of uranium in 1940. It has a half-life of 2.4 days, its unstable nucleus emits a beta particle to form plutonium-239.
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