Who discovered neptunium?

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A color-coded periodic table of the elements displays each element's symbol and atomic number, with categories such as alkali metals, noble gases, halogens, transition metals, and actinoid elements distinguished by different background colors. — transuranium element Modern version of the periodic table of the elements (printable).

Neptunium was discovered in 1940 by American physicist Edwin Mattison McMillan and American chemist Philip Hauge Abelson at the University of California at Berkeley.123

Working at the university's cyclotron facility, the pair exposed uranium oxide to neutrons, resulting in the production and identification of element 93. This achievement marked the first time a transuranium element—an element with an atomic number greater than 92—was positively produced and identified. For this discovery, McMillan later shared the 1951 Nobel Prize for Chemistry with Glenn T. Seaborg.132