Neptunium is an element that was found to be created during nuclear test explosions in World War II. It was the first man-made transuranium (following uranium) element.
Neptunium (symbol Np) has more than 92 protons in its nucleus. It is element number 93 and the mass number of its most stable isotope is 237.
The transuranium elements were prepared by the bombardment of the nuclei of uranium or more complex elements with neutrons and alpha particles. When uranium is bombarded with the neutrons, a new element is produced, neptunium. Np is unstable and forms still another man-made element, PLUTONIUM, which is also unstable.