Neptunium is a metallic chemical element which is classified among the actinide elements on the periodic table. It is extremely rare in nature, existing in only trace amounts in ores which contain uranium. All of the neptunium used in research is produced artificially, through the neutron bombardment of elements like uranium. Because this element is radioactive and it could potentially be used to create nuclear weapons, access to it is restricted in some regions of the world.
When isolated, neptunium is silvery in color, and very reactive, combining with other elements to form an assortment of compounds, like other elements in the actinide series. It is also naturally radioactive, as are its isotopes. The element is also highly ductile. It is identified with the atomic number 93, making it the first of the transuranic elements, and its symbol is Np.
Transuranic elements are elements with atomic numbers higher than that of uranium. These elements are all radioactive, with extremely short half lives which make them rare or nonexistent in nature, although traces of their presence can be detected. These elements must be created synthetically for scientific study, and they are extremely unstable, which makes them challenging to research.
Credit for the discovery of neptunium is generally given to Edwin McMillan and Philip Abelson, researchers at the University of California, Berkeley. They discovered the element in 1940 and named it for the planet Neptune, as it followed uranium on the periodic table, and uranium had been named for the planet Uranus. The next element in this series, plutonium, follows this naming scheme.
Because this element is radioactive, it does pose health risks, as exposure to or ingestion of this element could cause radiation damage ranging from mild sickness to death, depending on the exposure. However, since this element is so rare, average individuals are unlikely to encounter it, and the people who deal with neptunium deal with it in such small amounts that the risk is fairly low. Scientists who work with radioactive elements observe basic safety precautions when handling them, and they restrict access to elements which could potentially be used in high-yield nuclear weapons for reasons of national security.