[mass noun] The chemical element of atomic number 93, a radioactive metal of the actinide series. Neptunium was discovered as a product of the bombardment of uranium with neutrons, and occurs only in trace amounts in nature.
- ‘They had to be named after the next two planets, and so were called neptunium and plutonium - both found at Berkeley using the new cyclotron.’
- ‘All isotopes of neptunium are radioactive, the longest lived being neptunium - 237 with a half life of 2,140,000 years.’
- ‘When struck by neutrons, nuclei of neptunium and other nuclear materials can fission into two smaller nuclei.’
- ‘The new elements were named neptunium and plutonium, respectively.’
- ‘Just as Neptune comes right after Uranus in the solar system, so, too, does neptunium come right after uranium in the periodic table.’
- ‘Each tank round is 10 pounds of solid uranium - 238 contaminated with plutonium, neptunium, americium.’
- ‘The Berkeley cyclotron created many elements never found in nature - including plutonium, which directly follows neptunium in the table.’
- ‘In Basra they have found the bombs that were used had enriched uranium in them - neptunium.’
- ‘They produced neptunium, which decayed by beta emission, shunting the element one place further along the Periodic Table.’
- ‘As beta decay does not change the atomic mass, the isotope of the new element number 93, neptunium, also has mass 239.’
Late 19th century: from Neptune, on the pattern of uranium (Neptune being the next planet beyond Uranus).