Neptunium breaks down to produce plutonium used in bombs and americium.
it is also used in smoke detectors
Explanation;
Neptunium may be made by bombarding uranium with neutrons. However Neptunium atoms disintegrate to form plutonium.
Neptunium is useful. When Neptunium is bombarded with neutrons it is used to produce plutonium-238 which is used for spacecraft generators and terrestrial navigation beacons.
Plutonium used in bombs and americium. it is also used in smoke detectors.
Additionally, Neptunium is used in neutron detection equipment.