Periodic Table -> Neptunium
Neptunium DetailsNeptunium Symbol:
NpNeptunium Atomic Number:
93Neptunium Atomic Weight:
(237.05)What is Neptunium?
(atomic number 93, symbol Np) is a radioactive element belonging to the actinide series. It is a fairly reactive metal with silvery color, and at least 3 allotropes exist. Of all actinoids, neptunium is the element with the highest density. It is a ductile metal that forms a number of chemical compounds. Chemically, neptunium is very reactive and is attacked by acids, steam, and oxygen, but not by alkalis. It exists in different oxidation states from neptunium (II) to neptunium (VII).
Neptunium has no commercial application, but Np-237 is used in devices that detect high-energy neutrons. The element has a long half-life, which makes it a key contributor to radiation. It is not clear what will happen to containment over a long period of time. If scientists find a way to mobilize nuclear waste and extract neptunium, this would minimize damage and environmental pollution.
The element was first produced by Philip H. Abelson and Edwin M. McMillian at the University of California. The researchers used slow moving neutrons to bombard uranium and produced the isotope neptunium-239. It had a half-life of around 2.4 days. Discoveries of neptunium were falsely reported as ausonium and bohemium in 1934 and later as sequanium in 1939. The search for this element was encumbered because scientists used the periodic table to predict the chemical properties of neptunium. The actinides series were not included in the periodic table, and this placed uranium below tungsten, protactinium below tantalum, and thorium below hafnium. The periodic table suggested that eka-rhenium, as it was often named, should be similar to rhenium and manganese. Because of this misconception, it was impossible to isolate neptunium from minerals. The isolation of small quantities of the element was attempted in the late 1930s. Otto Hahn and his colleagues confirmed the chemical properties and production of uranium-239, but the researchers were unsuccessful at detecting and isolating neptunium.
Neptunium has four oxidation states - +3, +4, +5, and +6. Its ionic radium and Vanderwaals radius are unknown. The element has 8 isotopes but none of them is stable. One of its isotopes, neptunium-237 is fissionable and decays into thalium-205 and bismuth-209. This is unlike other heavy nuclei that form lead isotopes. The decay chain of neptunium is referred to as the neptunium series. Neptunium, like americium, plutonium, uranium, and protactinium, forms a dioxo neptunyl core in +6 and +5 oxidation states. Artificial neptunium-237 is produced through the reaction of lithium or barium vapor and 237NpF at a temperature of around 1200 °C. Neptunium is mainly extracted as a by-product of plutonium and from nuclear fuel rods.
The element has 19 radioisotopes, and the most stable ones are Np-237, Np-236, and Np-235. All remaining radioisotopes have a half-life of less than 4.5 days. The main decay mode after Np-237 is beta emission and before is electron capture. The main products after Np-237 are plutonium isotopes and before are uranium isotopes.
The element is found in uranium ores in small quantities and occurs naturally on earth. It plays no role in living organisms and is never encountered outside research laboratories and nuclear facilities. Some studies have indicated that exposure to neptunium can lead to bone cancer. It is mainly deposited in the bones and small amounts are retained in the liver.
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