Properties and Overview of Plutonium

Overview:

Plutonium (Pu) symbolized by Pu and with an atomic number of 94, is a radioactive metallic element that plays a significant role in nuclear energy and weapons. Discovered in 1940 by a team of scientists led by Glenn T. Seaborg, plutonium is a member of the actinide series and is known for its complex physical and chemical properties and its significant implications for safety and environmental concerns. Its discovery was initially linked to the Manhattan Project, where plutonium was used to develop nuclear weapons, and it remains a critical material in both military and civilian nuclear technologies. Physically, plutonium is a dense metal with a silvery-gray appearance that tarnishes when exposed to air, forming a dull coating of oxides and hydrides. It is highly dense, with a density of approximately 19.86g/cm³, making it one of the densest elements. Plutonium has a low melting point for a metal, at 640°C, and a boiling point of 3,228°C. One of plutonium's most notable physical characteristics is its ability to exist in multiple allotropes or different structural forms, depending on the temperature and pressure. There are six known allotropes of plutonium at ambient pressure, each with distinct crystal structures and properties. These allotropes vary significantly in density and volume, which complicates the handling and fabrication of plutonium due to the risk of volume changes and associated stress in materials containing the metal.
Chemically, plutonium is highly reactive and exhibits a variety of oxidation states, ranging from +3 to +7, with +4 and +6 being the most stable in aqueous solutions. This versatility in oxidation states leads to a complex chemistry, where plutonium can form numerous compounds, including oxides, halides, and hydrides. Plutonium readily oxidizes when exposed to air, forming a layer of plutonium dioxide (PuO₂) on its surface, which can flake off and expose fresh metal to further oxidation. This oxide layer contributes to the metal's reactivity and complicates its storage and handling. Plutonium's chemistry is also characterized by its ability to form complexes with organic ligands, influencing its environmental mobility. Additionally, plutonium can react with hydrogen to form plutonium hydride, a compound that poses a risk of pyrophoricity, meaning it can spontaneously ignite in air.
Safety concerns regarding plutonium are profound, primarily due to its high radioactivity and toxicity. Plutonium is an alpha-emitter, meaning it releases alpha particles during radioactive decay. Although alpha particles cannot penetrate the skin, they pose a severe health risk if plutonium is inhaled, ingested, or enters the body through a wound. Once inside the body, plutonium can accumulate in bones, liver, and other organs, where it continues to emit radiation, potentially causing cancer and other health issues. The most common isotope of plutonium, Pu-239, has a half-life of 24,100 years, contributing to long-term environmental and health concerns. Handling plutonium requires strict safety protocols to prevent contamination, including glove boxes, proper ventilation, and protective clothing. In addition to its radiological hazards, plutonium is also chemically toxic, further complicating its handling and disposal.

Production:

Plutonium is produced primarily through the irradiation of uranium-238 in nuclear reactors. When uranium-238 absorbs a neutron, it is converted into uranium-239, which subsequently undergoes beta decay to form neptunium-239 and then plutonium-239. This isotope of plutonium, Pu-239, is fissile, meaning it can sustain a nuclear chain reaction, making it crucial for nuclear weapons and nuclear reactors. In reactors, plutonium is often created as a byproduct of uranium fuel, and it can be reprocessed and used as mixed oxide (MOX) fuel, blended with uranium to generate power. The production and reprocessing of plutonium involve complex chemical separations to isolate plutonium from other elements and isotopes, requiring advanced technology and stringent security measures due to the material's potential for weaponization.

Applications:

Applications of plutonium are primarily focused on the nuclear sector. In the context of nuclear weapons, Pu-239 is a crucial material due to its ability to undergo rapid fission, releasing a massive amount of energy in a very short time. This property was harnessed in the atomic bomb dropped on Nagasaki in 1945, and it remains a central component of modern nuclear arsenals. In civilian applications, plutonium is used in mixed oxide (MOX) fuel, where it is combined with uranium to power nuclear reactors. MOX fuel helps to utilize the plutonium generated in reactors, contributing to nuclear fuel recycling and reducing the need for enriched uranium.
Beyond its use in energy and weapons, plutonium also has applications in space exploration. Plutonium-238, a different isotope from Pu-239, is used as a heat source in radioisotope thermoelectric generators (RTGs). These devices convert the heat released by the radioactive decay of Pu-238 into electricity, providing power for spacecraft and other remote systems where solar power is not feasible. RTGs powered by plutonium have been used in missions such as the Voyager probes, the Curiosity Mars rover, and the New Horizons mission to Pluto, enabling long-duration exploration of distant and harsh environments in space.

Summary:

Plutonium is a complex and highly significant element with diverse physical and chemical properties that have profound implications for technology and safety. Its role in nuclear energy and weapons underscores its strategic importance, while its radioactivity and toxicity present considerable challenges regarding handling, storage, and environmental impact. Despite these challenges, plutonium remains a critical material in various applications, particularly nuclear power and space exploration. The production and management of plutonium require advanced technology and rigorous safety protocols to mitigate the risks associated with its use.

See a comprehensive list of atomic, electrical, mechanical, physical and thermal properties for plutonium below: