Plutonium

Plutonium, with the atomic number 94 and symbol Pu, is a radioactive element in the actinide series of the periodic table. Discovered by Glenn Seaborg in 1941, it was named after the planet Pluto. Its discovery completed the series of elements that begins with uranium. Plutonium was identified through the beta decay of neptunium-239, providing conclusive evidence of its existence.

1.0Introduction 

Plutonium (Pu) is a radioactive element with atomic number 94 in the actinide series of the periodic table. It is one of the most important transuranium elements due to its use as nuclear reactor fuel and in nuclear weapons. Plutonium has a silvery-white appearance but quickly oxidises to a yellowish tarnish when exposed to air.

Plutonium-239, along with uranium-235, is one of the two fissile materials used in nuclear weapons and certain nuclear reactors. It is almost absent and is produced by bombarding uranium-238 with neutrons in a reactor. Since uranium-238 is abundant in most reactor fuel, plutonium-239 is continuously generated. As plutonium-239 can undergo fission to release energy, it contributes to nuclear reactors' energy production.

2.0 Physical Properties of Plutonium

• Appearance: Silvery-white solid under normal conditions but oxidises in air, turning dull grey, yellowish, or olive green.
• Molecular Mass: 244.06420 g/mol.
• Density: 19.85 g/cm³, varying between 16.00 and 19.86 g/cm³ depending on the allotrope.
• Melting Point: 640°C.
• Boiling Point: 3228°C.
• Oxidation: Readily oxidises in air.
• Electrical Resistivity: Exhibits extremely high resistivity at room temperature, which increases as the temperature decreases.
• Density During Melting: Unlike most materials, plutonium's density increases by 2.5% during melting. The liquid metal’s density decreases linearly with temperature.
• Viscosity and Surface Tension: Liquid plutonium shows high viscosity and surface tension near its melting point compared to other metals.

3.0Chemical Properties of Plutonium

• Allotropes: Plutonium exists in six different crystal structures, with the alpha form being stable at room temperature.
• Electrical Resistance: It has the highest electrical resistance compared to other metals.
• Reactivity: Plutonium dissolves in acids and can exist in multiple oxidation states in aqueous solutions, showing distinct colours for each ion:
• Pu³⁺: Blue-lavender.
• Pu⁴⁺: Yellow-brown.
• PuO₂⁺: Pink.
• PuO₂²⁺: Yellow or pink-orange.
• Pu⁷⁺: Green.
• Oxidation States: Plutonium commonly exhibits oxidation states from +3 to +6.
• Fission Reaction: Plutonium-239 undergoes fission as follows: 

${}_{94}{\mathrm{Pu}}^{239}+{}_0{\mathrm{n}}^1\to {}_{94}{\mathrm{Pu}}^{240}\stackrel{73\%}{\to }40{\mathrm{Zr}}^{103}+{}_{54}{\mathrm{Xe}}^{134}+3_0{n}^1+207.1\mathrm{MeV}$

4.0Applications of Plutonium

Plutonium has limited uses, with only two of its five isotopes having specific applications. These include energy production on Earth in space and nuclear weapons. Some general uses of plutonium are:

• A source of energy for electricity generation.
• Fuel in nuclear reactors.
• A neutron source for calibrating neutron detection equipment.
• A threshold detector for measuring neutron energies.