Polonium, also called as Radium F is a rare radioactive semi metal with an atomic weight of 210 and atomic number 84 and its symbol is Po. Its atomic volume is 22.23 cm3/mol. It is found in Uranium ores. It was discovered by Marie S. curie in 1898, it’s named after her country Poland. It is chemically unstable and all its 33 isotopes are radioactive. It is chemically similar to bismuth and tellurium. It is produced by bombarding bismuth with electrons in a nuclear reactor. It dissolves readily in dilute acids and partially in alkali. Till date, there hasn’t been solid evidence as to whether it is a metalloid or a post transition metal.
As said earlier, Polonium is a very rare element and is usually found in very small quantities in uranium ores. It is generally obtained by the decay of uranium or by chemical processing of uranium ores. It is found in broad leaved vegetables and in small amounts in tobacco leaves too. Polonium otherwise is obtained by a nuclear reaction. Proton and neutron capture are the two processes. It involves irradiation of Bismuth 209 with an atomic number 83 with thermal neutrons. This forms Bismuth 210 which decays to form Polonium.
209Bi + 1n → 210Po + e-
Metallic polonium can be obtained by fractional distillation of bismuth or by electrodepositing onto a metal surface. Even after such a tedious procedure, only few milligrams of polonium can be produced. The largest isolation was from 37 tonnes of radium residue, which produced around 40 curies of Polonium. (1 curie = 37 Gigabecquerels. One Becquerel is defined as the activity of a quantity of radioactive material in which one nucleus decays per second.) For long lived isotopes of polonium, proton bombardment of bismuth is performed in a cyclotron, as the neutron bombardment usually produces short half-life isotopes of polonium. Polonium is in the solid state form, although it has 2 metallic allotropes. The alpha form is an example of simple cubic and the beta form is rombohedral.
It is in the 6th period (row) and 16th group (column). Its position can categorizes it as a metal, non-metal or a metalloid. It is considered a metal as its electrical conductivity reduces with increase in temperature.
Density (g/cc): 9.32 Melting Point (K): 527
Boiling Point (K): 1235 Appearance: Silvery-gray metal
Atomic Radius (pm): 176 Atomic Volume (cc/mol): 22.7
Covalent Radius (pm): 146 Ionic Radius: 67 (+6e)
Specific Heat (@20°C J/g mol): 0.125 Fusion Heat (kJ/mol): (10)
Evaporation Heat (kJ/mol): (102.9) Debye Temperature (K): n/a
Pauling Negativity Number: 2.0 First Ionizing Energy (kJ/mol): 813.1
Oxidation States: 6, 4, 2 Electronic Configuration: [Xe] 4f14 5d10 6s2 6p4
Lattice Structure: Simple Cubic (SC) Lattice Constant (Å): 3.350
Polonium has a half-life of about 139 days. Half-life is the time taken for a radioactive element to decay to half the amount. It is so powerful that it emits that many alpha particles as what 4.5g of radium would, in one second. It usually emits a blue glow caused by its excitation of surrounding air. One in about a 100,000 emissions causes an excitation in the nucleus which results in gamma emission. It’s the alpha particles and not the occasional gamma particles which cause the decay of 210Po. As briefed earlier, polonium dissolves readily in diluted acids and partially soluble in alkali solution. The hydrogen component is a liquid at room temperature. Polonium follows the same biochemical pathways as tellurium and selenium.
They are used as static eliminators. It is used to eliminate static charge in machinery involved in spinning of synthetic fiber, paper rolling, and manufacture of plastic sheets. 210Po are used is brushes to clean dust from photographic films and camera lenses. A capsule of half a gram of polonium can reach temperatures up to 5000 degrees. It is used as an alpha source or a heat source in thermoelectric cells of a satellite. Since it has a short life, it has been phased out of use for this particular application. It is used as a neutron source. When mixed with beryllium, polonium acts as a neutron source. This was one of the principle neutron initiators in the first generation of atomic bombs. Polonium is also used as a poison as in the case of Alexander Litvinenko poisoning.
Polonium has entered into our daily lives through water, food, living cells and tissues due to the mining boom. Its concentration in soil is similar to the concentration it has in uranium ores. Polonium is emitted to the atmosphere during the production of elemental phosphorous. Due to its presence in air and soil a lot of broad leaved vegetables have very small traces of polonium present. Even tobacco leaves have polonium deposits due to the atmosphere. This increases the risk of elevated polonium deposits in smokers than in non-smokers.
Since alpha particles can’t travel long as they are stopped by our external layer of skin, external exposure to Po 210 does not harm and is not a risk until it’s outside the body of human beings. It usually gets inside the human body through consumption of food, drinking water or breathing. If absorbed by the body it can cause severe damage to the organic tissues. Almost 50 to 90% of the consumed polonium is excreted through fesses, urine. The remaining 10% gets stored in organs like the spleen, liver and kidneys. Polonium cannot be used as an alternative fuel for power production as it is a very rare element and it decays very quickly. Lifetime cancer risks increase. Usually lung cancer occurrences are high.