Polonium
Polonium is a chemical element with the symbol Po and atomic number 84, discovered in 1898 by Marie and Pierre Curie. A rare and highly radioactive element with no stable isotopes, polonium is chemically similar to bismuth and tellurium, and it occurs in uranium ores. Applications of polonium are few, and include heaters in space probes, antistatic devices, and sources of neutrons and alpha particles. Because of its position in the periodic table, polonium is sometimes classified as a metalloid. However, other sources say that on the basis of its properties and behavior, it is "unambiguously a metal".
Occurrence and production
Because of the small abundance, isolation of polonium from natural sources is a very tedious process. The largest batch was extracted in the first half of the 20th century by processing 37 tonnes of residues from radium production. It contained only 40 Ci (9 mg) of polonium-210. Nowadays, polonium is obtained by irradiating bismuth with high-energy neutrons or protons.
Neutron capture
Synthesis by (n,γ) reaction
In 1934 an experiment showed that when natural 209Bi is bombarded with neutrons, 210Bi is created, which then decays to 210Po via β decay. The final purification is done pyrochemically followed by liquid-liquid extraction techniques. Polonium may now be made in milligram amounts in this procedure which uses high neutron fluxes found in nuclear reactors. Only about 100 grams are produced each year, practically all of it in Russia, making polonium exceedingly rare.
This process can cause problems in lead-bismuth based liquid metal cooled nuclear reactors such as those used in the Soviet Navy's K-27. Measures must be taken in these reactors to deal with the unwanted possibility of 210Po being released from the coolant.
Proton capture
Synthesis by (p,n) and (p,2n) reactions
It has been found that the longer-lived isotopes of polonium can be formed by proton bombardment of bismuth using a cyclotron. Other more neutron-rich isotopes can be formed by the irradiation of platinum with carbon nuclei.
| Symbol | Po | |
| Atomic Number | 84 | |
| Atomic Weight | 208.9824 | |
| Oxidation States | +2,+4 | |
| Electronegativity, Pauling | 2.2 | |
| State at RT | solid | |
| Melting Point, K | 527 | |
| Boiling Point, K | 1235 |
Appearance and Characteristics
Harmful effects:
Polonium is harmful both through its chemical toxicity and its radioactivity. Polonium-210 is an alpha emitter. As such it is very hazardous if swallowed or inhaled. Exposure to polonium increases the risk of getting various cancers.
Characteristics:
- Polonium is a rare, silvery-gray, radioactive low-melting metalloid.
- Polonium readily reacts with dilute acids, but only slightly with alkalis.
- All of its isotopes are radioactive.
- 210Po emits a blue glow, as the air around it is excited by the decay products. 1 gram of Po emits as many alpha particles as 5 kilograms of radium. The energy released by polonium’s alpha decay is considerable and heats the volume around it. The energy released is so large (140 W/g) that a capsule containing about half a gram reaches a temperature above 500 oC.
Uses of Polonium
- Polonium is used to eliminate static electricity produced during processes such as rolling paper, wire and sheet metal. However, beta decay sources are more commonly used as they are less dangerous.
- 210Po can be used as an atomic heat source but because of the isotope’s short half-life (138.4 days), it doesn’t provide power for long-term uses.
- Polonium is also used in anti-static brushes to eliminate dust on photographic film. It is sealed in brushes to control the radioactive emissions.
