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Jai Ganesh

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Polonium

Polonium

Gist

Polonium (Po, atomic number 84) is a rare, highly radioactive metal discovered by Marie and Pierre Curie in 1898. It has no stable isotopes, with Polonium-210 (210Po) being the most common, formed as a decay product of uranium-238. Although Po-210 poses no external hazard, internal contamination from inhalation or ingestion can cause significant internal radiation doses, leading to severe health effects or death. Its industrial applications include the removal of static electricity in industries like paper and metal rolling. 

Polonium has limited industrial uses, including antistatic devices, heat sources for space equipment, and neutron sources for research and nuclear applications. However, its extreme radioactivity and short half-life make it dangerous and challenging to handle, with potential applications for poisoning and in the development of atomic weapons.

Summary

Polonium is a chemical element; it has symbol Po and atomic number 84. A rare and highly radioactive metal (although sometimes classified as a metalloid) with no stable isotopes, polonium is a chalcogen and chemically similar to selenium and tellurium, though its metallic character resembles that of its horizontal neighbors in the periodic table: thallium, lead, and bismuth. Due to the short half-life of all its isotopes, its natural occurrence is limited to tiny traces of the fleeting polonium-210 (with a half-life of 138 days) in uranium ores, as it is the penultimate daughter of natural uranium-238. Though two longer-lived isotopes exist (polonium-209 with a half-life of 124 years and polonium-208 with a half-life of 2.898 years), they are much more difficult to produce. Today, polonium is usually produced in milligram quantities by the neutron irradiation of bismuth. Due to its intense radioactivity, which results in the radiolysis of chemical bonds and radioactive self-heating, its chemistry has mostly been investigated on the trace scale only.

Polonium was discovered on 18 July 1898 by Marie Skłodowska-Curie and Pierre Curie, when it was extracted from the uranium ore pitchblende and identified solely by its strong radioactivity: it was the first element to be discovered in this way. Polonium was named after Marie Skłodowska-Curie's homeland of Poland, which at the time was partitioned between three countries. Polonium has few applications, and those are related to its radioactivity: heaters in space probes, antistatic devices, sources of neutrons and alpha particles, and poison (e.g., poisoning of Alexander Litvinenko). It is extremely dangerous to humans.

Details

Polonium (Po) is a radioactive, silvery-gray or black metallic element of the oxygen group (Group 16 [VIa] in the periodic table). The first element to be discovered by radiochemical analysis, polonium was discovered in 1898 by Pierre and Marie Curie, who were investigating the radioactivity of a certain pitchblende, a uranium ore. The very intense radioactivity not attributable to uranium was ascribed to a new element, named by them after Marie Curie’s homeland, Poland. The discovery was announced in July 1898. Polonium is extremely rare, even in pitchblende: 1,000 tons of the ore must be processed to obtain 40 milligrams of polonium. Its abundance in the Earth’s crust is about one part in {10}^{15}. It occurs in nature as a radioactive decay product of uranium, thorium, and actinium. The half-lives of its isotopes range from a fraction of a second up to 103 years; the most common natural isotope of polonium, polonium-210, has a half-life of 138.4 days.

Polonium usually is isolated from by-products of the extraction of radium from uranium minerals. In the chemical isolation, pitchblende ore is treated with hydrochloric acid, and the resulting solution is heated with hydrogen sulfide to precipitate polonium monosulfide, PoS, along with other metal sulfides, such as that of bismuth, Bi2S3, which resembles polonium monosulfide closely in chemical behaviour, though it is less soluble. Because of the difference in solubility, repeated partial precipitation of the mixture of sulfides concentrates the polonium in the more soluble fraction, while the bismuth accumulates in the less soluble portions. The difference in solubility is small, however, and the process must be repeated many times to achieve a complete separation. Purification is accomplished by electrolytic deposition. It can be produced artificially by bombarding bismuth or lead with neutrons or with accelerated charged particles.

Chemically, polonium resembles the elements tellurium and bismuth. Two modifications of polonium are known, an α- and a β-form, both of which are stable at room temperature and possess metallic characteristics. The fact that its electrical conductivity decreases as the temperature increases places polonium among the metals rather than the metalloids or nonmetals.

Because polonium is highly radioactive—it disintegrates to a stable isotope of lead by emitting alpha rays, which are streams of positively charged particles—it must be handled with extreme care. When contained in such substances as gold foil, which prevent the alpha radiation from escaping, polonium is used industrially to eliminate static electricity generated by such processes as paper rolling, the manufacture of sheet plastics, and the spinning of synthetic fibres. It is also used on brushes for removing dust from photographic film and in nuclear physics as a source of alpha radiation. Mixtures of polonium with beryllium or other light elements are used as sources of neutrons.

Element Properties

atomic number  :  84
atomic weight  :  210
melting point  :  254 °C (489 °F)
boiling point  : 962 °C (1,764 °F)
density  :  9.4 g/{cm}^{3}
oxidation states  :  −2, +2, +3(?), +4, +6.

Additional Information:

Appearance

A silvery-grey, radioactive semi-metal.

Uses

Polonium is an alpha-emitter, and is used as an alpha-particle source in the form of a thin film on a stainless steel disc. These are used in antistatic devices and for research purposes.

A single gram of polonium will reach a temperature of 500°C as a result of the alpha radiation emitted. This makes it useful as a source of heat for space equipment.

It can be mixed or alloyed with beryllium to provide a source of neutrons.

Biological role

Polonium has no known biological role. It is highly toxic due to its radioactivity.

Natural abundance

Polonium is a very rare natural element. It is found in uranium ores but it is uneconomical to extract it. It is obtained by bombarding bismuth-209 with neutrons to give bismuth-210, which then decays to form polonium. All the commercially produced polonium in the world is made in Russia.

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