polonium

Discovery

Polonium was discovered by Marie and Pierre Curie in 1898 as they were exploring the radioactivity of pitchblende. Marie Curie was from Warsaw, Poland. At the time of their discovery, Poland was existing as parts of Russia, the Kingdom of Prussia, and Austria. As a nod to Poland’s independence, which it would regain in 1918, Marie and Pierre named the new element Polonium. This marked the first time an element was named for political reasons. Marie won the Nobel Prize in Chemistry for the discovery of polonium and radium in 1911.

Chemical Properties

Polonium is a rare and highly radioactive silver-white metal (sometimes categorized as a metalloid). Polonium is chemically similar to tellurium, but also has some similarities to its neighbor bismuth. Polonium is soluble in dilute acids and slightly soluble in bases. Solutions of polonium first appear pink because of the Po2+ ion, but then rapidly turn yellow because the alpha decay of polonium ionizes the solvent and oxidizes the Po2+ to Po4+. Since polonium also releases alpha particles upon decay, this process is accompanied by bubbling, heat and light emission from laboratory glassware due to absorption of the alpha particles.

Physical properties

Most of the known chemistry of polonium is based on the naturally occurring radioactiveisotope polonium-210, which is a natural radioactive decay by-product of the uranium decayseries. Its melting point is 254°C, its boiling point is 962°C, and its density is 9.32g/cm³.
Po-210 is a strong emitter of alpha particles. One gram of Po-210 will produce about 140watts of energy, making it ideal as a lightweight thermoelectric power source for space vehicles.It has a half-life of 138.39 days.
Po-209, the most stable isotope of polonium, decays into lead-205 by alpha decay. It costsabout $3,000 per microcurie, which is a very small amount of polonium.

Isotopes

There are 41 isotopes of polonium. They range from Po-188 to Po-219. Allof them are radioactive with half-lives ranging from a few milliseconds to 102 years,the latter for its most stable isotope Po-209. Polonium is involved with several radioactivedecay series, including the actinium series, Po-211 and Po-215; the thoriumseries, Po-212 and Po-216; and the uranium decay series, Po-210, Po-214, and Po-218.

Origin of Name

Named for Poland, the native country of Marie Curie, who discovered the element.

Occurrence

Polonium is found only in trace amounts in the Earth’s crust. In nature it is found inpitchblende (uranium ore) as a decay product of uranium. Because it is so scarce, it is usuallyartificially produced by bombarding bismuth-209 with neutrons in a nuclear (atomic) reactor,resulting in bismuth-210, which has a half-life of five days. Bi-210 subsequently decays intoPo-210 through beta decay. The reaction for this process is ²⁰⁹Bi(_n,γ )²¹⁰Bi → ²¹⁰Po + β^-. Onlysmall commercial milligram amounts are produced by this procedure.

History

Polonium was the first element discovered by Mme. Curie in 1898, while seeking the cause of radioactivity of pitchblende from Joachimsthal, Bohemia. The electroscope showed it separating with bismuth. Polonium is also called Radium F. Polonium is a very rare natural element. Uranium ores contain only about 100 μg of the element per ton. Its abundance is only about 0.2% of that of radium. In 1934, it was found that when natural bismuth (²⁰⁹Bi) was bombarded by neutrons, ²¹⁰Bi, the parent of polonium, was obtained. Milligram amounts of polonium may now be prepared this way, by using the high neutron fluxes of nuclear reactors. Polonium^-210 is a low-melting, fairly volatile metal, 50% of which is vaporized in air in 45 hours at 55°C. It is an alpha emitter with a half-life of 138.39 days. A milligram emits as many alpha particles as 5 g of radium. The energy released by its decay is so large (140 W/g) that a capsule containing about half a gram reaches a temperature above 500°C. The capsule also presents a contact gamma-ray dose rate of 0.012 Gy/h. A few curies (1 curie = 3.7 × 10¹⁰ Bq) of polonium exhibit a blue glow, caused by excitation of the surrounding gas. Because almost all alpha radiation is stopped within the solid source and its container, giving up its energy, polonium has attracted attention for uses as a lightweight heat source for thermoelectric power in space satellites. Thirty-eight isotopes and isomers of polonium are known, with atomic masses ranging from 192 to 218. All are radioactive. Polonium^-210 is the most readily available. Isotopes of mass 209 (half-life 102 years) and mass 208 (half-life 2.9 years) can be prepared by alpha, proton, or deuteron bombardment of lead or bismuth in a cyclotron, but these are expensive to produce. Metallic polonium has been prepared from polonium hydroxide and some other polonium compounds in the presence of concentrated aqueous or anhydrous liquid ammonia. Two allotropic modifications are known to exist. Polonium is readily dissolved in dilute acids, but is only slightly soluble in alkalis. Polonium salts of organic acids char rapidly; halide amines are reduced to the metal. Polonium can be mixed or alloyed with beryllium to provide a source of neutrons. It has been used in devices for eliminating static charges in textile mills, etc.; however, beta sources are more commonly used and are less dangerous. It is also used on brushes for removing dust from photographic films. The polonium for these is carefully sealed and controlled, minimizing hazards to the user. Polonium^-210 is very dangerous to handle in even milligram or microgram amounts, and special equipment and strict control are necessary. Damage arises from the complete absorption of the energy of the alpha particle into tissue. The maximum permissible body burden for ingested polonium is only 0.03 μCi, which represents a particle weighing only 6.8 × 10^-12 g. Weight for weight it is about 2.5 × 10¹¹ times as toxic as hydrocyanic acid. The maximum allowable concentration for soluble polonium compounds in air is about 2 × 10¹¹ μCi/cm3. Polonium- 209 is available on special order from the Oak Ridge National Laboratory at a cost of $3600/μCi plus packing costs.

Characteristics

Polonium is more metallic in its properties than the elements above it in group 16. It isthe only element in group 16 that is naturally radioactive. It is in a position on the periodictable of elements where it can be a metal, metalloid, or nonmetal. It is more often considereda metal because of its electrical conductivity decreases with an increase in temperature.
As an oxide, it is similar to the reddish color of tellurium oxide. Chemically, it behavessimilar to tellurium, lead, and bismuth.

Uses

There are not many uses for polonium. Probably the most important is as a source of alphaparticles (nuclei of helium atoms) and high-energy neutrons for research and radiation studies.It is also used to calibrate radiation-detection devices.
Polonium is used to eliminate static electricity in industrial processes, such as rolling outpaper, wire, or sheet metal in mills. Polonium is also sometimes used in “brushes” to removedust from photographic film and in the manufacturing of spark plugs that make ignition systemsin automobiles more efficient, particularly in extremely cold temperatures. It can also beused as a portable, low-level power source and, since polonium is fissionable, used in nuclearweapons and nuclear electric power plants.

Definition

polonium: Symbol Po. A rare radioactivemetallic element of group 16(formerly VIB) of the periodic table;a.n. 84; r.a.m. 210; r.d. 9.32; m.p.254°C; b.p. 962°C. The element occursin uranium ores to an extent ofabout 100 micrograms per 1000 kilograms.It has over 30 isotopes, morethan any other element. The longestlivedisotope is polonium-209 (halflife103 years). Polonium hasattracted attention as a possible heatsource for spacecraft as the energyreleased as it decays is 1.4×10⁵J kg^-1s^-1. It was discovered by MarieCurie in 1898 in a sample of pitchblende.

Definition

A radioactive metallic element belonging to group 16 of the periodic table. It occurs in very minute quantities in uranium ores. Over 30 radioisotopes are known, nearly all alphaparticle emitters. Polonium is a volatile metal and evaporates with time. It is also strongly radioactive; a quantity of polonium quickly reaches a temperature of a few hundred degrees C because of the alpha emission. For this reason it has been used as a lightweight heat supply in space satellites. Symbol: Po; m.p. 254°C; b.p. 962°C; r.d. 9.32 (20°C); p.n. 84; stablest isotope ²⁰⁹Po (half-life 102 years).

Hazard

Even though polonium is a rare element, it is a very dangerous radiation source and shouldbe avoided.
Cigarette smoke contains a minute amount of polonium, along with many other carcinogenicchemicals, many of which can cause lung cancer. Over one hundred trace elements andcompounds have been identified in cigarette smoke besides polonium. Some examples arenicotine, cresol, carbon monoxide, pyridine, and the carcinogenic compound benzopyrene.