Polonium

History

It is the first element discovered by Pierre and Marie Curie in 1898 in their research on the Radioactivité of the Pechblende. It is only later that they discovered the Radium. The word polonium was thus chosen in homage at the Polish origins of Marie Skłodowska-Curie.

Physical properties

Polonium (isotope 210) is a metal at low melting point and relatively volatile: indeed, 50% of a given mass of this element evaporate in the air with 50 ⁰ C in 45 hours.

It is a transmitter of Rayonnement alpha. 210 Po has one period of Demi-vie 138 days.

It is generated thereafter disintegrations which on the basis of the Uranium 238, and passing inter alia by the Radium 226, the Radon 222 and the Plomb 210 lead to polonium 210 then end in lead 206 stable.

Decay chain: uranium 238 - > particles alpha - > thorium 234 - > beta-> protactinium 234 - > beta - > uranium 234 - > alpha - > thorium 230 - > alpha - > radium 226 - > alpha - > radon 222 - > alpha - > polonium 218 - > alpha - > lead 214 - > beta - > bismuth 214 - > beta - > polonium 214 - > alpha - > lead 210 - > beta - > bismuth 210 - > beta - > polonium 210 - > alpha - > lead 206 (stable)

It disintegrates by emitting particles alpha whose typical energy is of 5,3 million electrons volts. For comparison the energy transported by the rays of the sun (visible field) is only about some electrons volts. These particles alpha are ionizing rays of strong energy able to generate major damage at the time of their interactions with the living matter (cells, DNA). The exposure to the Ionizing rays increases the risks of Cancer, genetic anomalies, and could have many medical consequences others that cancers. Polonium 210 presents a very strong specific activity.

Only one gram of polonium 210 presents an activity of 166.000 billion Becquerel S and consequently emits 166.000 billion particles alpha a second. For comparison 1 milligram of polonium 210 as many emits at each second particles alpha than 4,5 grams of radium 226 or 13,5 tons of uranium 238.

A radioactive element naturally present in the environment and the food chain Polonium 210 is present in infinitesimal quantity (in mass) in the Earth's crust. But taking into account its very strong radioactivity, the results expressed in becquerels per kilogram of ground are not negligible.

The radioactivity of polonium 210 is so high that it releases an important heat (140 Watts per gram). Thus, according to the National laboratory of Argonne to the USA, the temperature of a capsule containing approximately a half-gram of polonium 210 can exceed 500 °C. This property was used to develop light thermo-electric generators used for example in the space field like energy source for the satellites.

Uses

Source alpha,
Source of Neutron S, mixes some with the Béryllium: this last emits a neutron during the absorption of a particle alpha, produced by the ²¹⁰Po. This system is used as primary education source with the starting of the nuclear reactors, like detonator in the first nuclear bombs or the space field like energy source for the satellites.

Poison: it is with this substance that the former Russian spy would have been poisoned, Alexandre Litvinenko. The cost of the polonium-210 amount which would have killed it is estimated at 25 million US dollars (Berliner Zeitung). The quantity of polonium 210 which “would have been managed to him” was probably very high - since it led to its death in 3 weeks. By using toxicological data on the animals of laboratory, one can imagine that they were a few micrograms of polonium 210.

The activity of one microgram is approximately 166 million becquerels. Under these conditions, least body secretion (saliva on glass, perspiration on a touched object, a seat where he sat down, etc) could lead to the deposit on these objects of a considerable quantity of polonium 210 (several hundred becquerels, even much more).

Precautions

Polonium is a highly radioactive and toxic element. Even for small quantities (some Microgram S), the handling of 210 Po is very dangerous and requires special equipment and strict procedures. Absorbed in fabrics, it causes direct damage by particulate emission alpha. The absorption from 1 to 10 micrograms is sufficient to cause death.

The acceptable maximum activity for introduced polonium is only of 1.100 Becquerel, that is to say the equivalent with 6,6 × 10 -12 gram. With identical mass, polonium is approximately 10 6 time more toxic than the Cyanide of sodium or the Cyanide potassium.

Because of use of Manure containing Phosphate of calcium, the Tabac contains 210 Po. The smoke inhaled by the smokers contains a negligible but already dangerous proportion of polonium.

an American study estimated that the “natural” polonium inhalation, via the cigarette smoke, “counts for at least 90% of all the lung cancers raised among smokers”

Notes and references of the article

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