Polonium

Polonium has more isotopes than any other element, all of which are radioactive. Polonium dissolves readily in dilute acids, but is only slightly soluble in alkalis.

Weight for weight it is about 2.5 x 1011 times as toxic as hydro cyanic acid (HCN). Polonium has been found in tobacco as a contaminant and in uranium ores.

Polonium is radioactive and present only in extremely low abundances in the environment. It is quite metallic in nature despite its location beneath oxygen in the periodic table. It is made in very small quantities through a nuclear reaction of bismuth. Neutron irradiation of 209bismuth (atomic number 83) gives 210polonium (atomic number 84).

209Bi + 1n ЃЁ 210Po + e-

Polonium-210, 210Po, transmutes into the lead isotope 206Pb by the emission of an Ñ"Ñ---particle. The half-life for this process is just over 138 days meaning that after 138 days one-half of the original 210Po has disappeared and after 2 times 138 days 3/4 has gone.

21084Po ЃЁ 20682Pb + 42He

Polonium metal is unique in that it is the only element whose structure (known as the -form) is a simple cubic array of atoms in which each atom is surrounded by six other polonium atoms. On gentle warming to 368C, this converts into a second form known as the Ñ"А-form.

It is suggested that poisoning by polonium-210 may have caused the death of Alexander Litvinenko, said to be a former Russian spy, in November 2006. Following his death at the end of November 2006, traces of polonium were found at several places he had visited before becoming ill. Before his death it was thought that thallium, or even radio thallium, might have been the cause of his illness. At the time of writing it is not clear who killed him, but not surprisingly the Russians deny it. Polonium-210 decays through the emission of Ñ"Ñ---particles and these emissions are normally easy to stop, but they are very dangerous if the polonium is inside the body.

The short half life of polonium-210 and the heat generated with the above radioactive decay means that polonium metal generates considerable heat (141 W), meaning that the metal and its compounds self-heat. This is a useful property and polonium can be used as a small heat source (if expensive!). It can be used in space satellites for this purpose and is especially desirable as there are no moving parts. It was also