Radioactive Element Polonium.
One of the great and ultimately tragic Tales of Chemistry.
Jun 8, 2008
This is an intensely radioactive element, and on ingestion into the body, will irradiate any cells in its vicinity, leading to rapid breakdown of DNA and other cell molecules. It is one trillion times as toxic as cyanide.
Polonium is a member of the same group of elements as oxygen and sulphur. Mendeleev predicted its existence in 1891 following his development of the Periodic Table.
Radioactivity
The first radioactive elements to be discovered, in 1789 and 1815 respectively, were uranium and thorium. Radioactivity was then an unknown phenomenon, and remained so until Henri Becquerel, in 1896, noticed the effect of uranium’s ore, pitchblende, on a photographic plate. He placed a piece of the ore near the sealed plate in a laboratory drawer. A key lay on top of the plate. When the plate was developed, it contained an image of the key, which could only have been formed by invisible rays coming from the rock.
Discovery
Subsequent investigations showed that the pitchblende was far more radioactive than could be explained by uranium alone. After many months’ labour, starting with several tonnes of ore, Becquerel’s colleagues, Pierre and Marie Curie, isolated less than a gram of a new element, which they named polonium, in honour of Marie Curie’s birth country, Poland.
For their discovery of radioactivity, Becquerel and the Curies shared the Nobel Prize for Physics in 1903. Marie Curie received a second Nobel Prize, this time for Chemistry, in 1911, for her discoveries of polonium and another radioactive element, radium.
Marie Curie died of leukaemia in 1934 as a result of her years of exposure to radium. Her daughter, Irene, followed her parents into scientific research. Along with her husband, Frederick Joliot, she was awarded the Nobel Prize for Chemistry in 1935 for work on artificial radioactivity. In 1956, she also died of leukaemia, probably caused by her exposure to polonium following a laboratory accident fifteen years earlier.
Polonium Isotopes
Polonium is one of the ten least abundant elements in the Earth’s crust. It exists as several isotopes, with mass numbers from 194 to 218. All atoms of polonium contain 84 protons in their nuclei. The differences in mass number are due to varying numbers of neutrons. The most common isotope, and the one responsible for poisoning Alexander Litvinenko, is polonium-210.
Uses of Polonium
Extraction of polonium from uranium ore is very inefficient, and it is now obtained, to the extent of around 100 grams each year, by neutron-bombardment of the metal bismuth in a nuclear reactor. Its intense radioactivity means that it generates much energy, and is used as a heat source in space satellites. When alloyed with beryllium, it provides a source of neutrons in nuclear weapons.
It was used, for a time, to remove the static electricity that often builds up on textiles during their manufacture. The radiation from the polonium caused the air in its vicinity to become ionised. This, in turn, allowed the static to leak away. A similar mechanism prevented dust from clinging to photographic film during its manufacture. Nowadays, a safer alternative is used.
The minuscule concentration of polonium in rocks means that it is unlikely to enter our diet. Nevertheless, it is a natural decay product of the radioactive gas, radon, which is present in low concentrations in air, and is therefore found to a tiny extent in all our bodies.
