Chemistry in its element: polonium


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Chris Smith

Hello, this week in Chemistry in its element the story of a substance that was named to snub Russia, power space probes keeps paper static free and has even been used as a murder weapon in London. To reveal the secrets of Marie Curie's element, and that's polonium, here's Johnny Ball

Johnny Ball

Polonium, (element 84), was discovered in 1898 and named after Poland, the homeland of Marie Curie (Ne Sklodowska) who found it with her husband Pierre Curie. This loyalty was a direct affront to Russia who had dominated Poland for so long. The only way she could become educated whilst a teenager, was by risking imprisonment by the Russians by attending secret underground schools, which had to change locations every couple of days. It was only by escaping to Paris, following her older brother and sister, that she was able to forge a career. She was so poor in the early years in Paris, that she sometimes fainted through lack of food. Still she worked tirelessly.

In 1894 she met Pierre, who had made a name for himself in discovering piezoelectricity and was one of her lecturers. They married in July 1895. She wore a black dress as it would be serviceable for her work in the laboratory. They did not exchange rings, but bought each other a bicycle, on which they honeymooned.

X rays had been discovered by Roentgen (Nov 95) and uranium radiation by Becquerel (Feb 96) in Paris. Working with him (98), Marie coined the phrase "radioactivity" and decided to make this here object of study, because no one else was doing it. They realised that radiation was coming from the very atoms and that this was a sign of the atoms breaking up. Only by studying the break up of atoms through radiation, were scientists able to clearly understand how atoms are made up. For this the Curies and Becquerel shared the Nobel Prize for Physics in 1903.

The discovery of polonium (July 98) was no mean task. Pitchbende, a uranium bearing ore, seemed to be far to radio active than could be accounted for by the uranium. The couple got the waste ore free, after the uranium had been removed. They sieved and sorted by hand, ounce by ounce, through tons of pitchblende before tiny amounts of polonium were discovered. With the polonium extracted, there was clearly something far more radioactive left behind and soon they had isolated the much more important element radium in December 1898. Radium was so named as it glowed in the dark.

Pierre died in a tragic accident in 1906. In driving rain he seemed to walk in front of a large horse-drawn wagon, and a wheel shattered his head. Some think  the pain he was in as a result of radiation burns and sickness may have caused his lack of awareness. Marie was devastated, but her work continued. For discovering polonium and radium, she received the Nobel Prize for Chemistry in 1911, becoming the only woman ever to receive two such prizes.

However, there was still more success due for the family. Her daughter Irene also became a scientist, and in 1934, Marie saw Irene and her husband Frederick Joliot-Curie produce the first ever artificial radioactive element. This led to our modern ability to manipulate almost every element for our specific scientific needs. Irene and Frederick also received the Nobel Prize in 1935, but sadly Marie had now died.

Natural polonium, Po-210, is still very rare and forms no more than 100 billions of a gram per ton of uranium ore. Because it is so rare, polonium is made by first making bismuth (also found in pitchblende). Bismuth-209 is found and then artificially changed to bismuth-210 which then decays to form polonium-210. This process requires a nuclear reactor, so it is not an easy element to source.

It was a shocking discovery that the former Russian agent Alexander Litvinenko was poisoned with this very radioactive element. The alpha particles it emits are so weakly penetrating it could easily have been carried in a simple sealed container, and would have to be ingested, for example in a cup of tea, to do any serious harm. However, once inside the body, as it continued to disintegrate, it would become fatal.

Polonium has a position in the periodic table that could make it a metal, a metalloid or a nonmetal. It is classed as a metal as its electrical conductivity decreases as its temperature rises. Because of this property it is used in industry to eliminate dangerous static electricity in making paper or sheet metal.

Because of its short half life, its decay generates considerable heat (141 W per gram of metal). It can be used as a convenient and very light heat source to generate reliable thermoelectric power in space satellites and lunar stations, as no moving parts are involved.

Chris Smith

Johnny Ball lifting the lid on the radioactive element polonium discovered by Marie Curie and her husband Pierre. Next time on Chemistry in its element we remain radioactive much like the substance itself with earth scientist Ian Farnan.

Ian Farnan

Anyone familiar with the iconic image of the mushroom cloud understands the tremendous explosive power of a correctly controlled detonation of plutonium. The energy density is mind-boggling: a sphere of metal 10 cm in diameter and weighing just 8 kg is enough to produce an explosion at least as big as the one that devastated Nagasaki in 1945.

Chris Smith

Ian Farnan with what promises to be an explosive edition of Chemistry in its element next week. I'm Chris Smith, thank you for listening and see you next time.


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