Monday, March 22, 2010
THE Greek philosopher Empedocles, who lived in Sicily, is said to have committed suicide by jumping into the volcano so no trace of his mortal remains would be found and people would think he was a god.
The idea that the world is composed of four ingredients, earth, air fire and water, is Empedocles’s great legacy. It has been one of the most persistent notions in western thought, although there are 92 naturally occurring elements and not just four.
The heaviest element, uranium, drives the turbines of power stations without emitting greenhouse gases. It’s a Jeckyll and Hyde substance, however. Appalling weapons of mass destruction can be fashioned from it and the waste products produced during its peaceful applications remain lethal for tens of thousands of years. This element could save or destroy mankind. A recently published book, Uranium Wars: the Scientific Rivalry That Created The Nuclear Age, gives a fascinating account of its discovery and exploitation in peace and war. The author, Amir D Aczel, is a research fellow in the history of science at Boston University.
In the early 16th century, silver deposits were discovered in Saxony, Germany, and a new town, Joachimstal, became the centre of the largest mining operation in Europe. Bismuth and cobalt were also present, as was an apparently useless dark compound which the miners called ‘pitchblende’, combining the German words for ‘blind’ and ‘mineral’. Nobody paid much attention to pitchblende until 1789, when the pharmacist Martin Klaproth applied new analysis techniques to it. Pitchblende, he reported, contained a previously unknown and strange kind of ‘half metal’.
He named it after the planet Uranus which had recently been discovered. It would be the 19th century, however, before scientists managed to refine the substance to its pure metallic form. Then, in 1895, German physicist Wilhelm Röntgen stumbled accidentally on a curious property of the material; it emitted energy. Radioactivity had been discovered.
There are 92 protons and 146 neutrons in the core of a uranium atom. This huge wobbly structure is unstable and particles are flung off from time to time, releasing some of the energy which bound them to the atom.
Uranium decays very slowly but a form of it which has 235 particles in its nucleus, rather than the usual 238, breaks down much more quickly. A sample of uranium 238 will take 4.5 billion years to decay to half it size, whereas a 235 sample would be halved in only 700 million years. When it comes to extracting energy from uranium, the 235 isotope is the one to use.
However, only seven in a thousand uranium atoms are 235s. Filtering out this isotope, an activity in which Iran is engaged at present, is a difficult process.
Austrian physicist Lise Meitner is one of several female scientists neglected by the Nobel Prize Committee. A Jew, she fled to Sweden when the Nazis took over Austria and while there, she came up with the concept of nuclear fission. Lighter elements can be formed when a uranium nucleus meets a stray neutron; atoms can be split.
Then, in 1942, Enrico Fermi built a radioactive pile in a basement at Chicago University. If a highly-radioactive substance is compressed enough, he demonstrated, the particles flung off by disintegrating atoms smash other ones and a runaway chain reaction results.
Aczel celebrates the work of Meitner, Fermi and the other nuclear physicists. He has an interesting take on the Manhattan Project and on the efforts of German scientists to develop the bomb. In autumn 1941, a famous meeting took place in Copenhagen between the great German physicist Werner Heisenberg, and Niels Bohr, who developed the basic model of the atom.
Was Heisenberg seeking absolution from his former teacher for attempting to make a bomb? Was there to be a secret agreement between Allied and Axis scientists to avert its development by either side? Aczel, who met Heisenberg, has his own theory as to what took place. His ‘biography’ of uranium is a joy to read.
Uranium Wars by Amir D Aczel is published by Palgrave Macmillan.
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