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Its worth mentioning that at the time the Einstein-Szilard letter was written, a lot was unclear about what exactly a nuclear weapon would be. What was certain is that uranium could sustain a nuclear chain reaction, and this could produce an explosion several orders of magnitude greater than chemical reactions. Back of the envelope calculations and common sense, based on what was known at the time, indicated that the amount of uranium needed would probably be many tons. The Einstein letter indicates that a uranium weapon could very well be too heavy to deliver by air, and gives an example of such a weapon being stored on a ship that is detonated in port. Though the possibility of a chain reaction in uranium was all but certain, the practical and economic feasibility of a nuclear bomb was much less so. The spirit of the letter was basically a heads up, saying that this sort of thing might be possible, lots of German physicists know this, and Germany has access to high quality uranium reserves in occupied Czechoslovakia. The letter does not directly advocate the construction or use of such weapons, but calls for serious attention to be devoted to the matter since the Germans would probably be doing so. While Roosevelt took the letter seriously and formed an Advisory Committee to study and keep an eye on things, no real effort was taken towards making a nuclear weapon based on Einstein's letter. About 3 years later, two (Austrian and German born) scientists working in the UK, Otto Frisch and Rudolf Peierls, realized that 1.) Uranium that was isotopically enriched to be nearly pure U-235 would allow efficient and powerful nuclear weapons to be made with kilogram quantities of uranium and 2.) the required isotopic separation was technically and most likely economically feasible. In fact, due to the lack of good experimental data at the time, their calculations actually underestimated the critical mass of U-235 and their report indicated that a bomb could be made with just 1 pound of it. This was communicated in a secret memorandum to the government of the UK and eventually US, and it was this memorandum that really lit a fire under everyone's rear end to start working on a bomb. Something else to point out, is that Einstein's famous "E=mc^2" from special relativity, which he published in 1905, was not important in illustrating the potential possibility of nuclear weapon. The discovery of fission in 1938by Otto Hahn--23 years later--was what made physicists realize that a nuclear chain reaction, and therefore an atomic weapon, could be possible.
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Jan 25, 2016 10:19
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| # ¿ May 17, 2024 15:08 |
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