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Authors: Geoffrey Brooks
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considerable.â
The idea of the instantaneous explosive chain reaction in a reactor is grounded in an error of theory caused by failing to take into the mathematical reckoning the small fraction of relatively long-lived neutrons which are emitted up to a minute after fission. What should have been done in the mathematical theory was to average the slowing down and diffusion time of the lifetime of the prompt neutrons liberated within a micro-second of fission added to the mean lifetime of the 0.75% of neutrons which emerge up to 80 seconds after fission occurs. That calculation would have shown that while neutron density increases exponentially with time, the stable Period of the Reactor is not âless than 1 secondâ but is about 54 seconds.
The delayed neutrons play the decisive role in the safe control of modern atomic energy plants and without them nuclear power reactors would not be feasible. Heisenberg may have been genuinely under a misapprehension. On the other hand, he may have realized that this would be a useful error to have in hand if he wanted to obstruct the development of a nuclear reactor.
In later reports he was never challenged when he relied on the argument as a reason for proceeding at slow ahead with the interminable low-level experiments which filled the next five years. Knowingly or not, Professor Heisenberg accepted that the Period of the Reactor was less than one second in length, after which the reactor blew up. After the war, in his reproduction report respecting the Haigerloch B8 experiment published in FIAT Review of German Science 1939â1945 Heisenberg acknowledged that his theory had been at fault, admitting:
âAmerican work shows that the Period of the Reactor is substantially extended by the delayed emergence of a number of those neutrons liberated during the fission process.â
And in a report about the German project prepared by A. Weinberg and L. Nordheim for A. H. Compton on 8 November 1945 the authors were of the opinion that the importance of delayed neutrons for the stability of a nuclear reactor had probably not been considered. Even if Heisenberg knew all along, however, he could hardly say so in 1947. So, throughout the Second World War, Heisenberg believed, or let it be thought that he believed, that the Uranbrenner â the atomic pile for power â was impossible because the reactor would explode one sixth of a second after it went critical. He did not explain this fact in writing when setting down the theory originally, although one would think he must have informed his superiors at the Heereswaffenamt of his fears confidentially. To make some sense out of the fact that Heisenberg and the Uranium Project spent the war years performing interesting experiments of subreactor geometry, and obviously had no intention of actually bringing an experiment beyond the critical point since there was sufficient heavy water available in aggregate to moderate a working reactor by 1944 but no enthusiasm for doing so, Heisenberg must have convinced Hitler of the impossibility of building a working pile. Hitler did not want a nuclear reactor in any case because it was Jewish Physics. Probably he just waved a hand in dismissal, allowing Heisenberg and the reactor project to appear to be doing something useful to keep enemy Intelligence on the hop. That really is the only logical conclusion to be drawn from the manner in which the project was conducted.
The Basis of Reactor Design
The surest method of realizing energy production from the fissioning of uranium lay in enriching the U 235 isotope, Heisenberg explained: the more the enrichment the smaller the reactor would be. If the proportion of theU 235 isotope in the uranium material were to be enriched by 50%, from 0.7% to 1%, success was practically certain. However, such a proceeding was prohibitively expensive.
Natural uranium could be used in the reactor vessel in conjunction with another substance, a
The idea of the instantaneous explosive chain reaction in a reactor is grounded in an error of theory caused by failing to take into the mathematical reckoning the small fraction of relatively long-lived neutrons which are emitted up to a minute after fission. What should have been done in the mathematical theory was to average the slowing down and diffusion time of the lifetime of the prompt neutrons liberated within a micro-second of fission added to the mean lifetime of the 0.75% of neutrons which emerge up to 80 seconds after fission occurs. That calculation would have shown that while neutron density increases exponentially with time, the stable Period of the Reactor is not âless than 1 secondâ but is about 54 seconds.
The delayed neutrons play the decisive role in the safe control of modern atomic energy plants and without them nuclear power reactors would not be feasible. Heisenberg may have been genuinely under a misapprehension. On the other hand, he may have realized that this would be a useful error to have in hand if he wanted to obstruct the development of a nuclear reactor.
In later reports he was never challenged when he relied on the argument as a reason for proceeding at slow ahead with the interminable low-level experiments which filled the next five years. Knowingly or not, Professor Heisenberg accepted that the Period of the Reactor was less than one second in length, after which the reactor blew up. After the war, in his reproduction report respecting the Haigerloch B8 experiment published in FIAT Review of German Science 1939â1945 Heisenberg acknowledged that his theory had been at fault, admitting:
âAmerican work shows that the Period of the Reactor is substantially extended by the delayed emergence of a number of those neutrons liberated during the fission process.â
And in a report about the German project prepared by A. Weinberg and L. Nordheim for A. H. Compton on 8 November 1945 the authors were of the opinion that the importance of delayed neutrons for the stability of a nuclear reactor had probably not been considered. Even if Heisenberg knew all along, however, he could hardly say so in 1947. So, throughout the Second World War, Heisenberg believed, or let it be thought that he believed, that the Uranbrenner â the atomic pile for power â was impossible because the reactor would explode one sixth of a second after it went critical. He did not explain this fact in writing when setting down the theory originally, although one would think he must have informed his superiors at the Heereswaffenamt of his fears confidentially. To make some sense out of the fact that Heisenberg and the Uranium Project spent the war years performing interesting experiments of subreactor geometry, and obviously had no intention of actually bringing an experiment beyond the critical point since there was sufficient heavy water available in aggregate to moderate a working reactor by 1944 but no enthusiasm for doing so, Heisenberg must have convinced Hitler of the impossibility of building a working pile. Hitler did not want a nuclear reactor in any case because it was Jewish Physics. Probably he just waved a hand in dismissal, allowing Heisenberg and the reactor project to appear to be doing something useful to keep enemy Intelligence on the hop. That really is the only logical conclusion to be drawn from the manner in which the project was conducted.
The Basis of Reactor Design
The surest method of realizing energy production from the fissioning of uranium lay in enriching the U 235 isotope, Heisenberg explained: the more the enrichment the smaller the reactor would be. If the proportion of theU 235 isotope in the uranium material were to be enriched by 50%, from 0.7% to 1%, success was practically certain. However, such a proceeding was prohibitively expensive.
Natural uranium could be used in the reactor vessel in conjunction with another substance, a
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