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The Manhattan Project Heritage Preservation Association, Inc. "Preserving, Exhibiting, Interpreting and Teaching the History of the Manhattan Project" |
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Manhattan Project History
The Early Years (1900 - 1939)
"FISSION"
| "Perhaps you can suggest some fantastic explanation. We understand that it (uranium) really can't break up into barium...so try and think of some other possibility. Barium isotopes with much higher atomic weights than 137? If you can think of anything that might be publishable, then the three of us would be together in this work after all. We don't believe this is foolishness or that contaminations are playing tricks on us" - Communication from Otto Hahn (in Berlin) to Lise Meitner (in Stockholm) requesting some explanation for the strange results they were getting from their experiments with uranium; December 1938. |
| "Oh what idiots we have been! Oh but this is wonderful. This is just as it must be!" - Niels Bohr; upon being informed (by Otto Frisch) of Hahn and Strassman's "strange" results; January 3, 1939. |
| "Young man, let me explain to you about something new and exciting in physics" - Niels Bohr; whispering in the ear of Herbert Anderson at Pupin Hall, Columbia University; January 1939. |
In 1935, Lise Meitner, Otto Hahn and Fritz Strassman began work to sort out all of the substances into which the heaviest of natural elements transmuted under neutron bombardment. By early 1938, they had identified no fewer than ten different half-life activities. At the same time, Irene Curie began looking into uranium and came up with results which contradicted those of Hahn and Meitner. The debate raged on. Not long after, Hahn and Strassman (Lise Meitner had by now fled to Stockholm after her Jewish origins came under question after the Nazis marched into Austria) succeeded in identifying no fewer than 16 different radioactive substances with varying half-lifes. Three of these substances were previously unknown isotopes, and were felt to be isotopes of radium. At this time, the 59 year old Otto Hahn was unquestionably the ablest radiochemist in the world. He would need all of his 40 years of experience to decode uranium. After several more weeks of tedious work, it seemed that these "radium" isotopes must be barium, element 56, slightly more than half as heavy as uranium. At first they could not believe the results they were seeing and cabled Lise Meitner in Stockholm for some sort of confirmation. Her reply seemed to suggest that although it appeared to be "impossible", they should keep an open mind. Hahn and Strassman continued with further refinements and again cabled Meitner: "Our radium proofs convince us that as chemists we must come to the conclusion that the three carefully-studied isotopes are not radium, but, in fact, barium." On January 3rd of 1939, Otto Frisch returned to Copenhagen from visiting his aunt, Lise Meitner, and informed Niels Bohr of Hahn's "barium" hypothesis. Niels Bohr was immediately gleeful as if he had been expecting such results. That same day, Lise Meitner cabled Hahn again: "I am fairly certain now that you really have a splitting towards barium and I consider it a wonderful result for which I congratulate you and Strassman very warmly...You now have a wide, and beautiful field of work ahead of you..." What they had succeeded in doing, for the first time, was "splitting" an atom. As a final step, these results need further interpretation. Lise Meitner in Stockholm and her nephew in Copenhagen did so by long-distance telephone. Frisch carried out some further confirming experiments in his own lab using a simple ionization chamber. Over the following weekend, aunt and nephew conferred by phone to prepare two papers for Nature: a joint explanation of the the reaction and Frisch's report of the confirming evidence of his experiment. Both reports - "Disintegration of uranium by neutrons: a new type of nuclear reaction" and "Physical evidence for the division of heavy nucleii under neutron bombardment" - used the new term "fission" for the first time. The "word" spread like wild-fire. Leo Szilard, having read the Hahn-Strassman paper wrote to Lewis Strauss on January 25, 1939: "I feel I ought to let you know of a very sensational new development in nuclear physics. In a recent paper...Hahn reports that he finds when bombarding uranium with neutrons the uranium 'breaks up'...This is entirely unexpected and exciting news for the average physicist. The department of physics at Princeton, where I have spent the last few days, was like a stirred-up ant heap. Apart from the purely scientific interest there may be another aspect of this discovery, which so far does not seem to have caught the attention of those to whom I spoke. First of all it is obvious that the energy released in this new reaction must be very much higher than all previously known cases...This in itself might make it possible to produce power by means of nuclear energy, but I do not think that this possibility is very exciting, for the cost of investment would probably be too high to make the process worthwhile. I see...possibilities in another direction. These might lead to large-scale production of energy and radioactive elements, unfortunately also perhaps to atomic bombs. This new discovery revives all the hopes and fears in this respect which I had in 1934 and 1935, and which I have as good as abandoned in the course of the past two years."
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