The Manhattan Project

by Cynthia C. Kelly

  Working for Otto Frisch

  J. Wechsler waited in alphabetical order alongside the other new Army recruits for job placement at Los Alamos. Once inside, he had “a very strange job interview.” Curious about his new boss, Wechsler recalls looking up his name in Who’s Who in Physics.

  From AHF Oral Histories

  INTERVIEW WITH J. WECHSLER

  The Ws are pretty far down the alphabet and I became a little concerned that all the good jobs might disappear. But they finally got to me and I went inside. The person who was interviewing me had a pretty heavy Austrian accent. He asked me about what I like to do. He asked me if I liked music. I told him I played the piano and the trombone and he seemed very interested in that.

  I thought that this was a very strange job interview. He asked me what kind of pieces I like to play on the piano. I had not been playing much since I joined the army but I told him some of the things I liked. Then he talked about interests I had in technical things. I was kind of intrigued with him but I was not sure who he was.

  Finally he said, “You’re going to work with me. You should be back tomorrow. There will be instructions for you when you show up at the gate.” I was done with my interview. I wasn’t sure what I was getting into or what I would be doing.

  The only thing I knew was that the name of my new boss was Otto Frisch. I asked some others who this fellow was and someone suggested, “You probably have access to the technical library. Why don’t you go over and find out who Otto Frisch is?” That seemed like a pretty good idea so I headed over there.

  I looked up the Who’s Who in Physics and found Otto’s name. I read what he was known for in physics and got very, very impressed.

  Back at the laboratory the next day, I was sitting there at my bench looking at Otto. He looked up all of a sudden and said, “What are you looking at?”

  I said, “I’m looking at you.”

  “Why are you looking at me?”

  “Well, I know who you are.”

  He said, “I told you who I was.”

  “Yeah, but I think I know what we are doing and I think I know what this piece of junk is here that I am working on.”

  And he said, “Well, if you think you know what we are doing, you had better get back to work.”

  That was my introduction to the field of weapons. It turned out I was working on a large fission chamber which had been modified. Otto told me later he had originally worked on it in Denmark, shipped it to England with him and then over here to Los Alamos. He had had all kinds of people working on it but it had never quite worked right. He said, “You have a challenge.” I modified the monstrosity and within a week, I had it working. Otto was mighty impressed and started suggesting other things we would work on.

  Otto had so many ideas and regardless of the problem, he could think of a way of approaching it. While he was a great pianist, he was not really skilled with his hands. He wanted me to bounce ideas off of and to be his hands. Although I only worked with Otto for four months, we became very close friends.

  THE MAUD BEHIND THE MAUD COMMITTEE

  The name “MAUD,” adopted as the code name for the British committee looking into the feasibility of producing an atomic bomb, is actually not an acronym. Instead, “Maud” is the name of a former governess employed by Danish physicist Niels Bohr. After Germany occupied Denmark in April 1940, Bohr sent a telegram to his former colleague Otto Frisch in England that ended with instructions to pass his words along to “Maud Ray, Kent.” Mistakenly thinking that “Maud” was a cryptic reference to something related to their work, the committee called itself the “M. A. U. D. [or MAUD] Committee.” Not until after the war was Maud Ray identified as the Bohrs’ governess.

  Likely to Lead to Decisive Results

  The Maud Report was a progress report drafted by James Chadwick on the British “Tube Alloy” project to determine the feasibility of an atomic bomb. Predicting that uranium bombs could be constructed in time for use in World War II, the report recommends collaborating with the Americans to develop such a weapon “with the highest priority.”

  From Report on the Use of Uranium for a Bomb, Outline of Present Knowledge

  BY THE MAUD COMMITTEE, MARCH 1941

  1. General Statement

  Work to investigate the possibilities of utilizing the atomic energy of uranium for military purposes has been in progress since 1939, and a stage has now been reached when it seems desirable to report progress.

  We should like to emphasize at the beginning of this report that we entered the project with more skepticism than belief, though we felt it was a matter which had to be investigated. As we proceeded we became more and more convinced that release of atomic energy on a large scale is possible and that conditions can be chosen which would make it a very powerful weapon of war. We have now reached the conclusion that it will be possible to make an effective uranium bomb which, containing some 25 lb of active material, would be equivalent as regards destructive effect to 1,800 tons of T.N.T. and would also release large quantities of radioactive substance, which would make places near to where the bomb exploded dangerous to human life for a long period. The bomb would be composed of an active constituent (referred to in what follows as 235U) present to the extent of about a part in 140 in ordinary Uranium. Owing to the very small difference in properties (other than explosive) between this substance and the rest of the Uranium, its extraction is a matter of great difficulty and a plant to produce 2–4 lb (1 kg) per day (or 3 bombs per month) is estimated to cost approximately £5,000,000, of which sum a considerable proportion would be spent on engineering, requiring labour of the same highly skilled character as is needed for making turbines.

  In spite of this very large expenditure we consider that the destructive effect, both material and moral, is so great that every effort should be made to produce bombs of this kind. As regards the time required, Imperial Chemical Industries after consultation with Dr. Guy of Metropolitan-Vickers, estimate that the material for the first bomb could be ready by the end of 1943. This of course assumes that no major difficulty of an entirely unforeseen character arises. Dr. Ferguson of Woolwich estimates that the time required to work out the method of producing high velocities required for fusing (see paragraph 3) is 1–2 months. As this could be done concurrently with the production of the material no further delay is to be anticipated on this score. Even if the war should end before the bombs are ready the effort would not be wasted, except in the unlikely event of complete disarmament, since no nation would care to risk being caught without a weapon of such decisive possibilities.

  We know that Germany has taken a great deal of trouble to secure supplies of the substance known as heavy water. In the earlier stages we thought that this substance might be of great importance for our work. It appears in fact that its usefulness in the release of atomic energy is limited to processes which are not likely to be of immediate war value, but the Germans may by now have realized this, and it may be mentioned that the lines on which we are now working are such as would be likely to suggest themselves to any capable physicist.

  By far the largest supplies of uranium are in Canada and the Belgian Congo, and since it has been actively looked for because of the radium which accompanies it, it is unlikely that any considerable quantities exist which are unknown except possibly in unexplored regions.

  2. Principle Involved

  This type of bomb is possible because of the enormous store of energy resident in atoms and because of the special properties of the active constituent of uranium. The explosion is very different in its mechanism from the ordinary chemical explosion, for it can occur only if the quantity of 235U is greater than a certain critical amount. Quantities of the material less than the critical amount are quite stable. Such quantities are therefore perfectly safe and this is a point which we wish to emphasize. On the other hand, if the amount of material exceeds the critical value it is unstable and a reaction will develop and multiply itself with enormous rapidity,
resulting in an explosion of unprecedented violence. Thus all that is necessary to detonate the bomb is to bring together two pieces of the active material each less than the critical size but which when in contact form a mass exceeding it.

  3. Method of Fusing

  In order to achieve the greatest efficiency in an explosion of this type, it is necessary to bring the two halves together at high velocity and it is proposed to do this by firing them together with charges of ordinary explosive in a form of double gun.

  The weight of this gun will of course greatly exceed the weight of the bomb itself, but should not be more than 1 ton, and it would certainly be within the carrying capacity of a modern bomber. It is suggested that the bomb (contained in the gun) should be dropped by parachute and the gun should be fired by means of a percussion device when it hits the ground. The time of drop can be made long enough to allow the aeroplane to escape from the danger zone, and as this is very large, great accuracy of aim is not required.

  4. Probable Effect

  The best estimate of the kind of damage likely to be produced by the explosion of 1,800 tons of T.N.T. is afforded by the great explosion at Halifax N.S. in 1917. The following account is from the History of Explosives. “The ship contained 450,000 lb. of T.N.T., 122,960 lb. of guncotton, and 4,661,794 lb. of picric acid wet and dry, making a total of 5,234,754 lb. The zone of the explosion extended for about ¾ mile in every direction and in this zone the destruction was almost complete. Severe structural damage extended generally for a radius of 1⅛ to 1¼ miles, and in one direction up to 1¾ miles from the origin. Missiles were projected to 3–4 miles, window glass broken up to 10 miles generally, and in one instance up to 61 miles.”

  In considering this description it is to be remembered that part of the explosives cargo was situated below water level and part above.

  5. Preparation of Material and Cost

  We have considered in great detail the possible methods of extracting the 235U from ordinary uranium and have made a number of experiments. The scheme which we recommend is described in Part 11 of this report and in greater detail in Appendix IV. It involves essentially the gaseous diffusion of a compound of uranium through gauzes of very fine mesh.

  In the estimates of size and cost which accompany this report, we have only assumed types of gauze which are at present in existence. It is probable that a comparatively small amount of development would enable gauzes of smaller mesh to be made and this would allow the construction of a somewhat smaller and consequently cheaper separation plant for the same output.

  Although the cost per lb. of this explosive is so great it compares very favourably with ordinary explosives when reckoned in terms of energy released and damage done. It is, in fact considerably cheaper, but the points which we regard as of overwhelming importance are the concentrated destruction which it would produce, the large moral effect, and the saving in air effort the use of this substance would allow, as compared with bombing with ordinary explosives.

  6. Discussion

  One outstanding difficulty of the scheme is that the main principle cannot be tested on a small scale. Even to produce a bomb of the minimum critical size would involve a great expenditure of time and money. We are however convinced that the principle is correct, and whilst there is still some uncertainty as to the critical size it is most unlikely that the best estimate we can make is so far in error as to invalidate the general conclusions. We feel that the present evidence is sufficient to justify the scheme being strongly pressed.

  As regards the manufacture of the 235U we have gone nearly as far as we can on a laboratory scale. The principle of the method is certain, and the application does not appear unduly difficult as a piece of chemical engineering. The need to work on a larger scale is now very apparent and we are beginning to have difficulty in finding the necessary scientific personnel. Further, if the weapon is to be available in say two years from now, it is necessary to start plans for the erection of a factory, though no really large expenditure will be needed till the 20-stage model has been tested. It is also important to begin training men who can ultimately act as supervisors of the manufacture. There are a number of auxiliary pieces of apparatus to be developed, such as those for measuring the concentration of the 235U. In addition, work on a fairly large scale is needed to develop the chemical side for the production in bulk of uranium hexafluoride, the gaseous compound we propose to use.

  It will be seen from the foregoing that a stage in the work has now been reached at which it is important that a decision should be made as to whether the work is to be continued on the increasing scale which would be necessary if we are to hope for it as an effective weapon for this war. Any considerable delay now would retard by an equivalent amount the date by which the weapon could come into effect.

  7. Action in U.S.

  We are informed that while the Americans are working on the uranium problem the bulk of their effort has been directed to the production of energy, as discussed in our report on uranium as a source of power, rather than to the production of a bomb. We are in fact cooperating with the United States to the extent of exchanging information, and they have undertaken one or two pieces of laboratory work for us. We feel that it is important and desirable that development work should proceed on both sides of the Atlantic irrespective of where it may be finally decided to locate the plant for separating the 235U, and for this purpose it seems desirable that certain members of the committee should visit the United States. We are informed that such a visit would be welcomed by the members of the United States committees which are dealing with this matter.

  8. Conclusions and Recommendations

  (i) The committee considers that the scheme for a uranium bomb is practicable and likely to lead to decisive results in the war.

  (ii) It recommends that this work be continued on the highest priority and on the increasing scale necessary to obtain the weapon in the shortest possible time.

  (iii) That the present collaboration with America should be continued and extended especially in the region of experimental work.

  “‘Wild’ notions about atom bombs”

  Dr. Vannevar Bush met the announcement of the discovery of fission in 1939 and predictions that a single bomb that could wipe out greater Boston with great skepticism. However, as head of the National Defense Research Committee, he decided to support research on uranium in 1940. Despite his early reluctance, Bush became one of the prime movers of the Manhattan Project. Concerned with secrecy and control, he pushed for the project to be under Army management, as described from G. Pascal Zachary in his biography of Bush.

  From Endless Frontier: Vannevar Bush, Engineer of the American Century

  BY G. PASCAL ZACHARY

  I wish that the physicist who fished uranium in the first place had waited a few years before he sprung this particular thing on an unstable world. However, we have the matter in our laps and we have to do the best we can.

  —VANNEVAR BUSH

  Bush’s reaction to the hoopla over fission was characteristic. A man of sober judgments, he took special delight in pricking inflated technical claims. Of the sensational claims made for atomic explosions, he was intensely skeptical. One Boston writer suggested that “an unscrupulous dictator, lusting for conquest,” might “wipe Boston, Worcester and Providence out of existence” with a single bomb dropped from an airplane. Bush thought this an “extremely remote” possibility. He feared such absurd talk raised the “real danger” of a public panic similar to the one that in October 1938 followed Orson Welles’s compelling radio account of the fictional landing in New Jersey of invaders from Mars.

  At first, Bush tried to debunk “wild” notions about atom bombs. Aided by Carnegie physicist Merle Tuve, he failed to make headway against the fission-inspired hysteria. Bush consoled himself with the view that fission’s “great impracticability” meant it was premature for war planners to take it into account. He felt it wise to continue “softpedaling a bit” the possibility of
an atomic bomb.

  Others were less cautious. A few immigrant physicists obtained the imprimatur of Albert Einstein and, through an intermediary, convinced Roosevelt in September 1939 to form a committee to coordinate research on a fission explosive. The president asked Lyman Briggs, chief of the U.S. Bureau of Standards, to chair the “uranium” committee. A political appointee nearing retirement, Briggs was the government’s top civilian research official, but he was slow-moving and unfamiliar with atomic science. By the spring of 1940, the committee had funded just $6,000 worth of research. The government’s inaction had upset a growing number of physicists.

  Bush knew of the frustration with the uranium committee because Tuve was one of its scientific advisers. But Bush was reluctant to take any bold steps, doubting the military value of fission. “I am puzzled as to what, if anything, ought to be done in this country in connection with it,” he wrote a colleague on May 2, 1940. His preference was “to do nothing,” but he found this course impractical. “The difficulty of doing nothing is that one is not likely to know what others are doing. The whole thing may, of course, fizzle. Someone may discover a barrier to the chain reaction. It seems, however, undesirable to simply sit and wait for this to occur.”

  Already laying plans to direct war research through his National Defense Research Committee, Bush did not wish to leave out fission. He felt the nascent field would benefit from NDRC attention. “There is no competent organization to handle all aspects” of fission, which is “floating about loose” and “most decidedly cannot be ignored in times like these,” he wrote on May 15. “After conferring with the Army and the Navy… I now propose… to centralize to some extent the work which is going along in various laboratories along these lines.”