MAUD Report

A report by the Military Application of Uranium Detonation (MAUD) Committee on the use of Uranium for a bomb states the following:

“[PART I]

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.

At the beginning of this report, we entered the project with more skepticism than belief, though we felt it was a matter that had to be investigated. As we proceeded, we became more and more convinced that releasing atomic energy on a large scale was possible and that conditions could be chosen, making it a potent weapon of war. We have now concluded 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 significant quantities of a radioactive substance which would make places near to where the bomb exploded dangerously to human life for an extended period. The bomb would be composed of an active constituent (referred to in what follows as -U) present to the extent of about a part in 140 in ordinary Uranium. Owing to the minimal difference in properties (other than explosive) between this substance and the rest of the Uranium, its extraction is harrowing. A plant to produce 2V4 lb (I kg) per day (or three bombs per month) is estimated to cost approximately 95,000,000 pounds, of which sum a considerable proportion would be spent on engineering, requiring the labor of the same highly skilled character as is needed for making turbines.

Despite this enormous expenditure, we consider that the material and moral destructive effect is so significant that every effort should be made to produce bombs of this kind. As regards the time required, Impe-rial Chemical Industries, after consultation with Dr. Guy of Metropolitan–Vickers, estimated that the material for the first bomb could be ready by the end of 1943. This assumes that no significant 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 they wandered before the bombs were 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 great trouble to secure supplies of the substance known as heavy water. We thought the meaning might be essential to our work in the earlier stages. It appears that its usefulness in releasing atomic energy is limited to processes that are not likely to be of immediate war value. Still, the Germans may by now have realized this, and it may be mentioned that the lines on which we are currently working are such as would be likely to suggest themselves to any capable physicist.

By far, the most extensive supplies of Uranium are in Canada and the Belgian Congo. Since it has been actively looked for because of the radium accompanying 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 unique properties of the active constituent of Uranium. The explosexplosionry is different in its mechanism from the ordinary chemical explosexplosionit can occur only if the quantity of -U is more significant than a certain critical amount. Portions of the material less than the necessary amount are pretty stable. Such parts are, therefore, perfectly safe, and this is a point that 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 explosion-precedented 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
To achieve the most excellent efficiency in an explosexplosionis 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 explosives in the form of a double gun.

The weight of this gun will significantly exceed the importance of the bomb itself, but ‘Should not be more than a ton, and it would undoubtedly 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 weapon should be fired using a percussion device when it hits the ground. The drop time can be long enough to allow the airplane 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 damage likely to be produced by the explosion of 1,800 tons of T.N.T. is afforded by the incredible 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, totaling 5,234,754 lb. The zone of the explosion for about 3/4 mile in every direction in this zone, and the destruction was almost complete. Severe structural damage is generally extended for a radius of 1-1/8 to 1-1/4 miles and in one direction up to 1-3/4 miles from the origin. Missiles were projected to 3-4 miles; window glass is generally broken up to 10 miles, anti to 61 mils in one instance.”

Considering this description, it must be remembered that part of the explosives cargo was situated below water level and above.

5. Preparation of Material and Cost
We have thoroughly considered the possible methods of extracting the 235U from ordinary Uranium and have done several experiments. The scheme 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 gauze’s excellent mesh.

In the size and cost estimates accompanying this report, we have only assumed types of gauze presently in existence. A comparatively small amount of development would probably enable gauzes of smaller mesh to be made. 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 excellent, it compares very favorably with ordinary explosives regarding energy released and damage was done. It is, in fact, considerably cheap. Still, their points which we feel are of overwhelming importance, are the concentrated destruction which would produce a sizeable 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 great difficulty of the scheme is that the main principle cannot be tested on a small scale. Even producing a bomb of the minimum critical size would involve a significant expenditure of time and money. We are convinced that the principle is correct. While there is still some uncertainty about the required 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 strongly-pressed scheme.
As regards the manufacture of Uranium 235, we have gone nearly as far as we can on a laboratory scale. The principle of the method is specific, and the application does not appear unduly difficult as a piece of chemical engineering. The need to work on a larger scale is apparent, and we are having difficulty finding the necessary scientific personnel. Further, if the weapon is to be available in, say, two years from now, it is essential to start plans for the erection of a factory. However, no considerable expenditure will be needed till the 20-stage model has been tested. It is also necessary to begin training men who can ultimately act as supervisors of the manufactureSeveralral auxiliary pieces of apparatus are needed, such as those for measuring the concentration of the 2″‘U. In addition, work on a reasonably large scale is required to create the chemical side to produce the bulk of uranium hexafluoride, the gaseous compound we propose to use.

It will be seen from the preceding that a stage in work has now been reached at which it is essential 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 the gun 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 energy production, as discussed in our report on Uranium as a power source, rather than to the production of a bomb. We are 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 essential 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 25U. 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 dealing with this matter.

8. Conclusions and Recommendations

• The committee considers that the scheme for a uranium bomb is practicable and likely to lead to decisive results in the war.
• It recommends continuing this work on the highest priority and increasing the scale necessary to obtain the weapon in the shortest possible time.
• The present collaboration with America should be continued and extended, especially in experimental work.”