312. Memorandum From Bethe to Killian 1

[Facsimile Page 1]


  • Clean Weapons

[text not declassified]

It has been stated publicly that it would be possible to develop completely clean weapons in the course of five or more years of further testing. In my opinion, complete cleanliness has no significance [Typeset Page 1326] in military applications of nuclear weapons. The military application mostly contemplated is the use of a clean weapon in a ground burst against a hard enemy target. In such an application, the neutrons coming from the weapon will create radioactivity in the soil next to the weapon. This radioactivity will be carried up with the debris of the weapon itself and will cause fallout in the neighborhood.

It has been estimated that the radioactivity in the ground is at least 1% of the radioactivity which would be produced in a pure fission weapon of the same yield. Since the radioactive materials formed in the ground are different from fission products, the radioactivity will change with time in a different way from that of fission products. However, calculations at Los Alamos indicate that this difference is not very great, and that at any time the radioactivity created in the soil will be of the order of 1% or more of the corresponding fission activity

[text not declassified] [Facsimile Page 2] for sometime to come. It is conceivable that further technical progress and testing may make it possible to return to lead even for the smaller weapons, but this seems quite difficult, quite far in the future, and would undoubtedly be connected with a further loss in yield for a given weight.

For these reasons, and particularly because of the radioactivity necessarily produced in the ground, it does not seem of practical interest to develop clean weapons of a cleanliness of better than 1%. Whether such a development is technically feasible is not known at this time. [text not declassified]

According to Dr. Teller, Dr. Brown of the Livermore Laboratory, head of its Theoretical Division, is the person most competent on the development of clean weapons. In a recent conversation with him he was very skeptical whether a completely clean nuclear weapon could be developed.

The only circumstance in which a completely clean thermonuclear device might be of interest would be for peaceful applications. I do not know of any such applications at present. In the case of a deep, underground explosion for peaceful purposes, I believe that there would be other means of protection from the radioactivity than complete cleanliness. Besides, I do not think that the uncertain possibility of some peaceful applications would be a sufficient reason to continue nuclear testing merely for the purpose of developing a completely clean nuclear weapon.

Hans A. Bethe
  1. Source: Development of clean weapons. Secret; Restricted Data. 2 pp. Eisenhower Library, Records of the President’s Science Advisory Committee, Nuclear Weapons.