icon At the laboratory

At the laboratory

icon At the museum

At the museum





The aim of this web site is to explain radioactivity and its applications to the general public.

icon The Franck Report

The Franck Report

The Scientists who opposed dropping atomic bombs on Japan

In June 1945, shortly before the atomic bombs on Hiroshima and Nagasaki, a group of Chicago physicists, who were involved in the Manhattan project, proposed to reveal the existence of the bomb to the world by a demonstration over an uninhabited area, in the presence of representatives of the future United Nations. This report, named after the Nobel Prize in Physics James Franck, was presented in Washington on June 12 to a special committee of the US government, the Interim Committee. The report followed a memorandum that had been unsuccessfully presented to War Secretary of State James Byrnes by Leo Szilard. It was Leo Szilard who signed with Einstein in 1939, the letter explaining to President Roosevelt the possibility of nuclear weapons and was at the origin of the President’s awareness and after 1942 of the Manhattan project.

The Szilard memorandum exposed, with remarkable prescience of the future, the consequences of the use of the atomic bomb, and in particular the danger of the nuclear arms race and the proliferation that would inevitably follow.

The committee rejected the solution of a demonstration of the atomic weapon, considered attractive, because it would save lives, but impossible to organize in a sufficiently convincing way to bring the war to an end.

Szilard’s memorandum, the Franck Report, honors those scientists who, in the middle of the war, sought to prevent the deaths of tens of thousands of innocent civilians. The spectrum of the Hiroshima and Nagasaki victims continues to haunt our societies since 1945. Nevertheless, if there had been only one single demonstration, the temptation would have been great to resort to the atomic weapon during the conflicts which occured after the second world war. Despite the nuclear arms race between the United States and the Soviet Union with arsenals sufficient to destroy our planet, the leaders of the great powers have shown restraint and wisdom. For the other nations, a non-proliferation treaty accompanied by controls has been put in place : a treaty, certainly not perfect, but respected with the exception today of North Korea.

James Franck and Leo Szilard
The report bears the name of James Franck (1882-1965), German physicist, 1925 Nobel Prize in Physics, who after 1933 continued his research in the United States before participating to the Manhattan project. An eminent physicist of Hungarian origin, Leo Szilard (1898-1964) emigrated in 1938 to the United States.
© DR ©

EXTRACT : Conclusions of Franck Report

The development of nuclear power not only constitutes an important addition to the technological and military power of the United States, but also creates grave political and economic problems for the future of this country.

Nuclear bombs cannot possibly remain a “secret weapon” at the exclusive disposal of this country, for more than a few years. The scientific facts on which their construction is based are well known to scientists of other countries. Unless an effective international control of nuclear explosives is instituted, a race of nuclear armaments is certain to ensue following the first revelation of our possession of nuclear weapons to the world. Within ten years other countries may have nuclear bombs, each of which, weighing less than a ton, could destroy an urban area of more than five square miles. In the war to which such an armaments race is likely to lead, the United States, with its agglomeration of population and industry in comparatively few metropolitan districts, will be at a disadvantage compared to the nations whose population and industry are scattered over large areas.

We believe that these considerations make the use of nuclear bombs for an early, unannounced attack against Japan inadvisable. If the United States would be the first to release this new means of indiscriminate destruction upon mankind, she would sacrifice public support throughout the world, precipitate the race of armaments, and prejudice the possibility of reaching an international agreement on the future control of such weapons.

Much more favorable conditions for the eventual achievement of such an agreement could be created if nuclear bombs were first revealed to the world by a demonstration in an appropriately selected uninhabited area.

If chances for the establishment of an effective international control of nuclear weapons will have to be considered slight at the present time, then not only the use of these weapons against Japan, but even their early demonstration may be contrary to the interests of this country. A postponement of such a demonstration will have in this case the advantage of delaying the beginning of the nuclear armaments race as long as possible. If, during the time gained, ample support could be made available for further development of the field in this country, the postponement would substantially increase the lead which we have established during the present war, and our position in an armament race or in any later attempt at international agreement will thus be strengthened.

On the other hand, if no adequate public support for the development of nucleonics will be available without a demonstration, the postponement of the latter may be deemed inadvisable, because enough information might leak out to cause other nations to start the armament race, in which we will then be at a disadvantage. At the same time, the distrust of other nations may be aroused by a confirmed development under cover of secrecy, making it more difficult eventually to reach an agreement with them.

If the government should decide in favor of an early demonstration of nuclear weapons it will then have the possibility to take into account the public opinion of this country and of the other nations before deciding whether these weapons should be used in the war against Japan. In this way, other nations may assume a share of the responsibility for such a fateful decision.

To sum up, we urge that the use of nuclear bombs in this war be considered as a problem of long-range national policy rather than military expediency, and that this policy be directed primarily to the achievement of an agreement permitting an effective international control of the means of nuclear warfare.

The vital importance of such a control for our country is obvious from the fact that the only effective alternative method of protecting this country, of which we are aware, would be a dispersal of our major cities and essential industries.

Members of the Committee:

James Franck (Chairman)
Donald J. Hughes
J. J. Nickson
Eugene Rabinowitch
Glenn T. Seaborg
J. C. Stearns
Leo Szilard


Learn more :

Atomic Archives :The Franck Report