Many books have been written about the history of nuclear weapons, and they have become more detailed as more information, previously inaccessible, is made available. But Richard Rhodes’s book seems unique, not only for its length of 886 pages (788 without the notes), but for his unusually broad interpretation of what is relevant background material. No person is mentioned without a paragraph or so about his physical appearance and the essentials of his biography. These characterizations, though terse, give a lively picture of the person, and for all those whom I have known, an accurate one, with very few lapses (Heisenberg did not have red hair). For the leading actors in the story there are more detailed profiles. The one of Niels Bohr goes back to his grandfather.

An introductory chapter is devoted mainly to Leo Szilard’s realization in 1933 that the existence of the neutron, just discovered, might make a chain reaction possible. He expected that there might be nuclei which, on being hit by a neutron, would give up further neutrons, and that energy would be released in this process. These neutrons would hit other nuclei, and the result would be a chain reaction, which would continue until the number of suitable nuclei was reduced below a critical amount, or the material was dispersed. Szilard expected that the nucleus of beryllium might serve for this purpose, but this was a misguided idea. Such a result, Szilard felt, would justify the speculations by H.G. Wells and others about the liberation of atomic energy on a large scale for industrial and military purposes, although Lord Rutherford—who had discovered the atomic nucleus—had called such speculations “moonshine.” Szilard was, in fact, not the only one to see this point; others did so, including the Soviet theoretical physicist Lev Davydovich Landau. But in the early Thirties nobody knew by what nuclear process such a chain reaction could be implemented.

The full story involves the elements of nuclear physics, and Rhodes takes us through this subject, starting with the discovery of radioactivity by Henri Bequerel in 1896, to the discovery of fission and of the secondary neutrons from fission. The story necessarily involves technicalities not easily accessible to the non-scientist. Rhodes manages to explain the relevant points briefly in simple language, so as to give the reader a feeling for the nature and relevance of the argument. He often explains the nature of an experiment or a device by a happily chosen analogy.

So we are taken through the development of nuclear physics. Some of the explanations contain minor errors, which show that the writer is not a physicist, but they will not prejudice the understanding of the nonphysicist reader. Since the narrative is more or less in chronological order, the history of nuclear physics is interspersed with the relevant political history—including the air raids and gas warfare of the First World War, and the Gallipoli adventure in which Harry Moseley, a brilliant physicist who provided experimental confirmation of Rutherford and Bohr’s model of the atom, was killed.

Later comes an account of the rise of the Nazis in Germany, introduced by a brief history of the Jews in Europe and of anti-Semitism in Germany. The refugees included many scientists who played a large part in the atomic-weapons program. It has been suggested that the reason for the large number of refugees in this work was the fact that they had special reason to hate Hitler’s Germany and to be afraid of Hitler getting the bomb first; but the more plausible reason was, at least in Britain, that the locals were already engaged in urgent war work, and refugees were the main source of available manpower, until the project gained sufficient urgency for people to transfer from other war research.

The academic physics story ends with fission. Enrico Fermi, who had shown the way to the use of neutrons to study nuclei, believed his uranium experiments led to “transuranics”—elements heavier than uranium—and did not accept the explanation based on fission when this was suggested by a German chemist, Ida Noddack. The discovery of fission had to wait for the work of Otto Hahn and Fritz Strassmann in Berlin. Simple experiments on fission were immediately started in most nuclear physics laboratories of the world, and soon the presence of secondary neutrons was found in Paris and New York.

The great excitement came not only because one was dealing with a completely unexpected phenomenon in physics, but also because now a chain reaction had become a reasonable possibility. From now on the narrative is interrupted by glimpses of world events, as well as by shifts of the scene between many centers, including Germany, the Soviet Union, and Japan. The reader feels almost as if he is watching a three-ring circus, but Rhodes’s racy presentation rivets his attention.


Quite early on, Bohr had argued that the observed fission was caused predominantly in the rare isotope uranium 235, present in natural uranium only in a proportion less than 1 percent. Only very fast neurons, faster than most of those produced in fission, would cause fission in the dominant isotope, 238. Fermi did not believe Bohr until about a year later Bohr was proved right by direct experiment.

From this it followed that no explosion could be caused in natural uranium. This left only two possibilities open: one was to slow down all the neutrons until they were thermal, by using a “moderator,” a light substance with whose nuclei the neutrons would collide and be slowed down. In that case the chain reaction would proceed very slowly, and the developing heat would blow the uranium apart before the chain reaction had got very far. This method was therefore useful only for a controlled chain reaction, which could produce power.

The other was to work with nearly pure 235. This would yield a new weapon of fantastic power, but required separating the isotopes of uranium, a procedure that was “evidently” prohibitive in cost and effort.

A number of groups decided to try for the slow chain reaction, although they all thought of the eventual development of a weapon. The most active group was that of Fermi and Szilard at Columbia University. Szilard had been dreaming of a chain reaction all the time, and now it had become more real. He was also particularly afraid of Hitler getting the bomb first. Fermi probably was first attracted by the challenge to start the first chain reaction (which he did) after missing by an inch the discovery of fission.

Other groups with similar aims were in Germany (Kurt Diebner and Heisenberg) and in Paris (Fréderic Joliot and co-workers). In England a group under George Thomson concluded after preliminary work that a chain reaction in natural uranium was not practical, even with the best available moderators to slow the neutrons; so the group adjourned. Physicists in the Soviet Union and Japan were interested and did some experiments with fission, but did not then attempt to develop a chain reaction.

These are some of the circus rings that Rhodes presents to us in chronological order, but most of the space is rightly taken up by the developments in the United States. Fermi and Szilard decided that the most promising “moderator” to slow down the neutrons, so as to make them most effective, was graphite, but tests showed that the graphite swallowed up so many neutrons that the chain reaction would not take place. Fermi had the hunch that the graphite they were using still contained impurities in amounts too small to detect by chemical analysis, but large enough to contribute strongly to the neutron loss. Efforts to purify the graphite further proved him right.

In Germany the nuclear physicist Walther Bothe was accused of wrong measurements on graphite. Probably his measurements were correct; but he did not have Fermi’s intuition that the “pure” graphite was still too impure. The German physicists therefore decided on heavy water (water in which the hydrogen is replaced by its heavy isotope, deuterium). Heavy water is very difficult to extract from natural water; supplies for experiments were obtainable only from a plant in Norway, which was sabotaged by Norwegian patriots. The German scientists, led by Heisenberg, never succeeded in producing a chain reaction. They did not attempt isotope separation on an industrial scale, which they (probably rightly) regarded as too big an effort for Germany in wartime.

Fermi and Szilard, by now with several collaborators, needed larger quantities of graphite to extend their experiments toward an actual chain reaction. They appealed to various government agencies for support, but the bureaucracy moved very slowly. Even after Szilard and Edward Teller had persuaded Einstein to write a letter to Roosevelt the only result was that a committee under Lyman Briggs was appointed, which did not proceed with any sense of urgency.

In England it was pointed out by Otto Robert Frisch and the present reviewer that a bomb of uranium 235 would not be as large as had been assumed intuitively, and that its explosion would release enormous energy. Their reasoning was theoretical, since experiments on the nuclear behavior of uranium 235 were not made until much later, but they relied on the very convincing theory of Niels Bohr. The British authorities showed growing interest. Further research was commissioned by the “MAUD” committee, whose report indicated that the separation of the uranium isotopes in the necessary quantities was not impossibly difficult, and that it would lead to a new powerful weapon.

Information on what this report contained reached the United States in various ways but does not seem to have had much effect until Ernest O. Lawrence, whose enthusiasm was aroused by a personal report from Mark Oliphant, the Australian physicist, started to agitate for urgency. His pressure, added to all the others’, caused a change in pace. The work was put in the overall charge of Colonel Leslie Groves, of the Army Corps of Engineers, who was promoted to brigadier general in the process. The problem of isotope separation was now tackled seriously by three different methods, and the entire project was firmly directed toward a bomb.


However, it had been found in the meantime that, in a chain reaction, some neutrons hit uranium 238 without causing fission, but cause it to change into a new element, neptunium, which in turn decays to the rather long-lived plutonium. According to Bohr’s theory, plutonium should also be capable of a fast chain reaction, so it was an alternate weapons material to uranium 235. The slow reactors, larger versions of the assembly of uranium and graphite by which Fermi produced the first chain reaction in December 1942, were now seen as suppliers of bomb material.

There were still many hurdles to be overcome. Rhodes runs through the troubles of the gaseous diffusion plant at Oak Ridge. Gaseous diffusion was one of the ways of separating isotopes, which depended on membranes or “barriers” with very fine pores, yet strong enough to stand a pressure difference and inert enough to withstand the very corrosive uranium hexafluoride, the only known gaseous compound of uranium. He tells us about the electromagnetic separation method pioneered by Lawrence, which needed for its magnet coils more copper than was available in wartime, so that the coils were instead made of silver borrowed from the US Treasury. The third method of isotope separation, liquid thermal diffusion, was proved by Philip Abelson rather late. It involves a large but very simple plant, which consumes a prodigious amount of power. All three methods contributed to yielding the separated uranium for the Hiroshima bomb.

We are told of the reactor design problems, of arguments over the most effective method of cooling, and of the surprise when one of the fission products, an isotope of xenon, swallowed too many neutrons, which would have made the reactors unworkable if they had not been designed with spare space for additional uranium.

Rhodes describes how Oppenheimer built up the Los Alamos Laboratory on a mesa in New Mexico for studying the fast-neutron physics and bomb design—and later for bomb manufacture. We are told how he inspired a large number of first-rate scientists with a sense of urgency and common purpose, and how he managed to keep down the natural friction between the civilian scientists and the army officers who were running the place. Here there was a surprise, too: it turned out that besides the isotope plutonium 239, which was the weapons material, the Hanford Engineer Works in Washington state, which consisted of reactors for its production, yielded also some plutonium 240, which undergoes fission spontaneously very fast. This meant that, to start the explosion, the parts of a bomb would have to be put together very quickly, otherwise the fission of a plutonium 240 atom would initiate the reaction when the parts had approached only close enough to make conditions just critical, and a weak explosion would result.

So a new technique for assembling the bomb had to be adopted: the “implosion” method, in which a sphere of plutonium is compressed by the detonation of an explosive shell around it, instead of firing the two halves of the bomb at each other in a gun barrel, as was sufficient for uranium 235. The implosion method is much more subtle than the other, and much harder to test without an actual bomb explosion. It was decided to test such a weapon at Alamagordo (the “Trinity” test). There were doubts up until the last minute whether it would work. The test confirmed that the design was right, and showed the enormous explosive power of the new weapon.

Meanwhile there had been many discussions about what to do with this weapon. There was little doubt that it would be used on Japan as soon as it was available. One argument for this was undoubtedly that the expenditure incurred by the project, without the knowledge of Congress, by now added up to $2 billion, and the military would be blamed if this had made no contribution to the war. More substantially, the argument was that the use of this weapon would surely lead to the surrender of Japan, thus obviating the need for an invasion, which, it was said, was going to cost more lives (even more Japanese lives) than the bomb.

The idea of a demonstration in the presence of invited observers was considered, but rejected. A scientific panel made up of Lawrence, Fermi, and Oppenheimer, among others, concluded in July 1945 that “we can propose no technical demonstration likely to bring an end to the war; we see no acceptable alternative to direct military use.” There was also as yet no complete confidence in the reliability of the design. The Trinity test, it was said, was not conclusive proof that the bomb would explode when dropped from an airplane, and if the Japanese were told of the weapon and it then failed to explode, this would be exploited by Japanese militarists. The obvious alternative of dropping a bomb unannounced on a thinly populated area of Japan, to demonstrate its effect, was not, as far as I know, ever considered. It would have involved killing some people and destroying some buildings; the effects of an explosion in the desert, as at Alamagordo, were stunning to the experts, but would not mean much to the layman.

In reporting the discussions that led to the decision to drop the bomb on Hiroshima and Nagasaki, Rhodes reminds us of the history of the terror bombing of cities. From the early widespread indignation at the bombing of Guernica and Rotterdam, attitudes changed to such an extent that the deliberate fire raids on Hamburg, Dresden, and Tokyo were considered an acceptable form of warfare. Without this background the atomic bomb raids on Japan might not have taken place.

A group of scientists in Chicago tried to prevent the bomb being used and wrote a memorandum (known as the “Franck report,” after the physicist James Franck) which never reached the decision-makers in Washington. At the time it was taken to Washington, nine days after Roosevelt’s death, the top people were too busy and passed the matter on to men of no influence. Rhodes does not mention this report. It is interesting that the Chicago scientists, who were concerned with reactors, had stronger feelings against the use of the bomb than those in Los Alamos, who were making the bomb. The reason may lie in the presence in Chicago of a few people like Franck and Szilard, or it may be that the Chicago group, whose work was essentially complete, were free to discuss fundamental issues, while the Los Alamos people were working all-out to finish their job and had little time or inclination to consider them.

Niels Bohr, who had escaped from German-occupied Denmark in 1943, when he was about to be arrested, and joined the atomic energy project, was thinking of the years ahead. He saw the danger of a nuclear arms race developing after the war, and sought ways of trying to counteract this by creating more confidence, and more openness between the West and the Soviet Union. Roosevelt listened to him with seeming interest, but did not act on his suggestions; Churchill completely failed to understand him and became very hostile. In 1950 Bohr addressed an “Open Letter” to the United Nations, again without much response.

Most of the book is written objectively, leaving judgment to the reader, but in a number of places the author’s personal opinion is apparent. Leo Szilard is his hero, although he fairly describes his many eccentricities, and his occasional arrogance, which must have been trying for the administrators. But Rhodes rightly admires his imaginative grasp, and his indefatigable insistence that the threat of nuclear weapons must be taken seriously.

It is also clear that Rhodes disapproves of the trend to regard the bombing of cities as a legitimate form of warfare. He is critical of the British and American air force officers and statesmen who took pride in the efficiency of their operations against cities, and justified them on the dubious grounds of “breaking the will to resist.”

He evidently does not think highly of the process by which the use of the bombs was decided. The ancient city of Kyoto was removed from the list of targets, he notes, only by the personal insistence of Secretary of War Stimson, who happened to be familiar with its cultural significance. The conduct of the war, he says, had been “stupid and barbarous,” and “the barbarism was not confined to the combatants or the general staffs. It came to permeate civilian life in every country” and “was perhaps the ultimate reason Jimmy Byrnes, the politician’s politician, and Harry Truman, the man of the people, felt free to use and compelled to use a new weapon of mass destruction on civilians in undefended cities.” I happen to share the author’s opinions in all these respects.

The very wide coverage evidently required a great deal of research, and the bibliography of books and articles consulted runs to thirteen pages. Most of these sources are sensibly quoted or summarized, but in the pieces of the story that I happen to know well I could detect a number of slips. For example, Rhodes misunderstands the story of Professor Lindemann (Lord Cherwell). Rhodes says that tailspins were “recognized maneuvers in air fighting by 1916, a good way to shake off an attacker,” and that Lindemann was the first to study them scientifically. In fact, during the First World War it was considered fatal for a plane to get into a spin. There was a theory about how to correct this, and Lindemann volunteered to learn to fly and to get his plane deliberately into a spin. The Oxford physics professor who narrowly missed discovering X-rays was Clifton, not Frederick Smith. Otto Stern was not a Galician, but a native of Silesia, then part of Germany. These slips are all minor, and mostly have a marginal relevance to the subject of the book, but they tend to undermine one’s confidence in the details of what one does not know independently.

Rhodes’s prose is generally lively and readable. Just occasionally one has to reread a sentence to get its sense, either because it is obscured by a complicated structure, or because it uses “he” after referring to two people.

Some expressions seem a little strange, as when Rutherford “roared up” from New Zealand. Or in the context of one phase of the gas warfare during the First World War, “Germany…blamed the French and courted a succession of increasingly desperate breakthroughs.” About the possibility of a chain reaction starting in nature, “If fission had proceeded more energetically the bombs would have slept forever in their ores.” The reader will not understand the remark that “children would be born…behind a post office” because he has not been told that the Los Alamos address was a post office box number. I was puzzled by the term “remuda,” and wonder how many readers will know it stands for a relay of horses.

Overall the extensive research invested in this book has been used to good purpose. The reader moves easily through its 788 pages and will find them instructive throughout.

This Issue

November 5, 1987