The Scientists and the Bomb

By RUDOLF E. PEIERLS

IN his survey of the events leading to the decision to use atomic bombs at Hiroshima and Nagasaki, Charles Curran underlined the questions asked by Earl Attlee in the Observer about the scientific knowledge then available concerning the consequences. As one of the scientists who worked on the development of the atomic bomb, l can comment on the state of knowledge at the time, although I have no inside knowledge of the discussions that took place about policy.

In assessing the consequences of an atomic explosion one must distinguish between the immediate and the long-term effects. The immediate effects consist of damage and injuries caused at the time of the explosion to the target cities and to their inhabitants, although some of the injuries may take time to appear. The nature and magnitude of these effects were clearly known, both from theoretical predictions and from the New Mexico test which preceded Hiroshima. In particular it was known that both blast and heat would cause damage and casualties, and that instantaneous radioactive radiations would add to the casualties. These effects were what made the atomic bomb a powerful weapon of war. The destruction and casualties caused in this way were, as is clear from the figures quoted by Curran, on a similar scale to:those caused by air raids with other weapons.

I do not know whether all the details of the action of the bomb were foreseen. For example, I believe that 'flash burn,' i.e. the intense radiant heat produced at the instant of the explosion which can set fire to inflammable objects and cause burns to people, was greater than had been expected, but I doubt whether a more precise assessment would have made any difference to the decision to use the weapon.

The amount of radioactive radiation produced, and its effect on people, was foreseen. However, it was not easy to predict (and I believe it is not known with certainty even today) how many casualties were directly due to radiation, because near the centre of the explosion, where the radia- tion is most intense, many people lost their lives through blast and fire, and it was therefore a question how many of the people who succumbed to their effects would in any case have later suc- cumbed to the effects of radiation.

The possibility of death and injury due to radia- tion was clearly known. It is debatable whether morally there is much difference between killing people by radiation and in other ways. One feature which distinguishes this type of injury from those received in conventional warfare is perhaps that children born to people who have received, but survived, intense doses of radiation may in some cases be affected. It is still not known how many cases of this kind were caused by the two bombs in Japan. The number is likely to be small, and, while I do not wish to suggest that even a few cases of this kind are not a serious matter, other forms of warfare also result in damage to health" which may affect the next generation.

_ The first reports of American research teams studying the effects of atomic weapons in Japan after the war showed a desire to prove how small the radiation casualties had been. I believe this was connected with doubt whether a weapon which acted largely through radiation might not come into the category of gas warfare as defined in international conventions, so that its use would have been contrary to these conventions.

In certain cases radioactivity persists for some time after- the explosion in the neighbourhood of the target, and this would cause injury to people entering the area after the raid. Whether this happens or not depends particularly on the height at which the bomb is exploded. In the New Mexico test the bomb was set off on a tower, i.e. close to the ground, and dangerous radiation per- sisted for a few days. In some of the later tests in the Pacific, in which the explosion took place under water, the delayed radiation was much more pronounced. Such persistent radiation is not expected when a bomb is exploded at a con- siderable height, as was the case in the raids on Japan. In that case most of the radioactive pro- ducts are carried by the hot gases into the upper atmosphere, unless one is dealing with unusual weather conditions, when a rain cloud may form after the explosion and the rain may bring down some of the material. As far as is known there was no dangerous delayed radiation at Hiroshima or Nagasaki.

The more recent concern with fall-out and pos- sible genetic effects does not relate to the instan- taneous radiation, or to the delayed ground activity near the target which I have Amentioned, but to the activity carried into the upper atmo- sphere which filters down to the earth's surface over a period of months or more. It is, of course, not confined to the target area, but is spread over a belt extending around the earth at a certain latitude. It may cause concern from the genetic point of view because its effects are cumulative. If many individuals are exposed to relatively weak radiation for long periods there is a danger that some of their reproductive cells may have suffered damage which can cause abnormality in their descendants. Some of this damage is 'reces- sive,' i.e. it does not show up if only one of the parents' cells was affected, but will result in a deficiency if both parents were affected in the same way.

At the present time there is still a controversy going on between the experts on the question whether the genetic and other effects of fall-out due to the many tests of atomic and hydrogen bombs which have taken place since the war are approaching a level where they represent an appreciable danger. Remembering the large num- ber of tests carried out, and remembering also that these included atomic bombs of much greater power than those used during the war, and in particular also hydrogen bombs which are vastly more powerful, and produce very much more radiation, it would seem clear that the fall-out caused by the first two or three atomic bombs could not possibly have been serious. I have never yet heard a claim that fall-out from the Hiroshima and Nagasaki bombs has caused any serious effects.

I believe, therefore, that one may answer Earl Attlee's questions in the sense that there are no scientific facts of major relevance which are now known and which were not known to the states- men who had to take the decision in 1945.

My own view is that the decision to use these bombs on large cities in Japan, in. particular the second one, was quite wrong, but for reasons which have nothing to do with the long-term effects mentioned by Earl Attlee. Even on the most extreme view of the genetic and other hazards of fall-out these long-term effects are surely insignificant compared to the loss of life and suffering caused at the time of the explosion.

Injury and death are part of warfare, but they can be justified only by military necessity, and therefore the vital question is that also discussed by Charles Curran, whether the war could have been brought to an end without destroying Hiro- shima and Nagasaki. Assume that it was not known to the Allies how close Japan was to defeat, and assume that only the power of atomic weapons could have enforced surrender. Could a demonstration of this power in a less devastating way have been sufficient?

It is probably true that a demonstration on a desert island would not have done. The first bomb test in the New Mexico desert was staggering only to the scientists who knew how to evaluate the readings of their instruments, and who knew the significance of the large area around the centre of the explosion where the intense heat had fused the sand into a glass-like crust. Even to the scientists the photographs of the devastation in Japan came as a shock although they were capable of imagining what was going to happen.

It would probably not have been practical to give advance warning of such a demonstration, • and to invite Japanese scientists to test the power of the explosion for themselves, because it takes time to develop and arrange suitable instruments, and it would not have been easy for the scientists to explain their conclusions to the military leaders. Also, as has been pointed out, there was the pos- sibility that such a publicised test might be a failure, since there was still doubt about the reliability of the mechanism.

But nobody has yet explained why it was not possible to select as a target a sparsely inhabited place, or perhaps a military camp of limited size. Then there would have been casualties, but not on the tragic scale of an attack on a large city. This would have demonstrated the power of devasta- tion of the bomb, and no special technical know, ledge would have been needed to translate the destruction into what it could do to a city.

Nor is it clear why it was necessary to drop a second bomb three days after the first one, rather than give the Japanese Government more time to react to the first one.

One important factor which probably in- fluenced this decision was not stressed by Charles Curran, and that is the small number of bombs available at the time. Apart from the bomb tested in New Mexico, the two used in Japan were the only ones ready. The next one would have been available shortly, but after that the production facilities would have delivered further bombs to the base in the Pacific only at intervals.

Would this have mattered? Why was it neces- sary to achieve victory at once? I have heard the argument that the plans for the invasion of Japan were already well advanced, and that, it' the war was not over by the date set for the invasion, this would have had to proceed, and it might well have caused more loss of life, even to the Japanese. than the atomic bombs. This sounds like an argu- ment against 'wasting' one of the few ready bombs on a demonstration raid which might or might not achieve its object. I believe it was also the argu- ment for following the first attack almost immed- iately by a second one, so as to create the impres- sion that this was going to continue and that only immediate surrender would prevent a continuing atomic bombardment.

But this argument presupposes that the date of the invasion was inflexible, and that only the end of the war could stop it. I cannot imagine that it would have been impossible to postpone the inva- sion so as to allow time for a 'model' raid, or at least to await the ultimate reactions to Hiro- shima, and to await* the assembly of further bombs if these really proved necessary. Perhaps the reason was that too few of the military leaders in America and Britain had been brought into the picture about atomic energy, and that it therefore was too difficult to convince those actively con- cerned with invasion plans that the new weapon created a completely new situation. short of actually using it to achieve surrender.

In making these remarks I do not wish to attack the men who were in the unenviable position of having to take the decision in 1945. It is easy to moralise today. and I. for one, would not claim that the arguments I sketched were clear in my mind at the time. I feel fortunate in not having been part of the inner councils, but I feel no con- fidence that, had I been. my advice would have been in favour of what I now know to be the obvious answer.