by Joan Smith
In 1927, five employees of the Radium Luminous Material Company in New Jersey sued for damages after suffering rotting jaws and spines. The women were employed to paint the luminous dials of wrist watches, using radium paint. They used to lick their brushes to a fine point after dipping them into the paint; by 1924, nine of them were dead and many crippled. When the case came to court, Marie Curie was among the well-wishers who sent them messages of sympathy. They settled for lump sums of $10,000, and small pensions.
But the evidence of the horrifying effects of radiation on human beings did nothing to deter the quest for further knowledge. What the rays were composed of, and their relationship to the atom, exercised the minds of scientists throughout Europe, and beyond. The reason for this fascination was that the particles emitted by radioactive substances seemed to offer the first real hope of achieving the impossible - splitting the nucleus of the atom, and thereby liberating vast quantities of energy.
The word ‘atom’ has a Greek root and means ‘indivisible’. Until the end of the nineteenth century, this is exactly what the atom was thought to be - an indestructible piece of matter resembling a golf ball. But the work of physicists was to change this picture irrevocably in the early years of the twentieth century. It was an unprecedented time for physics, with momentous discoveries coming thick and fast as scientists took up each other’s exciting new ideas and developed them further. The devastating link between discoveries about the atom and the bomb was to be provided by Albert Einstein.
One of the key scientists in the field was Ernest Rutherford, who was born in New Zealand in 1871 but did his pioneering work in England in the first decades of the twentieth century. Rutherford examined the radiation given off by uranium, and gave the names alpha and beta rays to the two kinds he found. Meanwhile a French contemporary, Villard, discovered a third type, gamma rays.
The significance of this work on the nature of radiation is that it produced the revolutionary new idea that atoms are not indestructible. Radioactivity, it turned out, was the spontaneous disintegration of the nucleus of the atom, throwing out part of itself in the process. Rutherford and Niels Bohr, the Danish physicist who would later work on the Manhattan Project, produced a new theoretical model of the atom which was based on the solar system. In this model, the nucleus takes the place of the sun, and the electrons occupy the place of the planets.
The phenomenon of radioactivity raised the hypothesis that it might be possible to split the atom artificially, with the loss of a small amount of mass from the nucleus in the process. The implications of this possibility only became clear with the publication of a series of papers in 1905 by Albert Einstein.
Einstein said that mass and energy are equivalent - different sides of the same coin - and came up with a formula to measure the amount of energy which would be released by converting one into the other. Einstein’s formula, E = mc2, demonstrates how much energy would be released by the conversion of even a small mass. E stands for energy, m for mass, and c for the speed of light. Since c is 186,000 miles per second, it is evident that even if m is small, you will end up with a very large quantity of energy.
Physicists began to cast around for ways of splitting the nucleus of the atom artificially. They tried alpha particles, but found they were usually repelled by the nucleus. In 1932, in England, James Chadwick discovered the neutron, thereby completing the model for the structure of the atom - it was now clear that it consisted of a nucleus made of protons and neutrons, and a number of electrons in its outer structure - and at the same time putting science firmly on the road to what would be known as nuclear fission.
While scientists began bombarding a variety of elements with neutrons, in the hope of splitting the nucleus of the atom in two, many people remained sceptical. In 1933, Rutherford, who had by then been made a peer, told the annual meeting of the British Association that anyone who predicted the release of atomic energy on a large scale was ‘talking moonshine’. But in 1935, Frédéric Joliot-Curie, son-in-law of Marie Curie, said that scientists who were able to construct and demolish elements ‘may also be capable of causing nuclear transformations of an explosive character… If the propagation of such transformations in matter can be brought about, in all probability vast quantities of useful energy will be released.’
In the end, scientists achieved the splitting of the atomic nucleus without realizing what they had done. In 1934, the Italian Enrico Fermi produced infinitesimal amounts of what he thought were completely new substances by bombarding uranium, the heaviest naturally occurring element, with neutrons. He believed he had produced new, heavier elements. It was not Fermi but the German chemist Ida Noddack, who suggested a different interpretation - that Fermi might have achieved a ‘new type of nuclear disintegration brought about by neutrons.’ At the time, no one took the idea seriously.
Otto Hahn, a German chemist, working with Fritz Strassman, repeated the experiment and found barium among its products. Far from being a completely new, heavier element than uranium, barium is actually much lighter. Instead of turning into a heavier substance by absorbing a neutron, the uranium appeared to have become much lighter. At Christmas, 1938, Hahn wrote to a former colleague, Lise Meitner, an Austrian physicist who had taken refuge in Sweden from the Nazi persecution of the Jews.
Meitner told her nephew, Otto Frisch, with whom she was spending Christmas, about the results outlined in Hahn’s letter. Slowly, they realized the implication of Hahn’s finding. They remembered Neils Bohr’s description of the nucleus of the atom as similar to a drop of liquid. ‘It looked as if the absorption of the neutron had disturbed the delicate balance between the forces of attraction and the forces of repulsion inside the nucleus,’ Frisch said later. ‘It was as if the nucleus had first become elongated and then developed a waist before dividing into two more or less equal parts in just the same way that a living cell divides.’
The most significant thing about fission, as Frisch decided to call the process, was that the combined weight of its products would be less than that of the original nucleus of uranium. The loss of mass would be only a fifth of a proton - but Einstein’s equation had shown that this would be sufficient to produce a great deal of energy.
If Frisch and Meitner were right, it should be possible to detect the energy given off, in the form of a measurable electric pulse. They worked out that the amount of energy released, according to Einstein’s equation, should be 200,000,000 electron volts. Frisch devised equipment capable of making an accurate measurement and repeated the experiment. It produced exactly the result they had predicted.
The news that the nucleus of the atom had been split galvanized other scientists. Niels Bohr read the paper written by Hahn and Strassman, explaining their findings, while he was attending a meeting of the American Physical Society in Washington. He told other scientists about it on 26 January 1939, adding details of Meitner and Frisch’s theory about fission. Some physicists rushed from the room to repeat the experiment for themselves. Meitner and Frisch published their conclusions in a letter in Nature, the British scientific journal, on 11 February 1939.
In 1939, as the countries of Europe moved inexorably towards the outbreak of the Second World War, the release of vast quantities of nucleur energy began, for the first time, to seem more than a fantasy. Meanwhile, as early as 1934, Leo Szilard, a Hungarian physicist, had come up with one of the key ideas for producing sufficient energy to make an atom bomb, that of the chain reaction - when the neutron hits the nucleus of the first atom and splits it, more neutrons are thrown out at the point of fission, which then split further atoms, and this process is then repeated.
In the late 1930s, Szilard became obsessed with the idea that Nazi Germany might be able to solve the problems still standing in the way of the bomb. In 1939, as the achievement of Hahn and Strassman became known and the political situation worsened, Szilard’s obsessive quest to persuade the British and American governments to make the bomb took on greater urgency.
&nb
sp; He hit on the idea of involving Albert Einstein, then living in the US. He persuaded Einstein to send President Roosevelt a letter, dated 2 August 1939, which predicted that uranium would soon be turned into ‘a new and important source of energy’. It said that an atom bomb, exploded in a port, might well destroy all of it, along with some of the surrounding territory. The letter, whether written by Einstein or just signed by him at Szilard’s prompting, urged Roosevelt to consider making the atom bomb. It succeeded in persuading Roosevelt to take action - he set up a Uranium Committee which, although it moved cautiously, started looking at the possibility.
What was probably the most vital piece of work at this stage was actually done in England. When war broke out, the German scientist Rudolf Peierls happened to be out of Germany on a visit and he refused to go back. He moved to Birmingham University, where he worked with Otto Frisch, by now also a refugee from the Nazis. In March 1940, the two scientists produced a three-page memorandum for the British government. Margaret Gowing, official historian of atomic energy in Britain, describes it as ‘a remarkable example of scientific breadth and insight’. It was, she says, ‘the first memorandum in any country which foretold with scientific conviction the practical possibility of making a bomb and the horrors it would bring.’
September 1939 put a stop to the free exchange of ideas between scientists which had made the atom bomb a possibility. Frisch and Peierls were doing their work at the very time when the veil of secrecy was falling on science. Although, to the horror of people like Szilard, papers on nuclear fission were published in 1939, the outbreak of the war brought with it a reversal of the tradition of openness between scientists.
That such a change was inevitable in the circumstances did not prevent it bringing with it far-reaching and baleful effects. The US government developed a proprietorial attitude to anything associated with nuclear energy both during and after the war, an effect which led directly to the arms race which continues today. At the beginning of the war, the US overestimated Germany’s capacity to work out how to make the atom bomb; by the end of it, the American government clung obstinately to the illusion that the US was decades ahead of the USSR in nuclear technology and should hang on to that advantage, come what may. Scientists in Britain and the US pleaded with their governments to dispel Russia’s suspicions about the West’s intentions by sharing nuclear secrets: a course, they thought, which offered the best chance of controlling the terrifying weapons demonstrated at Hiroshima and Nagasaki.
But the US government remained obdurate, and tried to maintain its pre-eminence in the field by closing the doors even to its close ally, Britain. America’s illusion of superiority was shattered only four years after the nuclear attack on Japan: the USSR exploded its first bomb in Soviet central Asia in August 1949. But by then the damage had been done and the arms race was already well under way.
Towards the end of the war, it became clear from intelligence reports that Hitler’s Germany was a long way from making an atom bomb - its efforts had been hampered both by the exodus of scientists from Germany and by a decision to use a technical process which required a substance called heavy water, the greatest supply of which had been successfully removed from France just before the German invasion. The US government’s motives in going on with the Manhattan Project, after the removal of the threat which gave birth to it, are a matter of conjecture. On the one hand, work was stepped up so that the bomb would be ready to drop on the Japanese before the end of the war. At the same time, General Leslie Groves, the army engineer in charge of the project, told scientists in 1944: ‘You realize that all our work is against the Russians?’ One scientist who had gone to work on the project from a British university, Polish-born Joseph Rotblat, remembers to this day the effect this revelation had on him. ‘To me, this came as a terrible shock. The Russians were our allies. Thousands were dying every day stemming the advance of the Germans. I never really got over that.’
Nevertheless, at the outbreak of the war, the scientists who pushed their governments to make the atom bomb did so out of fear and loathing for Hitler. In Birmingham, Otto Frisch and Rudolf Peierls worked on their famous memorandum, which was to offer striking new solutions to a number of the technical problems involved in making the bomb.
British scientists had been trying to work out a way of making a bomb from uranium, the heaviest naturally occurring element. To understand the problems to which Frisch and Peierls now suggested answers, we have to return to our model of an atom as a miniature solar system consisting of a central nucleus of protons and neutrons, with a number of electrons in its outer structure.
Which element an atom belongs to is determined by the number of protons in its nucleus - an atom of carbon, for instance, always has six - and this number is balanced by an equal number of electrons. But an element can occur in different forms, known as isotopes, which behave slightly differently from each other. What differentiates one isotope from another is the number of neutrons in the nucleus, the number of protons remains constant, and they acquire their names by the addition of the protons and the neutrons.
The two isotopes of uranium which were exercising the minds of scientists at the outbreak of the war were Uranium 235 and Uranium 238. U235 atoms split much more readily when bombarded by neutrons but form only 0.7 per cent of naturally occurring uranium, the remainder being U238.
Scientists believed that bombarding natural uranium with neutrons would split insufficient atoms to start the chain reaction necessary for a nuclear explosion. Even if the problems could be overcome, very large amounts of rare uranium, running into tons, would be needed. The Frisch-Peierls Memorandum suggested that a much smaller amount of uranium - as little as a kilogram - would be needed if the U235 could be separated out from the U238. They also came up with a possible method of carrying out the separation.
The paper ended with a prophetic description of the horrors of the bomb that might be made from this process. They estimated that, one day after the explosion, the radiation would be equal to that from one hundred tons of radium. A cloud of radioactivity would kill everybody ‘within a strip estimated to be several miles long’. Rain would make the situation worse by carrying radioactive material firmly down to the ground, where it would linger. ‘Effective protection is hardly possible,’ they wrote. ‘Houses would offer protection only at the margins of the danger zone.’ Deep cellars might be comparatively safe, but even this protection would depend on access to uncontaminated air.
As a result of the Frisch-Peierls Memorandum a subcommittee of the Committee for the Scientific Survey of Air Warfare was set up. The sub-committee, whose brief was to look into the possibility of a uranium bomb, was given an uninformative title - The Maud Committee.
The name, deliberately intended to obscure its activities, was based on a misreading of a telegram from Niels Bohr to Otto Frisch. Bohr sent the telegram to England as Germany invaded Denmark; it ended with the curious phrase, ‘TELL COCK CROFT AND MAUD RAY KENT’. The reference to John Cockcroft, a scientist working in the Ministry of Supply, was comprehensible, but the last part of the message was a puzzle. Frisch and Cockcroft worked out that it might be a garbled anagram of RADIUM TAKEN, a message that the Germans had snatched Denmark’s radium stocks. For this reason, a former governess called Maud Ray, who lived in Kent, never received the reassurring message Bohr had sent her about the safety of his family. The phrase preyed on the scientists’ minds, however, and the committee ended up with the name Maud. (Much later, it turned out that the name had been ingeniously interpreted by civil servants as an acronym for Military Application of Uranium Detonation.)
Under the supervision of the Maud Committee, work on the feasibility of the bomb project began in April 1940. Many of the scientists who made important contributions at this time were later to carry on their work in the US as part of the Manhattan Project.
The nerve centres for the work were Oxford, Liverpool, Cambridge and Birmingham. A team based at Oxford worked on the separa
tion of U235 from natural uranium. Frisch joined Chadwick at Liverpool, leaving Peierls behind in Birmingham. Peierls’s team was soon joined by the German, Klaus Fuchs, who played an important role in work on the size of the bomb. The importance of all this work cannot be overstressed. Robert Jungk, in his history of the first atomic scientists, Brighter than a Thousand Suns, wrote: ‘The countless administrative and technical obstacles which blocked the road to the release of atomic energy were finally overcome simply and solely by the determination and obstinacy of the scientists resident in the Anglo-Saxon countries… They repeatedly took the initiative in bringing that mighty weapon into the world.’
Just over a year after the setting up of the Maud Committee, in the summer of 1941, it produced two reports. One was on the use of uranium for power, the other on its use in a bomb. The bomb report showed how far matters had progressed. ‘We have now reached the conclusion that it will be possible to make an effective uranium bomb,’ it said, going on to estimate that a 25 pound bomb would produce the effect of 1,800 tons of TNT.
Margaret Gowing has written that ‘there is no doubt that the work of the Maud Committee had put the British in the lead in the race for a bomb.’ If it had not existed, she says, ‘the Second World War might well have ended before an atomic bomb was dropped.’
Until the autumn of 1942, there had been considerable cooperation and exchanges of information between Britain and the US about work on the atom bomb. In October 1941, President Roosevelt had been told of the Maud Committee’s conclusion that a uranium bomb was feasible. He decided to speed up the American effort and increase the flow of information to and from Britain. On the day before the Japanese attack on Pearl Harbor, which took place on 7 December 1941, and brought the US into the war, scientists in the uranium section of the Office of Scientific Research and Development were informed of the new programme.