The First War of Physics (11 page)

If one works on the assumption that Germany is, or will be, in the possession of this weapon, it must be realized that no shelters are available that would be effective and that could be used on a large scale. The most effective reply would be a counter-threat with a similar bomb.

Frisch and Peierls had already realised that the only defence would be deterrence.

Oliphant sent the memorandum to Henry Tizard, an Oxford chemist and chairman of the Aeronautical Research Committee. Although its preoccupation was radar, this was one of the most important committees concerned with the application of science in wartime. Tizard recommended that a small advisory committee be set up, which was eventually to consist of Oliphant, George Thomson, professor of physics at Imperial College London,
⁵
and Patrick Blackett, professor of physics at Manchester University. Thomson was appointed as chairman of the committee. Blackett was involved with other war projects and did not join the committee immediately. John Cockcroft, who with Ernest Walton had been the first physicist to ‘split the atom’, also joined. With the outbreak of war, Cockcroft had taken the position of Assistant Director of Scientific Research in the Ministry of Supply, working primarily on radar. As enemy aliens, Frisch and Peierls were excluded.

The pace was forced somewhat at the beginning of April by a visit to London by Jacques Allier, who reported to Thomson, Oliphant and Cockcroft on the work of the French nuclear scientists in Paris and the German physicists’ interest in heavy water. The British committee met for the first time on 10 April 1940 at the Royal Society in London. Denmark and Norway had been invaded by German forces just the day before.

However, when the committee considered the Frisch-Peierls memorandum, it was met with general scepticism. Some small-scale experiments on separating U-235 using uranium hexafluoride might be justified, the committee concluded, but this was not likely to become a project of real military significance. Tizard thought that the French had become ‘unnecessarily excited’ by the existence of the German nuclear programme. The comparison with the first meeting of Briggs’ Advisory Committee on Uranium seemed complete.

But there the similarities ended. In a letter dated 16 April, Thomson invited Chadwick to join the committee, which met for the second time eight days later. When he heard of the details of the Frisch-Peierls proposals, Chadwick was embarrassed. He admitted that he had reached similar conclusions, but had not felt justified in raising the possibility of a U-235 bomb until more experiments had been performed. Chadwick’s support for the technical content of the memorandum greatly enhanced its credibility. The committee now realised that an atomic bomb was feasible in principle. The physicists were electrified by the possibility.

Frisch and Peierls had understood the implications of what they had discovered. But there was never any question in their minds as to the morality of initiating a project that could produce a weapon of unimaginable destructive power, a weapon capable of ‘killing large numbers of civilians’. Frisch later wrote:

Why start on a project which, if it was successful, would end with the production of a weapon of unparalleled violence, a weapon of mass destruction such as the world had never seen? The answer is very simple. We were at war, and the idea was reasonably obvious; very probably some German scientists had had the same idea and were working on it.

Fear drove them. Fear that such a weapon might be delivered into the hands of a regime capable of subjugating Europe, if not the world. A regime capable of perpetrating an evil beyond their darkest imaginings.

Spontaneous fission

Peierls and his Russian wife Genia moved into a more spacious house in Edgbaston in Birmingham and at their invitation Frisch moved from his cramped bedsit to lodge with them. Genia was a phenomenon. She ran the house ‘with cheerful intelligence, a ringing Manchester voice and a Russian’s sovereign disregard of the definite article’. She taught Frisch to shave every day and to dry dishes as fast as she could wash them up.

As they waited patiently for news of the reaction to their memorandum, Frisch became increasingly concerned about his own position. He was summoned by the police to answer a barrage of questions concerning his status – did he have any dependent relatives, was he studying for an examination, was he about to get a degree which would allow him to find work? Genia was convinced he was about to be interned, along with other enemy aliens, on the Isle of Man. She made him buy some cotton shirts that even a bachelor could launder. Through his scientific contacts he tried to get the message to the authorities that he was involved in important war work. This seemed to do the trick. He never heard from the police again and, fortunately, never had to launder his cotton shirts.

The small apparatus Frisch had set up to separate U-235 was going to require a considerable amount of time and patience to produce quantities of the isotope sufficient to make measurements. This was patience he did not possess. He therefore worked out an alternative ‘quick-and-dirty’ method of making the necessary measurements. This involved bombarding natural uranium with slow neutrons which, according to Bohr and Wheeler, would cause fission only in U-235. He decided to revert to a relatively old method of generating neutrons, using gamma radiation from radium to dislodge neutrons from a beryllium target. This was a method that had been overtaken by the development of more modern high-tension equipment, and Lawrence’s cyclotrons.

Armed with a small amount of highly radioactive radon gas that he had extracted from a sample of radium stored deep underground in Derbyshire’s Blue John Cavern, he produced neutrons from beryllium which he used to bombard about a gram of uranium enclosed in an
ionisation chamber. He made a series of measurements over a 36-hour period, taking naps on a camp bed in the laboratory between measurements. He made two important discoveries.

What had first appeared a puzzling experimental artefact turned out to be spontaneous fission in natural uranium. The U-235 ‘liquid drops’ are so unstable that every now and then one will fall apart all by itself, producing fission fragments and secondary neutrons. The second discovery was that Frisch had overestimated the rate at which U-235 nuclei are fissioned by slow neutrons. This meant that he had underestimated the critical mass of U-235 required to support a chain reaction. Fortunately, in the meantime Peierls had worked out that the critical mass could be reduced by surrounding it with a substance that would reflect any escaping neutrons back into the fissile material. So they were back pretty much where they started.

Peierls had also been thinking about isotope separation. He had consulted Franz Simon, a first-rate chemist who had been born to a Jewish family in Berlin and had won the Iron Cross, first class, during the First World War. He had been rescued from Germany and brought to Oxford by Lindemann in 1933. Frisch had opted for the Clusius-Dickel thermal diffusion method because it had seemed the simplest, but Simon and Peierls were not convinced this method would work. Simon thought that ordinary gaseous diffusion through a porous barrier might be more effective. Peierls wrote to Thomson, urging the committee to consult with Simon, and then wrote to Lindemann. Simon and Peierls approached Lindemann in person in June 1940. Peierls could not translate Lindemann’s grunts, but thought he had been convinced by their arguments.

Maud Ray Kent

In Stockholm, Meitner had noted the paper by Segrè, published in
Physical Review
, in which he had reported his failed attempt to find rhenium-like chemical properties in the mysterious substance with the characteristic 2.3-day decay time. Segrè had speculated that the mysterious substance
was nothing more than a fission fragment. Meitner was convinced it was element 93.

To prove this she needed access to a source of neutrons. Through late winter she waited patiently for Siegbahn’s cyclotron to become operational, before giving up and going to Copenhagen to use the cyclotron in Bohr’s institute. She arrived on the afternoon of 8 April 1940.

Bohr himself was in Norway on the final leg of a lecture tour. He dined with King Haakon VII that evening. It was a gloomy occasion. The King and his government officials were depressed at the prospect of an impending German invasion. Bohr travelled back to Copenhagen on the night train, and was woken by Danish police with the news that Denmark had been invaded, too. Meitner woke in Copenhagen to the roar of German aeroplanes overhead.

Denmark was granted a semblance of self-rule. In return for co-operation with the German occupying force, the Danish government negotiated protection for Denmark’s 8,000 Jews, a condition that infuriated Hitler. Meitner was not threatened in occupied Denmark, and she stayed for three weeks before returning to Stockholm. Before she left, Bohr asked if she would send a telegram from Stockholm to British physicist Owen Richardson, a Bohr family friend, to advise him that he and his wife Margrethe were in good health, if not in good spirits.

The telegram read:

MET NIELS AND MARGRETHE RECENTLY BOTH WELL BUT UNHAPPY ABOUT EVENTS PLEASE INFORM COCKCROFT AND MAUD RAY KENT

Richardson passed the message to Cockcroft, who puzzled over its meaning. It was, perhaps, easy to be paranoid under the circumstances. German forces were tearing the heart out of continental Western Europe. German physicists were busy working on a secret project to build an atomic bomb. Germany had no cyclotron, but radium and beryllium were known to serve as a useful source of neutrons. Cockcroft became convinced that the last three words of Meitner’s telegram were, in fact, a crude coded message.
MAUD RAY KENT
was surely an anagram – albeit imperfect – for ‘radium taken’.
It was a message consistent with the idea that the Germans were taking control of all the radium they could get their hands on. It all pointed to a concerted effort by the Germans to develop their nuclear technology.

Cockcroft voiced his concerns to Chadwick, and Thomson decided to use the message as the basis for a new name for the advisory committee that had been assembled in response to the Frisch-Peierls memorandum. He called it the M.A.U.D. Committee, a name deliberately obscure and meant to throw any German intelligence agent off the scent.
⁶
It was, perhaps, also meant to serve as a reminder for all those involved and aware of Meitner’s telegram that they were now inexorably locked in a race with the Nazis to develop an atomic bomb.

Nobody thought to go back to Meitner to seek clarification.

Subsequent publication of the McMillan-Abelson paper confirmed what Meitner had suspected – the substance with the 2.3-day decay time was indeed element 93. Had not the war intervened, she would have been able to demonstrate this much herself, ending a search for transuranic elements that she had begun with Hahn in 1934. Among her many disappointments, this was most bitter.

‘Mad Jack’ Howard

Working at the Collège de France in Paris, Frédéric Joliot-Curie, Hans von Halban and Lew Kowarski had been one of the first research groups to demonstrate experimentally the possibility of a self-sustaining nuclear chain reaction in uranium. From that point they had moved quickly. By August 1939 they had recorded increased fission in blocks of uranium oxide immersed in ordinary water, although this activity was insufficient to support a chain reaction.

Halban, who had worked on neutron absorption in deuterium with Frisch at Bohr’s institute in Copenhagen in 1937, suggested that heavy water would make a much better moderator. Of course, this was a suggestion that was confirmed by the German physicists’ subsequent interest in stocks of heavy water from the Norsk Hydro plant at Vemork. He and Kowarski carried out calculations on all the possible candidates, including heavy water and ultra-pure graphite, and concluded that heavy water would work best.

Together they worked on the theory of chain reactions. By now wary of publishing their results in the open literature, they wrote a paper primarily to establish a claim to any original discovery. They lodged the paper, sealed in an envelope, with the French Academy of Science for safekeeping.

The 185 kilos of heavy water rescued by Allier from the Norsk Hydro plant were stored in an air-raid shelter at the Collège de France. However, the scientists had little opportunity to use these materials to put their theories to the test. As the Germans marched on Paris in early June 1940, Joliot-Curie received instructions from the French armaments minister not to allow the uranium and heavy water to fall into enemy hands.

Halban and Kowarski left Paris with their families and headed south. Joliot-Curie and his wife Irène, daughter of Marie Curie, followed. Halban loaded the 26 jerrycans of heavy water into a car with his wife Else and young daughter and drove to Le Mont-Dore, a spa town in central France. There they were joined by Allier. The heavy water was stored initially in the local women’s prison, then in the death cell in neighbouring Riom’s state prison. The condemned prisoners themselves carried the heavy water into the cell. Next morning the prison governor, perhaps nervous of the impending arrival of new masters, refused to release the heavy water until Allier threatened him with a loaded revolver.

Halban and Kowarski were busy setting up new laboratory facilities in the Villa Clair Logis at Clermont-Ferrand when, two days after the fall of Paris, the word came from Allier to evacuate France altogether. They headed for Bordeaux, where Charles Henry George Howard, twentieth Earl of Suffolk and thirteenth Earl of Berkshire, was waiting for them.

Howard was a character straight out of a Wodehouse novel. Having become the Earl of Suffolk and Berkshire at the age of eleven, ‘Jack’ Howard left Radley public school to work as a deckhand aboard the wool clipper
Mount Stewart
, and sailed for Australia. After a short spell in the
Scots Guards he returned to Australia and managed a sheep station in Queensland. Back in Britain, he studied for a degree in pharmacology at the University of Edinburgh and in 1937 was elected a Fellow of the Royal Society of Edinburgh. As the war began he joined the Ministry of Supply’s Department of Scientific and Industrial Research (DSIR) and was dispatched to Paris to act as liaison with the French Ministry of Armaments.