The First War of Physics (30 page)

Oppenheimer may have been somewhat shaken by the action taken against Lomanitz. He decided to come clean, and mention the approach by Eltenton. He mentioned the incident to Groves in August, but he withheld Chevalier’s name.

On 25 August 1943 Oppenheimer discussed the Lomanitz situation with Lyall Johnson in the latter’s office in Berkeley. He went on to suggest that Eltenton may have tried to acquire information about the work at the Rad Lab and should therefore be watched. Johnson called Pash, and Pash asked that Oppenheimer return for further discussions the next day.

When Oppenheimer returned to Johnson’s office, he was surprised to discover that Pash was present. A small microphone hidden in the base of Johnson’s telephone secretly recorded the ensuing conversation. Oppenheimer thought he had been asked to return for further discussions about Lomanitz, but Pash interrupted. He wanted to know about other groups interested in the work at the Rad Lab.

Oppenheimer was unprepared for this discussion. In his own mind he had already identified the guilty and the innocent and, in his arrogance, now sought to protect the innocent from the people whose job it was to judge these things for themselves.

¹
Consolidated Mining and Smelting signed an agreement with the OSRD on 1 August 1942, accepting millions of US dollars to build and operate a heavy water plant at Warfield, in a construction project named ‘Project 9’.

²
‘Lend-Lease’ aid to Britain, China, France, the Soviet Union and other Allied nations began in March/April 1941. The Allies were supplied with over $50 billion worth of
matériel
(equivalent to almost $700 billion in 2007) in exchange for (in Britain’s case) the establishment of American military bases.

³
Although Feklisov’s passport bore Fitin’s signature, he was not protected by diplomatic immunity.

⁴
The timing of this meeting is not clear, but it occurred sometime in the winter of 1942–43.

⁵
Serber’s lectures were faithfully noted down by Edward Condon, serving as one of Oppenheimer’s associate directors. The lecture notes were then bound together to make an introductory manual known as the ‘Los Alamos Primer’. This document was declassified and published in 1992.

⁶
In fact, the efficiency of a bomb – a measure of the amount of fissile material actually fissioned in an explosion compared to the total amount of fissile material – is proportional to the cube of the difference between the bomb mass and the critical mass.

⁷
Frisch had used a mixture of radium and beryllium in the experiments in which he discovered spontaneous fission in uranium.

Chapter 10

ESCAPE FROM COPENHAGEN

January–November 1943

D
espite receiving numerous invitations to visit America shortly after the Nazi occupation of Denmark, Niels Bohr had nevertheless decided it was his duty to remain. He wanted to do what he could to preserve the scientific institutions which he had helped to build, and the scientists who worked within them. And, indeed, the work did continue. Bohr and his team had access to a cyclotron
¹
and high-tension apparatus suitable for fission experiments. The lack of materials, especially metals, was alleviated somewhat by the Carlsberg Foundation, a generous sponsor of Denmark’s greatest physicist, which loaned Bohr’s institute a supply of metals from the Carlsberg brewery. Bohr probably thought he could sit out the war if not in comfort or free of concern, then at least in relative peace.

Eric Welsh thought rather differently. The veteran British SIS operative had figured that Bohr would be a valuable addition to Tube Alloys. Late in 1942 Tronstad had received a message indicating that Bohr would welcome the opportunity to see him again – interpreted as a hint that Bohr was
ready to leave Denmark. Welsh talked to ‘C’,
²
Sir Stewart Menzies, the head of the SIS, and they agreed that an approach to Bohr should be made to sound him out about coming to Britain.

Shortly afterwards, in January 1943, Chadwick was approached by the SIS in Liverpool and asked if he would draft a letter of invitation to Bohr. Once the details of the proposed escape, or ‘ex-filtration’ plan had been explained, Chadwick agreed. His letter, dated 25 January, offered a warm welcome should Bohr decide to leave Denmark, freedom to work on any scientific problems of interest, and a veiled request for Bohr’s support on the atomic programme. ‘Indeed I have in mind a particular problem in which your assistance would be of the greatest help’, he wrote.

The letter was reduced to a microdot and smuggled to Bohr hidden in the hollow handle of a key, stored on a ring alongside a number of other keys. A second key on the ring contained a duplicate microdot. Bohr was alerted to the imminent arrival of the message by Captain Volmer Gyth, an officer in the information division of the Danish general staff with connections to the Danish resistance. Gyth passed him a set of instructions to the effect mat: ‘Professor Bohr should gently file the keys at the point indicated until the hole appears. The message can then be syringed or floated out onto a microscope slide … It should be handled very delicately.’ Perhaps somewhat uncertain of his own abilities in the tradecraft of a spy, when Gyth offered to recover the microdot and provide him with a written version of the letter, Bohr gratefully accepted.

Bohr’s judgement of the situation was, however, unchanged. His desire was to remain in Denmark and continue his work at the institute. As far as he understood, the possibility of extracting U-235 from natural uranium in sufficient quantities to make a bomb was completely impractical. He gave his reasons in a reply but he also left open the possibility of coming to Britain, recognising that his circumstances could easily change. ‘However,’ he wrote, ‘there may, and perhaps in a near future, come a moment where things look different and where I, if not in other ways, might be able modestly to assist in the restoration of international collaboration in human progress.’ Gyth reduced Bohr’s letter to millimetre dimensions, wrapped it in foil and arranged to have it inserted in the hollow tooth of a courier, hidden beneath a filling.

Further correspondence ensued, though the manner of transmission of subsequent messages was rather more conventional. Bohr explained in more detail why he thought a fission bomb was impossible.

Separate ways

After successfully completing their sabotage mission, the Norwegian commandos of Swallow and Gunnerside went separate ways, as Falkenhorst and Reichskommisar Josef Terboven ordered a massive search. Rønneberg led Idland, Kayser, Strømsheim and Storhaug north towards the Swedish border. They arrived on Swedish soil fifteen days later, exhausted from a 250-mile trek that had not been without incident but which had been relatively straightforward. On reaching London they were greeted warmly and given a nice cup of tea.

Poulsson and Helberg headed for Oslo, intending to lay low for a while before making contact with the Norwegian underground. From Oslo, Poulsson escaped into Sweden before returning to Britain for a short while. Helberg, who had done time in a Swedish prison and was therefore known to the authorities, planned to head back to the Hardanger Plateau when the dust had settled. Acting on incorrect advice, on 25 March 1943 he arrived back in an area that was still crawling with German troops. Realising he had been spotted, he set off on skis as three German soldiers gave chase. Two gave up after an hour. After two hours, Helberg turned and faced his pursuer. The German emptied his Luger, missing with every shot. Now it was Helberg’s turn. He gave chase, bringing the German down with a single shot from his Colt .32.

More adventures were to follow. In darkness, Helberg fell over a precipice and broke his left shoulder. He reached his destination, a house he knew in the village of Rauland, only to find it full of German troops. He
bluffed his way through the next two nights, drinking and playing cards with the troops, and even managed to get medical attention for his shoulder. He moved to a hotel in Dalen, where he was unfortunate to get caught up in an altercation between Terboven, who was staying in the next room, and a young, attractive Norwegian woman who had spurned Terboven’s amorous advances. Helberg was rounded up with the other Norwegians in the hotel on the orders of a now incensed Terboven, and was told they were all to be sent to Grini concentration camp. Helberg jumped from the bus on the way to Oslo, avoiding grenades and pistol shots. He eventually managed to get to Sweden, avoided imprisonment, and boarded a plane bound for Britain on 2 June.

Haugland and Skinnarland moved their makeshift wireless operation to a location high in the mountains. They took cover under the snow and watched the German troops make a mess of the search on the Hardanger Plateau. Haugland completed Skinnarland’s wireless training before joining his brother, whom he was surprised to find leading the resistance in Oslo. He provided the resistance with further SOE-style training in the use of explosives.

Haukelid and Kjelstrup headed west on the Hardanger Plateau, where they stayed for much of the summer of 1943. Kjelstrup’s health began to suffer, and he returned to Britain to recuperate.

Somewhat improved apparatus

The loss of heavy water production from the Vemork plant was a major setback to the German programme. The loss was to prove temporary, however. Tronstad and Brun had believed that the destruction of the high concentration cells would halt production for a few years. But the damage was already repaired by 17 April 1943, and the plant was again producing small quantities of heavy water by the end of June.

By this time, the German War Office had ceased to take any interest in the programme. Diebner and his research team were transferred back to the broader Uranverein under the auspices of the Reich Research Council, although the team was allowed to continue working at the Army Ordnance
laboratory in Gottow. The two million Reichsmarks that had been promised by the War Office never materialised, and the Reich Research Council was left with the task of finding the money for itself. Speer remained an enthusiastic patron, however, and adequate funding was forthcoming.

Diebner may not have been a leading light in German theoretical physics, but he was an accomplished experimentalist. The reactor experiments that had been carried out so far under Heisenberg’s overall guidance had relied on configurations in which uranium metal plates and quantities of the heavy water moderator were organised in layers. Diebner had devised an alternative configuration based on a three-dimensional lattice of equally spaced cubes of uranium oxide or uranium metal immersed in a volume of moderator. Ingeniously, he further figured that he could do without an enveloping container of aluminium by freezing the heavy water moderator solid. In effect, the ‘heavy ice’ would function both as moderator and support structure.

He set up such a configuration in the low-temperature laboratory of the Reich Institute for Technical Chemistry. Reactor G-II consisted of about 230 kilos of uranium in the form of cubes and 210 kilos of heavy ice, arranged in a sphere about 75 centimetres in diameter. No self-sustaining chain reaction was generated but there was clear evidence for neutron multiplication, about one and a half times greater than the corresponding neutron multiplication in L-IV. Diebner was convinced that a self-sustaining chain reaction would be achieved with sufficient uranium and heavy water.

Heisenberg, however, made light of Diebner’s achievements. In a conference held in Berlin on 6 May he acknowledged the results from Diebner’s group but declared that the latter’s ‘somewhat improved apparatus’ had ‘yielded the same result’ as the previous year’s L-IV design. Heisenberg was planning a large-scale reactor experiment and had no intention of moving away from the layer configuration.

Subsequent experiments at the Gottow laboratory bore out Diebner’s conviction. The team repeated the uranium–heavy ice experiment with the same quantities of materials but this time with a lattice of uranium cubes suspended on fine alloy wires in a volume of liquid heavy water at normal
laboratory temperatures. A further experiment with over 560 kilos of uranium and nearly 600 kilos of heavy water yielded even more promising results. It was clear that the lattice design was superior to anything that had yet been produced in Berlin or Leipzig.