The First War of Physics (24 page)

Everyone involved would feel the pressure created by another delay, yet to trial a completely untested and potentially dangerous technology in the midst of a bustling city was to take an enormous risk. The term ‘meltdown’ had yet to be applied to a reactor that runs out of control, but the physicists involved had no difficulty imagining the consequences.

Fermi was able to reassure Compton that he could keep the chain reaction under control, relying on the fact that a small proportion of the secondary neutrons were emitted with some delay following fission. By operating the reactor so that its rate of production of neutrons fractionally exceeded the rate of neutron capture, the delayed neutrons would give the physicists enough time to respond should the chain reaction start to run away. Compton agreed, but decided not to inform the president of the University of Chicago just yet. When Compton advised Conant at a committee meeting on 14 November, Conant went white. Groves immediately started searching for an alternative site. But nobody told Compton to stop.

The morning of 2 December 1942 dawned cold, with temperatures falling below freezing, and a chill wind blew. Around mid-morning Fermi ordered that all but one of the cadmium control rods be removed from the reactor. The last control rod was then drawn halfway out, as the physicists carefully monitored the neutron intensity and compared the results with their estimates. Between 25 and 30 people watched from the balcony, including Szilard and Wigner.

By 2:00pm Compton had arrived and the group of observers had swelled to 42. Fermi ordered a repeat of their earlier experiment, and all but one of the control rods was withdrawn once more. With the last control rod about seven feet out of the pile, the chain reaction was almost self-sustaining, the pile almost critical. Fermi ordered that the rod be withdrawn another foot. As the rate of neutron production climbed inexorably, the steady click-click-click of the neutron counters became faster and faster until the clicks merged into a roar.

Physicist Herb Anderson described what happened next:

[W]e were in the high intensity regime and the counters were unable to cope with the situation anymore. Again and again, the scale of the recorder had to be changed to accommodate the neutron intensity which was increasing more and more rapidly. Suddenly Fermi raised his hand. ‘The pile has gone critical,’ he announced. No one present had any doubt about it.

The intensity of neutrons was now doubling every two minutes. If Fermi had let it run uncontrolled for another hour and a half, the reactor would have pushed on towards a million kilowatts, killing everyone in the room before melting down. Fermi shut the reactor down after just four and a half minutes. There had been nothing to see, and aside from the clicking of the neutron counters there had been nothing to hear. The reactor had produced a mere half-watt, but its significance that day was much, much greater than its output. The physicists had shown that it was possible to engineer the controlled release of the enormous and inexhaustible supply of energy bound in atomic nuclei.

Compton called Conant to tell him the news: ‘Jim,’ he said, ‘you’ll be interested to know that the Italian navigator has just landed in the new world.’

He had won his bet.
¹⁰

As the physicists celebrated, Szilard found himself standing alone with Fermi. ‘I shook hands with Fermi,’ he recalled, ‘and I said I thought this day would go down as a black day in the history of mankind.’

¹
Compton had estimated that, with access to a uranium–heavy water reactor operating at 100,000 kilowatts for two months, the Germans could have enough plutonium for six atomic bombs by the end of the year – a frightening prospect.

²
Oppenheimer omitted to mention his activities in support of the radical Federation of Architects, Engineers, Chemists and Technicians (FAECT) union, and the discussion groups he had organised with Chevalier. See Herken, p. 58.

³
Speer noted that Hitler would occasionally remark that ‘the scientists in their unworldly urge to lay bare all the secrets under heaven might someday set the globe on fire’. See Speer, p. 317.

⁴
There was no formal written report from the summer study group, and the figures were scaled down somewhat between the reports from Oppenheimer to Conant, and from Conant to Bush.

⁵
They were Flight Lieutenant A.R. Parkinson of the Royal Canadian Air Force, Flight Lieutenant A.E. Thomas, Pilot Officer G.W.S. De Gency, Flying Officer A.T.H. Haward, Flight Sergeants A. Buckton and G.M. Edwards, and Sergeant J. Falconer. They were buried in Helleland churchyard.

⁶
They were Pilot Officers N.A. Davies and H.J. Fraser of the Royal Australian Air Force, Lieutenant A.C. Allen, Lance Sergeant G. Knowles, Corporal J.G. Thomas, Lance Corporals F.W. Bray and A. Campbell, Sappers G.S. Williams, E.W. Bailey, C.H. Grundy, H.J. Legate, T.W. Faulkner, H. Bevan, L. Smallman and J.M. Stephen, and Drivers J.T.V. Belfield and E. Pendlebury. Their bodies were exhumed and reburied at Eiganes near Stavanger, with full military honours, in July 1945.

⁷
They were Sergeants M.F. Strathdee and P. Doig of the Army Air Corps, Lieutenant D.A. Methven, Lance Sergeant F. Healey, Sappers J.G.V. Hunter, W. Jacques and R. Norman, and Driver G. Simkins. Their bodies were reburied at Eiganes in August 1945.

⁸
They were Corporal J.D. Cairncross, Lance Corporal T.L. Masters, Sapper E.J. Smith and Driver P.P. Farrell. They are commemorated on the Brookwood Memorial in Surrey. Stabsarzt W.F. Seeling, Hauptscharfuehrer E. Hoffman and Unterscharfuehrer F. Feuerlein were found guilty of their murder at a war crimes tribunal in Oslo in December 1945. Seeling and Hoffman were executed. Feuerlein was given life imprisonment and handed to the Russians to answer charges relating to atrocities committed against Russian prisoners-of-war.

⁹
They were Lance Corporal W.M. Jackson, Sappers F. Bonner, J.F. Blackburn, J.W. Walsh and T.W. White. Their bodies were recovered and reburied at Vestre Gravlund, near Oslo.

¹⁰
Although it seems that he never did get the cigar from Lawrence.

Chapter 8

LOS ALAMOS RANCH SCHOOL

March 1942–March 1943

G
eorgei Flerov had become involved in research on nuclear fission not long after the publication of the Frisch-Meitner paper in early 1939. He had studied at the Leningrad Polytechnic Institute and had worked in Igor Kurchatov’s laboratory at the Fiztekh. Together with Lev Rusinov, Flerov had independently verified the production of secondary neutrons and indirectly confirmed that Bohr and Wheeler were right in their assertion that the rare isotope U-235 is responsible for fission in uranium. With Konstantin Petrzhak, he subsequently discovered that U-235 undergoes spontaneous fission.
¹

The outbreak of war in 1939 and the subsequent German invasion of the Soviet Union in 1941 caused the energies of Soviet physicists to be diverted away from problems of nuclear physics and towards essential war work. Flerov joined the Leningrad Air Force Academy to train as an engineer. However, he had glimpsed the possibility of an atomic bomb based on a fast neutron chain reaction and wasn’t altogether ready to abandon it. He wrote to several of his colleagues suggesting that research on nuclear fission be continued, to no avail.

When in late 1941 Flerov was stationed with his unit at Voronezh, not far from the front line, he decided to take advantage of its university library to catch up on the latest publications by Western nuclear scientists. He was particularly interested to find out how his work on spontaneous fission had been received in the scientific press.

What he found surprised and alarmed him. As he flicked through the pages of Western physics journals, he saw that there were simply
no
publications relating to nuclear fission research. He couldn’t believe that such an interesting and important topic had been abandoned. It certainly wasn’t the case that the leading figures in nuclear physics research had dropped the subject in favour of something else. Their names were similarly conspicuous by their absence.

The dogs were no longer barking. Flerov deduced that research on nuclear fission had become classified, a sign that American, British and – much more worryingly – German physicists were working on atomic bombs.

He decided to raise the alarm. He wrote a letter to Kurchatov in February 1942, recommending that research on fission in uranium be restarted in the Soviet Union. A further letter and a series of telegrams to Sergei Kaftanov, the recently-appointed State Defence Committee’s plenipotentiary for science, met only with stubborn silence.

In frustration, in April 1942 Flerov wrote a letter directly to Stalin.

Stalingrad

The MAUD Committee report on the feasibility of building an atomic bomb had arrived in Moscow in late September 1941, just as German forces were advancing on the city. The Soviet government evacuated to Kuibyshev in October and by December the Wehrmacht was dug in only 30 miles outside Moscow.

Consequently, nearly six months had passed when, in March 1942, Lavrenty Beria began properly to consider the material that had been
provided by Cairncross. Beria was head of the NKVD and a prominent member of the State Defence Committee. In the late 1930s he had presided over the closing stages of Stalin’s Great Purge of perceived enemies of the Soviet state, through show trials, executions and imprisonment of political dissidents in a network of brutal labour camps which Alexander Solzhenitsyn later called the ‘Gulag Archipelago’.

Beria was extremely suspicious. His first assumption was that this was disinformation planted by British or German agents designed to influence Soviet thinking and encourage wasteful expenditure on an ultimately futile project. However, he changed his mind after consulting with a trusted physicist who evaluated the report.

In March, Beria drafted a detailed memorandum to Stalin on the subject. He summarised the MAUD Committee conclusions and the British war cabinet’s decision. He emphasised the ‘importance and urgency of the practical utilization of the nuclear energy of uranium 235 for the Soviet Union’s military purposes’, before recommending the establishment of a consultative body of experts and the sharing of the espionage materials with a few ‘prominent specialists’.

In April the NKVD consulted with Soviet nuclear physicists about the prospects for a bomb, but did not share the MAUD Committee conclusions or the reports that were now arriving from Fuchs via the GRU. The physicists were inevitably cautious, but by the time Flerov’s letter to Stalin had arrived on his desk, Beria had already taken the decision to restart Soviet research on nuclear fission.

This was not to be an all-out effort to build an atomic bomb, since the Soviet Union was still fighting for its survival. Besides, so far as the physicists themselves understood, there were no large natural uranium deposits lying beneath Soviet soil. Instead, work was to begin on the feasibility of a Soviet bomb and an assessment of the potential threat from a German weapon. Planning proceeded slowly through the summer of 1942.

Although Hitler had failed in his mission to capture Moscow, by the late spring of 1942 the Eastern front had stabilised. Army Group South pressed on towards the Caucasus and the strategically important Soviet oil fields. They were making good progress, but Hitler, in frustration at his army’s
failures, had decided to take more direct control of his forces. At this point he decided to split his forces into two. One group would continue on to the Caucasus, while the German Sixth Army and, eventually, the Fourth Panzer Army were diverted 300 miles away towards the River Volga and the city of Stalingrad.

It was a puzzling decision. Stalingrad was a critical industrial city and the Volga an important means of communication. The city represented a gateway to the Urals and the north. Yet it was strategically less important than the oil fields to the south-east. It seems that Hitler feared that the Soviets would be able to launch attacks on his flanks from Stalingrad. It is also possible that Hitler was by now obsessed with the idea of destroying the ‘city of Stalin’.