The First War of Physics (12 page)

Howard’s mission was to ‘rescue’ valuable machine tools, millions of dollars’ worth of industrial diamonds, the heavy water, and about 50 French scientists. When bankers were reluctant to release the diamonds from their vaults to a man possessing only a letter of introduction from the French Minister of Armaments, he would nonchalantly let his jacket fall open to reveal Oscar and Genevieve, a pair of .45 automatics nestling in shoulder holsters. That tended to overcome the bankers’ inhibitions, and the diamonds were swiftly given up into his care.

His rather imaginative approach to his missions had earned him the nickname ‘Mad Jack’, and Halban and Kowarski quickly began to appreciate why. With the port under attack, and hundreds of thousands of refugees flocking to the docks seeking safe passage, chaos reigned. Howard, unshaven and covered in tattoos, simply got the crew of the British coal ship SS
Broompark
too drunk to set sail until he had completed his mission. With Halban, Kowarski, their families and the heavy water aboard, the ship sailed from the dock down the Gironde estuary on 19 June. A nearby ship hit a mine and sank. Joliot-Curie later claimed to the German invaders that it was on this ship that the heavy water had been stowed.

There were 25 women on board the
Broompark
, including Howard’s private secretary, Eileen Marden. When some of the women began to complain of sea-sickness, Howard administered his remedy of choice – champagne. Kowarski quickly learned to have absolute confidence in Howard’s abilities: ‘His infectious good humour made the entire trip seem like a schoolboy adventure.’
⁷

Joliot-Curie and Irene decided to return to Paris. Their reasons are obscure, but it may be that Irène refused to abandon French soil. JoliotCurie’s concern for his own academic status in England or concern for the continuity of French science may also have been factors.

The
Broompark
docked at Falmouth on 21 June 1940. Howard delivered the diamonds into the hands of Harold Macmillan, then an Undersecretary at the Ministry of Supply. The French physicists and their precious cargo reached London, where the heavy water was temporarily stored at Wormwood Scrubs prison, before being transferred into the care of the librarian at Windsor Castle. Halban and Kowarski joined the growing ranks of MAUD physicists and relocated to Cambridge’s Cavendish Laboratory, where they formed a research group to develop a uranium–heavy water reactor.
⁸

Frisch and Chips

Now that a decision had been taken to act on Frisch and Peierls’ memorandum, the émigré physicists were finally allowed to contribute, not directly to the MAUD Committee but to a technical sub-committee. Frisch welcomed the opportunity: ‘not only had our report started the whole thing, but we had also thought about many of the additional problems that would arise.’

Among the most pressing of problems was the separation of U-235, and it was by now clear that the facilities at Birmingham could not support work on both radar and the atomic bomb simultaneously. Frisch discussed the options with Chadwick in Liverpool, which at this time was not involved in war work. He returned to Oliphant with a proposal. Radar had to take priority in Birmingham; Liverpool offered greater access to laboratory facilities and a cyclotron, and although as an enemy alien Frisch was in principle prohibited from entering the port city of Liverpool, Chadwick had agreed to accommodate him there. Oliphant agreed, and Frisch moved to Liverpool in July 1940.

It was here that Frisch had his first experience of life under threat of German bombs. The Luftwaffe had failed to subdue Fighter Command in the Battle of Britain. Churchill, frequently given to colourful turns of phrase, was not exaggerating when he declared that never had so much been owed by so many to so few. Hitler suspended Operation Sealion indefinitely in mid-September 1940. Although this was Germany’s first defeat of the war, it did not substantially alter the reality of German supremacy in Western Europe. Hitler switched his attention to the Atlantic – he intended to cut off vital supply routes and simply starve Britain into submission.

In November 1940 the Luftwaffe targeted Britain’s major industrial cities and ports. Coventry was ‘blitzed’ on 14 November by more than 500 German bombers. Liverpool received some of the heaviest sustained bombing outside London, with over 300 air raids before the end of the year. Frisch was huddling under the staircase of his boarding-house during one particularly heavy raid, when a bomb blew in most of the windows. The landlady promptly quit and left without collecting the outstanding rents. Frisch also decided that the time had come to seek sanctuary in the suburbs.

In the laboratory Frisch worked with John Holt, a young student assigned to him by Chadwick. Frisch charged about energetically, with Holt trailing in his wake, and the pair earned the nickname ‘Frisch and Chips’. They quickly discovered that uranium hexafluoride is one gas for which the Clusius-Dickel method produces no discernible separation of isotopes. Peierls and Simon had been right to be suspicious.

Simon had been co-opted onto the MAUD Committee in the middle of 1940 and worked full-time at Oxford on the problem of separating U-235 by an alternative gaseous diffusion technique. In this method, isotope separation is achieved by virtue of the fact that gases diffuse through a
porous barrier at a rate that depends on their atomic or molecular weight. Lighter gases diffuse faster than heavier gases.

By December, Simon had worked out the details of a full-scale industrial plant that could separate as much as a kilo of U-235 per day. By his estimate, such a plant would cost about £5 million to construct, it would cover 40 acres and require some 60,000 kilowatts of electricity. He summarised his work in a detailed report and, not wishing to trust the report to the wartime postal service, he braved the bombing and journeyed to London shortly before Christmas 1940 to deliver it by hand to Thomson.

The comfort of restful sleep

Of all the MAUD Committee scientists, Chadwick probably had the widest perspective on the work that was now in hand. Although the British programme was committed to an approach based on U-235, the possibility of using other potentially fissionable materials such as element 94 had also been recognised by MAUD physicists. Production of element 94 in quantities sufficient for a bomb depended on the ability of the team at Cambridge to build a working nuclear reactor based on their uranium oxide-heavy water design. Chadwick had been so incensed by the publication of the McMillan-Abelson paper on element 93 that he had asked the British embassy to lodge an official protest. Lawrence was on the receiving end.

There were few in Liverpool to whom Chadwick could turn to discuss the visions that were now starting to haunt him. Frisch and Rotblat were getting along famously but they were not British citizens and Chadwick felt unable to confide in them. The other physicists working on the project were too young to be burdened with his dark thoughts. Weighed down by the inevitability of creating a weapon of inconceivable destructive power, the comfort of restful sleep began to elude him. He started to take sleeping pills.

He took sleeping pills for the rest of his life.

¹
Nuclear fusion involves the joining together of two light nuclei to form a heavier nucleus, accompanied by the release of energy.

²
Pronounced ‘piles’.

³
Note that the critical mass is the mass of fissionable material in which production of neutrons is balanced by their capture without further fission or escape to the surrounding environment. A mass of U-235 equal to the critical mass is therefore not explosive. To create an explosion, it is necessary to assemble a mass that is in excess of the critical mass. This is sometimes referred to as a super-critical mass.

⁴
For Chadwick this was history repeating itself. He had been trapped in Germany in August 1914 when, following Germany’s invasion of Belgium, Britain declared war.

⁵
George P. Thomson was the son of J.J. Thomson, who had discovered the electron in 1897. In a nice twist of history, J.J. Thomson won the 1906 Nobel prize for physics for showing that the electron is a particle, whereas his son won the 1937 Nobel prize for showing that it is a wave.

⁶
This did not stop inventive onlookers from trying to decipher what the acronym stood for. A popular choice was: Military Applications of Uranium Disintegration.

⁷
Howard went on to specialise in defusing unexploded bombs. He worked closely with his cockney driver, Fred Hards, and his secretary Eileen Marden, who would take notes while Howard examined the devices. They became known as the ‘Holy Trinity’. Tragically, all three were killed by a bomb on 12 May 1941. Howard was awarded a posthumous George Cross for ‘conspicuous bravery’. Harold Macmillan later wrote: ‘I have never known in a single man such a remarkable combination of courage, expert knowledge and indefinable charm.’

⁸
The French physicists’ adventure was turned into a feature film in 1949, titled
La Bataille de L’Eau Lourde
(The Battle for Heavy Water). It starred the physicists, playing themselves.

Chapter 4

A VISIT TO COPENHAGEN

October 1940–September 1941

T
he Virus House was ready in October 1940. In addition to a new laboratory, it also housed a special circular brick-lined pit about six feet deep into which a reactor vessel could be lowered. The pit could then be filled with water to act as both neutron shield and reflector, directing stray neutrons back into the reactor core, thereby prolonging any chain reaction that was initiated. It was in this pit that the world’s first experimental nuclear reactor was to be assembled.

In December, Heisenberg, Weizsäcker, Wirtz and two other Uranverein physicists packed a domed aluminium cylinder with alternating layers of uranium oxide and paraffin wax, the latter to be tested for its efficacy as a moderator. The cylinder was a little under 150 centimetres in diameter. They lowered the cylinder into the pit and inserted small quantities of radium and beryllium into the centre of the reactor vessel to provide a source of neutrons to initiate a chain reaction. None of the Uranverein physicists was quite sure what to expect.

The experiment, designated B-I, failed. The physicists were looking for evidence of neutron ‘multiplication’, increased production of neutrons at different points in the reactor which would signal progress towards a self-sustaining chain reaction. But they found that the number of neutrons
was actually diminished, rather than increased. The same arrangement was used in a repeat experiment (designated B-II) some weeks later. This time a little over six tons of uranium oxide was used, again with a paraffin wax moderator. The results were similar.

In Leipzig, Robert Döpel worked under Heisenberg’s direction to assemble an experimental pile with a different, concentric, arrangement of uranium oxide and paraffin wax. This experiment, designated L-I, was also negative. This merely served to confirm that a reactor could not be constructed using carbon and hydrogen as a moderator, at least in the form of paraffin wax.

In the meantime, experiments conducted by Bothe’s team in Heidelberg confirmed that heavy water would function quite effectively as a moderator. But what of graphite? Bothe had tended to dismiss his team’s earlier results on neutron absorption by graphite as the result of impurities and, through German Army Ordnance, he sought and obtained a quantity of pure graphite from the Siemens company. Siemens supplied a 100-centimetre sphere of electro-graphite claimed to be of the highest purity. In January 1941 he and Peter Jensen now found, much to their surprise, that purification had worsened, not improved, its performance. Bothe very much doubted that impurities could be to blame, and the physicists concluded that unless the uranium could be greatly enriched in U-235, graphite simply could not be used as a moderator in a nuclear reactor.

These results were undoubtedly affected by impurities – most probably boron contaminants arising from the manufacturing process which Szilard had the previous year taken great pains to exclude from samples of graphite used to make similar measurements at Columbia University. Göttingen physicist Wilhelm Hanle was suspicious of Bothe and Jensen’s results, however. Although he was not part of the Uranverein, Hanle carried out measurements of his own to show that impurities were indeed to blame and that graphite would function as an effective moderator. He reported his results to Army Ordnance.
¹