The invention of the nuclear reactor was one of the 20th century’s defining moments. The dawn of the atomic age may have been ushered in with the detonation of the first nuclear weapon, but the seeds for that moment and the huge socio-political changes that followed were sewn years before by scientists like Enrico Fermi.
Indeed, Fermi, an Italian physicist then working in America as a key figure in the Manhattan Project, made his vital breakthrough in 1942, producing the first man-made nuclear chain reaction on a squash court at the University of Chicago. Fermi’s reactor was the crucial test that enabled the advancement of the Manhattan Project, leading to the Trinity Test (the first detonation of a nuclear weapon in New Mexico) three years later and, of course, the ensuing bombings of Hiroshima and Nagasaki that ended World War Two.
A young prodigy
Born in Rome in 1901, Enrico Fermi’s interest in physics and mathematics was awakened in his early teens when he found an old 900-page tome that presented mathematics, classical mechanics, astronomy, optics and acoustics as they were understood at the time of its 1840 publication. This burgeoning fascination was noticed by a friend of his father’s, Adolfo Amidei, who knew enough about science to recognise the young boy’s brilliance. Amidei described Fermi as “a prodigy, at least with respect to geometry” and took it upon himself to cultivate Fermi’s intellect, offering mentorship and plenty of books.
Amidei’s expectations were quickly realised. Fermi graduated from high school in July 1918, having skipped the third year entirely, and won a fellowship of the Scuola Normale Superiore of Pisa. Having received his laurea (doctor’s degree) at the unusually young age of 20, Fermi embarked upon a formidable academic career. In 1926 he discovered the statistical laws (today known as the ‘Fermi statistics’) governing the particles subject to Pauli’s exclusion principle (now known as Fermions). A year later he was elected Professor of Theoretical Physics at the University of Rome.
By the end of his tenure in Rome, his ground-breaking study of the atomic nucleus had yielded a number of important breakthroughs, not least his 1934 proposal that neutrons (which had been discovered by James Chadwick two years earlier) could be used to split atoms. In 1938, Fermi, still just 37, received the Nobel Prize in Physics for his “demonstrations of the existence of new radioactive elements produced by neutron irradiation, and for his related discovery of nuclear reactions brought about by slow neutrons”.
Escape from fascist Italy
Receiving a Nobel Prize is a momentous enough moment in anyone’s life, but it came to have extra significance in the story of Enrico Fermi. When he was awarded the prize in 1938, on the cusp of World War Two, Benito Mussolini’s regime restricted travel for Italians whose work was deemed vital to national security. But Fermi’s accolade was important enough that he was given permission to visit Sweden to receive his prize.
Having been a member of the Fascist Party, Fermi had become disenchanted by 1938 and he was a vocal critic of the racial reforms introduced that year. For one thing, Fermi’s wife, Laura, was Jewish and likely faced persecution. Granted the chance to travel to Sweden, he took Laura and their two children with him. They never returned.
Having received his Nobel Prize in Stockholm, Sweden, Fermi and his family journeyed to New York where he was immediately offered positions at five universities. He accepted a role at Columbia and continued his study of neutrons. But it was a busy time for anyone working in atomic physics. Having barely had time to settle into his new life, Fermi’s work was rocked by news from Germany. In early 1939 Otto Hahn and Fritz Strassmann detected the element barium after bombarding uranium with neutrons, a result that signalled the possibility of nuclear fission.
To some extent, the discovery embarrassed Fermi, who had dismissed the possibility of fission three years earlier, but he quickly recognised the importance of the finding and its huge implications. Propelled by the potential realisation of a controlled nuclear chain reaction he began work on a series of experiments that would lead to the creation of the first nuclear reactor.
Fermi was also quick to recognise the potential military application of the German chemists’ discovery and expressed his concerns in a lecture at the Navy Department on 18 March 1939. A few months later he co-signed a letter (along with Albert Einstein, Edward Teller and Eugene Wigner) written by the physicist Leo Szilard and addressed to President Franklin D. Roosevelt. The letter warned that Germany might develop atomic bombs and suggested that the United States should start its own nuclear program.
The architect of the nuclear age
In February 1940, the US Navy awarded Columbia University $6,000 of funding, most of which Fermi and Szilard spent on purchasing graphite for the construction of a reactor that they hoped might verify the work of Hahn and Strassmann.
Two years of experiments ensued, accruing considerably more than $6,000 in expenses and entailing the construction of numerous ‘atomic piles’, but it wasn’t until the creation of the Chicago Pile-1 at Stagg Field, a largely unused American football ground on the outskirts of Chicago, that Fermi finally achieved a nuclear chain reaction.
Fermi and his team settled on the location – a space under the stands at Stagg Field that was only occasionally used as a squash and handball court – because, unlike most university-owned properties, it was on the outskirts of Chicago. They were keen to avoid the risk of building an operational reactor in a populated area.
Fermi oversaw the construction of a reactor that consisted of uranium and uranium oxide in a cubic lattice embedded in graphite. This construct was encased within a 25-foot cube-shaped balloon so that the air inside could be replaced by carbon dioxide. Considering the magnitude of the project it was a fairly makeshift construction job carried out with the assistance of 30 high school dropouts who were keen to earn some money before being drafted into the military.
The critical moment arrived on 2 December 1942. That morning the experiment proceeded as usual – control rods were removed from the pile one by one, eliciting encouraging results from the Geiger counter… Until proceedings were abruptly halted. The automatic control rod had reinserted itself due to its trip level being set too low. On the cusp of a historic breakthrough, Fermi decided to call for a lunch break.
The experiment resumed after lunch and the morning’s teasingly hopeful progress was soon verified; Fermi’s reactor achieved criticality and history was changed forever. The team opened a bottle of Chianti and toasted their breakthrough with paper cups.
Special project leader Arthur Compton was recorded notifying James B. Conant, chairman of the National Defence Research Committee:
Compton: The Italian navigator has landed in the New World.
Conant: How were the natives?
Compton: Very friendly