Nuclear energy. In the fall of 1942 they went to Goodyear Customers who wanted a kind of hot-air balloon, like the ones the American company had begun producing a few decades earlier and which were also used for airships. They simply didn't want it spherical or rounded in any way, but rather cubic.
It seems the Goodyear technicians were quite perplexed. They probably wondered, "How would a cube balloon fly?", perhaps trying to convince the buyers to change their minds. In reality, those customers didn't care about the flight. In fact, they came from the University of Chicago and worked on the top-secret project led by Enrico Fermi to develop the first nuclear fission chain reaction, known as the "Flying Cube." Chicago Pile-1.
They didn't mean to fly...
It is understandable, therefore, that they could not give too many details about the reasons for their purchase, that not only would they never have had to fly through the skies, but they would have remained in an underground space to act as a casing to contain the approximately 45.000 graphite blocks and the 50 tons between uranium oxide and metallic uranium that made up the pile.
A pile that came into operation exactly 80 years ago. At 15:25 p.m. on December 2, 1942, 23:25 p.m. in Italy, in a laboratory located beneath the stands of the University of Chicago's Stagg Field football stadium - unused at the time - the world was learning to master the energy of Nuclear fision thanks to the fundamental contribution of the Italian physicist. Less than three years later, that energy would be tragically exploited in the atomic bombs of Hiroshima and Nagasaki and, after the war, for peaceful purposes in the fission reactors that today produce about 10% of the world's electricity.
Enrico Fermi and the idea of ​​America
At first glance it would seem that Enrico Fermi decided to land in the United States of America solely for a question of financing awarded to universities and research institutes. Certainly, at the dawn of the 20th century, the scientific world was a hotbed. Consolidated, in the first two decades, what is called old Quantum Theory, The concepts of quantum mechanics began to take shape in the second half of the 1920s. Scientific discoveries followed one after another, and the human mind was projected into the ruthless investigation of the infinitely small.
The institute on Via Panisperna, in the heart of Rome, directed by Enrico Fermi and with collaborators such as Segrè, Amaldi, Pontecorvo, Majorana, Rasetti, D'Agostino, needed very expensive equipment to continue competing at the highest level of research. Probing the radioactivity of elements with the correct intuition of bombarding nuclei with neutrons required the need for a particle accelerator capable of generating them in beams of adequate energy and high intensity. For this reason, the nuclear energy became a crucial issue in these investigations.
It all started with artificial radioactivity
The scientific process that led to the December 2nd result began some fifteen years earlier, in 1926, with Fermi being called by the University of Rome to the first Italian chair of theoretical physics. There, Fermi founded the Via Panisperna group of students and directed their research into nuclear physics, which was emerging there thanks to the work of many European physicists. Spurred by the discovery of artificial radioactivity by Irène Curie and Frédéric Joliot, Fermi conducted a series of groundbreaking experiments in the mid-1930s that earned him the Nobel Prize in Physics in 1938. A year that culminated in two events that would have been fundamental for what happened in Chicago 80 years earlier.
Historic context
Despite the important funds granted by the State to the Institute, these did not allow them to obtain particle accelerators compatible with the objectives of the boys from Via PanispernaThe state, indeed. Because neglecting the Italian sociopolitical imprint of the 30s would be a very serious logical error. The radical rupture consummated by the reactionary movement led by Benito Mussolini in the previous decade in an Italy devastated by the First World War.
The undisputed dominance of the National Fascist Party and its ideological affinity with Adolf Hitler's National Socialist German Workers' Party when it seized power in a furious Germany in 1933. The prospects for diplomatic talks understandably collapsed under the erosion of the ill-disguised, centuries-old frictions of conflict and the future projects of the new dictators. This is the entrenched European scenario where science stands like a cathedral in the desert. The straw that broke the camel's back was, for Enrico Fermi, the promulgation of the racial laws in 1938, which saw Laura Capon, his Jewish wife, among those directly affected.This led him to seek refuge in the United States, where the development of science, including weak nuclear force, could move forward without interruption.
Christmas Eve, key day to travel
On Christmas Eve, Fermi and his family embarked on the Franconia liner for the United States, forced to leave Italy by the racial laws of fascism. A ship that, by the way, sailed several times through the troubled waters of World War II: bringing to the United States the physicist who would have been one of the protagonists of the Manhattan Project, transporting British troops to various war fronts and hosting Churchill and the British delegation in 1945 during the Yalta talks. And always during the Christmas period Lise Meitner, a brilliant Austrian physicist who, being Jewish, had had to flee Germany to Sweden.
Enrico Fermi, Laura and Niels Bohr landed in New York on January 2, 1939. Thus began the collaboration with Columbia University where Fermi would work as part of the nuclear research team. After the discovery of the Germans O. Hahn and F. Strassmann on the fissile and/or fissile nature of heavy elements, Fermi launched himself fully into the study of neutron economy in the fission reactions of the different isotopes of uranium, which would later be reflected in the creation of the first nuclear battery.
the atomic pile
Fermi confirmed the hypothesis raised by L.Szilard in 1933, about the possibility of having a series of nuclear chain reactions. The fission of the isotope U 235 It generates an average of 2,8 fast neutrons, with energies between 10 k eV and 10 MeV. Properly thermalized (slowed down) through heat dissipation in collisions with moderator nuclei, increasing the probability of causing the fission of other U nuclei. 235. Postponing the study of the dynamics of nuclear fission reactions for a future article, it will suffice here to state that the researchers had the possibility of building a battery that would house such chains of self-sustaining reactions.
A nuclear reaction that, compared to a common chemical combustion reaction, released energy approximately 10 million times greater, and whose military potential was immediately recognized by both the United States and Nazi Germany. Thanks also to Fermi's intuitions, the American program advanced much more rapidly, and a fundamental step was precisely the development of the atomic pile. This pile was a crucial step toward what we know today as nuclear weapons.
In fact, it takes place a rnuclear fission chain reactionThe fission of a uranium nucleus is induced by the collision of a neutron with it. The decay of uranium produces lighter nuclei and more neutrons, on average between two and three. When a sufficient amount of uranium is concentrated in a limited space, critical conditions can be reached, where for each fission reaction, on average, at least one of the neutrons produced causes another fragmentation. Depending on the level of criticality, the process can be self-sustaining and produce energy in a controlled manner—as occurs in civil reactors—or grow exponentially and suddenly release enormous power, as occurs in nuclear devices.
Chicago-Stack 1, Nuclear Power
The pile was composed of 5,6 tons of metallic uranium and 36 tons of uranium oxide pellets. These were alternated with 350 tons of graphite blocks, which served as a moderator and structural element. The only way to control the reaction and achieve a critical attitude, which indicates the beginning of a self-sustaining reaction, is by adjusting the travel of the control rods in the pile.
The pile goes into operation on December 2, 1942. In the early afternoon it reaches a critical setting and shuts down a few minutes later by reinserting all the control rods.. On that cold day of the sad years of World War II, the italian navigator arrived at the new world. But Beneath the epidermis of American nuclear scientific research lurked the Manhattan ProjectThus, alongside the ethical use of nuclear energy for electricity production, we are witnessing the immobilization of plutonium in military nuclear warheads. Two of them, Little Boy y Fat man, they first reduced Hiroshima and then Nagasaki to dust.
Joy for the discovery that a little later became a tragedy
At 15:25 p.m. on December 2, Chicago Pile-1 reached criticality in a completely controlled manner, demonstrating the feasibility of the process. Eugene Wigner, one of the physicists present, uncorked a bottle of Chianti to celebrate the event, honoring Fermi's Italian origins. Forty-nine scientists present signed the straw wrapper of the bottle, which is still preserved at the University of Chicago. But—as Leona Woods, a physicist involved in the project and then a twenty-three-year-old student, recalls—it was a silent toast, because, as Wigner himself would later declare, "We knew we were about to unleash a giant«. A giant that in little more than a couple of years would have ended the Second World War at the tragic cost of the destruction of Hiroshima and Nagasaki.
Science is not to blame, but the human being
An anniversary, that of December 2, 1942, is therefore full of meaning: a great scientific experiment, which has had an enormous impact on contemporary history. History cannot be written with "ifs," but it is likely that if the United States had not built the battery in Chicago, Nazi Germany might have successfully done so at some point, with easily imaginable consequences for the world.
Revealing the most intimate secrets of matter has been one of the greatest achievements of the human intellect and protagonist, with the Relativity and quantum mechanics, of the enormous revolution in our understanding of the world brought about by physics in the 20th century. Today, thanks to nuclear physics, diseases are cured, the human body is explored, and electricity is produced by fission in civil reactors without releasing greenhouse gases. It's not about science, which has made and will continue to make enormous contributions to the well-being of humanity and has so often been an instrument of peace, but about the use made of its results and that sense of responsibility and discernment that must never fail humanity.