"That's one small step for [a] man, one giant leap for mankind". (Neil Armstrong, commander of the Apollo 11 Moon landing mission)
These words spoken by American astronaut Neil Armstrong may also describe the amazing work of Italian (later American naturalized) physicist Enrico Fermi (1901 - 1954). His first investigative steps, performed in Italy, and later in New York and in Chicago, resulted in a gigantic endeavor when he achieved the first man-made nuclear reactor in the world. Enrico's leadership and genius were also instrumental in the design of the first atomic bomb on the Manhattan Project (Enrico Fermi). I think of Enrico as an explorer, in the same league as Neil Armstrong, Christopher Columbus, Marco Polo, and the Viking Leif Ericson. When Enrico had accomplished a self-sustained atomic chain reaction in Chicago, the head of the project Arthur Compton referred to the feat as "the Italian navigator has just landed in the New World, the secret phrase agreed to signal success".
"Give a kid a book, and you change the world. In a way, even the universe". (Neil deGrasse Tyson)
When Enrico was 13, he experienced a tragic event that deeply affected the family in Rome. Enrico kept his grief inside. His older brother, only a year older, and his "sole friend" died in the middle of a medical procedure "before the anesthesia was completed" (Atoms in the family my life with Enrico Fermi by Laura Fermi. 1954, University of Chicago Press). Enrico found solace in giving "himself to study for his own pleasure" (Atoms in the family by Laura Fermi). Sometimes he would go to an "outdoor market", and one day bought a 900-page book on mathematical physics (Enrico Fermi. In Wikipedia). The book discussed everything from the propagation of waves to the motion of the planets. Buying this book was truly a prophetic event in his life. The enthusiasm of this child evolved into one of the sharpest minds any scientist can hope to obtain. Enrico not only grew to be an exceptional theorist but also an avid experimenter, an uncommon combination found in the world of physics (from Atoms in the family my life with Enrico Fermi by Laura Fermi. 1954, University of Chicago Press).
Neutrons + Large Nucleus = Fission
"Sir, Some recent work by E. Fermi and L. Szilard, which has been communicated to me in manuscript, leads me to expect that the element uranium may be turned into a new and important source of energy..." (From a letter from Albert Einstein to President F.D. Roosevelt).
If American scientist Robert Oppenheimer is called the father of the atomic bomb, then Fermi is "the architect of the atomic bomb" (Enrico Fermi. In Wikipedia).
We live in the atomic age, "the period of history following the detonation of the first nuclear weapon" in 1945 (Atomic Age. In Wikipedia), and not forgetting the creation of the first man-made nuclear reactor in 1942 by Enrico and his team. We all know the benefits of nuclear energy, but we also know the dangers and the fragility of peace, especially as we watch the news about the current situation in Ukraine and feel the effects close to home. What an irony that nuclear fission was first discovered in an authoritarian regime such as Nazi Germany and very close to being discovered in Fascist Italy.
Enrico's experiments in Italy and a report from Irene Joliot-Curie (Madame Curie's daughter) working in Paris inspired the German chemist Otto Hahn (1879 - 1968) to repeat these experiments. Hahn went on to earn the 1944 Nobel prize in chemistry "for his discovery of the fission of heavy nuclei." In other words, the prize was given for the discovery that heavy atoms may split and release energy. The atom contained an incredible reservoir of energy waiting to be used in nuclear reactors and the making of atomic bombs.
The atom was split almost in half.
In Italy, it was Enrico Fermi who came close to discovering fission (1934) and traced the path of Otto Hahn in Germany. Fermi bombarded atoms of uranium (the heaviest atoms on Earth) with neutrons and was expecting, as a result, the production of atoms heavier than uranium (transuranic elements). Instead of discovering new elements (not until 1940 a transuranic element was confirmed, Neptunium), Fermi would've discovered fission, but "the sheet of foil he used to cover his uranium sample, which would have created fission, was too thick. It blocked the fission fragments from being recorded and went unnoticed" and Fermi wasn't expecting fission fragments (lighter atoms).
The confirmation of fission fragments was made by German Chemists Otto Hahn and Fritz Strassmann. They determined the identity of these fragments with "chemical evidence" and some of the fragments were from the element barium. Otto and Fritz thought that "this was incredible because the mass of barium is about half that of uranium".
Also, it was physicist Lise Meitner (1878 - 1968), who theoretically explained Otto's results with the help of Einstein's formula E=mc2 (Lise Meitner. In Wikipedia).
Lise Meitner ("praised by Albert Einstein as the German Marie Curie"- Lise Meitner, in Wikipedia) was also Otto Hahn's collaborator, but times in Germany were dangerous to somebody with Jewish ancestry. Lise fled to Sweden and continued to advise Otto "about their joint research". Lise and her nephew Otto Frisch, inspired by the concept of cell division in biology, coined the term "fission... to describe the disintegration of a heavy nucleus into two lighter nuclei of approximately equal size".
America
Enrico also fled Mussolini's Italy because of racial laws. His wife, Laura Fermi, was Jewish. They both took an opportunity to leave with their children when Enrico was awarded the Nobel prize in 1938 and was invited to attend the ceremony in Sweden. The plan was to leave "from Stockholm for the United States" (Laura Fermi, In Wikipedia). The words of Arthur Compton acquire a new meaning when "the Italian navigator" landed in the New World, as Laura Fermi describes it in her book Atoms in the family: "...Enrico said, as a smile lit his face...We have founded the American branch of the Fermi family".
Human entanglement: Irene, Frederic, James, Enrico, Otto, Lise
Irene Joliot-Curie (1897 - 1956) followed in her famous mother's footsteps (Madame Curie). Irene discovered artificial radioactivity working alongside her husband, Frederic Joliot. They were able to induce radioactivity by bombarding aluminum foil with alpha rays. Radioactivity wasn't there before, hence the concept of artificial radiation (Lise Meitner. In Wikipedia).
It is worth mentioning that Irene and Frederic almost discovered the neutron. What the Joliot-Curies thought were gamma rays were in fact neutrons. James Chadwick "repeated the experiment" and found "the particle he was searching for", the neutron. He is now credited for discovering the neutron in 1932. In 1934, Fermi used neutrons from "radon-beryllium neutron sources".
Irene and Frederic induced radioactivity with the bombardment of alpha particles, and Enrico Fermi, following in their footsteps, also induced radioactivity with the bombardment of neutrons. Fermi was following an idea from the discoverer of the neutron, again, James Chadwick, who noted that "neutrons could penetrate the atomic nucleus more easily" (Lise Meitner, In Wikipedia). As a result of experimenting with neutrons and large atoms, following in the steps of Fermi, Otto Hahn discovered nuclear fission and wrote a letter to Lise Meitner discussing his results. Meitner with the assistance of her nephew Otto Frisch calculated the mathematical confirmation of Hahn's results where nuclear fission is essential to nuclear energy, and nuclear energy is the necessary energy for chain reactions (Enrico's work on nuclear reactors and atomic bombs). The work of scientists is an entanglement, if I may describe it that way. You build on top of others' work, and sometimes, if not most of the time, the need to move forward is impossible without somebody else's discoveries or ideas.
Hey Neutrons, slow down!
Movement (kinetic energy) is equal to temperature, so it turns out that if a neutron is slowed down to a lower temperature, the chance of a chain reaction is more likely to occur. On the other hand, fast neutrons can also split the atom, but "one drawback of fast neutrons in reactors is that the probabilities of their capture by nuclei are comparatively small".
Edoardo Amaldi, Fermi's student and collaborator, and the others in the group were puzzled by the results when they irradiated a silver piece with neutrons. Edoardo explains: "We found also that the activation of this piece of silver was different according whether the sample was irradiated on a marble table or on a wooden table that was nearby". What Edoardo is telling us, some materials slow down neutrons more than others, thus increasing the chance for the neutron to stick to the atom's nucleus and cause radioactivity.
Materials that are "good moderators" (materials that slow down neutrons) are water (which is a coolant too), pure graphite (which is made of carbon), and heavy water (composed of heavier hydrogen rather than the common hydrogen in H2O). Enrico's first nuclear reactor in Chicago, in 1942, was a "uranium-graphite reactor".
Heavy water was used by the Germans in their nuclear program, where Werner Heisenberg, yes, the one who is known for the Uncertainty Principle and developing quantum theory, was involved as one of the research scientists.
Enemy mine
Fermi was both a theorist and an experimental physicist. He had the intelligence to formulate the theory behind a gas following the Fermi-Dirac statistics and write a lucid analysis of Beta decay (radioactivity), but at the same time, his experimental skills led him to discover artificial radioactivity by neutron induction. He migrated to the United States of America due to the authoritarian power known as Fascism. During the war and living in New Jersey, Fermi was categorized as an enemy alien. His patience and endurance to follow mandated restricted movements from his house to work on his experiments, first in New York and later in Chicago where he achieved how to extract energy in a controlled manner from splitting the atom, are testimony of his dedication to science. His hard work brought us, not only the first controlled chain reaction but eventually the first detonation of an atom bomb in the New Mexico desert (From Enrico Fermi, pioneer of the Atomic Age. By Ted Gottfried. 1992).
Enrico's wit
When the first atomic bomb exploded in New Mexico, Enrico saw the light but didn't hear the sound. His wife, Laura, was puzzled, "How is it that you didn't hear the sound?" Enrico answers: "I was concentrated on dropping small pieces of paper. The air blast dragged them along...I measured the path traveled by the bits of paper and that's how I calculated the power of the explosion". (Atoms in the family by Laura Fermi).
Fermi's name was immortalized in the periodic table of elements: Fermium. As well as Marie Curie and Pierre (Curium), Albert Einstein (Einsteinium), and Lise Meitner (Meitnerium), among other scientists.
After Fermi's success in the Manhattan Project and "after the detonation of the first Soviet fission bomb in August 1949, he strongly opposed the development of a hydrogen bomb on both moral and technical grounds". In Fermi's words: "The fact that no limits exist to the destructiveness of this weapon (the H-bomb) makes its very existence and the knowledge of its construction a danger to humanity as a whole. It is necessarily an evil thing considered in any light."
However, let us never forget that he was in a race against Nazism and its hatred when working on the Manhattan Project, and his momentous triumph gave hope to civilization when he landed in the "New World".
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