Enrico Fermi

Enrico Fermi (Italian: [enˈriːko ˈfermi]; 29 September 1901 – 28 November 1954) was a distinguished Italian-American physicist, widely recognized for his pivotal role in creating the world's inaugural artificial nuclear reactor, the Chicago Pile-1, and for his involvement in the Manhattan Project. In 1938, he was awarded 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." Fermi has been posthumously referred to as both the "architect of the nuclear age" and the "architect of the atomic bomb." Notably, he was among the rare physicists who achieved exceptional proficiency in both theoretical and experimental physics. Collaborating with his colleagues, Fermi submitted multiple patents concerning nuclear power applications, all of which were subsequently acquired by the U.S. government. His significant contributions spanned the development of statistical mechanics, quantum theory, and the fields of nuclear and particle physics.

Enrico Fermi (Italian: [enˈriːkoˈfermi]; 29 September 1901 – 28 November 1954) was an Italian–American physicist, renowned for being the creator of the world's first artificial nuclear reactor, the Chicago Pile-1, and a member of the Manhattan Project. He won the 1938 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". He has been called the "architect of the nuclear age" and the "architect of the atomic bomb". He was one of very few physicists to excel in both theoretical and experimental physics. With his colleagues, Fermi filed several patents related to the use of nuclear power, all of which were taken over by the US government. He made significant contributions to the development of statistical mechanics, quantum theory, and nuclear and particle physics.

Fermi's initial significant contribution was in the domain of statistical mechanics. Following Wolfgang Pauli's formulation of the exclusion principle in 1925, Fermi published a paper applying this principle to an ideal gas, utilizing a statistical framework now termed Fermi–Dirac statistics. Currently, particles adhering to the exclusion principle are designated as "fermions." Pauli subsequently hypothesized the existence of an uncharged, invisible particle emitted concurrently with an electron during beta decay, a postulate intended to uphold the law of conservation of energy. Fermi adopted this concept, developing a model that integrated the proposed particle, which he christened the "neutrino." His theoretical framework, initially known as Fermi's interaction and presently referred to as the weak interaction, elucidated one of nature's four fundamental forces. Through experiments involving the induction of radioactivity using the recently identified neutron, Fermi ascertained that slow neutrons were more readily captured by atomic nuclei compared to fast ones, subsequently developing the Fermi age equation to characterize this phenomenon. Upon bombarding thorium and uranium with slow neutrons, he inferred the creation of novel elements. Despite receiving the Nobel Prize for this purported discovery, these "new elements" were later identified as products of nuclear fission.

In 1938, Fermi departed Italy to evade the newly enacted Italian racial laws, which directly impacted his Jewish wife, Laura Capon. He subsequently immigrated to the United States, where he contributed to the Manhattan Project throughout World War II. At the University of Chicago, Fermi spearheaded the team responsible for designing and constructing Chicago Pile-1, which achieved criticality on December 2, 1942, thereby demonstrating the first human-initiated, self-sustaining nuclear chain reaction. He was present for the criticality of the X-10 Graphite Reactor in Oak Ridge, Tennessee, in 1943, and for the B Reactor at the Hanford Site the following year. At Los Alamos, Fermi directed F Division, a segment of which was dedicated to the development of Edward Teller's thermonuclear "Super" bomb. On July 16, 1945, he attended the Trinity test, the inaugural detonation of a full nuclear bomb, where he employed his distinctive Fermi method to estimate the weapon's yield.

Post-war, Fermi played a crucial role in establishing the Institute for Nuclear Studies in Chicago and served on the General Advisory Committee, presided over by J. Robert Oppenheimer, which provided counsel to the Atomic Energy Commission on nuclear issues. Following the detonation of the first Soviet fission bomb in August 1949, he voiced strong opposition to the development of a hydrogen bomb, citing both moral and technical objections. He was among the scientists who provided testimony in support of Oppenheimer during the 1954 hearing, which ultimately led to the revocation of Oppenheimer's security clearance.

Fermi conducted significant research in particle physics, particularly concerning pions and muons, and theorized that cosmic rays originated from material accelerated by magnetic fields within interstellar space. Numerous accolades, theoretical concepts, and scientific institutions bear Fermi's name, including the Fermi 1 (breeder reactor), the Enrico Fermi Nuclear Generating Station, the Enrico Fermi Award, the Enrico Fermi Institute, the Fermi National Accelerator Laboratory (Fermilab), the Fermi Gamma-ray Space Telescope, the Fermi paradox, and the synthetic element fermium. This distinction places him among only 16 scientists honored with an element named after them.

Early Life

Born in Rome, Italy, on 29 September 1901, Enrico Fermi was the third child of Alberto Fermi, a division head in the Ministry of Railways, and Ida de Gattis, an elementary school teacher. He had an elder sister, Maria, and an elder brother, Giulio. Following a period of wet nursing in a rural community, Enrico rejoined his family in Rome at the age of two and a half. Despite being baptized Catholic to honor his grandparents' wishes, his family lacked strong religious observance; Fermi maintained an agnostic stance throughout his adult life. In his youth, he shared interests with Giulio, engaging in the construction of electric motors and playing with various electrical and mechanical devices. Tragically, Giulio passed away in 1915 during surgery for a throat abscess, and Maria died in an airplane crash near Milan in 1959.

While at a local market in Campo de' Fiori, Fermi discovered a 900-page physics treatise, Elementorum physicae mathematicae. Authored in Latin by Jesuit Father Andrea Caraffa, a professor at the Collegio Romano, this volume comprehensively covered mathematics, classical mechanics, astronomy, optics, and acoustics, reflecting the scientific understanding prevalent at its 1840 publication. Alongside his scientifically inclined friend, Enrico Persico, Fermi undertook various projects, including the construction of gyroscopes and experiments to measure Earth's gravitational acceleration.

Enrico frequently met his father, Alberto, outside his office after work, and in 1914, he was introduced to Alberto's colleague, Adolfo Amidei, who regularly accompanied his father part of the way home.

Aware of Adolfo's interest in mathematics and physics, Enrico seized an opportunity to pose a question about geometry. Adolfo recognized that the young Fermi was inquiring about projective geometry and subsequently provided him with a book on the topic by Theodor Reye. Within two months, Fermi returned the book, having successfully solved all the problems presented, some of which Adolfo considered challenging. Upon verifying Fermi's accomplishment, Adolfo characterized him as "a prodigy, at least with respect to geometry," and continued to mentor him, supplying additional texts on physics and mathematics. Adolfo observed Fermi's exceptional memory, which enabled him to retain the content of books thoroughly and return them promptly after reading.

Scuola Normale Superiore in Pisa

Fermi completed high school in July 1918, having bypassed his third year. Following Amidei's recommendation, Fermi acquired German language skills to access contemporary scientific literature and subsequently applied to the prestigious Scuola Normale Superiore in Pisa. Amidei believed the Scuola offered superior developmental opportunities for Fermi compared to the Sapienza University of Rome at that period. Due to the recent loss of their son, Fermi's parents reluctantly consented to his four-year residency in the school's accommodations, away from Rome. Fermi achieved first place in the challenging entrance examination, which featured an essay on "Specific characteristics of Sounds." The 17-year-old Fermi notably employed Fourier analysis to derive and solve the partial differential equation governing a vibrating rod, prompting the examiner to declare, post-interview, that he was destined to become an outstanding physicist.

While attending the Scuola Normale Superiore, Fermi engaged in pranks with fellow student Franco Rasetti, leading to a close friendship and professional collaboration. He received guidance from Luigi Puccianti, the director of the physics laboratory, who acknowledged having little to impart to Fermi and frequently requested instruction from him instead. Fermi's profound understanding of quantum physics prompted Puccianti to assign him the task of organizing seminars on the subject. During this period, Fermi acquired proficiency in tensor calculus, a fundamental technique for general relativity. Although initially selecting mathematics as his primary field of study, he soon transitioned to physics. He largely pursued self-directed learning, focusing on general relativity, quantum mechanics, and atomic physics.

Upon his admission to the physics department in September 1920, Fermi joined a small cohort. Given the department's limited enrollment, comprising only Fermi, Rasetti, and Nello Carrara, Puccianti granted them unrestricted access to the laboratory for their research endeavors. Fermi proposed that they investigate X-ray crystallography, leading the trio to produce a Laue photograph, which is an X-ray image of a crystal. In 1921, during his third year of university studies, Fermi's initial scientific contributions appeared in the Italian journal Nuovo Cimento. The inaugural paper was titled "On the dynamics of a rigid system of electrical charges in translational motion" (Sulla dinamica di un sistema rigido di cariche elettriche in moto traslatorio). Notably, this work foreshadowed future developments by expressing mass as a tensor, a mathematical construct frequently employed to characterize objects in motion and undergoing transformation within a three-dimensional spatial context. While classical mechanics defines mass as a scalar quantity, relativistic theory posits its variation with velocity. His second publication, "On the electrostatics of a uniform gravitational field of electromagnetic charges and on the weight of electromagnetic charges" (Sull'elettrostatica di un campo gravitazionale uniforme e sul peso delle masse elettromagnetiche), explored related concepts. Employing principles of general relativity, Fermi demonstrated that a charge possesses a mass equivalent to U/c§1415§, where U represents the system's electrostatic energy and c denotes the speed of light.

The initial paper appeared to highlight a discrepancy between electrodynamic and relativistic theories regarding the computation of electromagnetic masses, with the former predicting a value of 4/3 U/c². Fermi resolved this issue the following year in an article titled "Concerning a contradiction between electrodynamic and the relativistic theory of electromagnetic mass," where he elucidated that the perceived inconsistency stemmed from relativistic principles. This particular paper garnered significant recognition, leading to its translation into German and subsequent publication in the German scientific journal Physikalische Zeitschrift in 1922. Also in 1922, Fermi submitted his article "On the phenomena occurring near a world line" (Sopra i fenomeni che avvengono in vicinanza di una linea oraria) to the Italian journal I Rendiconti dell'Accademia dei Lincei. Within this publication, he analyzed the Principle of Equivalence and introduced the concept of "Fermi coordinates." His work demonstrated that along a world line proximate to the timeline, space exhibits characteristics akin to Euclidean space.

In July 1922, Fermi presented his thesis, "A theorem on probability and some of its applications" (Un teorema di calcolo delle probabilità ed alcune sue applicazioni), to the Scuola Normale Superiore, earning his laurea at the remarkably early age of 20. His dissertation focused on X-ray diffraction images. At that time, theoretical physics was not formally recognized as an academic discipline in Italy, meaning only experimental physics dissertations were typically accepted. Consequently, Italian physicists were hesitant to adopt novel concepts such as relativity, which originated in Germany. However, Fermi's proficiency in experimental laboratory work mitigated any significant challenges this academic climate might have presented.

In 1923, while contributing to the appendix for the Italian translation of August Kopff's book, Fundamentals of Einstein Relativity, Fermi became the first to identify the immense nuclear potential energy inherent within Einstein's equation (E = mc§78§), suggesting its potential for exploitation. He posited that, "It does not seem possible, at least in the near future, to find a way to release these dreadful amounts of energy—which is all to the good because the first effect of an explosion of such a dreadful amount of energy would be to smash into smithereens the physicist who had the misfortune to find a way to do it."

During 1923–1924, Fermi undertook a semester of study with Max Born at the University of Göttingen, where he encountered Werner Heisenberg and Pascual Jordan. Subsequently, from September to December 1924, Fermi pursued studies in Leiden under Paul Ehrenfest, supported by a Rockefeller Foundation fellowship secured through the intervention of mathematician Vito Volterra. In Leiden, he met Hendrik Lorentz and Albert Einstein, and established friendships with Samuel Goudsmit and Jan Tinbergen. From January 1925 to late 1926, Fermi held a teaching position in mathematical physics and theoretical mechanics at the University of Florence, collaborating with Rasetti on experiments investigating the influence of magnetic fields on mercury vapor. Concurrently, he contributed to seminars at the Sapienza University of Rome, delivering lectures on quantum mechanics and solid-state physics. During his presentations on the nascent field of quantum mechanics, particularly when discussing the exceptional predictive accuracy of the Schrödinger equation, Fermi frequently remarked, "It has no business to fit so well!"

Following Wolfgang Pauli's announcement of his exclusion principle in 1925, Fermi published a paper titled "On the quantization of the perfect monoatomic gas" (Sulla quantizzazione del gas perfetto monoatomico), wherein he applied the principle to an ideal gas. This publication was particularly significant for Fermi's statistical formulation, which elucidates the distribution of particles within systems comprising numerous identical particles that adhere to the exclusion principle. Shortly thereafter, British physicist Paul Dirac independently developed this concept, also demonstrating its relationship to Bose–Einstein statistics. Consequently, this statistical framework is now designated as Fermi–Dirac statistics. In recognition of Dirac's work, particles that conform to the exclusion principle are presently termed "fermions," while those that do not are referred to as "bosons."

Professorship in Rome

In Italy, professorships were awarded through a competitive process (concorso) for vacant academic chairs, with applicants evaluated based on their publications by a committee of professors. Fermi initially sought a chair in mathematical physics at the University of Cagliari in Sardinia but was narrowly overlooked in favor of Giovanni Giorgi. In 1926, at the age of 24, he applied for a professorship at the Sapienza University of Rome. This particular position represented a newly established chair, one of the inaugural three in theoretical physics across Italy, created by the Minister of Education at the behest of Professor Orso Mario Corbino. Corbino held multiple roles: professor of experimental physics at the university, director of the Institute of Physics, and a member of Benito Mussolini's cabinet. As chair of the selection committee, Corbino envisioned that this new professorship would elevate the standards and prestige of physics within Italy. The committee ultimately selected Fermi over Enrico Persico and Aldo Pontremoli. Corbino subsequently assisted Fermi in assembling his research group, which soon included distinguished students such as Edoardo Amaldi, Bruno Pontecorvo, Ettore Majorana, and Emilio Segrè, alongside Franco Rasetti, whom Fermi appointed as his assistant. This group quickly became known as the "Via Panisperna boys," a moniker derived from the street housing the Institute of Physics.

Fermi married Laura Capon, a science student at the university, on July 19, 1928. The couple had two children: Nella, born in January 1931, and Giulio, born in February 1936. On March 18, 1929, Mussolini appointed Fermi as a member of the Royal Academy of Italy, and on April 27, he became a member of the Fascist Party. However, Fermi later opposed Fascism following the promulgation of the 1938 racial laws by Mussolini, which aimed to align Italian Fascism more closely with German Nazism ideologically. These discriminatory statutes posed a threat to Laura, who was Jewish, and resulted in the dismissal of many of Fermi's research assistants.

While in Rome, Fermi and his research group made significant contributions across various practical and theoretical domains of physics. In 1928, Fermi published his seminal work, Introduction to Atomic Physics (Introduzione alla fisica atomica), which served as a contemporary and accessible textbook for Italian university students. To disseminate knowledge of the emerging field of physics, Fermi also delivered public lectures and authored popular articles targeting scientists and educators. His pedagogical approach included daily gatherings with colleagues and graduate students to collectively analyze problems, frequently drawn from his ongoing research. A testament to his influence was the increasing influx of foreign students to Italy. Among these international scholars, the most prominent was German physicist Hans Bethe, who arrived in Rome as a Rockefeller Foundation fellow and co-authored a 1932 paper with Fermi titled "On the Interaction between Two Electrons" (German: Über die Wechselwirkung von zwei Elektronen).

During this period, physicists encountered a perplexing phenomenon known as beta decay, characterized by the emission of an electron from the atomic nucleus. To uphold the principle of energy conservation, Pauli hypothesized the simultaneous emission of an invisible, chargeless particle possessing negligible or no mass. Fermi subsequently adopted this concept, initially developing it in a preliminary paper in 1933, followed by a more comprehensive publication the subsequent year that formally introduced the postulated particle, which Fermi designated as a "neutrino". His theoretical framework, initially termed Fermi's interaction and later recognized as the theory of the weak interaction, elucidated one of the four fundamental forces of nature. The neutrino's existence was experimentally confirmed posthumously, and Fermi's interaction theory provided the explanation for its elusive detectability. Upon submission of his manuscript to the British journal Nature, the editor rejected it, citing that its speculative content was "too remote from physical reality to be of interest to readers". According to David N. Schwartz, Fermi's biographer, it is peculiar that Fermi earnestly sought publication in Nature, given that the journal at the time exclusively published brief communications and was thus unsuitable for disseminating even a novel physical theory. A more appropriate venue, if any, would have been the Proceedings of the Royal Society of London. Schwartz concurs with the hypothesis proposed by some scholars, suggesting that the British journal's rejection influenced Fermi's younger colleagues (some of whom were Jewish and left-leaning) to abandon their boycott of German scientific publications following Hitler's ascent to power in January 1933. Consequently, Fermi's theory was published in Italian and German editions prior to its English translation.

In the introductory remarks to the 1968 English translation, physicist Fred L. Wilson observed:

Fermi's theory, aside from bolstering Pauli's proposal of the neutrino, has a special significance in the history of modern physics. One must remember that only the naturally occurring β emitters were known at the time the theory was proposed. Later when positron decay was discovered, the process was easily incorporated within Fermi's original framework. On the basis of his theory, the capture of an orbital electron by a nucleus was predicted and eventually observed. With time, experimental data accumulated significantly. Although peculiarities have been observed many times in β decay, Fermi's theory always has been equal to the challenge.
The consequences of the Fermi theory are vast. For example, β spectroscopy was established as a powerful tool for the study of nuclear structure. But perhaps the most influential aspect of this work of Fermi is that his particular form of the β interaction established a pattern that has been appropriate for the study of other types of interactions. It was the first successful theory of the creation and annihilation of material particles. Previously, only photons had been known to be created and destroyed.

In January 1934, Irène Joliot-Curie and Frédéric Joliot reported the successful induction of radioactivity in elements through alpha particle bombardment. By March of the same year, Gian-Carlo Wick, Fermi's assistant, offered a theoretical framework for this phenomenon, drawing upon Fermi's established theory of beta decay. Consequently, Fermi transitioned his focus to experimental physics, specifically utilizing the neutron, a particle discovered by James Chadwick in 1932. In March 1934, Fermi aimed to investigate the possibility of inducing radioactivity using a polonium-beryllium neutron source developed by Rasetti. Neutrons, lacking an electric charge, would not experience deflection by the positively charged atomic nucleus. This characteristic implied that neutrons required significantly less energy to penetrate the nucleus compared to charged particles, thereby eliminating the need for a particle accelerator, a device unavailable to the Via Panisperna group.

Fermi conceived the idea of substituting the polonium-beryllium neutron source with a radon-beryllium variant. He constructed this by filling a glass bulb with beryllium powder, evacuating the air, and subsequently introducing 50 mCi of radon gas, provided by Giulio Cesare Trabacchi. This new configuration yielded a significantly more potent neutron source, though its efficacy diminished in accordance with radon's 3.8-day half-life. Despite recognizing that this source would also emit gamma rays, Fermi theorized that these emissions would not compromise the experimental outcomes. His initial experiments involved bombarding platinum, a readily available element with a high atomic number, but these attempts proved unsuccessful. Subsequently, he experimented with aluminum, observing that it emitted an alpha particle, produced sodium, and then decayed into magnesium via beta particle emission. Unsuccessful with lead, he then utilized fluorine, in the form of calcium fluoride, which emitted an alpha particle, generated nitrogen, and subsequently decayed into oxygen through beta particle emission. In total, Fermi successfully induced radioactivity in 22 distinct elements. Fermi promptly published his discovery of neutron-induced radioactivity in the Italian journal La Ricerca Scientifica on March 25, 1934.

The inherent radioactivity of thorium and uranium complicated the analysis of neutron bombardment experiments involving these elements. However, after meticulously ruling out the presence of elements lighter than uranium but heavier than lead, Fermi deduced that novel elements, which he named ausenium and hesperium, had been synthesized. Chemist Ida Noddack proposed an alternative interpretation, suggesting that some experimental outcomes might have resulted in elements lighter than lead, rather than the formation of new, heavier elements. Her hypothesis was largely dismissed at the time, primarily because her research group had neither conducted experiments with uranium nor established a theoretical foundation for such a possibility. During that era, nuclear fission was considered theoretically improbable, if not entirely impossible. Although physicists anticipated the formation of elements with higher atomic numbers through neutron bombardment of lighter elements, the notion that neutrons possessed sufficient energy to cleave a heavier atom into two lighter fragments, as Noddack proposed, was not widely accepted.

The Via Panisperna group also observed several anomalous effects during their experiments. Notably, the experimental setup appeared to yield more favorable results when conducted on a wooden table compared to a marble surface. Recalling observations by Joliot-Curie and Chadwick regarding paraffin wax's efficacy in moderating neutrons, Fermi decided to incorporate it into his experiments. When neutrons traversed paraffin wax, they induced a hundredfold increase in radioactivity in silver compared to bombardments conducted without the paraffin. Fermi hypothesized that this phenomenon was attributable to the hydrogen atoms present in the paraffin. Analogously, the hydrogen content in wood accounted for the observed disparity between the wooden and marble tabletops. This hypothesis was further substantiated by replicating the effect using water. He concluded that collisions with hydrogen atoms effectively decelerated the neutrons. A neutron loses more energy per collision when interacting with nuclei of lower atomic numbers, consequently requiring fewer collisions to achieve a specific degree of deceleration. Fermi recognized that this deceleration led to increased radioactivity because slow neutrons exhibited a higher probability of capture compared to fast neutrons. To mathematically describe this process, he formulated a diffusion equation, subsequently termed the Fermi age equation.

In 1938, Fermi was awarded the Nobel Prize in Physics at the age of 37 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." Instead of returning to Italy after receiving the prize in Stockholm, Fermi and his family proceeded to New York City in December 1938, where they sought permanent residency. Their decision to relocate to America and become U.S. citizens was primarily motivated by Italy's prevailing racial laws.

Manhattan Project

Upon his arrival in New York City on January 2, 1939, Fermi received immediate offers from five universities, ultimately accepting a position at Columbia University, where he had previously delivered summer lectures in 1936. He was informed that in December 1938, German chemists Otto Hahn and Fritz Strassmann had identified barium following the neutron bombardment of uranium, a phenomenon subsequently interpreted by Lise Meitner and her nephew Otto Frisch as nuclear fission. Frisch experimentally corroborated this finding on January 13, 1939. The news of Meitner and Frisch's interpretation of Hahn and Strassmann's discovery was conveyed across the Atlantic by Niels Bohr, who was scheduled to lecture at Princeton University. Isidor Isaac Rabi and Willis Lamb, two Columbia University physicists working at Princeton, learned of the discovery and relayed it to Columbia. While Rabi claimed to have informed Fermi, Fermi later attributed the disclosure to Lamb:

I remember very vividly the first month, January, 1939, that I started working at the Pupin Laboratories because things began happening very fast. In that period, Niels Bohr was on a lecture engagement at the Princeton University and I remember one afternoon Willis Lamb came back very excited and said that Bohr had leaked out great news. The great news that had leaked out was the discovery of fission and at least the outline of its interpretation. Then, somewhat later that same month, there was a meeting in Washington where the possible importance of the newly discovered phenomenon of fission was first discussed in semi-jocular earnest as a possible source of nuclear power.

Noddack's earlier hypothesis was ultimately validated. Fermi had discounted the prospect of fission based on his computations, having overlooked the binding energy generated when a nuclide possessing an odd number of neutrons assimilated an additional neutron. For Fermi, this revelation resulted in significant professional embarrassment, as the transuranic elements for which he had partially received the Nobel Prize were not transuranic elements but rather fission products. He consequently appended a footnote addressing this correction to his Nobel Prize acceptance speech.

Scientists at Columbia resolved to investigate the energy release associated with the nuclear fission of uranium when bombarded by neutrons. On January 25, 1939, in the basement of Pupin Hall at Columbia, an experimental team including Fermi executed the inaugural nuclear fission experiment in the United States. Additional team members included Herbert L. Anderson, Eugene T. Booth, John R. Dunning, G. Norris Glasoe, and Francis G. Slack. The following day, the fifth Washington Conference on Theoretical Physics commenced in Washington, D.C., jointly sponsored by George Washington University and the Carnegie Institution of Washington. There, the findings regarding nuclear fission were disseminated more widely, thereby stimulating numerous subsequent experimental demonstrations.

French scientists Hans von Halban, Lew Kowarski, and Frédéric Joliot-Curie initially demonstrated that uranium, when bombarded by neutrons, emitted more neutrons than it absorbed, thereby indicating the potential for a chain reaction. Enrico Fermi and Herbert L. Anderson independently confirmed this finding a few weeks later. To facilitate larger-scale fission experiments, Leó Szilárd procured 200 kilograms (440 lb) of uranium oxide from the Canadian producer Eldorado Gold Mines Limited. Subsequently, Fermi and Szilárd collaborated on developing a device capable of achieving a self-sustaining nuclear reaction, which would later be known as a nuclear reactor. A significant challenge was the high neutron absorption rate by hydrogen in water, making a self-sustaining reaction unlikely with natural uranium and water as a neutron moderator. Fermi, drawing on his neutron research, proposed using uranium oxide blocks with graphite as a moderator instead of water, which would theoretically reduce neutron capture and enable a self-sustaining chain reaction. Szilárd then devised a practical design: a "pile" consisting of uranium oxide blocks interspersed with graphite bricks. Szilárd, Anderson, and Fermi co-authored a paper titled "Neutron Production in Uranium." However, their differing work habits and personalities often led to difficulties in their collaboration.

Enrico Fermi was one of the first scientists to alert military officials to the potential implications of nuclear energy, delivering a lecture on this topic at the Navy Department on March 18, 1939. Although the Navy's response did not fully meet his expectations, they did allocate $1,500 to support further research at Columbia University. Later that year, Leó Szilárd, Eugene Wigner, and Edward Teller drafted a letter, subsequently signed by Albert Einstein, which was sent to U.S. President Franklin D. Roosevelt. This letter cautioned that Nazi Germany might be developing an atomic bomb. In response, President Roosevelt established the Advisory Committee on Uranium to investigate these concerns.

The Advisory Committee on Uranium allocated funds enabling Fermi to acquire graphite, which he then used to construct a preliminary pile of graphite bricks on the seventh floor of the Pupin Hall laboratory. By August 1941, Fermi had amassed six tons of uranium oxide and thirty tons of graphite, materials he subsequently employed to build an even larger experimental pile in Schermerhorn Hall at Columbia University.

On December 18, 1941, the S-1 Section of the Office of Scientific Research and Development, formerly known as the Advisory Committee on Uranium, convened. With the United States' entry into World War II, the urgency of its mission intensified. While the committee's primary focus had been on producing enriched uranium, committee member Arthur Compton identified plutonium as a viable alternative, noting its potential for mass production in nuclear reactors by late 1944. Consequently, Compton decided to consolidate plutonium research efforts at the University of Chicago. Fermi, though initially hesitant, relocated, and his research team was integrated into the newly established Metallurgical Laboratory at that institution.

Given the unknown ramifications of a self-sustaining nuclear reaction, constructing the inaugural nuclear reactor on the University of Chicago campus, situated within a densely populated urban area, was deemed imprudent. Arthur Compton initially secured a site within the Argonne Woods Forest Preserve, approximately 20 miles (32 km) from Chicago, and contracted Stone & Webster for its development. However, an industrial dispute halted this work. Subsequently, Fermi convinced Compton that the reactor could be safely constructed in the squash court located beneath the stands of the University of Chicago's Stagg Field. Construction of the experimental pile commenced on November 6, 1942, culminating in Chicago Pile-1 achieving criticality on December 2. Although the pile was initially designed to be roughly spherical, Fermi's ongoing calculations indicated that criticality could be attained without completing the entire structure as originally planned.

This experiment represented a pivotal achievement in the pursuit of energy, exemplifying Fermi's characteristic meticulous approach, where every stage was precisely planned and all calculations were rigorously performed. Upon the successful initiation of the first self-sustained nuclear chain reaction, Compton communicated this breakthrough via a coded telephone call to James B. Conant, who served as the chairman of the National Defense Research Committee.

Conant was contacted by telephone at the President's office, Harvard University. The communication conveyed a coded message: "Jim, you will be interested to know that the Italian navigator has just landed in the new world." This was followed by a semi-apologetic clarification, as the S-1 Committee had been informed that the reactor's completion would require an additional week or more: "the earth was not as large as he had estimated, and he arrived at the new world sooner than he had expected."

Conant responded with excitement, inquiring, "Is that so?" He then asked, "Were the natives friendly?"

The reply confirmed, "Everyone landed safe and happy."

For the continuation of research without posing a public health hazard, the reactor was subsequently disassembled and relocated to the Argonne Woods site. At this new location, Fermi oversaw experiments concerning nuclear reactions, capitalizing on the extensive availability of free neutrons generated by the reactor. The laboratory's scope rapidly expanded beyond physics and engineering, incorporating the reactor for applications in biological and medical research. Initially operating under Fermi's direction as an integral component of the University of Chicago, Argonne was established as an independent entity with Fermi as its director in May 1944.

On 4 November 1943, when the air-cooled X-10 Graphite Reactor at Oak Ridge achieved criticality, Fermi was present to address any potential malfunctions. Technicians roused him prematurely to ensure his observation of the event. The operationalization of X-10 represented a significant advancement within the plutonium project. This facility yielded crucial data for reactor design, facilitated the training of DuPont personnel in reactor operation, and generated the initial small quantities of reactor-produced plutonium. Fermi acquired American citizenship in July 1944, at the earliest permissible date under existing legislation.

In September 1944, Fermi initiated the B Reactor at the Hanford Site by inserting the inaugural uranium fuel slug; this facility was specifically engineered for the large-scale production of plutonium. Similar to the X-10, this reactor was conceived by Fermi's team at the Metallurgical Laboratory and constructed by DuPont, though it featured a significantly larger scale and employed water-cooling. Within the subsequent days, 838 tubes were loaded, leading to the reactor's criticality. Shortly after midnight on 27 September, operators commenced the withdrawal of control rods to initiate plutonium production. Initially, operations proceeded without issue; however, approximately at 03:00, the power level began to decline, culminating in a complete reactor shutdown by 06:30. Both the Army and DuPont sought explanations from Fermi's team. Investigations were conducted on the cooling water to ascertain the presence of leaks or contamination. The following day, the reactor unexpectedly restarted, only to cease operation again within a few hours. The issue was ultimately attributed to neutron poisoning caused by xenon-135 (Xe-135), a fission product characterized by a half-life of 9.1 to 9.4 hours. Both Fermi and John Wheeler independently concluded that Xe-135 was responsible for neutron absorption within the reactor, consequently impeding the fission process. Emilio Segrè, a colleague, advised Fermi to consult Chien-Shiung Wu, who was then preparing a manuscript on this subject for publication in the Physical Review. Reviewing the draft, Fermi and his scientific colleagues corroborated their hypotheses: Xe-135 demonstrably absorbed neutrons, exhibiting an exceptionally large neutron cross-section. DuPont had diverged from the Metallurgical Laboratory's initial design, which specified 1,500 tubes arranged circularly, by incorporating an additional 504 tubes to occupy the corner sections. Initially, scientists had deemed this design modification an instance of over-engineering, representing an inefficient allocation of resources; however, Fermi recognized that loading all 2,004 tubes would enable the reactor to achieve the requisite power level and optimize plutonium production.

In April 1943, Fermi presented Robert Oppenheimer with a proposal concerning the potential use of radioactive byproducts from enrichment processes to contaminate the German food supply. This proposition arose from concerns regarding the perceived advanced state of the German atomic bomb project, coupled with Fermi's contemporary skepticism about the rapid development of an atomic bomb. Oppenheimer subsequently deliberated on this "promising" proposal with Edward Teller, who advocated for the application of strontium-90. James B. Conant and Leslie Groves received briefings on the matter; however, Oppenheimer stipulated that the plan would only proceed if the weapon could contaminate a sufficient quantity of food to cause the demise of half a million individuals.

By mid-1944, Oppenheimer successfully recruited Fermi to Project Y, located in Los Alamos, New Mexico. Upon his arrival in September, Fermi assumed the role of an associate director, overseeing nuclear and theoretical physics, and was subsequently appointed head of F Division, which bore his name. This division comprised four distinct branches: F-1 Super and General Theory, led by Teller, focused on the "Super" (thermonuclear) bomb; F-2 Water Boiler, under L. D. P. King, managed the "water boiler" aqueous homogeneous research reactor; F-3 Super Experimentation, directed by Egon Bretscher; and F-4 Fission Studies, headed by Anderson. On July 16, 1945, Fermi witnessed the Trinity test and devised an experimental method to estimate the bomb's yield by releasing paper strips into the blast wave. By measuring the distance these strips were propelled by the explosion, he calculated the yield to be ten kilotons of TNT, whereas the actual yield was approximately 18.6 kilotons.

Fermi, alongside Oppenheimer, Compton, and Ernest Lawrence, served on the scientific panel responsible for advising the Interim Committee regarding target selection. This panel concurred with the committee's recommendation that atomic bombs should be deployed without prior warning against industrial targets. Similar to his colleagues at the Los Alamos Laboratory, Fermi learned of the atomic bombings of Hiroshima and Nagasaki via the public address system within the technical area. Fermi held the conviction that atomic bombs would not effectively deter nations from initiating conflicts, nor did he consider the prevailing conditions suitable for the establishment of a world government. Consequently, he chose not to affiliate with the Association of Los Alamos Scientists.

Post-War Activities

On July 1, 1945, Fermi was appointed the Charles H. Swift Distinguished Professor of Physics at the University of Chicago, though he and his family did not leave the Los Alamos Laboratory until December 31, 1945. In 1945, he was inducted into the US National Academy of Sciences. The Metallurgical Laboratory was redesignated as Argonne National Laboratory on July 1, 1946, marking it as the inaugural national laboratory established under the Manhattan Project. The geographical proximity between Chicago and Argonne facilitated Fermi's engagement at both institutions. At Argonne, he pursued experimental physics, conducting research on neutron scattering in collaboration with Leona Marshall. Furthermore, he engaged in discussions on theoretical physics with Maria Mayer, contributing to her development of insights into spin–orbit coupling, which subsequently earned her the Nobel Prize.

On January 1, 1947, the Atomic Energy Commission (AEC) superseded the Manhattan Project. Fermi held a position on the AEC General Advisory Committee, a prominent scientific body presided over by Robert Oppenheimer. Additionally, he regularly dedicated several weeks annually to the Los Alamos National Laboratory, engaging in collaborations with Nicholas Metropolis and with John von Neumann on the phenomenon of Rayleigh–Taylor instability, which describes the dynamics at the interface of two fluids with differing densities.

Following the detonation of the initial Soviet fission bomb in August 1949, Fermi, in conjunction with Isidor Rabi, authored a robust report for the committee, articulating opposition to the development of a hydrogen bomb based on both ethical and technical considerations. Despite this, Fermi maintained his involvement in hydrogen bomb research at Los Alamos in a consulting capacity. Collaborating with Stanislaw Ulam, he determined that the requisite quantity of tritium for Teller's thermonuclear weapon model would be prohibitively large, and even with such a substantial amount, the propagation of a fusion reaction could not be guaranteed. In 1954, Fermi was one of several scientists who provided testimony in support of Oppenheimer during the Oppenheimer security hearing, which ultimately led to the revocation of Oppenheimer's security clearance.

During his later career, Fermi maintained his academic affiliation with the University of Chicago, where he co-founded the institution subsequently designated as the Enrico Fermi Institute. His doctoral students in the post-war era included Owen Chamberlain, Geoffrey Chew, Jerome Friedman, Marvin Goldberger, Tsung-Dao Lee, Arthur Rosenfeld, and Sam Treiman. Jack Steinberger was a graduate student, and Mildred Dresselhaus was significantly influenced by Fermi during their overlapping year as PhD students. Fermi conducted pivotal research in particle physics, particularly concerning pions and muons. He formulated the initial predictions of pion-nucleon resonance, employing statistical methodologies, as he posited that precise solutions were unnecessary when the underlying theory was inherently flawed. In a collaborative publication with Chen Ning Yang, he theorized that pions might constitute composite particles, an idea subsequently elaborated upon by Shoichi Sakata. This concept has since been superseded by the quark model, which posits that pions are composed of quarks, thereby completing Fermi's original model and validating his methodological approach.

Fermi authored a seminal paper, "On the Origin of Cosmic Radiation," positing that cosmic rays originated from material accelerated by interstellar magnetic fields, a hypothesis that generated a notable divergence of opinion with Teller. Fermi also investigated the complexities of magnetic fields within the spiral arms of galaxies. Furthermore, he contemplated what is now recognized as the "Fermi paradox": the apparent contradiction between the high probability of extraterrestrial life and the absence of observed contact.

Nearing the end of his life, Fermi expressed reservations regarding society's collective capacity to make judicious decisions concerning nuclear technology, stating:

Some of you may ask, what is the good of working so hard merely to collect a few facts which will bring no pleasure except to a few long-haired professors who love to collect such things and will be of no use to anybody because only few specialists at best will be able to understand them? In answer to such question[s] I may venture a fairly safe prediction.

The history of science and technology has consistently taught us that scientific advances in basic understanding have sooner or later led to technical and industrial applications that have revolutionized our way of life. It seems to me improbable that this effort to get at the structure of matter should be an exception to this rule. What is less certain, and what we all fervently hope, is that man will soon grow sufficiently adult to make good use of the powers that he acquires over nature.

Death

In October 1954, Fermi underwent an "exploratory" surgical procedure at Billings Memorial Hospital, after which he returned home. Fifty days later, he succumbed to inoperable stomach cancer at his Chicago residence, at the age of 53. Fermi had suspected that working in proximity to the nuclear pile entailed significant risks, yet he persisted, believing the potential benefits outweighed the dangers to his personal safety. Notably, two of his graduate student assistants who also worked near the pile subsequently died from cancer.

A memorial service was conducted at the University of Chicago chapel, where colleagues Samuel K. Allison, Emilio Segrè, and Herbert L. Anderson delivered eulogies mourning the loss of one of the world's most brilliant and productive physicists. His remains were interred at Oak Woods Cemetery, following a private graveside service for immediate family, officiated by a Lutheran chaplain.

Impact and Legacy

Legacy

Enrico Fermi garnered numerous accolades for his scientific contributions, including the Matteucci Medal (1926), the Nobel Prize in Physics (1938), the Hughes Medal (1942), the Franklin Medal (1947), and the Rumford Prize (1953). His pivotal role in the Manhattan Project was recognized with the Medal for Merit in 1946. Fermi's distinguished career also led to his election as a member of the American Philosophical Society in 1939 and a Foreign Member of the Royal Society (FRS) in 1950. A commemorative plaque honoring Fermi is located in the Basilica of Santa Croce, Florence, often referred to as the Temple of Italian Glories due to its numerous interments of notable Italian artists, scientists, and historical figures. In 1999, Time magazine included Fermi in its compilation of the twentieth century's top 100 influential individuals. Fermi was widely acknowledged as a rare twentieth-century physicist who demonstrated exceptional proficiency in both theoretical and experimental domains. Emilio Segrè, a radiochemist and nuclear physicist, characterized Fermi as "the last universal physicist in the tradition of great men of the 19th century," asserting that he "was the last person who knew all of physics of his day." Similarly, chemist and novelist C. P. Snow remarked, "if Fermi had been born a few years earlier, one could well imagine him discovering Rutherford's atomic nucleus, and then developing Bohr's theory of the hydrogen atom. If this sounds like hyperbole, anything about Fermi is likely to sound like hyperbole."

Fermi was renowned as an inspirational educator, distinguished by his meticulous attention to detail, clarity, and thorough preparation of his lectures. These lecture notes were subsequently compiled into published books. His extensive collection of papers and notebooks is currently preserved at the University of Chicago. Victor Weisskopf observed that Fermi "always managed to find the simplest and most direct approach, with the minimum of complication and sophistication." Despite possessing considerable mathematical prowess, Fermi consistently favored straightforward solutions, eschewing complex theoretical frameworks when simpler alternatives were available. He was celebrated for his ability to rapidly and accurately resolve problems that perplexed others. This distinctive approach to deriving approximate and swift solutions through "back-of-the-envelope" calculations became informally recognized as the "Fermi method," a technique now widely integrated into educational curricula.

Fermi frequently highlighted the historical context that Alessandro Volta, during his laboratory work, could not have foreseen the profound future implications of electricity research. Fermi's legacy is predominantly associated with his foundational contributions to nuclear power and nuclear weaponry, notably the conceptualization and construction of the inaugural nuclear reactor, alongside his involvement in the development of the first atomic and hydrogen bombs. His extensive scientific oeuvre has demonstrated remarkable longevity and influence. Key elements of this enduring work encompass his theory of beta decay, investigations into non-linear systems, the discovery of slow neutron effects, studies of pion-nucleon collisions, and the formulation of Fermi–Dirac statistics. Furthermore, his prescient hypothesis regarding the non-fundamental nature of the pion significantly advanced the subsequent exploration of quarks and leptons.

In his personal demeanor, Fermi embodied simplicity. He exhibited remarkable vigor and a keen enthusiasm for games and sports, where his competitive nature frequently emerged. For instance, he engaged in tennis with considerable intensity and assumed a guiding role during mountain climbs. He could be characterized as a benevolent dictator; an anecdote recalls Fermi, at a mountain summit, declaring, "Well, it is two minutes to two, let's all leave at two o'clock," to which everyone promptly and obediently complied. This inherent leadership and self-assurance earned Fermi the moniker "The Pope," signifying the perceived infallibility of his pronouncements in physics. He once articulated his pragmatic approach, stating, "I can calculate anything in physics within a factor 2 on a few sheets; to get the numerical factor in front of the formula right may well take a physicist a year to calculate, but I am not interested in that." While his leadership was compelling, it occasionally posed a challenge to the autonomy of his collaborators. A memorable incident at his residence involved Fermi intervening when his wife was cutting bread, asserting a different philosophy on the task, taking the knife, and proceeding with the cutting, convinced of his method's superiority. Yet, these actions were not perceived as offensive; rather, they contributed to his charming persona, endearing him to others. His interests outside of physics were notably limited; upon hearing music played on Teller's piano, he admitted his musical appreciation extended only to simple melodies.

Nomenclature Honoring Fermi

Numerous entities have been named in honor of Fermi. These include the Fermilab particle accelerator and physics laboratory in Batavia, Illinois, which received its designation in his honor in 1974. Additionally, the Fermi Gamma-ray Space Telescope, named in 2008, acknowledges his significant contributions to cosmic ray research. Furthermore, three nuclear reactor facilities bear his name: the Fermi 1 and Fermi 2 nuclear power plants located in Newport, Michigan; the Enrico Fermi Nuclear Power Plant situated in Trino Vercellese, Italy; and the RA-1 Enrico Fermi research reactor in Argentina. The synthetic element Fermium, identified from the remnants of the 1952 Ivy Mike nuclear test, was named to commemorate Fermi's profound impact on the scientific community. Consequently, he is among 16 scientists recognized by having a chemical element named in their honor.

Since 1956, the United States Atomic Energy Commission, and subsequently the U.S. Department of Energy from 1977 onward, has bestowed its most prestigious accolade, the Fermi Award, in his memory. Notable recipients of this award include Otto Hahn, Robert Oppenheimer, Edward Teller, and Hans Bethe.

Publications

• Introduction to Atomic Physics (Italian edition). Bologna: N. Zanichelli. 1928. OCLC 9653646.Physics for High Schools (Italian edition). Bologna: N. Zanichelli. 1929. OCLC 9653646.Molecules and Crystals (Italian edition). Bologna: N. Zanichelli. 1934. OCLC 19918218.Thermodynamics. New York: Prentice Hall. 1937. OCLC 2379038.Physics for Technical Institutes (Italian edition). Bologna: N. Zanichelli. 1938.Physics for Scientific High Schools (Italian edition). Bologna: N. Zanichelli. 1938.Elementary particles. New Haven: Yale University Press. 1951. OCLC 362513.Notes on Quantum Mechanics. Chicago: The University of Chicago Press. 1961. OCLC 1448078.Patents
  • US Patent 2206634, "Process for the Production of Radioactive Substances", issued July 1940
  • US Patent 2836554, "Air Cooled Neutronic Reactor", issued April 1950
  • US Patent 2524379, "Neutron Velocity Selector", issued October 1950
  • US Patent 2852461, "Neutronic Reactor", issued September 1953
  • US Patent 2708656, "Neutronic Reactor", issued May 1955
  • US Patent 2768134, "Testing Material in a Neutronic Reactor", issued October 1956
  • US Patent 2780595, "Test Exponential Pile", issued February 1957
  • US Patent 2798847, "Method of Operating a Neutronic Reactor", issued July 1957
  • US Patent 2807581, "Neutronic Reactor", issued September 1957
  • US Patent 2807727, "Neutronic Reactor Shield", issued September 1957
  • US Patent 2813070, "Method of Sustaining a Neutronic Chain Reacting System", issued November 1957
  • US Patent 2837477, "Chain Reacting System", issued June 1958
  • US Patent 2931762, "Neutronic Reactor", issued April 1960
  • US Patent 2969307, "Method of Testing Thermal Neutron Fissionable Material for Purity", issued January 1961

  References

  Sources

  Bernstein, Barton J. "Four Physicists and the Bomb: The Early Years, 1945-1950." Historical Studies in the Physical and Biological Sciences (1988) 18#2; this article examines the roles of Oppenheimer, Fermi, Lawrence, and Compton.

  • Bernstein, Barton J. "Four Physicists and the Bomb: The Early Years, 1945-1950" Historical Studies in the Physical and Biological Sciences (1988) 18#2; covers Oppenheimer, Fermi, Lawrence and Compton. online
  • Galison, Peter, and Barton Bernstein. "In any light: Scientists and the decision to build the Superbomb, 1952–1954." Historical Studies in the Physical and Biological Sciences 19.2 (1989): 267–347.

  "To Fermi – with Love – Part 1." Voices of the Manhattan Project 1971 Radio Segment.

  • "To Fermi – with Love – Part 1". Voices of the Manhattan Project 1971 Radio Segment
  • "The First Reactor: 40th Anniversary Commemorative Edition." United States Department of Energy, December 1982.
  • "The Story of the First Pile."
  • The Story of the First Pile
  • Enrico Fermi's Case File at The Franklin Institute, detailing his contributions to theoretical and experimental physics.
  • "Remembering Enrico Fermi." Session J1. APS April Meeting 2010, American Physical Society.
  • Rhodes, Richard. "Time 100: Enrico Fermi." *Time*, 29 March 1999.
  • Enrico Fermi's period of residence with Paul Ehrenfest in Leiden.