Neutrons Fermi, Enrico

Fermi, Enrico. (1901-1954). An Italian physicist who later became a U.S. citizen. He developed a statistical approach to fundamental problems of physical chemistry based on Pauli s exclusion principle. He discovered induced or artificial radioactivity resulting from neutron impingement, as well as slow or thermal neutrons. He was professor of physics at Columbia (1939) and awarded the Nobel Prize in physics in 1938. He was the first to achieve a controlled nuclear chain reaction, directed the construction of the first nuclear reactor at the University of Chicago (1942), and worked on the atomic bomb at Los Alamos. He also carried on fundamental research on subatomic particles using sophisticated statistical techniques. Element 100 (fermium) is named after him. 

When getting the first graphite-uranium pile close to critical conditions in Chicago in December 1942, the scientists were prepared to take necessary countermeasures and return the pile to a safe condition. They even had redundant and independently diverse possibilities to do this (control rods and liquid neutron poison). Enrico Fermi, the scientist responsible also took the human factor seriously. He asked his crew to go for a lunch break just before the experiment was entering the most interesting phase. 

In the mid-1930s Enrico Fermi (1901-1954), an Italian physicist, tried to synthesize a new element by bombarding uranium—the heaviest known element at that time— with neutrons. Fermi hypothesized that if a neutron were incorporated into the nucleus of a uranium atom, the nucleus might undergo beta decay, converting a neutron into a proton. If that happened, a new element, with atomic number 93, would be synthesized for the first time. The nuclear equation for the process is ... 

In 1934, the element with the most known protons was uranium, with 92. But that year, itaiian physicist Enrico Fermi thought he had synthesized eiements with higher atomic numbers. After bombarding a sampie of uranium with neutrons, Fermi and his co-workers recorded measurements that seemed to indicate that some uranium nuciei had absorbed neutrons and then undergone beta decay ... 

Experiments were conducted during the Metallurgical Project, centered at the University of Chicago, and led by Enrico Fermi. Subcritical assembhes of uranium and graphite were built to learn about neutron multiphcation. In these exponential piles the neutron number density decreased exponentially from a neutron source along the length of a column of materials. There was excellent agreement between theory and experiment. 

Tn their years together Hahn and Meitner did significant research on beta- and gamma-ray spectra. They discovered the new element protoactinium-91 and, at Meitner s suggestion, took up, and made great progress with, work on neutron bombardment of nuclei that Enrico Fermi had commenced in Rome. In 1938, this research was suspended when Adolph Hitler annexed Austria and Meitner had to flee Germany. 

Pauli called his hypothetical particle the neutron. Naturally it bore no relationship to the neutron of which Rutherford spoke, which Chadwick was soon to discover. But the confusion that might have resulted was avoided when Enrico Fermi suggested adding the Italian diminutive suffix -ino to the name. Pauli s particle was thus christened the neutrino ( little neutral one ). 

The element was discovered in the pitchblende ores by the German chemist M.S. Klaproth in 1789. He named this new element uranium after the planet Uranus which had just been discovered eight years earlier in 1781. The metal was isolated first in 1841 by Pehgot by reducing the anhydrous chloride with potassium. Its radioactivity was discovered by Henry Becquerel in 1896. Then in the 1930 s and 40 s there were several revolutionary discoveries of nuclear properties of uranium. In 1934, Enrico Fermi and co-workers observed the beta radioactivity of uranium, following neutron bombardment and in 1939, Lise Meitner, Otto Hahn, and Fritz Strassmann discovered fission of uranium nucleus when bombarded with thermal neutrons to produce radioactive iso-... 

Enrico Fermi on his voyage to the new world postulated that a third particle was needed to balance the emission of the electron in 3 decay. However, the existing conservation laws also had to be satisfied, so there were a number of constraints on the properties of this new particle. Focusing on the decay of a neutron as a specific example, the reaction is already balanced with respect to electric charge, so any additional particle must be neutral. The electrons were observed with energies up to the maximum allowed by the decay Q value so the mass of the particle must be smaller that the instrumental uncertainties. Initially, this instrumental... 

The first scientific attempts to prepare the elements beyond uranium were performed by Enrico Fermi, Emilio Segre, and co-workers in Rome in 1934, shortly after the existence of the neutron was discovered. This group of investigators irradiated uranium with slow neutrons and found several radioactive products, which were thought to be due to new elements. However, detailed chemical studies by Otto Hahn and Fritz Strassman in Berlin showed these species were isotopes of the known elements created by the fission of uranium into two approximately equal parts (see Chap. 11). This discovery of nuclear fission in December of 1938 was thus a by-product of man s quest for the transuranium elements. 

The fact that uranium is capable of undergoing a process known as fission was discovered as an indirect result of the use of neutrons as projectiles in the production of artificial radioactive isotopes. At the University of Rome, the Italian physicist Enrico Fermi bombarded many different elements with neutrons and thereby produced many new radioactive isotopes. The use of neutrons as projectiles has the distinct advantage that the collision of these uncharged particles with... 

The discovery of fission was a complete surprise and also a great shock, because it shattered fundamental ideas of nuclear behavior that had guided the investigation. The surprise was evident in the events of December 1938. On December 10, Enrico Fermi was awarded the Nobel Prize in physics. He and his group in Rome had been the first to irradiate uranium with neutrons and to propose that transuranium elements had been formed in the process. In his Nobel lecture, Fermi was so confident of the first two, elements 93 and 94, that he referred to them by name ausonium and hesperium. But at that very moment, the Berlin team of Otto Hahn, Lise Meitner, and Fritz Strafimann was on the verge of identifying barium among the uranium products. By the end of the year, they understood that uranium had split, explained the fission process, and concluded that the transuranium elements were false. When Fermi published his Nobel lecture, he added a footnote to that effect, but by then ausonium and hesperium were themselves footnotes (if that) in the history of science. [1]... 

American physicist Enrico Fermi, recipient of 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. ... 

Late in 1938, in Berlin-Dahlem, an experimenter in nuclear chemistry touched off a wave of excitement throughout the world which even reached the front pages of the most conservative newspapers. At the Kaiser Wilhelm Institute for Chemistry, only a few miles from Hitler s Chancellery, three researchers had proceeded to repeat some experiments first performed by Enrico Fermi in Rome in 1934. The Italian scientist, in an attempt to produce the Curies artificial radioactivity in the very heavy elements by bombarding them with neutrons, believed he had created an element (No. 93) even heavier than uranium. 

Fermium s namesake Enrico Fermi taught physics and did research at the University of Rome from 1926 to 1938. During this period, he learned how to use neutrons to change elements from one form (isotope) to another. He received the Nobel Prize in physics in 1938 for these discoveries. 

Lying just below barium in the periodic table, radiums chemistry is essentially identical to bariums chemistry. In fact, there is a famous story in which confusion between the two elements played an important role. In the 1930s, Italian physicist Enrico Fermi (1901-54) and his coworkers were investigating the action of neutrons on samples of uranium. (The neutron had only been discovered in 1930. Its use in physics was still relatively new.) Their expectation was that the absorption of neutrons by uranium would lead to the production of transuranium elements (elements lying beyond uranium in the periodic table), as shown by the following equation ... 

Enrico Fermi receives the Nobel Prize in physics for the discovery of nuclear reactions brought about by slow neutrons. ... 

In Germany in 1938, Otto Hahn and Fritz Strassmann, skeptical of claims by Enrico Fermi and Irene Johot-Curie that bombardment of uranium by neutrons produced new so-called transuranic elements (elements beyond uranium), repeated these experiments and chemically isolated a radioactive isotope of barium. Unable to interpret these findings, Hahn asked Lise Meitner, a physicist and former colleague, to propose an explanation for his observations. Meitner and her nephew, Otto Frisch, showed that it was possible for the uranium nucleus to be spfit into two smaller nuclei by the neutrons, a process that they termed fission. The discovery of nuclear fission eventually led to the development of nuclear weapons and, after World War II, the advent of nuclear power to generate electricity. Nuclear chemists were involved in the chemical purification of plutonium obtained from uranium targets that had been irradiated in reactors. They also developed chemical separation techniques to isolate radioactive isotopes for industrial and medical uses from the fission products wastes associated with plutonium production for weapons. Today, many of these same chemical separation techniques are being used by nuclear chemists to clean up radioactive wastes resulting from the fifty-year production of nuclear weapons and to treat wastes derived from the production of nuclear power. 

At the start of the twenty-first century, scientists beheve that all matter is made up of tiny particles called fermions (named after American physicist Enrico Fermi). Fermions include quarks and leptons. Leptons include electrons (along with muons and neutrinos) they have no measurable size, and they are not affected by the strong nuclear force. Quarks, on the other hand, are influenced by the strong nuclear force. They are the fundamental particles that make up protons and neutrons (as well as mesons and some other particles). Both protons and neutrons are classified as baryons, composite particles each made up of three quarks. 

---