Biography of Niels Bohr | Danish physicist.


(Niels Henrik David Bohr;) Copenhagen, 1885-1962) Danish physicist. Considered one of the most dazzling figures of Contemporary Physics and theoretical contributions and their practical work, as one of the fathers of the atomic bomb, he was awarded in 1922 with the Nobel Prize in Physics "for his research about the structure of atoms and radiation that emanates from them".

Niels Bohr
Although principles of classical physics, the Atomic model, which incorporated the model of atom Planetary Rutherford and the notion of how much action introduced by Planck, allowed to explain both the stability of the atom and its properties of emission and absorption of radiation. In this theory, the electron can occupy some stationary orbits in which does not radiate energy and emission and absorption processes are conceived as a stationary orbit electron transitions to another.
Niels Bohr studied higher studies in physics at the University of Copenhagen, where he obtained the degree of doctor in 1911. After being revealed as a firm promise in the field of nuclear physics, he joined England to expand their knowledge in the prestigious Cavendish Laboratory of Cambridge University, under the tutelage of sir Joseph John Thomson (1856-1940), British chemist awarded Nobel Prize in 1906 for his studies about the passage of electricity through gases inside that had allowed him to discover the electron particle previously sensed and baptized by George Johnstone Stoney (1826-1911).
Precisely to the study of electrons was dedicated the doctoral thesis which he had just read the young Bohr in Copenhagen, and that led to British territory in hopes of seeing it translated into English. But, whatever that Thomson will play not enthused by the work of the Danish scientist, Bohr decided to abandon the Cavendish Laboratory and moving on to the University of Manchester, where took the teachings of another Nobel Laureate Ernest Rutherford (1871-1937), to expand their knowledge about the radioactivity and the models of the atom.
From then on, close collaboration, supported by strong bonds of friendship was established between both scientists, should be as durable as fruitful. Rutherford had developed a theory of the atom that was entirely valid at a speculative level, but that could not be sustained within the laws of classical physics. Bohr, in a display of courage that was unpredictable as shy and withdrawn, he dared to ignore the problems that hindered the progress of Rutherford with a solution as simple as risky: said, simply, that the movements that were inside the Atom are ruled by non-traditional physical laws.
In 1913, Niels Bohr reached celebrity world within the field of physics by publishing a series of tests that revealed his particular model of the structure of the atom. Three years later, the Danish scientist returned to his hometown to occupy a place of Professor of theoretical physics at his old alma mater; and in 1920, thanks to the international prestige that he gained by his studies and publications, got the necessary subsidies to the Foundation of the so-called Nordic Institute for theoretical physics (later known as Niels Bohr Institute), whose leadership took from 1921 until the date of his death (1962).

Niels Bohr (1922) laboratory
In a very short time this Institute was erected, together with German universities of Munich and Göttingen, in one of the three vertices of the European triangle where developing major research on the physics of the atom. In 1922, the year in which Bohr was definitely as a scientist of universal popularity with the obtaining of the Nobel Prize, devoted his son came into the world Aage Niels Bohr, who would follow his father's footsteps and work with him in several investigations. Also Ph.d. in physics, he was, like his father, College Professor of this subject and director of the Nordic Institute for theoretical physics, and would receive the Nobel Prize in 1975.
Immersed in their research on the atom and quantum mechanics, Niels Bohr formulated in 1923, the principle of correspondence, which spiked in 1928 with the principle of complementarity. As a result of this latest contribution was forming around her figure the so-called Copenhagen school in quantum mechanics, whose theories were fought fiercely (and certainly in vain) by Albert Einstein (1879-1955). Despite these differences, always held on a plane theoretical (as Einstein could only counter the proposals of Bohr mental Musings), the father of the theory of relativity recognized in the Danish physicist "one of the greatest scientists of our time".
In the Decade of the 1930s, Niels Bohr spent long seasons in the United States of America, where he led the first news about nuclear fission, discovered in 1938 by Otto Hahn (1879-1968) and Fritz Strassmann (1902-1980), that would lead to nuclear weapons of mass destruction works in Berlin. For five months he worked with J. A. Wheeler at the Institute for advanced study in Princeton (New Jersey), and announced, along with his collaborator, that plutonium was to be fissionable, just as it was uranium.
Returning to Denmark, he was elected President of the Royal Danish Academy of Sciences (1939). He returned to settle in Copenhagen, where continued researching and teaching until in 1943, following the German occupation, he had to leave his native country because of his Jewish origins. His life and that of his became so endangered it was forced to set out his family in a small fishing boat and to head to Sweden. A few days later, Bohr took refuge in the United States and, under the pseudonym of Nicholas Baker, began to collaborate actively in the so-called Manhattan project, developed in a laboratory in Los Alamos (New Mexico), which resulted in the production of the first atomic bomb.

Niels Bohr in an image taken in 1950
At the end of the second World War (1939-1945), he returned to Denmark, and again at the head of the Nordic Institute for theoretical physics. Since then, conscious of the devastating applications that could have their research, he devoted himself to convince his colleagues of the need to use the findings of the nuclear physics with useful and beneficial purposes.
Pioneer in the Organization of symposia and international conferences on peaceful nuclear energy use, published in 1951 and reported a manifesto signed by more than one hundred eminent scientists, in which it was stated that public authorities should ensure the use of phaseout for purposes all over the world peaceful. Therefore, in 1957, received the atoms for peace award, convened by the Ford Foundation to encourage scientific research on the progress of mankind.
Director, since 1953, the European Organization for Nuclear Research, Niels Henrik David Bohr died in Copenhagen during the autumn of 1962, at the age of seventy-seven, after having left printed some so valuable works such as spectra and Atomic Constitution theory (1922), light and life (1933), atomic theory and description of the nature (1934) The mechanism of nuclear fission (1939) and Atomic Physics and human knowledge (1958).
The Atomic model of Bohr
The first relevant contributions of Bohr to contemporary physics took place in 1913, when, to tackle the problems that had met his teacher and friend Rutherford, said that internal movements taking place in the Atom are governed by particular laws, beyond the traditional physics. In line with this statement, Bohr also noted that electrons, when they are in certain stationary States, cease to radiate energy.
In fact, Rutherford had glimpsed a hydrogen atom consisting of a proton (i.e. a central positive charge) and a negative particle that would revolve around the proton in a similar way to the movement described by the planets in their orbits around the Sun. But this theory was in contravention of the laws of traditional physics, since, according to the known up to then, a moving electric charge had to radiate energy, and, therefore, the atom could not be stable.
Niels Bohr accepted, in part, Rutherford atomic theory, but surpassed it by combining it with quantum theories of Max Planck (1858-1947). In three articles published in the Philosophical Magazine in 1913, Bohr formulated four postulates: 1) an atom has a number of stationary orbits, in which electrons don't radiate or absorb energy, but they are moving. (2) the electron revolves around its core so that centrifugal force serves to balance accurately the electrostatic attraction of the opposite charges. (3) the angular momentum of the electron in a steady state is a multiple of h / 2 p (where h is Planck's quantum universal constant).
According to the postulated fourth, when an electron passes a steady state of more power to less (and, therefore, closer to the nucleus), the variation of energy is emitted in the form of a quantum electromagnetic radiation (i.e., a photon). And, conversely, an electron only interacts with a photon whose energy allows you to move from a stationary State to another of higher energy.

Werner Heisenberg and Niels Bohr in
the Copenhagen Conference (1934)
Put another way, the radiation or absorption of energy only has place when an electron passes from a higher (or lower) energy orbit to another (more or less), which is located near (or far) with respect to the core. The frequency f of the emitted or absorbed radiation is determined by the relationship: E1 - E2 = hf, where E1 and E2 are the energies corresponding to the transit of the electron orbits. Merced to the latter and more complex postulated, Bohr could explain why, for example, hydrogen atoms give distinct wavelengths of light, appearing in the spectrum of hydrogen as a fixed distribution of light known as the Balmer series lines.
Initially proposed by Bohr Atomic model baffled most of the scientists around the world. His way of explaining the structure of an atom was to ignore (at least in some small parts of the Atom) a principle accepted physics. Bohr's atomic theory seemed almost a scam: invent a model simply by the fact of that could work well. But following that his colleague and teacher Rutherford warmly thank you for these postulates, numerous researchers from Central and Northern Europe began to be interested by the ideas of the Danish physicist, and some of them, like the Germans James Franck (1882-1964) and Gustav Hertz (1887-1975), provided new data confirming the validity of the Bohr model.
Bohr's atomic theory was applied, in effect, to the study of the hydrogen atom, although then you could generalize to other surface elements, thanks to the breadth and development that provided him with the work of Arnold Sommerfeld (1868-1951), which improved the structure model of the Danish to explain fine spectrum. That is why the principles released by Niels Bohr in 1913 may be considered as the basis on which contemporary nuclear physics is based.
The principle of correspondence
With the formulation of these postulates, Niels Bohr was able to, in effect, give a quantitative explanation for the spectrum of hydrogen; and, fundamentally, he managed to establish the principles of the quantum theory of the atom in the most clear and concise manner. But, above all, his great success was noted that these principles were irrational from the point of view of classical mechanics, and warn that they needed a new limitation on the use of the ordinary concepts of causality.
To fix the circumstances in that they had to agree the new theories of quantum mechanics and classical mechanics, Bohr in 1923 established the principle of correspondence, under which quantum mechanics must be run towards the theory of traditional physics dealing with macroscopic phenomena (or, said otherwise, whenever the values of the quantum constants become negligible).
Using this principle, Niels Bohr and his collaborators, among which was the young Werner Karl Heisenberg (1901-1976), another future Premio Nobel de Física, plotted an approximate picture of the structure of atoms that have many electrons; and they got other achievements such as explain the nature of x-rays, the phenomena of the absorption and emission of light by atoms and the periodic variation in the chemical behavior of the elements.
The principle of complementarity
In 1925, his assistant Heisenberg formulated the principle of indetermination or uncertainty, according to which it was utopian idea in order to achieve, in the field of cloud microphysics, a full knowledge of the reality of nature itself, or any of the things that make it up, since the instruments used in experimentation are natural objects subjected to the laws of traditional physics.
This luminous principle of Werner Heisenberg Bohr turn suggested a new rule: the so-called principle of complementarity in quantum mechanics (1928). Based on the duality wave-particle recently enunciated by the young Louis de Broglie (1892-1987), i.e., from the observation that light and electrons Act sometimes as waves and others as particles, Bohr said that, in both cases, or the properties of light and the electrons can be observed at the same time, even though they are mutually complementary and necessary for a correct interpretation.
In other words, the principle of complementarity expresses that a rigid separation of Atomic objects and instruments that measure their behavior there is. Both are, in the opinion of Bohr, complementary: elements of different categories, including phenomena belonging to a same atomic system, but only recognizable in experimental situations which are physically incompatible.
Following this reasoning, Niels Bohr also were considered to be complementary certain descriptions, usually causal and spatio-temporal, as well as to certain physical as accurate position and time properties. In his valuable essay entitled light and life (1933), the Danish scientist, giving a good example of his unique sense of philosophical speculation, analyzed the implications of human of the principle of complementarity.
Nuclear fission
In the Decade of the 1930s, the growing interest of all Western scientists for the study of the interior of the nucleus of the atom (with abundant experimentation in this regard) led Bohr to the detailed study of the difficulties when trying to interpret the new knowledge acquired so suddenly by atomic physics. It was as well as conceived his own model of nucleus, which compared with a liquid drop, and proposed the theory of the phenomena of nuclear decay.
This was laying the groundwork for nuclear fission, which would end up giving rise to the most powerful instrument of extermination conceived until then by the human being: the atom bomb. Bohr did not, however, first to the discovery of fission nuclear, achieved for the first time, as already stated above, by Otto Hahn and Fritz Strassmann in Berlin in 1938.
On January 15, 1939 he led the first news of this scientific achievement to the United States of America, where it showed that the uranium-235 isotope is responsible for most of the fissions. At the Institute for advanced study in Princeton (New Jersey), a fruitful period of collaboration with J. A. Wheeler, he outlined a new theory of the mechanism of fission, according to which the element 94 would have identical behavior to the one observed in the U-235 in the process of nuclear fission. The element 94 would be awarded a year later by Glenn Theodore Seaborg (1912-1999), and received the name neptunium and plutonium is then of the uranium in the periodic table.
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