Edit this paragraph Compton Effect Introduction to Compton Effect
The study of Compton scattering phenomenon took a decade or two to get the correct results. Compton effect is the first experimental proof of Einstein's hypothesis that photons have momentum. This occupies an important position in the history of physics development. When photons interact with particles in a medium, they can make light propagate in any direction. This phenomenon is called light scattering and Compton effect.
1922, when American physicist Compton studied the scattering of X-rays by electrons in graphite, he found that the wavelengths of some scattered waves were slightly larger than those of incident waves. He thinks this is because when a photon collides with an electron, some energy of the photon is transferred to the electron. Compton assumes that photons, like real particles such as electrons and protons, have not only energy but also momentum. During the collision, energy and momentum are conserved. Short-wave electromagnetic radiation is scattered after entering matter. Among the scattered waves, there are waves with increased wavelength in addition to the original waves. The larger the atomic number of the scatterer, the smaller the ratio of the intensity of the added wavelength to the intensity of the original wavelength. According to this idea, the equation is listed and the wavelength difference before and after scattering is obtained. The results are completely consistent with the experimental data, thus confirming his hypothesis. This phenomenon is called Compton effect.
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Compton studied the composition of light after X-rays were scattered by lighter substances (graphite, paraffin, etc.). ) at 1922 ~ 1923, it is found that there are components with the same wavelength and longer wavelength in the scattered spectrum. This scattering phenomenon is called Compton scattering or Compton effect. Compton projected 0.7 1 angstrom of X-rays onto graphite, and then measured the X-ray intensity scattered by graphite molecules at different angles. When θ = 0, there is only single-frequency light equal to the incident frequency. When θ ≠ 0 (such as 45, 90,135), it is found that the scattered light has two frequencies. One has the same frequency as the incident light, and the other has a lower frequency than the incident light. The deviation of the latter increases with the increase of angle. The discovery process of Compton effect is in May of Physical Review, 1923. A.H. Compton published the effect he found on the topic of quantum theory of light element X-ray scattering, and explained it with light quantum hypothesis. He wrote (A.H. Compton, Phys.Rev, 21(1923) p.): "From the point of view of quantum theory, it can be assumed that any special X-ray quantum is not scattered by all the electrons in the radiator, but is consumed by a special electron, and this special electron is directed to a certain electron. The curvature of the radiation quantum path leads to the change of momentum. As a result, the scattered electrons recoil and the momentum is equal to the change of X-ray momentum. The energy of scattered rays is equal to the energy of incident rays minus the kinetic energy of recoil of scattered electrons. Since the scattered light should be a complete quantum, its frequency will also decrease proportionally with the energy. Therefore, according to quantum theory, we can predict that the wavelength of scattered radiation is greater than that of incident radiation, and "the intensity of scattered radiation is greater in the forward direction than in the reverse direction of the original X-ray, which is measured by experiments. "Compton explained the direction and intensity distribution of radiation with charts (see right). According to the conservation of energy and momentum, and considering the relativistic effect, the scattering wavelength is: Δ λ = λ-λ0 = (2h/mc) sin2 (θ/2) △λis the difference between the incident wavelength λ 0 and the scattering wavelength λ θ, h is Planck constant, c is the speed of light, m is the rest mass of electrons, θ. This simple reasoning has long been common sense for modern physicists, but Compton is hard to do. It took more than ten or twenty years to study this phenomenon, and Compton got the correct result at 1923. Compton himself took a detour for five years. This history shows the uneven course of the emergence and development of modern physics from one side. As can be seen from the above formula, the change of wavelength depends on θ and has nothing to do with λ0, that is, the absolute value of wavelength change is certain for a certain angle. The smaller the wavelength of incident light, the greater the relative value of wavelength change. Therefore, Compton effect is more significant for γ rays than for X rays. This has been the case in history. As early as 1904, British physicist A.S.Eve first discovered the signs of Compton effect when studying the absorption and scattering characteristics of gamma rays. Radium tubes emit gamma rays, which are scattered by scatterers and then thrown into electrometer. Insert an absorber in the path of incident light or scattered light to test its penetration. Yves found that scattered light is usually "softer" than incident light. (A.S.Eve, Phil. Mag.8 (1904) p.669.) Later, the scattering of gamma rays was studied by many people, and the British D.C.H.Florance got a clear conclusion in 19 10, Compton effect.
It is proved that the scattered secondary rays depend on the scattering angle and have nothing to do with the material of the scatterer. The larger the scattering angle, the greater the absorption coefficient. The so-called light softening is actually that the wavelength of light has become longer. At that time, the essence of γ -ray was not yet determined, and it could only be expressed according to experimental phenomena. 19 13, J.A.Gray of McGill University redone the gamma ray experiment, which confirmed rowlands's conclusion and further measured the radiation intensity accurately. He found: "The properties of monochromatic gamma rays will change after being scattered. The larger the scattering angle, the softer the scattered light. " (J.A. Gray, Phil.Mag., 26 (1913) p.611. The experimental facts are clearly in front of physicists, but there is no correct explanation. Compton also received γ scattering at 19 19. He measured the wavelength of γ -ray with accurate method and determined the fact that the wavelength became longer after scattering. Later, he changed from gamma-ray scattering to x-ray scattering. After the Kα line of molybdenum was scattered by graphite crystal, the scattering intensities in different directions were measured in a free chamber. From some curves published by Compton, it can be seen that the X-ray scattering curve obviously has two peaks, one is equal to the wavelength of the original ray (unchanged line) and the other is longer (changed line). The deviation between the variable line and the constant line changes with the change of scattering angle, and the larger the scattering angle, the greater the deviation. Wu, a Compton student, went to study in the United States from China, which made great contributions to the further study and verification of Compton effect. In addition to many convincing experiments on Duane's denial, he also confirmed the universality of Compton effect. He tested the X-ray scattering curves of various elements, and the results were all in line with Compton's quantum scattering formula. Compton and Wu published a paper on 1924 entitled "Wavelength of light elements scattering molybdenum Kα line". (A.H. Compton and Y.H. Wu, Proc .Nat.Acad.Sei,10 (1924) p.27.) They wrote: "The important point of this picture is that the spectra obtained from various materials are almost the same in nature. In each case, the invariant line P appears at the same place as the fluorescence MoKa line (Kα spectral line of molybdenum), and the peak of the change line appears at the position M predicted by the above quantum formula of wavelength change, which is within the allowable experimental error range. " Wu's most outstanding contribution to Compton effect lies in measuring the curve of the intensity ratio R of variable line and constant line with the atomic number of the scatterer in X-ray scattering, which confirms and develops Compton's quantum scattering theory. Einstein played a particularly important role in affirming Compton effect. As mentioned earlier, Einstein further developed the optical quantum theory in 19 16. According to his suggestion, Bert and Geiger also tried to test who was right and wrong in classical theory and optical quantum theory with experiments, but both failed. When Einstein learned the results of Compton experiment in 1923, he enthusiastically publicized and praised Compton experiment in meetings and newspapers for many times and talked about its significance. Einstein also reminded physicists to pay attention to: don't just see the particle nature of light. Compton relies on the fluctuation of X-ray to measure its wavelength in the experiment. He published a short article entitled Compton Experiment in the supplement of Berlin Daily on April 20 1924, with a sentence: "... the most important question is to consider how far we should go to give the properties of projectiles to particles or photons of light." (R.S. Chancrin (editor. ), A.H. Compton Scientific Paper, University of Chicago Press, (1973)) It is because of the efforts of Einstein and others that the wave-particle duality of light has been widely recognized. The experimental results show that (1) scattered light contains λ > in addition to the same spectral line as the original wavelength λ0. The spectral line of λ0. (2) The change of wavelength δλ=λ-λ0 increases with the increase of scattering angle φ (the angle between scattering direction and incident direction). (3) For scattering materials with different elements, the change of wavelength δ λ is the same at the same scattering angle. The intensity of scattered light with wavelength λ decreases with the increase of atomic number of scatterer. Compton successfully explained these experimental results with photon theory. X-ray scattering is the result of elastic collision between a single electron and a single photon. Conservation of momentum and energy before and after collision. After simplification, Δ λ = λ-λ 0 = (2h/m0C) sin2 (/θ 2) is called Compton scattering formula. λ=h/(m0c) is called Compton wavelength of electrons. Why do scattered light have the same wavelength as incident light? Internal electrons cannot be considered as free electrons. If photons collide with such electrons, the Compton effect
It's equivalent to colliding with the whole atom. In the collision, the energy transmitted by photons to atoms is very small, and almost keeps its own energy unchanged. In this way, the original wavelength remains in the scattered light. Because the number of electrons in the inner layer increases with the increase of the atomic number of the scatterer, the intensity with wavelength λ0 increases and the intensity with wavelength λ decreases. Compton scattering is meaningful only when the wavelength of incident light is close to that of electrons, which is why X-ray is chosen to observe Compton effect. In photoelectric effect, the incident light is visible light or ultraviolet light, so Compton effect is not obvious.
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(1) Classical explanation (explanation of electromagnetic waves) When monochromatic electromagnetic waves act on charged particles with a wavelength smaller than that, they cause forced vibration and radiate electromagnetic waves with the same frequency in all directions. Classical theory can explain the scattering with constant frequency, but it can't reasonably explain Compton effect! (2) Photon theory explains that X-rays are photons with e=hν, which collide with free electrons completely elastically, and the electrons gain some energy, so the scattered photon energy decreases, the frequency decreases and the wavelength becomes longer. This process assumes that the conservation of momentum and energy is still true, then the electron: p = m0vE=m0V2/2 (assuming that the electron starts to rest and the potential energy is ignored) photon: P=h/λ where (h/m0C) = 2.34×10-12m is called Compton wavelength.
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1. The order of magnitude of the scattering wavelength change lD is 10- 12m. For the visible wavelength l~ 10-7m, LD
Constant, the frequency of scattered light is constant. The discovery of Compton effect and the consistency of theoretical analysis and experimental results not only strongly confirm the correctness of photon hypothesis, but also confirm that the interaction process of microscopic particles strictly abides by the law of conservation of energy and momentum.
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Professor arthur holly compton is a famous American physicist and the discoverer of Compton effect. Compton was born in Worcester, Ohio on September 1892 and died in Berkeley, California on March 1962 at the age of 70. Compton was born in a senior intellectual family, and his father was a philosophy professor and dean of college of wooster. Compton's eldest brother Carl is the head of the physics department of Princeton University, and later became the dean of MIT. He is Compton's closest and best scientific leader.
After graduating from Compton Middle School, he was promoted to college of wooster. Hospital has a long history and tradition, which has a decisive influence on Compton's life and career. Here, his basic education almost completely determines his attitude towards life and science all his life. Outside the college, Compton is familiar with many interesting things, such as the summer camp in Michigan, Carl's early scientific experiments and so on. These are also important for Compton's future scientific career. 19 13 After graduating from college of wooster, Compton entered Princeton University for further study. 19 14 got the master's degree, 19 16 got the doctor's degree. His doctoral thesis was first directed by O W Richardson and then by H L Cook. After receiving his doctorate, Compton taught physics at the University of Minnesota (1916-1917) for one year, and then worked as a research engineer at Westinghouse Electric and Manufacturing Company in East Pittsburgh, Pennsylvania for two years. During this period, Compton did a lot of original work for the army signal corps to develop aviation instruments; And also obtained the design patent of sodium vapor lamp. The latter work is closely related to his later establishment of the fluorescent lamp industry in Nellapak, Cleveland, Ohio, USA. During his stay in Naira Park, he worked closely with Zay Jeffries, the technical director of General Electric Company of the United States, which promoted the development of fluorescent lamp industry and made the development of fluorescent lamp enter the most active era. Compton's career as a scientist began with the study of X-rays. As early as when he was studying in university, he put forward a new theoretical viewpoint in his graduation thesis, to the effect that the intensity of X-ray diffraction in crystals is related to the electron distribution of atoms contained in crystals. During his tenure at Westinghouse (1917 ——1919); Compton continued his research on X-rays. Starting from 19 18, he made theoretical and experimental research on X-ray scattering. Compton put forward the hypothesis of electron finite linearity (radius1.85×10-10 "cm) according to J·J· Thomson's classical theory, and explained the observation relationship between density and scattering angle. This is a simple beginning, but it leads to the concept of "Compton wavelength" of electrons and other elementary particles. This concept was later developed in his own X-ray scattering and quantum theory of quantum electricity Compton.
Mechanics has fully developed. During this period, his second research was started at 19 17 with Oswrald Rognley of the University of Minnesota, and it was about determining the X-ray reflection density of magnetic crystals by using magnetization effect. This study shows that the electron orbital motion has no effect on the magnetization effect. He believes that ferromagnetism is caused by the inherent characteristics of electrons, which are a basic magnetic charge. The correctness of this view was later proved more strongly by the experimental results of J C Stearns, a student he directed at the University of Chicago. After the First World War, Compton went to England for further study from 19 19 to 1920, and engaged in research at Cavendish Laboratory in Cambridge. At that time, Cavendish laboratory was in the most prosperous era, and many promising young British scientists moved here from the battlefield to study with Rutherford and J·J· Thomson. Compton thinks this is one of the most inspiring periods, during which he not only established a relationship with Rutherford; I met Thomson. At that time, Thomson spoke highly of his research ability, which greatly encouraged Compton and made him more confident in his point of view. The friendly relationship between Compton and Thomson lasted until the last moment of his life. During his stay in Cambridge, Compton switched to gamma rays for scattering experiments because the high-voltage X-ray device was not suitable. This experiment not only confirmed the early research results of other scientists at T A Gray, but also laid the foundation for Compton to further study the X-ray scattering experiment. After that, Compton returned to the United States on 1920, and served as Wayman Crow Professor and Head of Physics Department of Washington University in St. Louis. Here he made the greatest discovery for him. At that time, Compton projected X-rays from molybdenum target onto graphite to observe the scattered X-rays. He found that it contains two components with different frequencies, one with the same frequency (or wavelength) as the original X-ray, and the other with a frequency smaller than the original parent X-ray. This frequency change has a certain relationship with the scattering angle. The first component that does not change the frequency can be explained by the usual wave theory, because according to the wave theory of light, scattering does not change the frequency of incident light. However, the second component, which appears less frequently in the experiment, is puzzling and cannot be explained by classical concepts. Facing the facts observed in this experiment, Compton put forward his own explanation in 1923. He believes that this phenomenon is caused by the collision between light quantum and electron. Optical quantum not only has energy, but also has some momentum similar to mechanical meaning. In the process of collision, photons transfer some energy to electrons, reducing its energy and thus its frequency. In addition, according to the conservation of energy and momentum of colliding particles, the dependence between frequency change and scattering angle can be derived, which can well explain the facts observed by Compton. In this way, people have to admit that light has the nature of particles in addition to the well-known fluctuations. This shows that a beam of light is composed of several separated particles, which have Compton effect in many ways.
Faces exhibit the same properties as ordinary matter particles. Compton's scientific research results are published in many journals. 1926, he synthesized his published papers and wrote a book "x-rays and electrons". 1923, Compton accepted the position of professor of physics at the University of Chicago (R·A· Millikan once held this position) and worked with Michelson. Here, he named his first study "Compton Effect". Because of a series of experiments of Compton effect and its theoretical explanation, he shared the 1927 Nobel Prize in Physics with A T R Wilson of Britain. He was only 35 years old at this time. In the same year, he was elected as an academician of the National Academy of Sciences, and 1929 became a professor of C H Swift. From 65438 to 0930, Compton turned his main interest from studying X-rays to studying cosmic rays. This is because the interaction between high-energy gamma rays and electrons in cosmic rays is an important aspect of Compton effect (today, the anti-Compton effect of the interaction between high-energy electrons and low-energy photons is an important research topic in astrophysics). During the Second World War, many physicists were concerned about the "uranium problem", and Compton was no exception. 1941l65438+1October 6, Compton, as the chairman of the uranium Committee of the National Academy of Sciences, published a report on the military potential of atomic energy, which promoted the development of nuclear reactors and atomic bombs. Lawrence discovered plutonium at the University of California. Soon, the metallurgical laboratory in Manhattan was responsible for plutonium production, and these aspects were mainly led by Compton and Lawrence. Fermi's first nuclear chain reactor was also supported and encouraged by Compton. At the end of the war, Compton accepted the position of President of Washington University in St. Louis. It was in this school that he made the biggest physical discovery 25 years ago-"Compton effect". 1954, Compton reached the age of retiring from the administrative leadership position of the university. After retirement, he continued to lecture, teach and write books. During this period, he published the book Atomic Exploration. This is a masterpiece, which completely and systematically brings together the research results of all colleagues of Manhattan Project during the war. Compton is one of the greatest scientists in the world. The Compton effect he discovered is the core of developing quantum physics. This discovery earned him an indisputable position among great scientists.