Discovery
From 1922 to 1923, Compton studied the light components of X-rays scattered by lighter substances (graphite, paraffin, etc.), and found that the scattering spectrum except for the wavelength is the same as the original wavelength. In addition to the components, there are components with longer wavelengths. This kind of scattering phenomenon is called Compton scattering or Compton effect. Compton projected 0.71 angstroms of X-rays onto the graphite, and then measured the intensity of the X-rays scattered by the graphite molecules at different angles. When φ=0, there is only a single frequency light equal to the incident frequency. When φ≠0 (such as 45°, 90°, 135°), two frequencies of scattered light are found. 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 as the angle increases.
The discovery process of the Compton effect
In the "Physical Review" in May 1923, AH Compton titled "The Quantum Theory of X-ray Scattering by Light Elements" , Published the effect he discovered, and explained it with the light quantum hypothesis. He wrote (AHCompton, Phys. Rev., 21 (1923) p.): "From the point of view of quantum theory, it can be assumed that any particular X-ray quantum is not scattered by all electrons in the radiator, but is All of its energy is consumed by a special electron, which turns around and scatters the rays in a special direction, which is at a certain angle to the incident beam. The bending of the radiation quantum path causes a change in momentum. As a result, The scattered electrons recoil with a momentum equal to the change in X-ray momentum. The energy of the scattered rays is equal to the energy of the incident rays minus the kinetic energy of the scattered electrons. Since the scattered rays should be a complete quantum, their frequency will also be proportional to the energy Therefore, according to quantum theory, we can expect that the wavelength of the scattered radiation is greater than that of the incident radiation, and the intensity of the scattered radiation is greater in the forward direction of the original X-ray than in the reverse direction, as measured by the experiment."
Compton uses the diagram (see right)
Explain the distribution of ray direction and intensity, according to the conservation of energy and momentum, taking into account the relativistic effect, the wavelength offset, that is, the Compton deviation Shift formula:
that is, Δλ=λ-λ0=(2h/mc)sin^2(φ/2)
△λ is the difference between the incident wavelength λ0 and the scattering wavelength λ, h is Planck's constant, c is the speed of light, m is the rest mass of the electron, and φ is the scattering angle.
This simple reasoning has long become common knowledge for modern physicists, but Compton is not easy to come by. The research on this kind of phenomenon took one to twenty years, and Compton got the correct result in 1923, and Compton himself took a detour for five years. This history illustrates modern physics from one side. The uneven course of production and development.
It can be seen from the above formula that the change of wavelength is determined by φ and has nothing to do with λ0, that is, for a certain angle, the absolute value of the change of wavelength is certain. The smaller the wavelength of the incident ray, the greater the relative value of the wavelength change. Therefore, the Compton effect is more pronounced for gamma rays than for X rays. History is exactly like this. As early as 1904, the British physicist A.S.Eve first discovered the signs of the Compton effect when studying the absorption and scattering properties of gamma rays. The radium tube emits gamma rays, which are scattered by the scattering objects and then projected to the electrometer. Insert an absorber on the way of incident or scattered rays to test its penetration. Ive found that the scattered rays are often "softer" than the incident rays. (ASEve, Phil.Mag.8 (1904) p.669.)
Later, the problem of γ-ray scattering was studied by many people, and DCHFlorance of the United Kingdom obtained the It is clearly concluded that the scattered secondary rays are determined by the scattering angle and have nothing to do with the material of the scattering object, and the larger the scattering angle, the greater the absorption coefficient.
In 1913, J.A. Gray of McGill University redone the gamma ray experiment, which confirmed Florance’s conclusion and further accurately measured the ray intensity. He found: "The properties of monochromatic gamma rays will change after being scattered. The larger the scattering angle, the softer the scattered rays." (JAGray, Phil. Mag., 26 (1913) p.611.) The softening of the rays actually means that the wavelength of the rays becomes longer. At that time, the nature of γ-rays was not yet known, so it had to be expressed based on experimental phenomena.
The experimental facts are clearly presented to the physicist, but no correct explanation can be found. Compton was also exposed to the problem of gamma scattering in 1919. He measured the wavelength of gamma rays with precise means and confirmed the fact that the wavelength became longer after scattering. Later, he switched from γ-ray scattering to X-ray scattering. After the molybdenum Kα line is scattered by the graphite crystal, the scattering intensity of different azimuths is measured with a free cell. It can be seen from part of the curve published by Computon that the X-ray scattering curve obviously has two peaks, one of which has a wavelength equal to the wavelength of the original ray (invariant line), and the other has a longer wavelength (variable line). The deviation of the invariant line varies with the scattering angle, and the larger the scattering angle, the greater the deviation.
Compton students, Wu Youxun, who went to the United States to study from China, made a great contribution to the further research and testing of the Compton effect. In addition to doing many persuasive experiments against Duane’s denial , Also confirmed the universality of the Compton effect. He tested the X-ray scattering curves of various elements, and the results all met Compton's quantum scattering formula. Compton and Wu Youxun's paper published in 1924 was titled: "Wavelength of Molybdenum Kα Lines When Scattered by Light Elements". (AHComptonandY.H.Woo, Proc.Nat.Acad.Sei, 10 (1924) p.27.) They wrote: "The important point of this picture is that the spectrum obtained from various materials is almost completely in nature. Consistent. In each case, the invariant line P appears in the same place as the fluorescent MoKa line (the Kα spectrum of molybdenum), and the peak of the invariant line appears in the above-mentioned wavelength change quantum within the allowable experimental error range. The formula predicts the position M.
Wu Youxun’s most prominent contribution to the Compton effect is to determine the curve of the intensity ratio R of the variable and invariant lines in X-ray scattering with the atomic number of the scatterer. , Confirmed and developed Compton’s quantum scattering theory.
Einstein played a particularly important role in affirming the Compton effect. As mentioned earlier, Einstein further developed in 1916 Light quantum theory. According to his suggestion, Botte and Geiger (Geiger) also tried to use experiments to test the classical theory and light quantum theory who is right and who is wrong, but without success. When Einstein learned the results of Compton experiment in 1923 , He enthusiastically promoted and praised Compton’s experiment, and repeatedly talked about its significance in conferences and newspapers.
Einstein also reminded physicists: Don’t just see light particles. In the experiment, Compton relied on the volatility of X-rays to measure its wavelength. He published a short article entitled "Compton Experiment" in the supplement of the "Berlin Daily" on April 20, 1924. There is such a sentence Words: "...The most important question is to consider how far the particles or light quanta of light should be given to the properties of the projectile. "(RS Shankland (ed.), Scientific Papers of A. H. Compton, Univ. of Chicago Press, (1973))
It is precisely because of the efforts of Einstein and others that the wave-particle duality of light is rapidly acquired It is widely recognized.
Experimental results:
(1) In addition to the spectrum line of the original wavelength λ0, there are also the spectrum line of λ>λ0 in the scattered light.
>(2) The change in wavelength Δλ=λ-λ0 increases with the increase of the scattering angle φ (the angle between the scattering direction and the incident direction).
(3) For different The scattering material of the element, under the same scattering angle, the change in wavelength Δλ is the same. The intensity of the scattered light with a wavelength of λ decreases with the increase of the atomic number of the scattering object. Compton successfully explained these experimental results by using the photon theory. The scattering of X-rays is the result of the elastic collision between a single electron and a single photon. The momentum and energy before and after the collision are conserved. After simplification, Δλ=λ-λ0=(2h/m0c)sin^2(φ/2) is called CommScope The scattering formula. λ=h/(m0c) is called the Compton wavelength of electrons. Why is there a spectrum line in the scattered light with the same wavelength as the incident light? Inner electrons cannot be regarded as free electrons. If a photon collides with this electron , Which is equivalent to colliding with the entire atom. The energy transmitted by the photon to the atom in the collision is very small, almost keeping its own energy unchanged. In this way, the original wavelength of the light is retained in the scattered light. Because the number of inner electrons varies with the scattering objects The atomic number increases with the increase, so the intensity of the wavelength λ0 increases, and the intensity of the wavelength λ decreases.
Compton scattering only occurs at the wavelength of the incident light and the Compton of electrons. When the wavelength is comparable, the scattering is significant, which is why X-rays are used to observe the Compton effect. In the photoelectric effect, the incident light is visible light or ultraviolet light, so the Compton effect is not obvious.
Discoverer
Professor Arthur Holly Compton is a famous American physicist and discoverer of the "Compton effect." Compton was born on September 10, 1892 in Wu, Ohio. Stuart, died on March 15, 1962 in Berkeley, California, at the age of 70.
Compton was born in a family of senior intellectuals. His father was a professor and dean of philosophy at Worcester College . Compton’s eldest brother Karl (KarL) is the dean of the Department of Physics at Princeton University and later became the dean of the Massachusetts Institute of Technology. He is Compton’s closest and best science leader.
Kang After graduating from high school, Putton was promoted to Worcester College. The college has a long history and tradition, which has a decisive influence on Compton's life career. Here, his basic education almost completely determines his life. Attitudes towards life and science. Outside the college, Compton is familiar with many things of interest, such as summer camps in Michigan and Carl’s early scientific experiments and many more. All of these will also play an important role in Compton's future scientific career.
In 1913, after graduating from Worcester College, Compton entered Princeton University for further studies. He obtained a master's degree in 1914 and a doctorate in 1916. His doctoral dissertation was first directed by O.W. Richardson and later completed under the direction of H.L. Cooke. After obtaining a PhD in philosophy, Compton worked as a one-year physics teaching job at the University of Minnesota (1916-1917), and then worked as a two-year research engineer at Westinghouse Electric and Manufacturing Company in East Pittsburgh, Pennsylvania. During this period, Compton did a lot of original work for the Army Communications Corps to develop aeronautical instruments; and also obtained a patent for the sodium vapor lamp design. This latter work is closely related to his future establishment of the fluorescent lamp industry in Nella Park, Cleveland, Ohio. During Nella Park, he worked closely with General Electric’s technical director Zay Jeffries to promote The development of the fluorescent lamp industry has brought the development of fluorescent lamps into 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 the university, he put forward a new theoretical insight in his graduation thesis. The general idea is that the intensity of X-ray diffraction in a crystal is related to the distribution of electrons in the atoms contained in the crystal. During the Westinghouse period (1917-1919); Compton continued to engage in X-ray research. Since 1918, he has studied X-ray scattering in both theoretical and experimental aspects. After the quantitative agreement between the scattering data, according to JJ Thomson’s classical theory, Compton proposed the hypothesis of electronic finite linearity (radius 1.85×10-10”cm) to illustrate the observational relationship between density and scattering angle This was a simple beginning, but it led to the later formation of the "Compton wavelength" concept of electrons and other elementary particles. This concept was later fully obtained in his own quantum theory of X-ray scattering and quantum electrodynamics. Development.
His second research during this period was started with Oswrald Rognley at the University of Minnesota in 1917. This is about determining the effect of magnetization on magnetism. The density of X-ray reflections of crystals. This study shows that the orbital motion of electrons has no effect on the magnetization effect. He believes that ferromagnetism is caused by the inherent characteristics of electrons, which is a basic magnetic charge. This view is correct. Sex was later proved by his student J·C·Stearns at the University of Chicago with experimental results.
After the Second World War, from 1919 to 1919 In 1920, Compton went to England for advanced studies and conducted research at the Cavendish Laboratory in Cambridge. At that time, the Cavendish Laboratory was in its most prosperous era, and many young and promising British scientists moved here from the battlefield. Follow Rutherford and J.J. Thomson for research. Compton considers it to be the most inspiring era, during which time he not only established a relationship with Rutherford; but also was able to meet with Thomson. At that time, Thomson spoke highly of his research ability, which greatly encouraged Compton and made him more confident in his own opinions. Compton's friendly relationship with Thomson has been maintained until the last moment of life. .
During the Cambridge period, due to the inapplicability of high-pressure X-ray equipment, Compton switched to gamma-ray scattering experiments. This experiment not only confirmed the earlier research of T·A·Gray by other scientists As a result, it also laid the foundation for Compton’s in-depth research on X-ray scattering experiments.
After that, Compton returned to the United States in 1920 and served as Weiman K Law (WaymanCrow) Chair Professor and Head of the Department of Physics. Here he made one of his greatest discoveries. At that time, Compton projected X-rays from a molybdenum target onto graphite to observe the scattered x Ray. He found that it contains two different frequency components, one of the frequency (or wavelength) is the same as the original incident X-ray frequency, and the other is lower than the original incident X-ray frequency. There is a certain relationship between the change and the scattering angle. For the first component that does not change the frequency, the usual wave theory can be used to explain, because according to the wave theory of light, scattering does not change the frequency of the incident light. And in the experiment, the second This reduced frequency component is puzzling. It cannot be explained by classical concepts. Faced with the facts observed in this kind of experiment, Compton in 1923 Presented his own explanation. He believes that this phenomenon is caused by light quantum and