X-ray is a kind of high frequency, short wavelength, and high energyelectromagnetic wave。
The frequency and energy of X-ray are second only toGamma ray, frequency range 3 × 10sixteen~3×10twentyBetween Hz[16], corresponding wavelength is 0.01nm~10nm[12], the energy is 100eV~10MeV[13]。X-rays are penetrating, but there are differences in density and thickness between human tissues. When X-rays penetrate different tissues of the human body, they are absorbed to different degrees. After imaging processing, different images can be obtained[1]。
In 2023,Scientists have taken the first single atom X-ray signal[15]。
X-ray is actually an electromagnetic wave with very short wavelength,wavelengthAbout 0.01-10nanometer。[12]
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The simplest way to generate X-rays is to hit the metal target with accelerated electrons.During the impact, the electrons suddenly decelerate, and their lost kinetic energy will be released in the form of photons, forming a continuous part of the X-ray spectrum, called bremsstrahlung.By increasing the acceleration voltage, the energy carried by the electron increases, and it is possible to knock out the inner electrons of the metal atom.The inner layer then forms a hole, and the outer electron transitions back to the inner layer to fill the hole, while emitting photons with a wavelength of about 0.1nm (equivalent to the frequency of 3EHz and the energy of 12.4keV).Since the energy emitted from the outer electron transition is quantized, the wavelength of the emitted photons is also concentrated in some parts, forming a characteristic line in the X spectrum, which is called characteristic radiation[7]。
When high-speed electrons bombard targets, the interaction process with target materials is very complex.Some high-speed electrons enter the target material near the atomic nucleus. Under the strong electric field of the atomic nucleus, the magnitude and direction of the velocity change, and part of the kinetic energy is converted into the energy (hv) of X photons and radiated out.This radiation is called bremsstrahlung.Some high-speed electrons enter the atoms of the target material. If they interact strongly with the inner electrons of an atom, it is possible to transfer part of the kinetic energy to the electron, making it separate from the atom, so that there is a vacancy in the inner electron layer of the atom. The vacancy will be filled by the transition of the outer electrons, and an X photon will be emitted during the transition,The energy of the emitted X photon is equal to the energy difference between the two energy levels. This radiation is called characteristic radiation[2]。
When high-speed electrons bombard the anode, the energy of the above two kinds of radiation, the electronic kinetic energy converted into X-ray energy is less than 1%, and more than 99% are converted into heat energy, thus increasing the anode temperature.Therefore, the materials with high melting point should be selected for the areas directly impacted by electrons on the anode.Theoretical and experimental results show that under the same speed and number of electron bombardment, the total number of photons or total energy of photons emitted by targets made of various substances with different atomic numbers Z are different, and the total energy of photons is close to ZtwoIs proportional.Therefore, the larger the X-ray is, the higher the efficiency is.Therefore, tungsten (Z=74) and its alloy are the most appropriate materials when considering high melting point, large atomic number and other technical requirements.If longer wavelength X-ray is needed, lower tube voltage should be used, such as breast fluoroscopy. It is better to use (Z=42) as the target.Since the target has a large amount of heat, the anode is made of copper with a large thermal conductivity. Tungsten or molybdenum targets hit by electrons are embedded on the anode to better derive and dissipate heat[2]。
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X-ray diagnosis
X-ray is used in medical diagnosis mainly based on the penetration, differential absorption, photosensitivity and fluorescence of X-ray.As X-rays pass through the human body, they are absorbed to varying degrees. If the amount of X-rays absorbed by bones is more than that absorbed by muscles, the amount of X-rays after passing through the human body will be different. In this way, the density distribution information of each part of the human body will be carried, and the intensity of fluorescence or photosensitivity caused on the fluorescent screen or photographic film will be greatly different,Therefore, shadows of different densities will be displayed on the fluorescent screen or photographic film (after developing and fixing).According to the contrast of shades, combined with clinical manifestations, laboratory results andpathologic diagnosis To judge whether a part of the human body is normal[9]。
Industrial field
Because of its strong penetrability, X-ray is not only used in medicine, but also used in industry for industrial flaw detection.X-ray can excite fluorescence, ionize gas and sensitize photosensitive emulsion, so X-ray can be detected by ionization meter, scintillation counter and photosensitive emulsion film[10]。
Hazards and protective measures
——When X-ray is exposed, the staff should stand behind the control panel[11]。
——When the patient needs to be supported or held, the staff should wear lead skirts and gloves[11]。
——Non radiation room personnel are not allowed to enter the X-ray room without permission. If other personnel are needed, they should also stand behind the console when X-ray exposure occurs[11]。
——When conducting radiation operation, it may be injured by X-ray. Wear light loss film that can measure the exposure, and check the light shielding film regularly[11]。
——Only after receiving the application form for X-ray taking from the doctor or qualified medical staff can X-ray photos be taken[11]。
X-rays can cause harm.X-rays are invisible and imperceptible rays. When people are in the X-ray beam, they will not feel it immediately.Operators who often stay around the X-ray machine or patients who are repeatedly examined by X-ray will cause lasting damage to their health. It should also be remembered that not only the direct beam of X-ray can cause damage, but also scattered X-ray can cause damage[11]。
When people are exposed to X-ray, no place near the X-ray tube is safe. Only the back of the control panel is safe. No one except the patient is allowed to enter the X-ray room. If the patient needs to be supported or the patient needs to be held for X-ray exposure, the parents or relatives of the patient must also wear lead skirts and gloves.When carrying out X-ray, do not let the hospital nurses or other personnel who do not wear lead skirts or lead gloves help the patients[11]。
Since patients do not often receive X-ray irradiation, and only a small part of the patient's body is exposed to X-ray, the harm of patients to X-ray is very small, but it is important to strive for success once, so that the second X-ray irradiation can be avoided[11]。
X-ray operators, doctors and nurses who work in the X-ray room for many years will suffer from the harm of X-ray, but if they pay attention at any time and follow the operating procedures, the harm of X-ray can be avoided[11]。
It must be known that X-rays are invisible and invisible, which may cause harm to human body[11]。
Discovery History
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X-ray
GermanyUniversitaet Wuerzburg President and Director of Institute of PhysicsRoentgenProfessor (1845-1923) discovered X-ray when he was engaged in cathode ray research[4]。
Roentgen
On the evening of November 8, 1895, he studied cathode rays.In order to prevent external light from affectingThe discharge tubeIn order to prevent the visible light in the tube from leaking out of the tube, he blackened all the rooms and made a cover for the discharge tube with black hard paper.In order to check whether the envelope leaks light, he connected the power supply (the electrode of the Zhukov coil) to the discharge tube. He was satisfied when he saw that the envelope did not leak light.However, when he cut off the power supply, he accidentally found a flash on a small workbench one meter away. The flash came from a fluorescent screen.howeverCathode rayOnly a few centimetres can be carried out in the air, which is the conclusion confirmed by others and his own experiments.So he repeated the experiment and moved the screen away step by step until fluorescence was still visible 2 meters away.Rontgen thought it was not cathode ray.After repeated experiments, Roentgen was convinced that this was a new kind of ray that had not yet been known, so he named it X-ray.He found that X-ray can penetrate thousands of pages of books, 2-3 cm thick wood, several cm thick hard rubber, 15mm thick aluminum, etc.But 1.5mmLead plateIt almost completely blocks the X-ray.He accidentally found that X-rays could penetrate the muscles to reveal the outline of the hand bone. So when his wife came to see him in the laboratory, he asked her to put her hand on the photographic negative wrapped in black paper, and then directed the X-ray for 15 minutes. After development, the negative clearly showed his husband's hand bone, and the wedding ring on his finger was also very clear.This is a historic photo, which shows that human beings can use X-ray to see through bones through skin and flesh.On December 28, 1895, Roentgen submitted the first X-ray paper "A New Ray - Preliminary Report" to the Weirzburg Society of Physical Medicine. The report described the experimental device, practice, and the nature of the initially discovered X-ray.The discovery of X-ray quickly led to a new discovery - the discovery of radioactivity[4]。
X-ray pictures of both hands
Since Roentgen discovered X-ray, many physicists have been actively studying and exploring. In 1905 and 1909,BaccaratPolarization of X-ray has been found successively, but it is still unclear whether X-ray is an electromagnetic wave or particle radiation.1912 German physicistLaueIt is found that X-ray diffraction occurs when it passes through the crystal, which proves the fluctuation of X-ray and the periodicity of the internal structure of the crystal. The article "X-ray interference phenomenon" was published[6]。
Soon after Laue's article was publishedBraggWith the attention of father and son, WH. Bragg has been a professor of physics at Leeds University, while WL. Bragg has just graduated fromUniversity of CambridgeGraduated atCavendish Laboratory 。Because they are both X-ray particle theorists, both of them tried to explain Laue's photos with X-ray particle theory, but their attempt failed.After repeated research, Little Prague successfully explained Laue's experimental facts.He clearly explained the formation of X-ray crystal diffraction in a more concise way, and proposed the famousBragg equation：
This result not only proves the correctness of the interpretation of Little Bragg, but also proves that the information of crystal structure can be obtained by X-ray[6]。
Old Prague designed the first X-ray spectrometer in January 1913, and used this instrument to discover characteristic X-ray.Little Bragg used characteristic X-ray to analyze someAlkali halideThe crystal structure of diamond was successfully determined by cooperating with his father and verified by Laue method.Diamond structureThe determination of C indicates the conclusion that chemists have long believed that the four bonds of carbon atoms are arranged according to the regular tetrahedron shape.This pair ofX-ray crystallographyIs a very important event, which fully showsX-ray diffractionIt is used to analyze the validity of crystal structure, making it generally accepted by physicists and chemists[6]。
In 2023, American researchers first detected the signal generated by a single atom under the action of X-ray.This research was carried out by Ohio University, Argonne National Laboratory and other institutions in the United States. X-ray signals of a single iron atom and a single terbium atom embedded in the molecular framework were detected respectively.The relevant paper was published in the British journal Nature recently.[14]
classification
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In the electromagnetic radiation wave harmonic, the wavelength in the range of 0001-2.5A is X-ray.According to their wavelength and penetration, they can be divided into two categories: hard X-ray and soft X-ray.Hard X-ray, shorter wavelength is 0.05-0.1A, strong penetration soft X-ray, longer wavelength is 0.1-0.5A, weak penetration[8]。
characteristic
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physical characteristics
1、Penetrability。Because of its long wave length and large energy, when X-ray shines on the material, only part of it is absorbed by the material, and most of it passes through the atomic gap, showing a strong penetration ability.The ability of X-ray to penetrate materials is related to the energy of X-ray photons. The shorter the wavelength of X-ray, the greater the energy of photons, and the stronger the penetration.The penetrability of X-ray is also related to the density of the material, and the material with different density can be distinguished by using the property of differential absorption[5]。
2、Ionization。When a substance is irradiated by X-rays, the extranuclear electrons can be separated from the atomic orbit and ionized.The amount of ionized charge can be used to measure the exposure of X ray. According to this principle, an X ray measuring instrument is made.Under ionization, gas can conduct electricity;Some substances can react chemically;It can induce various biological effects in organism[5]。
3、Fluorescence。The X-ray wavelength is very short and invisible, but when it irradiates some compounds, such as phosphorus, platinum barium cyanide, zinc cadmium sulfide, calcium tungstate, etc., it can make the substance fluorescence (visible light or ultraviolet light), and the intensity of fluorescence is proportional to the amount of X-ray.This function is the basis for the application of X-ray in fluoroscopy. Using this fluorescence function, a fluorescent screen can be made to observe the image of X-ray passing through human tissues during fluoroscopy, or a sensitization screen can be made to enhance the sensitivity of the film during photography[5]。
4、Thermal action。Most of the X-ray energy absorbed by the material is converted into heat energy, which increases the temperature of the object[5]。
5、Interference, diffraction, reflection, refraction。These effects have been applied in X-ray microscopy, wavelength determination and material structure analysis[5]。
chemical properties
1. Photosensitivity.X-ray can sensitize the film just like visible light.The intensity of film sensitivity is proportional to the amount of X-ray. When X-ray passes through the human body, due to the different density of human tissues, the absorption of X-ray amount is different, and the sensitivity obtained on the film is different, so as to obtain the X-ray image[5]。
2. Colouring.Long term X-ray irradiation of certain substances, such as barium platinum cyanide, lead glass, crystal, etc., can dehydrate their crystals and change their colors[5]。
Biological characteristics
When X-rays irradiate biological organism, biological cells can be inhibited, destroyed or even necrosed, resulting in physiological, pathological and biochemical changes of organism to varying degrees.Different biological cells have different sensitivity to X-ray, and can be used to treat some diseases of the human body, especially tumors.While using X-ray, people found that the hair loss of patients, skin burns and staffVisual impairmentFor the problem of radiation injury such as leukemia, attention should be paid to the damage to the normal body and protective measures should be taken when using X-ray[5]。
