Atoms are stable and unstable.In addition to natural elements, unstable atoms are mainly formed by fragments generated during nuclear fission or fusion.These unstable elements will turn into stable atoms after emitting α, β, γ and other rays.Such unstable elements are called radioisotopes.According to the different radiation (or radiation) emitted in the process of radioactive isotope decay, radioactive decay can be divided into three categories: α, β and γ decay.Radioisotope technology has been widely used in many fields of the national economy, and has achieved remarkable economic benefits.[1-2]
Chinese name
radio isotope[3]
Foreign name
Radioactive isotope[3]
Features
Elements are radioactive and can be labeled[2]
Decay type
α. Beta and gamma decay[3]
Purpose
Applications such as tracing atoms and radioactive rays[2]
Decay series
Uranium series, thorium series and actinium series[3]
Of an elementatomfromNucleusandElectronicsAnd the nucleus consists ofprotonandneutronform.The same element has the same proton number, but can have different neutron numbers. This element with the same proton number but different neutron numbers is calledisotope。The atomic nuclear energy of some isotopes spontaneously emitsparticleorradial, release a certain amount of energy, at the same time, the number of protons or neutrons changes, thus transforming into the nucleus of another element.This feature of elements is calledradioactivityThis process is calledRadioactive decay, these elements are calledradioactive element。Radioactive isotopes are called radioisotopes.Elements that undergo radioactive decay are called parent, and elements formed by radioactive decay are called daughter.[3]
Decay type
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According to the particles or rays released or absorbed by radioactive elements, radioactive decay can be divided into the following types:[3]
（1）Alpha decayThe decay process in which radioactive elements spontaneously release alpha particles is called alpha decay.The alpha particle has a mass number of 4 and is composed of 2 protons and 2 neutronsAtomic numberHigh speed movement of 2Helium atom。The flow of alpha particles moving at high speed is alpha ray.Compared with its parent, the mass number of the radioactive element formed by alpha decay decreases by 4, and the atomic number decreases by 2.The decay process is as follows:[3]
（2）Beta decayThe radioactive element spontaneously converts a neutron in the nucleus into a proton and releases beta particles, which is called beta decay.The mass and charge of the beta particle are the same as those of the electron, and its essence is a high-speed moving electron.The fast moving beta particle stream is beta ray.Beta rays have much higher penetration than alpha rays.The mass number of the radioactive element formed by beta decay is unchanged compared with its parent, but the atomic number increases by one bit.The decay process is as follows:[3]
（3）Electron captureThe decay process in which a radioactive element spontaneously captures an extranuclear orbital electron and turns a proton into a neutron in the nucleus is called electron capture.The mass number of the radioactive element formed by electron capture is unchanged compared with its parent, but the atomic number is reduced by one bit.The decay process is as follows:[3]
(4) Homogeneous gamma transition.Generally, the new atomic nucleus formed by alpha decay or beta decay is in an unstable excited state, but this time is very short (about 10-13s），Fast transition to lowerenergy levelorground stateAnd emit γ ray (y ray is a kind of electromagnetic wave with very short wavelength and penetrating ability).This phenomenon only occurs in the energy level transition, while the nuclear mass number and atomic number remain unchanged, so no new elements are generated.However, the excited states of some nuclei exist for a long time and can be regarded as independent radioactivitynuclideThe daughter and parent formed by γ transition are calledIsomer。[3]
Decay law
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The most basic feature of radioactive elements is that they occur continuouslyisotopeDecay, and the result of decay is that the number of parent radioisotope is decreasing, but the number of atoms of its daughter will continue to increase.Since the decay of radioisotopes is not controlled by external temperature, pressure or chemical conditions, the size of their decay rate is completely an inherent characteristic of each radioactive element, and the number of atoms that decay is only related to time. If the number of parent radioactive elements at the initial time is N, after a period of time dt,The number of radioactive elements that have decayed dN is proportional to the product of the number of parent elements that have not decayed N and dt, that is[3]
Write the equation:[3]
It can be obtained by integrating the above equation[3]
Where: λ is the decay probability of each radioactive element atom in unit time, also called the decay constant;NzeroIs the number of radioactive element atoms at the beginning (t=0);N is the number of atoms remaining after time t.[3]
This formula shows that the decrease of the total atomic number of radioisotopes with time obeys the exponential law.This is the basic law of radioactive decay and the basic formula of radioisotope dating.The decay rates of different radioactive elements vary greatly. The larger the decay constant is, the faster the element decays. The decay rate does not remain unchanged throughout the decay time, but decreases with time. However, the decay constant of each radioactive element is certain.[3]
When the atomic number of radioactive element decays to half of the original (N=1/2Nzero）The time (T) experienced by the time is calledhalf life。[3]
Each radioactive element has a fixed half-life, such astwo hundred and thirty-eightThe half-life of U is 4.468 × 10ninea，two hundred and thirty-twoThe half-life of Th is 1.41 × 10tenA (14.1 billion years), called long-lived element.It is generally believed that radioactive elements have completely decayed after 10 half lives.[3]
Radioisotopes decay continuously. The number of atoms that decay in a unit time is called radioactive intensity, which can also be understood as radioactive activity.The common unit of radioactivity intensity is curie, which means that 3.7 × 10tenSecondary nuclear decay, with the symbol Ci.In addition to curie, dps and dpm were commonly used in the past.Where, dps refers to the decay times of radioactive elements per second; dpm refers to the decay times per minute.[3]
Decay series
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More than 230 species have been found in natureNatural radioactive element, most of which form stable nuclides after a nuclear decay, such asfortyK、fourteenC，However, the elements formed after the decay of some radioactive elements are still radioactive elements. There are about 50 such elements, and three unrelated radioactive series are formed, namelyuraniumSeriesthoriumSeries andActinium(uranium) series.[3]
application
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Radioisotope technology has been widely used in many fields of the national economy. Its application in industry, agriculture, medicine, resources and environment, and military scientific research has achieved remarkable economic, social, and environmental benefits. It is also one of the important aspects of nuclear energy utilization.[2]
Tracer atom
A stable chemical element is mixed with its radioactive isotopes. When they participate in the movement and change of various systems, because radioactive isotopes can emit rays, their location and quantity can be determined by measuring these rays.As long as the distribution and trend of radioisotopes are measured, various functions of stabilizing chemical elements can be determined.This method is called atomic tracer method and is widely used.[2]
(1) Application in petroleum industry.The material containing radioactive gamma ray is pressed into the outer channel of the well or into the formation, or into the formation surface near the perforation channel. The gamma logging is performed before and after this, and the distribution of injected tracer along the well profile can be known by comparing the two measured curves.If the cement sheath is broken due to poor cementing quality or perforation and other engineering construction, resulting in interlayer collusion, which will have adverse effects on oil production and water injection, it should be measured in time and string plugging measures should be taken.Radioactive tracer methodIt is one of the effective methods to check the serial slot.It can also be used when interlayer channeling, misperforation, etc. need to be pluggedRadioactive tracerCheck the sealing effect.Low permeability formation can increase production after fracturing, and tracer logging can check the fracturing effect.[2]
(2) Application in machinery industry.In mechanical engineering, some airframes will be dangerous when the wear exceeds a certain limit.Some radioactive substances can be placed at a specified depth away from the surface of the machine parts. When the machine parts are worn to this point, radioactive substances will appear in the wear debris taken away by the lubricating oil, so that corresponding measures can be taken.[2]
(3) Application in electronic industry.In semiconductor component manufacturing processTracer atomThe diffusion of impurities in semiconductors was studied by the method of.For example, diffusion of radioactive zinc into semiconductorsgermaniumThen grind it down layer by layer, measure its radioactive intensity, and you can know the distribution law of zinc diffused into germanium.[2]
(4) Application in agriculture.Tracer atoms can be used to study the effect of fertilization.For example, the fertilizer containing radioactive phosphorus was applied to the cotton roots at the mature stage, and the radioactivity in the cotton plant was found after measurementphosphorusVery few, which means that the roots seldom absorb fertilizer at the mature stage of cotton peach;If phosphorus fertilizer is sprayed on the leaves, radioactive phosphorus will soon be found in the cotton plant, which indicates that the leaves can absorb fertilizer and have better effect.[2]
Radioactive ray
The main applications of radioactive rays are:[2]
(l) Radiographic detection.Transmit γ ray through the sample, if there issand holesOr crack, the absorption of ray there will be reduced, so put a photographic negative behind the sample, and the developed negative will leave a corresponding trace.In addition, when the ray passes through the material, it is absorbed or scattered by the material according to certain rules, so that the density and thickness of the object can be measured.In oil exploration, γ ray can be used to study the nature of the formation, calculate the shale content, and distinguishlithology, measure the porosity in the rock stratum, find outSource rock, reservoir.[2]
(2) Application in medical treatment.Radioactive radiation can destroy the tissue of cancer and inhibit the development of cancer. It can also be used to disinfect, sterilize, and see through the human body.[2]
(3) Application in agriculture.After the seeds are properly irradiated by radiation, they can stimulate the growth and development, make the crops mature earlier, increase the yield, and cultivate new varieties.At present, China has carried out the promotion of rare earth agricultural technology, and achieved good economic benefits.[2]
(4) Application in chemical industry and other fields.For example, the use of radiation chemistry for milk fusion to produce adhesives;Use of nuclear radiation technologyPrinting and dyeing auxiliaries。When the ray passes through the material, it can ionize the molecule of the material, and use it to ionize the air to obtain the conductivity, thus eliminating the harmful accumulation of static electricity.[2]
application area
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For the measurement of rock age, scientists generally useIsotope datingNamely, the age of geological body is determined by the nuclear decay law of radioactive elements."After the formation of radioisotopes contained in rocks and minerals, the radioisotopes (parent) isolated from the surrounding environment continuously decay and decrease, and the stable isotopes (daughter) generated by decay correspondingly accumulate in the object and increase."[4]
The application of nuclear technology is a technology that uses the physical, chemical and biological effects produced by the interaction of radioisotopes and ionizing radiation with substances to carry out applied research and development.It has broad application prospects in environmental protection, materials and food processing.[5]
protect
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1. The places where radioisotope and ray devices are used must be equipped with protective facilities.The entrance must be equipped with radioactive signs and necessary protective safety interlocks, alarm devices or working signals.[6]
2. The unit must assign special personnel to check the radiation source andRay apparatusConduct management, regular inspection, maintenance and make written records.In case of failure of radioactive source, instrument and equipment, special personnel shall be assigned to deal with it.[6]
3. The user of radioisotope and radiation devices must operate in strict accordance with the safety operation procedures, strictly control the radiation dose, prevent harm to human body and avoid the occurrence of radiation accidents.[6]
4. The unit using radioisotopes and radioactive sources must set up a special source library, which shall be strictly managed to prevent leakage and loss.Establish and improve the registration system of storage, requisition and return;Provide necessary protectionInstrumentationAnd protective equipment;Establish emergency response plan.[6]
5. Personnel engaged in radiation related work shall have physical examination and regular physical examination before taking up their postsSanitation and epidemic prevention stationResponsible for unified arrangement, the competent leaders of all relevant units shall urge the personnel engaged in radiation related work to participate in physical examination, and provide funds and various guarantees.[6]
6. Units that have lost or leaked radioactive sources must immediately take protective measures to control the impact of the accident, protect the scene of the accident, and report to the competent department, provincial and municipal public securityHygiene and epidemic preventionDepartment report.[6]
7. All units must go through the annual inspection and certificate renewal procedures according to the management regulations of the Provincial Health Department.For cancellation and change of radioisotope and ray devices, it is necessary to go through cancellation and change procedures at the original approval department with the permit registration certificate.[6]
8. When the user of radioisotopes stops using radioisotopes, it shall properly dispose of radioisotopes and radiation sources, and submit the disposal report to the school security and technical safety department, so as to timely report to the municipal health and epidemic prevention station, the municipal public security bureau and the municipal environmental protection bureau.After examination and approvalSanitation and epidemic prevention stationThe Municipal Public Security Bureau cancels its license.[6]
9. The school will punish the relevant units and responsible persons in accordance with the provisions of the Regulations on the Management of Radiation Accidents issued by the Ministry of Health and the Ministry of Public Security for any accident caused by violation of these regulations.If serious consequences are caused and a crime is constituted, the judicial organ shall investigate the criminal responsibility according to law.[6]
