Radioactive refers to an element from unstable nuclei spontaneously emits the rays, (e.g., α-rays, beta] rays, gamma] rays, etc.) And decays to form stable element is stopped radiation (decay products), a phenomenon is known radioactivity.

Radioactivity Definition

The energy released during decay is called decay energy. Elements with an atomic number of 83 or above are radioactive, but some elements with an atomic number less than 83 (such as ruthenium) are also radioactive.


The atomic nature of certain elements spontaneously emits alpha or beta rays (and sometimes gamma rays) by nuclear decay, called Radioactivity. According to whether the nucleus is stable, the nuclides can be divided into stable nuclides and radionuclides.


The phenomenon in which the nucleus of an element spontaneously emits a certain ray and transforms it into the nucleus of another element, called radioactive decay. Nuclides that can undergo radioactive decay are called radionuclides (or radioisotopes).

Radioactivity Discovery

Of the more than 100 elements that have been discovered, there are more than 2,600 species of nuclides. Among them, there are only more than 280 stable nuclides, belonging to 81 elements.

There are more than 2,300 radionuclides, which can be divided into two categories: natural radionuclides and artificial radionuclides. Radioactive decay was first discovered from the radioactivity of natural heavy element uranium.

Radioactivity refers to the spontaneous emission of radiation from unstable nuclei (such as alpha rays, beta rays, gamma rays, etc.) to form stable elements and stop radiation (decay products). This phenomenon is called radioactivity.

The energy released during decay is called decay energy. Elements with an atomic number of 83 or above are radioactive, but some elements with an atomic number less than 83 (such as ruthenium) are also radioactive.

Radioactivity Description

The nature of certain substances that naturally occur that spontaneously emit alpha or beta or gamma rays are called natural radioactivity.

natural radioactivity

In 1896, the French physicist Becquerel first discovered the natural radioactivity of uranium nuclei in the study of uranium salts. In further research, he discovered that the radiation emitted by the uranium salt can ionize the air and can also penetrate the black paper to sensitize the photographic film.

He also found that changes in external pressure and temperature did not have any effect on the experiment. Becquerel’s discovery is far-reaching, and it gives people a new understanding of the microscopic structure of matter, and thus opens the door to nuclear physics.

In 1898, the Curies discovered more radioactive strontium and radium. Due to the epoch-making discovery of natural radioactivity, the Curies and Becquerel jointly won the 1903 Nobel Prize in Physics.

Since then, the Curies have continued to study the application of radium in chemistry and medicine, and in 1902 separated high-purity metal radium.

Therefore, Mrs. Curie won the 1911 Nobel Prize in Chemistry. In Becquerel basic research and human Curie wait, and later gradually discovered many other elements of radioactive nuclides.

The above findings have strongly promoted the theoretical research and practical application of radioactive phenomena.

Radioactivity Hazards

Under high doses of radiation, radioactivity has some detrimental effects on humans and animals. As 400 RAD [radirradiation (radiation absorbing)] and irradiated with 5% human deaths; if irradiated 650rad, 100% of the deaths.

The radiation dose is below 150 rad, the mortality rate is zero, but it is not without damage. It is often necessary to show some symptoms after 20 years.

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Radioactivity can also damage the genetic material of the dosage unit, mainly in causing genetic mutations and chromosomal aberrations, causing damage to one generation or even several generations.


Radioactive waste is radioactive material, the use of general physical, chemical, and biological methods are not able to destroy it or destroy, only by radionuclide the self-decay to the radioactive decay to a certain level.

Many radioactive elements of the half-life are very long, and the decay of radioactive elements is a new product, so compared to other waste radioactive waste there are many differences in the treatment and disposal.

(1) Treatment of radioactive wastewater

The treatment methods of radioactive wastewater mainly include dilution discharge method, placement decay method, coagulation sedimentation method, ion conversion method, evaporation method, asphalt solidification method, and cement solidification method, plastic curing method, and glass curing method.

(2) Treatment of radioactive waste gas

Radioactive solid waste is mainly various objects that are contaminated by radioactive materials and cannot be reused.

Types of Radioactivity

Radioactivity is divided into natural radioactivity and artificial radioactivity. Natural radioactivity refers to the radioactivity of naturally occurring radionuclides.

Most of them belong to three radiologic systems consisting of heavy elements (ie, lanthanides, uranium and actinides).

Artificial radioactivity refers to the radioactivity obtained by means of nuclear reactions. Artificial radioactivity was first discovered in 1934 by the French scientist Joliot Curie.

We know that many natural and artificially produced nuclei emit radiation spontaneously. In addition to α, β, and γ, there are other particles such as positrons, protons, neutrons, and neutrinos.

Nuclides that emit radiation spontaneously, called radionuclides (formerly known as radioisotopes), are also called unstable nuclides.

Experiments have shown that temperature, pressure, and magnetic fields do not significantly affect the emission of radiation.

This is because temperature and the like can only cause changes in the state of the extranuclear electrons, and the phenomenon of radiation is caused by internal changes in the nucleus.

The relationship between the states of electrons outside the nucleus is small. In addition to spontaneous fission, radiation phenomena are generally associated with decay processes, mainly related to alpha decay and beta decay processes.

Alpha radioactivity occurs during alpha decay. At this point, the remaining nuclear after decay (usually called the daughter nucleus) is reduced by 2 and the mass is reduced by 4 compared to the nucleus before decay (usually called the mother nucleus).

Alpha decay occurs when the mother nucleus emits alpha particles through strong interactions and tunneling effects.

Beta radioactivity occurs during beta decay. There are three types of beta decay:

1 beta decay, beta decay of positrons and neutrinos;

2 beta decay, beta decay of electrons and antineutrinos;

3 orbital electron trapping, capturing an orbital electron and releasing a micro the process of the child. Beta decay occurs through weak interactions.

Gamma radioactivity is often associated with alpha decay or beta decay. The daughter nuclei of alpha and beta decay are often in an excited state.

The nucleus in the excited state emits gamma rays and transitions to a lower excited state or ground state, which is called a gamma transition. Therefore, spontaneous emission of gamma rays is generally generated with alpha or beta rays.

The daughter nucleus formed by beta decay, when its excitation energy is high enough, may emit neutrons, protons or alpha particles, and may even cause fission.

These types of decay are called beta-delayed neutron emission (β-n), beta-delayed proton emission (β-p), beta-delayed alpha emission (β- α), and beta-delayed fission (β-f).

Spontaneous fission is another type of radiation phenomenon (see nuclear fission). Some heavy nuclei can spontaneously split into two nuclei of similar mass and emit several neutrons.

Proton radioactivity is also a type of radioactivity. For example, in an excited state, a proton can be spontaneously emitted, and the decay mode is as follows: This is an example of the proton radioactivity that is the only known to date that does not belong to a delayed proton.

Radioactive Decay

The radioactive nucleus can decay in many different forms – they reach a more stable state. The main types of decay are summarized in the table below.

A mass of A, the atomic number of Z nucleus is described in the table (A, Z ), with different sub-nuclear nucleus produced after nuclear decay parent noted in a manner described in this column “daughter nucleus.”

For example, (A,?,1, Z ) means “the number of sub-nuclear masses is one less than the parent nucleus (ie, one nucleus ), and the atomic number is one more than the parent nucleus (ie, one more proton ).

Decay type

Participating particles


Type of decay associated with nuclear emission

Alpha DecayA decay type in which an alpha particle ( A = 4, Z = 2) is emitted from the nucleusA ? 4, Z ? 2)
Proton Emissiona type of decay in which a proton (p) is emitted from the nucleusA ? 1, Z ? 1)
Neutron Emissiona type of decay in a neutron that emits a neutron (n)A ? 1, Z )
Double proton emissionThe decay type of two protons emitted simultaneously in the nucleusA ? 2, Z ? 2)
Spontaneous fissionThe nucleus spontaneously splits into two or more smaller nuclei and other particles
Cluster decayThe nucleus emits a cluster of smaller nucleuses or other particles of a particular type ( A 1, Z1)A ? A 1, Z ? Z1) + ( A 1, Z 1)

Various beta decay types

Beta DecayThe decay type of an electron (e) and an anti-electron neutrino (νe) emitted from the nucleusA , Z + 1)
Positron Emission (β decay)A decay type of a positron (e) and an electron neutrino (νe) emitted from the nucleusA , Z ? 1)
Electronic CaptureThe nucleus absorbs an orbital electron and emits a type of decay of a neutrino (the decaying nucleus exists in the form of an unstable excited state)A , Z ? 1)
Double Beta DecayThe decay type of two electrons and two antineutrinos emitted by the nucleusA , Z + 2)
Double Electron CaptureThe nucleus absorbs two orbital electrons and emits the decay type of the two neutrinos (the decayed nucleus exists in the form of an unstable excited state)A , Z ? 2)
Electron capture with positron emissionThe nucleus absorbs one orbital electron and then emits a decay type of a position and two neutrinos.A , Z ? 2)
Double positron emissionThe decay type of two positrons and two neutrinos emitted in the nucleusA , Z ? 2)

Conversion between the same kind of nucleus

Homogeneous isomerizationThe type of decay of high-energy photons ( γ-rays ) emitted by excited statesA , Z )
Internal conversionExcited state nucleus transfers energy to orbital electrons, and the orbital electrons are detached from the atomic decay type.(A, Z )


Earth birth

Space of cosmic rays

Human body



X-ray examination of cancer treatment


Nuclear power generation

Detect cracks in solder joints and metal castings

Industrial production line automatically on the quality control system

Measuring the thickness of the plated film

Eliminate static electricity


We know that fertilizer uptake and loss of pest control


Identification of the age to which the antiquities belong (radioactive dating method)

Education and other

Atmospheric nuclear test

TV set

Video display

Luminous watch

Smoke fire sensors

Fluorescent sign

Lightning rod

Decay Law

The decay of a radioactive nucleus is a statistical process, so the number of radioactive atoms decreases exponentially with time as it decays, called the exponential decay law.

Where No is the number of radionuclides at decay time t =0, N is the number of radionuclides at time t, and λ is the decay constant, indicating the extent to which the radioactive material decays with time.

For a radionuclide that determines the nuclear state, λ is a constant, which also represents the probability of decay of that nucleus per unit time.

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Radioactive disintegrations in a particular energy state per unit time -d N / D T, referred to as A. It can be seen from the exponential decay law that

A = -d N /d t = λ N.

The international unit of radioactivity is Beckler (Bq), which is defined as a decay per second, and the relationship with the usual unit Curie (Ci) of previous radioactivity is 1 Ci = 3.7 × 10 (10) Bq. The ratio of the radioactivity of a radioactive source to its mass is called the Specific Activity.

The method of measuring the activity depends on the type of radiation, the level of activity, etc., and is usually divided into two categories: absolute measurement and relative measurement.

Absolute measurements are measurements made directly by definition using a measuring device. In practical applications, most of the radioactive sources are β or αradioactivity, and the activity is mostly micro-curie.

The absolute measurement methods of such radioactivity are mainly small solid angle method, 4π counting method, and conforming method.

The relative measurement is carried out under the same conditions as the standard source of known activity and the sample to be tested, and the activity of the source to be tested can be calculated according to the ratio m2m2 of the count rate and the activity of the standard source.


The time required for the number or activity of a radioactive nucleus in a particular energy state to decay to half its original size is usually indicated by the symbol T ┩.

Average life expectancy refers to the average survival time of a radioactive nucleus in a particular energy state.

Using the exponential decay law, it is easy to obtain the relationship between the half-life T ┩ and the decay constant λor the average lifetime τ. The half-lives of various radionuclides vary greatly in a wide range.

Generally speaking, the farther the nuclides deviate from the β-stabilization line (see far away). The beta-stabilized nucleus) has a shorter half-life. Different methods are used for different ranges of half-life measurements.

For nuclide with a half-life of 10 seconds to seconds, the direct measurement of N ( t ) is used to determine to using the exponential decay law. For the nuclide with a half-life of several minutes to 1-2 years, the attenuation tracking method is used to measure the change of the detector count rate with time, and T ┩ is obtained.

For radionuclides with a half-life of more than 10 years, the radioactive ratio method is used. In addition, there are measurement sub-nuclear methods, etc. which are based on the exponential decay law of radioactivity. For very short half-life (less than 10 seconds) measurements, special techniques are required (see Nuclear Energy Lifetime Measurements).

Radioactive research is very important. The decay profile established by radioactivity-based research is one of the important bases for the study of nuclear structure theory.

Various nuclear properties and nuclear reaction mechanisms can be studied by measuring the decay characteristics of various nuclear states. A large number of nuclei away from the β-stability line are identified and studied based on their decay characteristics.

Radioactivity has important applications in many disciplines, including labor, agriculture, and military.

For example, beta-ray thickness and gamma-ray detection in industry, radiation breeding in agriculture and radiation-stimulated biological growth, and radiological diagnosis and radiation therapy in medicine are all effective (see Radioisotopes in Agriculture, Application, nuclear medicine).

Radioactive measurement of isotope tracing methods and activation analysis methods also play an important role in the application of nuclear technology.

Radioactive Pollution

According to statistics, between 1944 and 1999, including the Chernobyl nuclear accident, there were 405 radiological accidents worldwide, and more than 3,000 people were exposed, resulting in 120 deaths.


The types of radioactive accidents are mainly divided into the following nine types. The first reactor accident, for example, in 1986, the former Soviet Union ‘s Chernobyl nuclear power plant accident, nuclear power plant core melt, explode, causing the dispersion of radioactive substances in the air causing serious pollution. After the Chernobyl accident, it affected the content of iodine 131 in milk all over China.

It began to pollute heavily from Xinjiang and went east to Dalian and Shenyang. Under normal circumstances, there is no iodine 131 in milk; the second is a critical accident, the third is the loss of radioactive sources, the fourth is excessive exposure of industrial sources, the fifth is excessive medical exposure, the sixth is an accident in transportation, the seventh is an experimental accident; It is a deliberate act involving radioactive materials; nine is radioactive pollution of air, water, and food.

According to the “National Radiation Accident Cases Collection 1988-1998” jointly written by the Ministry of Health’s Health Legal System and Supervision Department and the Ministry of Public Security in 2001, 332 radioactive accidents occurred in China from 1988 to 1998, and the total number of people exposed to radiation was 966.

Radiation source loss accidents accounted for about 80% of all accidents, a total of 258 accidents, most of which were responsible accidents, 584 missing radioactive sources, of which 256 were not recovered.

Among them, on June 25, 1990, the staff of the Cobalt 60 source room of the Radiology Medical Research Office of the Second Military Medical University of Shanghai violated the regulations, causing 7 staff members to be exposed to large doses, two of which were on the 25th and 90th day after irradiation. Unfortunately, three other people also suffered from bone marrow type radiation sickness.

In 1992, when the Shanxi Cangzhou District Science and Technology Commission was relocated, the old site was transferred to the local environmental monitoring station.

The Cangzhou District Science and Technology Commission has introduced five cobalt 60 radiation devices for breeding. When the environmental monitoring station was further expanded, the Shanxi Provincial Environmental Protection Bureau was asked to dispose of the old radiation source.

However, it was not found out that there were several radioactive sources, which caused a radioactive source to remain underground and be taken home by a construction worker.

He started a headache and vomiting within an hour. His wife was pregnant at the time, and his father and brother were unfortunately exposed.


The hospital in Taiyuan did not know the cause, and the radio source fell out of his pocket, but no one could identify the source. As a result, the source was thrown into the garbage of the hospital. In the process, many people are exposed. Fortunately, the source of radiation was finally found. The incident resulted in three deaths and 10 injuries.

International Atomic Energy Agency China earlier radiological accidents recorded occurred in 1963 in Hefei, Anhui Three Mile Um.

The agricultural research cobalt 60 sources that were not used for many years was placed on the edge of the river pond. A child brought it home to play, causing the family and many villagers to be exposed, eventually killing two people.

In recent years, the National Nuclear Security Administration has also notified some radioactive accidents.

For example, on October 21, 2004, a privately-owned irradiation plant built in 1994 in Jining, Shandong Province, had its own static stacking cobalt 60 irradiation device malfunctioning, and the radioactive source did not fall back to the underground safe position.

The staff entered the irradiation room without monitoring, and the exposure time was about 10 minutes, and the distance was only 0.8 to 1.7 meters. Both of them rescued invalid deaths.

On April 11, 2008, five staff members of Shanxi Hengze Radiation Technology Co., Ltd., carrying the non-normally used dosimeter into the irradiation room without overloading the radioactive source, were exposed to overdose.

One of them died after being rescued, and the other four suffered from radiation sickness.

Radioactive sources used in agriculture, medical and other departments are registered and are managed by the environmental protection department.

The environmental protection department is very strict every year, and many training centers have been set up throughout the country for rigorous training, but accidents still occur from time to time.

The public is very concerned about nuclear power plants, but for safety reasons, nuclear power plants have strict guards that the general public cannot access. It is recommended that nuclear power plants set up public reception centers to popularize nuclear power knowledge and answer public concerns, which is necessary to relieve the public’s psychological problems.

In the normal operation of nuclear power plants, trace radionuclides will also be emitted, but they are all within the allowable range.

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The problem with Unit 2 of the Daya Bay Nuclear Power Plant in 2010 was the crack in the cladding of a fuel rod, which led to an increase in the radioactivity level of the primary circuit, and the measures were quickly restored to normal.

This cannot be said to be an accident. It should be said that it is a small incident and will not cause health effects.

As for the sewage disposal problems involved in nuclear power plants, the nuclear power plants under construction are highly environmentally friendly, and the shellfish and fish in the surrounding water bodies are tested to check whether the discharge of water from the nuclear power plants meets the discharge standards.

There are pollution problems in any large industrial enterprise, and nuclear power plants are no exception.