What is nuclear radiation

Nuclear radiation, commonly known as radioactivity, exists in all substances. Nuclear radiation is the microscopic particle flow generated during the transition of an atomic nucleus from one structure or energy state to another; All kinds of substances are composed of simple substances, which are called elemental components. The basic unit of an element is an atom, and any element that occupies the same position in the periodic table, has the same atomic number but different atomic masses is called an isotope. If an atom undergoes a spontaneous change in its atomic structure due to reasons other than external factors, we call it nuclear decay. Isotopes with this nuclear decay property are called radioactive isotopes. During the decay process, a special type of particle or radiation with a certain amount of energy is emitted, which we call nuclear radiation or radioactivity.

Types and properties of nuclear radiation

According to the different properties of nuclear radiation, the particles or rays emitted include alpha rays, beta rays, gamma rays, X-rays, etc.

*Alpha particles generally have an energy of 4-10MeV, and ionizing gases with alpha particles is much stronger than other radiation. Therefore, in detection, alpha radiation is mainly used for gas analysis to measure parameters such as gas pressure and flow rate.

Secondly, beta particles are actually high-speed moving electrons with a range of up to 20m in gasinstrumentIn China, the thickness, density, or weight of materials are mainly measured based on the radiation and absorption of beta particles; Measure the thickness of coverage based on the reaction and scattering of radiation, and utilize the high electrical power of beta particles to measure gas flow rate.

Thirdly, λ radiation is an electromagnetic radiation emitted from the nucleus of an atom. It has a strong penetrating ability in matter, with a range of several hundred nanometers in its gas and the ability to pass through solid matter several kilometers thick. Lambda rays are widely used in various detection instruments, especially in situations where radiation and penetration are required, such as metal flaw detection, side thickness measurement, and density measurement of objects.

Fourthly, X-rays are electromagnetic wave energy emitted by the excitation of inner layer electrons outside the atomic nucleus.

The hazards of nuclear radiation

When people are exposed to nuclear radiation, they may develop radiation sickness. This disease has symptoms. Within a few hours, you will feel nausea and vomiting, followed by symptoms such as diarrhea, headache, or fever. After the initial symptoms have passed, there may be a brief asymptomatic period, but new and more severe symptoms will appear several weeks later. At higher radiation doses, these symptoms may appear faster and more pronounced. Meanwhile, nuclear radiation can cause extensive, and often fatal, damage to the internal organs of the human body. Half of healthy adults cannot withstand a radiation dose of 4 Gy when exposed to nuclear radiation.

nuclear radiationsensor

A nuclear radiation sensor is a sensor that uses radioactive isotopes for measurement, also known as a radioactive isotope sensor. A nuclear radiation sensor operates based on the absorption, backscattering, or ionizing excitation of radiation by the substance being measured. A nuclear radiation sensor generally consists of a radiation source, a detector, and an electrical signal conversion circuit, which can detect parameters such as thickness and level.

Radiation sources and detectors are important components of nuclear radiation sensors, and radiation sources are composed of radioactive isotopes. A detector, also known as a nuclear radiation detector, can detect the intensity and changes of radiation. With the development of nuclear radiation technology, the application of nuclear radiation sensors is becoming increasingly widespread.

Nuclear radiation detector

A detector is a receiver of nuclear radiation, which is an important component of a nuclear radiation sensor. It refers to a material or device that can indicate, record, and measure nuclear radiation. Its purpose is to convert nuclear radiation signals into electrical signals, thereby detecting the strength and changes of radiation. At present, the main instruments used for detection include ionization chambers, scintillation counters, and Geiger counters.

ionization chamber

The ionization chamber is a simple principle in gas detectors. The normal operation of an ionization chamber is to use an electric field to collect all the charges generated by direct ionization in the gas. The ionization chamber consists of two basic electrodes, one is the high-voltage electrode and the other is the collection electrode. The chamber is filled with high-pressure gas argon, and the outside is a sealed shell. The principle of a gas detector is that when the detector is exposed to radiation, the radiation interacts with molecules in the gas, producing an ion pair consisting of an electron and a positive ion. These ions diffuse freely towards the surrounding area. During the diffusion process, electrons and cations can recombine to form neutral molecules. However, if a DC polarization voltage V is applied to the collection electrode and high voltage electrode that make up the gas detector to form an electric field, electrons and positive ions will be pulled towards the positive and negative poles respectively and collected. As the polarization voltage V gradually increases, the working state of the gas detector will change from the composite region, saturation region, proportional region, finite proportional region, Geiger region (G-M region) to the continuous discharge region.

Gas discharge counter tube (Geiger counter tube)

The Geiger counter tube is also a radiation detector designed based on the ionization effect of radiation on gases The main difference between it and the ionization chamber is that it operates in the gas discharge area and has an amplifying effect. Its structure is shown in the figure on the right The counting tube uses a metal cylinder as the cathode and a tungsten or molybdenum wire at the center of the cylinder as the anode, separated by an insulator between the cylinder and the wire. The counting tube is filled with gases such as argon and helium. For easy sealing, glass is commonly used as the outer shell of the counting tube, while the cathode is coated with metal or graphite inside the glass surface or a metal cylinder is used as the cathode inside the outer shell.

Scintillation counter

The phenomenon of material being excited by radiation and emitting pulsed light during the transition from the excited state to the ground state is called scintillation. The substance that can produce such a luminescent phenomenon is called a scintillator. The scintillation counter first converts radiation energy into light energy, and then converts light energy into electrical energy for detection. It consists of a scintillation body, a photomultiplier tube, and an output electrical device.

Proportional counter tube

It is composed of a cylindrical cathode and a core wire as the anode, sealed with rare gases such as nitrogen, carbon dioxide, hydrogen, methane, propane, etc. When radiation is injected to ionize a gas, due to the high electric field density near the core wire, electron collisions are accelerated, obtaining sufficient energy in the gas to collide with other gas molecules and atoms and generate new ion pairs; This process is repeated and amplified, and people refer to it as gas amplification. The amplification is applied near the core wire, so the nuclear radiation sensor can obtain a certain amplification factor independent of the incident area of the radiation. The cations generated by the amplification quickly leave the gas amplification area and produce output pulses. The size of the output pulse is proportional to the number of electron and cation pairs generated by the incident radiation, and the logarithm of electron and cation pairs is proportional to the energy of the radiation absorbed by the gas. Therefore, a proportional counter can detect the energy of the incident radiation. Proportional counter tubes are mostly cylindrical, spherical, or hemispherical in shape. The anode is very thin and the cathode diameter is large, mainly to maintain a strong electric field near the anode under low applied voltage, so as to have sufficient gas amplification factor. Proportional counter tubes can measure the energy of incident particles over a wide energy range, with high energy resolution, short resolution time, and fast counting capability.

Semiconductor detector

Semiconductor detectors are a rapidly developing type of radiation detector in recent years. We know that once a charged particle is incident on a solid, it interacts with electrons in the solid and loses energy before stopping. Charged particles incident on semiconductors generate electron and hole pairs during this process.

X-rays or gamma rays generate secondary electrons due to photoelectric effects, Compton scattering, electron pair generation, etc. These high-speed secondary electrons undergo the same process as charged particles to produce electrons and holes. If these generated charges are extracted, radiation can be converted into electrical signals. As for semiconductors, Si and Ge are mainly used, and research has also been conducted on materials such as GaAs and CdTe. At present, the developed semiconductor sensors include PN junction sensors, surface barrier sensors, lithium drift sensors, amorphous silicon sensors, etc. (end)