You must know the knowledge of ionizing radiation and nuclear radiation.

You must know the knowledge of ionizing radiation and nuclear radiation.

Radiation refers to the transmission of energy in the form of waves or subatomic particles moving, and the energy of the radiation radiates straight from all directions of the radiation source. It can be classified into ionizing radiation and non-ionizing radiation according to its energy level and the ability of ionized substances.

Ionizing radiation, which can also be called nuclear radiation or radioactive radiation, mainly refers to radiation with short wavelength, high frequency and high energy (dual form of particles or waves). Ionizing radiation can act on at least one electron from the ionization process inside an atom or molecule. The ionizing radiation includes high-energy particle waves such as α-rays (α particles), β-rays (β particles), and neutrons, and high-energy electromagnetic waves such as γ-rays and X-rays, and high-energy particle rays called cosmic rays are both.

Ionizing radiation is extremely harmful to the human body, because general ionizing radiation is invisible, and radioactive dust is extremely small and difficult to be detected, so the victim may be over-exposure or inhaled a large amount of radiation. dust. Excessive exposure or inhalation of a large amount of radioactive dust in a short period of time can cause acute radiation sickness, such as nausea, vomiting, abdominal pain and hair loss, and abnormalities in hematopoietic function, digestive system and nervous system; and long-term accumulation of radioactive elements In the body, it can cause chronic radiation sickness. Excess ionizing radiation is carcinogenic and teratogenic.

Behind ionizing radiation and electromagnetic radiation is a complex and professional system knowledge. To understand these two kinds of radiation and their respective hazards, we need to know them from many aspects. The following are some aspects about ionizing radiation and electromagnetic radiation. Basic knowledge, hope to help beginners quickly master them.

· What are the sources of natural radioactivity?

The natural radiation background in the environment is mainly composed of three parts: cosmic rays, yusheng radionuclides and radiation emitted by primary radionuclides.

Cosmic rays are mainly derived from the outer space of the earth. In order to find out the source of cosmic rays, experiments have been carried out to raise a large balloon equipped with a nuclear radiation detection device from sea level to high altitude, and observe the relationship between the ionization radiation particle fluence rate and the sea level. It was found that when the altitude was below 700 m, the particle fluence rate decreased sharply with increasing altitude. When the balloon height exceeds 700 m, the particle fluence rate increases rapidly as the height increases. In addition, it has been found that when the sun flares, the intensity of cosmic rays measured by the Earth is significantly enhanced, which proves that cosmic rays are generated in space outside the Earth.

Cosmic rays have primary and secondary points. Primary cosmic rays are high-energy radiation that is emitted from outer space into the Earth's atmosphere. Primary cosmic rays can be divided into "primary galaxy cosmic rays" and "primary solar cosmic rays" according to their sources. However, the former is the source of primary cosmic rays.

The primary galaxy cosmic rays are mainly composed of high-energy protons (~87%), accompanied by about 10% of the nucleus, and the rest are small amounts of heavy particles, electrons, photons, and micro-small. Primary cosmic rays have great kinetic energy, so their penetration ability is extremely strong. Primary solar cosmic rays mainly refer to charged particles released when the sun flares, and most of them are protons and alpha particles. However, these particles have lower energy and usually do not have a significant effect on the radiation dose on the Earth's surface.

Secondary cosmic rays are the product of the action of high-energy primary cosmic rays and the atmosphere. When the primary cosmic ray enters the atmosphere, the particles with great energy collide with the nucleus in the atmosphere, causing the nucleus to be torn apart. Such nuclear reactions are generally called "split reaction" or "fragmentation reaction".

In general, cosmic rays are habitually divided into "hard rays" and "soft rays" according to their energy levels. The "hard" part of cosmic rays mainly refers to high-energy particles with strong penetrating power, mainly referring to mesons and high-energy protons. The "soft" part of cosmic rays refers to low-energy particles that are more easily absorbed by substances, mainly electrons and photons.

When the high-energy primary cosmic ray reacts with the nucleus of the atmosphere, the reaction product contains a number of radionuclides in addition to the secondary cosmic ray particles. These nuclei are called "yusheng radionuclides". Although there are many varieties of Yusheng radionuclides, their content in the air is very low. Therefore, their actual contribution to environmental radiation is not significant, especially external exposure. However, the contribution of some nuclides to environmental radiation doses cannot be ignored, and it is also of great significance in scientific research.

The primary radionuclide and the nascent radionuclide are both natural radionuclides. The difference between the two is that the latter is produced by cosmic rays through the interaction with the atmospheric nucleus, while the former is formed from the earth and has existed in the earth's crust. Those radionuclides in the middle. It is therefore called the "native" radionuclide. Obviously, there may be many radionuclides formed simultaneously with the Earth, and only a few radionuclides with a sufficiently long half-life are likely to remain.

There are many varieties of natural radionuclides, their properties and status are different, and they are widely distributed in the environment. There are traces of natural radionuclides in rocks, soil, air, water, plants and animals, building materials, food and even humans. The crust is an important repository of natural radionuclides, especially native radionuclides. The radioactive materials in the earth's crust are mainly uranium and thorium. Among them, the natural radionuclides in the air mainly have surface exudates into the atmosphere and their daughter nuclei, and most of the natural radionuclides in animal and plant foods are.

The soil is mainly produced by the erosion and weathering of rocks. It can be seen that the radioactivity is transferred from the rocks. Due to the variety of rocks and the extent to which natural conditions are not consistent, it is expected that the concentration of natural radionuclides in the soil will vary widely. The geographical location, geological origin, hydrological conditions, climate, and agricultural history of the soil are all important factors affecting the content of natural radionuclides in the soil.

Radioactive materials present in rocks and soil are lost due to the leaching of groundwater, and natural radionuclides in groundwater are mainly derived from this pathway. In addition, the radionuclide adhered to the soil of the surface particles can be converted into dust or aerosol under the action of wind, and then transferred to the atmosphere and further migrated to plants or animals. Some soluble radionuclides in the soil are absorbed by the plant roots and then transported to the edible part, which is then eaten by the herbivores and then transferred to the carnivores, which ultimately becomes an important source of radionuclides in the food and in the human body. one. The concentration of natural radionuclides in ambient water is related to a variety of factors.

In addition, natural radioactive materials include cosmic rays. Cosmic rays are a stream of high-energy particles that are launched from the universe into the earth. They consist of protons, particles, and so on. Natural radioactivity has been adapted to humans and has not caused any harm.

· What is the activity?

Radioactivity refers to the number of atoms in which radioactive elements or isotopes decay per second. The current international unit of radioactivity is Becquerel, symbol Bq. 1Bq = 1 decay / second. The radioactivity of a unit mass or unit volume of radioactive material is called radioactivity ratio, or specific radioactivity.

We can use the gram radium equivalent to represent the relative activity of the gamma source. 1 gram of radium equivalent represents the ionization of gamma rays from a gamma source to air and 1 gram of a standard radium source (in a platinum-rhodium alloy tube with a wall thickness of 0.5 mm and 1 gram of radium that is in equilibrium with its daughter body) One gram of radium radioactivity is 3.7 × 1010 Bq.

· What is the amount of exposure?

The amount of exposure refers to the total amount of ionization capability of the radiation in the air. In the International System of Units, its unit is Roentgen (R). It is defined as producing 1 electrostatic unit of electricity in 1 cubic centimeter of air (1.293 milligrams of air) under standard conditions. Coulomb is currently used in units of kilograms (C/kg). It is equivalent to the charge value of X or γ ray producing a symbolic ion per kilogram of dry air under standard conditions of 2.58×10-4C, that is, 1R=2.58×10-4C/kg. The amount of exposure is only for air, only for X or gamma rays.

Another concept is the exposure rate or the illumination rate, which represents the increment of the exposure per unit time. The international unit of exposure rate is Coulomb per kilogram second.

· What is the absorbed dose?

Absorbed dose refers to the average energy of a unit mass of matter that receives ionizing radiation. It is the amount that describes the energy of ionizing radiation. When ionizing radiation interacts with a substance, some or all of its energy can be deposited in the illuminated medium. The unit of absorbed dose is rad, which is equivalent to 1 gram of material receiving 1 x 10-5 joules of energy. The currently used unit is Gy, which is equivalent to 1 kilogram of material receiving 1 joule of energy. 1Gy = 100rad.

Unlike the case of exposure, the absorbed dose is an amount of radiation suitable for any type of ionizing radiation and any type of irradiated material. It must be noted that when applying this metric, specify the specific substance to be involved, such as air, muscle or other specific materials. The amount of exposure and the absorbed dose are two completely different amounts of radiation. The amount of exposure can only be used as a measure of the X or gamma ray radiation field, describing the ionizing power of ionizing radiation in air; and the absorbed dose can be used for any type of ionizing radiation, reflecting the extent to which the irradiated medium absorbs radiant energy. However, between two different quantities, they can be converted to each other under certain conditions. For the same type, the same energy ray and the same substance, the absorbed dose is proportional to the amount of exposure. Since the average energy of X or gamma rays in generating a pair of ions in air is about 32.5 eV, the absorbed dose of X or gamma rays of 1R in air is about 0.838 rad; and the absorbed dose in soft tissue is about 0.931 rad.

· What is the dose equivalent?

The biological effects of environmental ionizing radiation are not only related to the absorbed dose value, but also closely related to the type of radiation, energy and irradiation conditions. In other words, in the case of receiving the same absorbed dose, if the type, energy or irradiation conditions of the ionizing radiation are different, the biological effects, regardless of the probability or severity, may vary. For example, if a ray can generate many ion pairs in a short circuit in the tissue, then it will cause more damage to human tissue. Therefore, at the same absorbed dose, the damage of fast neutrons and particles to human tissues is several times greater than that of electrons or electrons. In order to uniformly describe the degree of damage of various types of ionizing radiation to living organisms, in the field of nuclear radiation protection, a concept of "dose equivalent" is introduced, which is equal to the product of the absorbed dose and the coefficient describing the biological effects of different rays, the unit is Rem (rem), the current international unit is Svrt (Sv). 1Sv=100rem.

The same absorbed dose does not necessarily produce the same degree of biological effect, because biological effects are affected by factors such as radiation type, dose and dose rate, irradiation conditions, biological species and individual physiological differences. In order to compare the harmful effects caused by different types of radiation, some coefficients are introduced in the radiation protection. When the absorbed dose is multiplied by these correction factors, the same scale can be used to compare the severity or production of biological effects caused by different types of radiation exposure. Probability.

· What is the collective dose equivalent?

In environmental radioactivity, it is often necessary to make a scientific assessment of the harm that environmental radiation gives to a certain group. For example, when a nuclear facility discharges radioactive waste into its environment, it is required to estimate the dose equivalent of the radioactive waste discharged from the enterprise to the surrounding public to assess the extent to which the group is affected. At this time, the concept of "collective dose equivalent" must be used to evaluate, which is defined as: the effect that radiation gives to a group is the sum of the dose equivalents of each individual component.

The difference between dose equivalent and collective dose equivalent is that the former is for a single organism and the latter for a population. The international unit of collective dose equivalent is human? Sivot, the symbol is man? Sv.

· What is the effective dose equivalent?

The effective dose equivalent is the sum of the average dose equivalent received by each organ or tissue of the human body and the corresponding machine weight factor when the radiation effect of human tissue or organ is a random effect, that is, when the whole body is subjected to non-uniform irradiation, that is, For effective dose equivalents.

The SI unit of the effective dose equivalent is the same as the dose equivalent, ie, Swart (Sv), and the dedicated unit for temporary use is Rem. Effective dose equivalent is an important concept. It is a measure of the incidence of health effects caused by sources of radiation in vivo or in vitro (whether uniform or non-uniform) to assess the total extent of ionizing radiation to the human body. .

The table below gives a comparison of the radiation unit. The amount of radiation includes the radioactivity of the radioactive material, the intensity of the radiation field, and the absorbed dose of the substance being irradiated.

Radiation unit

· What is the effective dose size of natural radiation?

Natural radiation sources produce the highest exposures, which are much higher than those produced by their radiation sources (Table 1). Therefore, the increase in natural radiation introduced by human activities may also result in higher doses than other sources. However, due to the following reasons, natural radiation exposure often does not attract people's attention: (1) natural radiation has existed since ancient times; (2) natural radioactivity (such as radium) without special concentration is impossible to produce acute exposure to humans. of.

Estimated annual effective dose equivalents from natural sources of radiation in normal background areas (UNSCEAR, 1982 (1988))

·

How does ionizing radiation harm the human body?

When ionizing radiation passes through the body, the radiation acts on the body's life material molecules in two ways, namely direct action and indirect action. Direct action means that the radiation directly delivers energy to the living substance molecule (mainly DNA) on the ray track. Molecule) and ionize or be excited to cause damage. During this process, the molecules that receive the ray energy are themselves damaged. This is a purely physics process. The indirect effect means that the molecules of the living matter are not on the track of the ray and are not directly receiving the ray energy. The energy of the ray is absorbed by the water molecules or other molecules around the living substance molecule to be ionized or activated. Free radicals (ie, an extremely active atomic group) are then migrated at a certain distance to reach and react with the molecules of the living matter, eventually causing damage to the living matter. In this process, the water molecule is the direct recipient of the ray energy, and the living material molecule does not directly receive the energy of the ray, so it is called an indirect effect. There are both physical and chemical processes in the indirect process.

Taking water molecules as an example, the formation process of free radicals is illustrated.

"?OH" and "?H" in the above reaction formula are free radicals. The chemical nature of free radicals is very active and easily reacts chemically with various molecules, including DNA molecules.

Schematic diagram of radiation induced damage formation process

When the absorbed radiation dose reaches a certain level, the DNA in the nucleus can be damaged by the direct or indirect action of radiation. DNA damage has been observed in a variety of forms, including single-strand breaks, double-strand breaks, and base damage. Radiation-induced DNA damage is thought to be the initiation event of radiation damage, the starting point for all effects.

Under normal conditions, cells can repair single-strand breaks or double-strand breaks in DNA molecules within hours.

The repair of damaged DNA (also called repair replication) is the removal of a segment of the DNA molecule that contains damage (single-strand breaks, base damage, or other structural defects) under the action of an enzyme. And re-synthesize the new continuous double strand. Specifically, the DNA of the damaged part is cleaved by the action of the endonuclease, and a new single strand complementary to another single strand corresponding thereto is synthesized by the DNA polymerase.

Schematic diagram of DNA molecular structure

DNA molecular helix structure model

In most cases, DNA damage can be repaired normally. However, sometimes there are repair errors, that is, in the process of repairing DNA molecules, the order of base pairs is wrong, and there are many errors in the order of base pairs: some are in the position where they should be 密 or in the position It should be that there is a 嘌呤 in the position of the pyridine (this kind of error is called transversion); some are in the position where it should be A or C in the position of T, or vice versa (this error is called conversion) ); some have a base pair in the normal order (this error is called insertion); some are missing a base pair in the normal order (this error is called a missing); and in the normal order A period of alkali is reversed in order (this error is called inversion).

As mentioned above, the normal life course of a cell is determined by a pre-programmed procedure in the gene carried on the chromosome in the nucleus (ie, the order of base pairs on the DNA molecule), if the base pair on the DNA molecule The order has changed, the pre-programmed procedures have been disrupted, and the normal life processes of the cells have become confusing, that is, mutations have occurred.

The effects of mutations on the life processes of cells can be different. Some genes are crucial for the survival of cells. Mutations in this gene make the mutant cells either unable to survive, or the mutant cells themselves can survive but cannot undergo cell division. Both of these conditions are called cell death. Radiation-induced cell death is mostly the latter type of death, that is, radiation causes the irradiated cells to lose their ability to proliferate. This effect of radiation is called killing cells. In addition, radiation acts directly or indirectly on the cell membrane, causing cell damage and cell death. However, this often occurs when the radiation dose is high. In the low dose range where radiation protection is usually of concern, the mechanism of cell death is mostly the mutation of the cell's genes. Cell death is the basis for the deterministic effects of radiation.

The time to cell death can vary depending on the population of damaged cells. In a cell population with rapid cell division (such as lymphocytes in the blood), cell death can be expressed several hours after exposure. In a cell population with extremely slow cell division (such as nerve cells, etc.), death may be in several It won't happen even in months or even years.

Another possibility is that the misalignment of base pairs (mutations) produced during DNA damage repair occurs in genes that are not critical to cell survival. At this time, the cell carrying the mutated gene can continue to survive and continue cell division, but some properties of the cell change due to the presence of the mutated gene, and there may be some properties that the cell does not have under normal conditions. . This condition is called cell variability. If cell variability occurs in somatic cells, and the cells become capable of having tumor (cancer) cells (such as the potential for infinite proliferation of cancer cells, the ability to invade adjacent tissues, and the ability to metastasize to distant areas, etc.) ), it is called a malignant transformation. The malignant transformation of somatic cells caused by radiation is the carcinogenic effect of radiation. If the mutated cell is a germ cell (sperm cell or egg cell, or both), the effect of the variability will be on the embryo produced by the germ cell (that is, the individual from which the embryo develops) and all that it reproduces. It is manifested in the offspring, which is the genetic effect. Gene mutations induced by radiation in germ cells are the basis for the genetic effects of radiation. The classification of human gonads (testicles and ovaries) as key organs in radiation protection is precisely to prevent the occurrence of radiation genetic effects.

It should be noted that although radiation carcinogenesis and radiation-induced genetic damage have similarities in the induction mechanism, they are not exactly the same. It is generally believed that radiation-induced mutations in germ cells are a single biological event, while radiation-induced carcinogenesis is a multi-stage process with many stages. Radiation-induced cell variability may be one of the stages (although very Important startup phase). It is quite possible that radiation will also play a role in some stages after startup.

· What is the relationship between the injury to the human body and the effective dose?

The energy deposition of ionizing radiation is a random process, so even at very small doses, it is entirely possible to deposit enough energy in critical volumes within the cell and cause cell variability. The occurrence of biological effects (ie, genetic changes and malignant transformation of cells) due to cellular variation of individual cells is also a random event. Therefore, we refer to this type of radiation biological effect as a random effect to distinguish it from another type of non-random effect. The random effect is characterized by the fact that it does not have a threshold, which means that there is a certain probability even in the case of a small dose; the probability of occurrence of such an effect increases as the dose increases, and the effect is severe. The degree is independent of the dose. These characteristics of random effects are determined by the mechanism of their occurrence.

In another case, all or part of the tissue is irradiated, and a significant number of cells constituting the tissue are killed, and these cells cannot be compensated for by the proliferation of the surviving cells, thereby making the tissue or the tissue The constitutive organ function is affected and produces clinically detectable symptoms, and the effects produced by such an occurrence mechanism are called deterministic effects.

In the past, such effects were called "non-random effects" because they were not random. However, the mechanism by which such effects are based (radiation kills cells) is itself a random process, so what is called a "non-random effect" is not very suitable. In the 1990 Recommendation of the International Commission on Radiological Protection, the term "deterministic effect" was used to replace the "non-random effect". The deterministic effect means: "the consequence determined by the event that has occurred", that is to say, the deterministic effect is determined by the event "radiation kills the cell", although the event of killing the cell itself has Randomness.

The deterministic effect caused by ionizing radiation is that the exposure of the whole body or local irradiation can cause sufficient cell damage or death, thus affecting the function of the irradiated tissue or organ, which is a considerable number of cells. Or the result of a large proportion of cells collectively damaged. In most cases, the death of one or a small number of cells does not have any effect in the tissue made up of countless cells. This means that any deterministic effect occurs when a certain number or percentage of cells are affected. Therefore, the deterministic effect should have a threshold dose below which the number or proportion of cells affected is insufficient to produce a defined lesion or insufficient to cause clinical symptoms of such effects to occur. As the dose increases, the number of unaffected living cells will become less and less, the symptoms will become more and more serious, and the incidence of symptoms will be higher and higher. Therefore, the incidence and severity of deterministic effects increase with the dose. And increase. It can be seen that the deterministic effect is exactly the opposite of the random effect, that is, it has a threshold dose. The probability of an effect occurring at a dose below the threshold dose should generally be zero; the severity of the effect is related to the dose received, the higher the dose, the more severe the effect; if the radiation exposure is sufficiently severe, it may occur as a consequence of the exposure death. In general, death is the result of a severe reduction in the number of cells in one or more key organs of a human body or in a critical system.

In summary, it can be considered that there is a relationship between the two classification systems of radiation biological effects, namely:

From the above relationship, it can be seen that the non-carcinogenic effect in the somatic effect is a deterministic effect, while the carcinogenic effect in the somatic effect is a random effect, and the genetic effect is a random effect.

The above classification is the result of in-depth study of the mechanism of radiation biological effects, and has had a huge impact in the development of radiation protection. With the distinction between different radiation biological effects, the International Commission on Radiological Protection, in its 1977 Recommendation, explicitly states the purpose of radiation protection as "radiation protection aims to prevent harmful non-random effects (ie certainty) Effect) and limit the incidence of random effects to a level that is considered acceptable." That is to say, in the practice of radiation protection, different countermeasures should be taken for different effects. For deterministic effects, because of the threshold dose, and because the probability of occurrence of the dose below the threshold dose is zero, it can be "prevented". "It occurs; for random effects, because of its non-threshold nature, there is a certain probability of occurrence at any low dose, so it is objectively impossible to "prevent" such effects, only through Various measures reduce the dose and "limit" it to reduce the probability of such effects to an "acceptable level" (not an unrestricted reduction).

· What is the genetic effect of ionizing radiation?

If an organism is exposed to germ cells when exposed to ionizing radiation, and the gene is mutated in the irradiated germ cells, the situation will be different. In general, if the genetic mutation does not cause the death of the irradiated germ cells, and the germ cells may combine with the heterogeneous germ cells to form an embryo, the consequences of ionizing radiation exposure may be in the offspring of the irradiated organism. Shown in the middle. This type of radiation biological effect that occurs in the offspring of the irradiated individual is called the radiation genetic effect.

· What are the characteristics of the radiation genetic effect?

Radiation genetic effects are the result of exposure of the germ cells of an organism. Usually the radiation genetic effects have the following characteristics:

The genetic effect does not occur in the irradiated individual itself, but in some descendants of the individual's reproduction, and thus the connection between the effect and the individual's exposure is not easily found;

The time between the exposure of the organism to the appearance of the genetic effect is too long (more than the life of the organism, sometimes even several times the life, ie several generations);

Genetic effects are heritable, so in theory, their effects can be enormous.

· What is hernia?

The cockroaches in nature are produced by the decay of radium and are the only gaseous radioactive elements that humans are exposed to. The half-life of strontium is only 3.8 days. After strontium formation, it decays quickly and produces a series of radioactive products that eventually become stable elemental lead. The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) estimates that the annual effective dose of radiation from nature to the public is 2.4 mSv, with the contribution of strontium and its daughters accounting for 54%.

· What harm does 氡 have to the human body?

氡 Enters the body through breathing, and short-lived radionuclides produced during decay are deposited in the bronchi, lung, and kidney tissues. When some short-lived radioactive nuclei decay, the released alpha particles have the greatest damage to internal radiation, which can cause the respiratory epithelial exchange cells to be irradiated. Long-term internal irradiation may cause local tissue damage, and even induce lung cancer and bronchial cancer. It is estimated that in a person's life, if you live in a room environment with a concentration of 370 Bq/m3, 30 to 120 deaths per 1,000 people will die of lung cancer. When sputum and its daughters decay, they also emit γ-rays with strong penetrating power, causing external exposure to the human body.

If you live in a high-energy environment for a long time, it may cause harm to the human blood circulation system, such as leukopenia and thrombocytopenia, and severe leukemia. This kind of harm has a heavy lesson: In 1922, several archaeologists in Egypt discovered the tomb of the ancient Egyptian Dutangkamen Pharaoh, and then died bizarrely. Since then, the pharaoh's poisonous curse has gone without saying that people have legendary ancient Egypt. The man cast a poisonous spell in the pyramid, which made the man who hacked into the pyramid poison the curse and sent his life. Recently, indoor environment experts in Canada and Egypt have solved the mystery of the poison curse that has plagued people for nearly 80 years. They found that the pyramid contained a large number of dangerous suffocates, causing contact to die of lung cancer. Expert research has found that this deadly suffocating gas is released from the building pyramid stones and the decaying uranium contained in the soil. The three ancient Egyptian buildings with the highest radon are followed by the Shakkhamet Pyramids south of Cairo, the Abis Tunnel and the Sarabium Mausoleum. The indoor environment expert said: "It is the high content of helium that damages the health of Egyptian archaeologists that year."

The harm of radon to human health

· What are the sources of indoor cockroaches?

æ°¡ from building materials; æ°¡ from the bottom soil; æ°¡ that ventilates from the outdoor air into the room; æ°¡ that is released from the water supply and natural gas used for heating and kitchen equipment.

· What is the source of natural sputum and its effective dose size?

æ°¡ is the only nuclides recommended by the International Commission on Radiation Protection (ICRP) for specific data on the level of chronic exposure. In human exposure, in the case of a single nuclides, strontium and its daughters produce the largest amount of exposure, accounting for about 50% of the radiation produced by natural radiation.

Annual Effective Dose of Natural Radiation in Chinese Residents (Pan Ziqiang, 1997)

· How to prevent the harm of cockroaches to the human body?

Since the hazard of cockroaches is accumulated for a long time and is not easy to be detected, it must be highly valued and well publicized and protected. In order to reduce the concentration of indoor radon, the construction department should avoid the high-capacity areas when building new houses, and choose the building materials with low content as much as possible. The marketer must show the radioactivity level test certificate to the customer when selling the building materials. Residents should pay attention to the selection of decorative materials with low content when carrying out home decoration. Increasing indoor ventilation is the most convenient and effective way to reduce mites. When the doors and windows are open, the concentration of indoor rafts and their children is roughly equal to that in the external environment. Especially in winter, people are closed for shelter from wind and cold. In summer, air conditioning is installed for summer heat, so that the living room is often occupied by a closed space. As a result, the indoor cockroach gradually accumulates and the concentration rises, so it is especially important to open the window for ventilation in the summer.

For families with high concentrations of cockroaches, there are also simple remedies. The most common method of reducing the concentration of strontium is ventilation. Taking a typical house of about 120 square meters as an example, after the door and window were closed for one night, the concentration of cockroaches was 151 cubic meters. After opening the window for one hour, it was reduced to 48 cubic meters. For the basement, ventilation should also be addressed, and the walls and floors should be covered with a dense material or anti-mite coating to prevent the spread of the cockroaches. A good example here is the subway. Reporters and experts tested in the subways of Beijing and Guangzhou, respectively, and their radon concentrations were very low, ranging from 17 to 54 cubic meters. This is because the walls of the subway are covered with low-activity and dense materials, plus a strong ventilation system.

Households living in bungalows or first-floor buildings should block and seal the gaps in the indoor floor. It is also possible to reduce the concentration of radon by installing exhaust fans and using air fresheners.

· Is building ceramics radioactive?

Radioactive pollution in modern cities is almost ubiquitous, and people living in consumer goods such as glass, ceramics, and building materials have radioactive materials to varying degrees. Building ceramics are mainly formed by molding glazes of clay, sand, slag or industrial waste and some natural materials. Due to the geological history and formation conditions of these materials, there are more or less radioactive elements such as antimony, radium, potassium and the like. In particular, the glaze on the surface of building ceramics contains high-activity zirconium indium sand. Although the firing temperature of building ceramics is mostly at 1100~1300°C, it does not eliminate the radioactivity of these materials. The radioactivity level depends on the material and glaze. The radioactivity in the sub-species, and the radioactivity of the various varieties of the tiles varies.

In recent years, the radioactivity of natural stone has been supervised by the relevant state departments, and the radioactivity of building ceramics has also attracted people's attention. The recent test results of hundreds of users inspecting stone, ceramic tiles and 63 interior decorative surfaces in Tianjin show that according to the current national radioactive standards for building materials, ceramic tiles account for about 90% of the total number of interior finishes. In July 2000, an analysis and testing center of a large building ceramics production found that radioactive materials in polished building bricks, glazed tiles and other building materials ceramics exceeded the standard, and the unqualified rate exceeded 1/3. Last year, the inspection department of Sichuan Province measured 34 large building materials production plants in a certain province, and found that the number of manufacturers with excessive radioactivity was as high as 17!

· What are the hazards of radioactivity in building ceramics?

It is well known that radioactive materials are widely present in geological layers and have certain damage to the human body.我们的身体对放射性的承受能力有一定限度，过度了则有可能引起不适和病变。所以说，放射性物质超过一定标准就一定会造成危害。研究证明，建筑装饰材料放射性超标，直接影响消费者特别是儿童、老人和孕妇的身体健康。

建筑材料中的放射性危害主要有两个方面，即体内辐射与体外辐射：体内辐射主要来自于放射性辐射在空气中的衰变，而形成的一种放射性物质氡及其子体。氡是自然界唯一的天然放射性气体，氡在作用于人体的同时会很快衰退变成人体能吸收的核素，进入人的呼吸系统造成辐射损伤，诱发肺癌。统计资料表明，氡已成为人们患肺癌的主要原因，美国每年因此死亡的达5000~20000人，我国每年也约有50000人因氡及其子体致肺癌而死亡。另外，氡还对人体脂肪有很高的亲和力，从而影响人的神经系统，使人精神不振，昏昏欲睡。体外辐射主要是指天然石材中的辐射体直接照射人体后产生一种生物效果，会对人体内的造血器官、神经系统、生殖系统和消化系统造成损伤。

· 怎样看待建筑材料放射性污染的伤害案例？

近年来，由于广大消费者的室内环境意识不断增强，一些建筑材料放射性污染造成人体伤害的案例频频见于报端，使一些消费者到了谈"放射性"色变的程度。那么到底怎么看待这些放射性污染造成的伤害呢？从目前室内环境造成的一些伤害案件看，主要有这样几个特点：

加害主体不确定性。由于造成人体伤害的因素比较复杂，也不能排除除了室内环境污染造成伤害以外其他一些因素造成人体伤害的可能性。 造成人体伤害的因果关系复杂性。人生活在复杂的室内环境中，其健康损害往往由多种因素促成，如果缺乏必要的科学依据，则难以证实某种建筑材料与某健康损害结果之间的必然关系。 室内环境污染对人体伤害的潜伏性。据医学专家研究证明，癌症在人体内的潜伏期长达20年以上。 室内环境造成伤害的广泛性。这更增加了认定和衡量某种建筑和装饰材料中的有害物质对人体损害程度的困难。

另外，由于体质的差异性、有害物质的放射程度及用量、接角时间长短，造成的伤害也是不同的。所以，应该科学地分析室内环境污染物质对人体造成的伤害，提高人们的自我保护意识和室内环境意识，尽量减少和防止室内环境中的有害物质对人体的伤害。同时，对室内污染造成的伤害要进行具体分析，进行科学的评断。

· 消费者怎样保护自己不被建筑和装饰中的放射性物质伤害？

在进行写字楼和家庭装修时，要合理搭配和使装饰材料，最好不要在房间里大面积使用一种装饰材料。 为了防止室内的放射性物质过高，最好在新住房装修前进行放射性本底的检测，这样将有助于石材和通体砖品种的选择。 到建材市场选购石材和建筑陶瓷产品时，要向经销商索要产品放射性检测报告，要注意报告是否为原件，报告中商家名称和所购品名是否相符，另外还有检测结果类别（A 、B 、C）。 对商家没有检测报告的石材和瓷砖的产品，最好的方法是请专家用先进仪器进行放射性检测，然后再决定是否购买。 已经装修完的房间，可请专家到现场检测，如果放射性指标过高，必须立即采取措施进行更换；如果超大型标不高，可不必拆除，保持房间经常通风或选用有效的空气净化装置。

· 如何简单判断石材放射性情况？

一般来说石材分为大理石、花岗岩，大理石放射性比花岗岩小。可以根据石材的颜色可以简单判断辐射的强弱，红色、绿色、深红色的超标较多，如杜鹃红、印度红、枫叶红、玫瑰红等超标较多。

· 如何检测石材放射性？

在近几年的装修用材中，天然石材因其色彩丰富、自然、材质坚固耐久，而被越来越多的运用在各种公共设施中。石材固然会使满堂生辉，但也和自然界的其它物质一样，含有天然放射性元素--伽玛射线粒子。人们长期接收超高的伽玛放射性辐射，会引起辐射损伤、皮肤病，还会使肺癌、白血病发病率增高。

为了防止放射性元素含量过高的石材进入我们周围环境，我国早在1993年就制定了《天然石材放射性保护分类控制标准》，可是如何执行标准，正确、快速地测量岩石放射性核素，并且根据结果划分类别却十分困难。

以往传统的划分石材放射性类别的方法是将大块石材先粉碎，取重量300克左右的样品封存20天，然后进行伽玛放射性元素含量的测量划分。根据伽玛元素含量的高低，综合确定石材放射性类型，最快也要一个月时间，而且必须在实验室进行，不能广泛推广。费时费力，分析样品的费用也很高。

为了弥补过去方法的不足之处，科学家发明了现场快速石材放射性检测仪。这种专业的放射性检测仪能够在现场快速准确地测出石材的放射含量。采用了这种石材检测仪后，我们在进行装修时，就可以放心大胆的选择我们喜欢并且对身体无害的石材来美化我们的居室。而我们的居室也将在石材的映衬下，充满自然典雅的气息，成为美丽、温暖、安全的爱巢。

石材专用放射性检测仪（美国Inspector 多功能核辐射检测仪、放射性污染检测仪）

海关工作人员利用Inspector 多功能核辐射检测仪在现场快速对各类进出口石材的放射性辐射进行快速检测

· 是不是Ｂ、Ｃ类石材就是超标石材？

根据国家建材局和卫生部共同制定的建材行业标准《ＪＣ５１８－９３天然石材产品放射性防护分类控制标准》中，按放射性比活度把石材分为Ａ、Ｂ、Ｃ三类，每一类都有分类控制值，且Ａ、Ｂ、Ｃ三类都属于符合标准的石材，只是使用范围不同。标准规定：放射性比活度相对较小的为Ａ类石材，其使用范围不受限制；放射性比活度相对较高的为Ｂ类石材，除不易用于居室内饰面外，可用于其他一切建筑物的内外饰面；放射性比活度较高的为Ｃ类石材，只可用于建筑物的外饰面、海堤、桥墩及碑石、园林等外装修材料等。因此，不能笼统地说Ｂ、Ｃ类石材就是超标石材。

· 如何判断市场上大理石用于住宅内部装璜是否超标？

根据《产品质量法》第二十八条规定："易碎、易燃、易爆、有毒、有腐蚀性、有放射性等危险物品以及储运中不能倒置和其他有特殊要求的产品，其包装质量必须符合相应要求，依照国家有关规定作出警示标志或者中文警示说明，标明储运注意事项。"
购买大理石，应仔细察看是否有放射性警示标志或中文说明，如果没有，应视作无放射性或达到放射性安全标准。

· 放射性超标石材对人体是否会导致危害？

对这个问题，对低剂量照射，专业人士也有不同的看法，双方都缺少必要的流行病学调查临床数据。但有一点是肯定的：即对放射性的高剂量照射，肯定会对人体造成确定性效应的危害，而对于建材产品、石材产生的低剂量照射，有可能发生癌症，发生癌症的概率随剂量的升高而增大，一般为十万分之几。这一危险度并不比坐汽车、坐火车和从事建筑施工、矿山开采等行业的危险度高。石材标准的分类并不是有害还是无害的分界线，它需要做利益与代价分析，也即人类的某项实践活动当带来的利益大于付出的代价时，则这种实践是正当的。

总体而言，我国绝大部分石材品种是满足百姓家居装饰使用，其放射性水平同其它建材相当。当然，我们也不能否认确实有部分品种放射性水平与标准要求的A类产品偏高，这与石材取自的矿山有关。对此，只要我们合理选用石材，就不用担心其对人体健康的危害。

500pcs Poker Chips

500PCS 11.5 G DICE Poker Chips SETS with ALUMINUM CASE

Item	500pcs Poker Chips Set in Aluminum case
Component	500pcs Poker Chips; 2 playing cards; 5 dices; 3 Dealers
Size	Diameter: 40mm; thickness 3mm
Material	ABS+IRON
Weight	11.5g
Color	Red, Green, Black, Blue, white in stock

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