Average content of radioactive elements in the earth's crust (Clark's value: % by weight) Average content in igneous and metamorphic rocks Average content in (sedimentary) metamorphic rocks Average content in soils
Light-coloured granites Dark-coloured granites
Granites (white, green, red and mottled series, etc.) Granites (white, green, red and mottled series, etc.) Amphibolites (gray series) Basalts, gabbros, ultramafic rocks, serpentines Marbles Slates
Uranium 2×10-4 3.5×10-4 1.8×10-4 8×10-6 3×10-6 3×10-6 very fine -5 3×10-6 very trace 3.2×10-4 1×10-4
Thorium 1×10-3 1.8×10-3 7×10 -4 6×10-4 3×10-4 very trace 1.1×10-4 6×10-4
By comparing the average content of radioactive elements in natural stone with those in the earth's crust (See Table 1), the amount of its content can be determined by the size of the radiation intensity of various types of stone. As long as it does not exceed the average content in the earth's crust, it will not affect human health. The average content of various types of natural stone We can find: (1) as we mentioned above, whether in a variety of stone, on land or in the ocean there is a certain amount of radioactive elements (trace) radioactive elements; (2), by the hydrogeneration (deposition) of marble and slate generated by the content of radioactive elements in the class, generally lower than the average crustal content (of which only a small amount of the black slate may be slightly higher than the crustal average content). Black slate may be slightly higher than the crustal average, the reasons for which are described below); (3), in the igneous granite class ①, the dark series (including the black series, the blue series and the dark green series) granite and "line color series" in the gray series of granite, the content of radioactive elements are also lower than the crustal average; (4), only the "light series" in the true granite class and the "light series" of the metamorphic formation of schist, the content of radioactive elements is lower than the average crustal value. (4), only the "light-colored series" of true granite and the formation of igneous metamorphism of gneiss and granite gneiss, etc. (including the white series, red series, light-colored green series and mottled series), the content of radioactive elements is slightly higher than the average value of the earth's crust (see below for the reasons for the slightly higher content). So from Table 1 can be seen, in all natural decorative stone, marble, the vast majority of slate, dark series (including black, blue, dark green) and gray series of granite, its radioactive radiation intensity are small, even without any test can be confirmed is "A" products, can be used in the home interior decoration and any occasion.
For light-colored series of white, red, green and mottled series of granite, can not be generalized that the intensity of radioactive radiation are large, but only in the following cases, the intensity of its radioactive radiation may be large:
1, white granite, mainly granite class of white granite. White granite is generated in the late stages of underground magma condensation, its main component is silicon dioxide (Si02, that is, quartz), up to 73-77% in the rock. The stage of generation of this rock (i.e., the late stage of magma condensation) also happens to be the stage in which radioactive elements such as uranium, thorium, rubidium, cesium, potassium, and so on, in the underground magma are relatively aggregated. As all elements (including radioactive elements) in the distribution of the Earth are extremely uneven, if it happens to meet a certain region of the distribution of radioactive elements is relatively more (geologically known as the "background bias"), then this area of the white granite produced by the intensity of radioactive radiation is likely to be large.
2, red granite, potassium-containing minerals potassium feldspar is the main component of red granite, and potassium in the isotope of potassium-40 (40K) itself is a radioactive element. Therefore, the more potassium-containing minerals (light pink, pink, etc.) there are, the higher the radiation intensity is likely to be. In addition, in the red granite category, gneiss granite and granitic gneiss are included. This kind of ancient rock, which was created two to three billion years ago, not only contains a lot of potassium feldspar, but also sometimes contains a special mineral with a beautiful color (purplish-red, saucy-red, purple, etc.) - zircon (Zr-Si04). Chromite minerals are often mixed with uranium, thorium and other radioactive elements, thus making the red color of granite more colorful and luxurious at the same time, and then also improve the intensity of radiation, which is the famous "India red" and "South Africa red" radiation intensity is large (high) where the reason.
3, in the light series of green granite, sometimes containing a colorful and beautiful green, emerald green, blue-green special minerals - Tianhe stone. Tianhe stone itself is composed of weak radioactive elements of potassium, rubidium, cesium [(K, RbCs)(A1Si308)], so the valuable green granite containing this mineral, its radiation intensity may be large.
4, for the granite of the mottled series, because there are often potassium-bearing minerals and other minerals such as quartz to form a "big class crystal", constituting a beautiful mottled granite, so the intensity of its radiation may also be large.
From the above, it can be seen that in all the light-colored series of granite, only the "background high" area of white granite, containing potassium feldspar minerals (especially containing potassium-40 isotope more) granite, containing zircon minerals (old) metamorphic rocks and granite containing Tianhe stone minerals, may form the radiation intensity of radioactive and may have a certain degree of hazardous phenomena. And this part of the granite in all the light-colored series of granite in the number is relatively small (about 20% -25%), so most of the light-colored granite can still be assured that the use of bold.
So why a small amount of black slate stone radioactive radiation intensity is also likely to be large (high)? This is because, slate stone are from rivers, rivers, lakes, oceans deposited in the muddy rock change into, which the black slate contains more carbonaceous components. Carbonaceous and muddy in the water have Luo strong adsorption and adhesion, the water in all directions of radioactive substances and various impurities are adsorbed into itself, so that the radiation intensity of some black slate may be large.
But, China University of Geosciences, Prof. Cheng Ye-suke explained that we usually say that the radioactive hazards mainly refers to the radioactive elements produced in the process of decay "radon". Radon is a radioactive gas, if people live for a long time in radon concentration is too high in the environment, radon through the respiratory tract deposition in the lungs, especially trachea, bronchial tubes, and a large number of radiation, thus jeopardizing human health, naturally, there are also a very small number of cases is due to the stone itself and the radioactivity of the direct impact on human health. And "too high concentration" of the environment is the main cause of disease, Europe as early as 1937 found that the incidence of lung disease miners is 28.7 times the average person. The United States took measures after the Second World War to artificially control the radon concentration in mines, and the morbidity rate of miners was relatively low, with 907 miners of 3 years' service age investigated and found that 3 of them suffered from lung diseases. This shows that as long as man-made control, the harm of radon can be reduced to the lowest degree. Soil, which is more familiar to ordinary people, also releases "radon". The United States has conducted relevant surveys on national resources and delineated 32 areas which are unsuitable for habitation, and some of these areas have long been established as cities or residential areas. In the Yangjiang area of Guangdong Province in China, the radioactive radiation index reached 3.3mSv. The Ministry of Health has followed up the case for 26 years and has not found that the morbidity rate in the area is higher than that in other areas. So the normal radioactive effects are not terrible, people in the medical process to receive an X-ray fluoroscopy radiation dose is equal to the sum of several years of natural radiation, compared to the sun's radiation to be much larger, but also did not see how much of an impact on people.
For people under normal circumstances each year by the radiation of the total dose control, our standards do not exceed into 1mSv, and the United States is stipulated in the 2mSv without taking into account an indeterminate amount of radioactivity on the human body and air bacteria on the human body is the same as under normal circumstances, the human body's metabolism is fully capable of adapting to the body's function, do not produce physiological lesions. From the above conclusion, we understand that the vast majority of natural stone (about 85%) of the intensity of radioactive radiation are small, no harm to the human body; only a small number of natural stone containing some special components of radioactivity may be large. And China's stone radioactivity standards in the development has been fully taken into account to safeguard the health of the people of the series, in the total radiation dose of 1mSv under the premise of control, after deducting the nature as well as the radioactivity of other materials, divided into A, B, C three categories. Our standards are much lower than the International Commission on Radiological Protection stipulated 100 Baker / per square meter standard, but also more stringent than the corresponding standards in the United States.
According to the radiation caused by the radon gas produced to determine the provisions of class A products is 70 baker / per square meter, can be used anywhere; class B products is 90 baker / per square meter, can be used in addition to indoor finishes of all the buildings inside and outside the finishing materials. As for C products, they are only used as exterior finishing materials for buildings and for industrial purposes. In the decoration, it is important to avoid using C products for indoor (especially in people's homes)
People live in an environment where radon concentration can be ignored under normal circumstances. In particular, it should be pointed out that the indoor radioactive dirt must not be all blamed on the natural stone. In fact, the main source of radon gas indoors is the presence of radon gas in the soil is constantly released to the outside in small quantities, so bungalows, buildings in the basement and semi-basement radon gas content is relatively high, and in the use of coal ash residue burned into the wall bricks, the content of its radioactive material is often higher than the radioactivity of some special minerals of granite content. All kinds of home appliances (television, computer, refrigerator, microwave oven, etc.) are required to keep releasing small amounts of radiation. In addition, indoor decoration in the use of a variety of chemicals in the paint, decorative materials, are constantly releasing some harmful gases, especially formaldehyde and benzene to the most harmful to human beings. Compared with the stone released radon gas accounted for only 2%, which can be said to be insignificant. Even if the living room has been decorated with Class B products, the radon concentration will not necessarily increase much. Because the standard test with a 4 × 4 × 0.5 meters of the sample, and living room decoration with stone thickness of only 10 cm to 20 cm, the radioactivity will be greatly reduced.
The most effective and simplest way to remove all indoor pollutants is to strengthen indoor ventilation, tests show that: a completely closed windows and doors overnight radon content of up to 151 Baker / per square meter of the room, after an hour of ventilation through the windows, the radon content fell to 48 Baker / per square meter, fully compliant with the class A products ≤ 70 Baker / per square meter of the standard. Therefore, opening the window for half an hour to one hour after getting up and before going to bed every day can ensure the physical safety of the whole family. If you are worried about C products used in the home, you can use the China Stone Association and the relevant units to develop a hand-held "stone radioactivity detector" to detect the specific content of radioactive substances in the stone plate.
Overall, China's marble, slate radioactivity is very low, no need to test, can be regulated belongs to the A class products. The vast majority of granite belongs to class A products, the rest is also basically class B, so people can rest assured that the use.