Stone radioactivity refers to the radioactive substances produced by the three radioactive elements radium, thorium, and potassium contained in the stone during the decay process, mainly "radon" gas. If the content of decayable substances is too large, that is, the "specific activity" of radioactive substances is too high, it will be harmful to the human body. At present, all countries in the world have basically formulated standards for stone radioactivity.
In terms of numerical standards, the standards of China and Poland are the strictest. According to the test data of the Geological Survey Center of the National Building Materials Bureau and the Industrial Hygiene Laboratory of the Ministry of Health, the specific activity of granite stone is higher than that of marble and slate; from the perspective of stone color, the specific activity from high to low is Red, flesh red, off-white, white and black stone. However, most of the stones tested in our country are safe.
According to the building materials industry standard "JC518-93 Natural Stone Products Radiation Protection Classification Control Standard" jointly formulated by the National Building Materials Bureau and the Ministry of Health, stones are divided into three categories: A, B, and C according to the specific activity of radioactivity. Each category has Classification control value, and the three categories A, B, and C are all stone materials that meet the standards, but the scope of use is different. The standard stipulates that the relatively small radioactive specific activity is Class A stone, and its scope of use is not limited; the relatively high radioactive specific activity is Class B stone, which can be used for everything else except that it is not suitable for interior decoration. Internal and external finishes of buildings; Class C stones with high radioactive specific activity can only be used for external finishes of buildings, seawalls, bridge piers and steles, gardens and other exterior decoration materials. Therefore, it cannot be generally said that B and C stones are over-standard stones.