Studies On Radiological Dose Model And Measuring Method Of Undamaged Samples For Decorative Building Materials

Indoors absorbed dose rates in air would arise when materials with elevated levels of natural radionuclides are used. Because there is not accurate radiological dose model of building materials, the studies on health effect coming from materials are restricted.This paper discusses radiological dose model and limits of decorative building materials. And a new method of undamaged samples of decorative building materials is suggested.1. Studies on radiological dose models for some kind of decorative building materialsBecause there are different thickness, different densities and different specific activities between different kind of decorative building materials and soil, decorative building materials cannot be adopted the radiological dose model of soil. This paper calculated conversion factor between specific activities and absorbed dose rate for some kind of decorative building materials by Monte Carlo EGSnrc.Then the results show that gamma external dose model of granite is: D = 0.0648CRa +0.0750Cth + 0.0516CKThe gamma external dose model of polishing tiles is:D = 0.0273CRa + 0.0376Cth + 0.0227CK The gamma external dose model of color-glazed tiles is:D = 0.0190CR, + 0.021 5Cth+ 0.01 71 CK Here, D is absorbed dose rate in air, nGyh-1; CRa, Cth, CK are the specific activities of 232Th, 226Ra and 40K, Bqkg-1; The constants in above formulas are conversion factor between specific activities of 232Th, 226Ra and ^K and absorbed dose rate of decorative building materials.The absorbed dose rates in air for decorative building materials calculated by above models are in keeping with the test values.2. The radiological limits of different kind for decorative building materialsThis paper adopted gamma external dose model of different decorative building materials in calculating radiological limits of different kind of decorative building materials. A 0.3mSv restriction on the effective dose per year is used according to ICRP 82 for granite and polishing tiles. A 0.05mSv annual effective dose limit is adopted in color-glazed tiles according to the limit for consumer substances containing radioactive materials.The results show that limits of granite aregamma external exposure limit: Cth/570 + CRa/660 + CK/830 ≤ 1internal exposure limit: CRa/200≤ 1Limits of polishing tiles are:gamma external exposure limit: Cth/1140 + Caa/1570 + CK/1890≤1internal exposure limit: CRa/200 ≤1Limits of color-glazed tiles are: gamma external exposure limit: Cth/332 + CRa/375+CK/417 internal exposure limit: 226Ra specific activity in glaze CRa/1000≤1Although the annual effective dose limits used in calculating radiologicalVIlimits of different kind of decorative building materials in this paper are lower than the annual effective dose limits used in national criteria of China, "Limit of radionuclides in building materials", the radiological limits of granite and polishing tiles in this paper are more easy than limit of national criteria. Because the conversion factors between specific activities and absorbed dose rate of decorative building materials are far lower than the conversion factors of soil. The annual effective dose limit of "consumer substances containing radioactive materials" is adopted by color-glazed tiles, and radioactive levels of surface color-glazed tiles are higher, so its gamma external exposure limit is more strict than the limit of national criteria. The internal exposure limit of color-glazed tiles is greatly different from the limit of national criteria.3. Method of undamaged samples and critical values of decorative building materialsOn the basis of radionuclides decay outline, the ratio between the alpha and beta activities and the gamma ray activity of every nuclide is fixed. Measurement of gamma ray activities can be transformed to that of alpha ray and beta ray activities. When natural radionuclides are well distributed in materials, there is fixed interrelationship...