【作者】 毛亚虹；

【导师】 林理彬；

【作者基本信息】 四川大学 ， 核技术及应用， 2003， 博士

【摘要】 如果使用天然放射性核素比活度增高的建筑材料，室内空气中剂量率就相应升高。但目前对于建材的辐射剂量还缺乏较精确的定量表示，从一定程度上制约了建筑材料这种持续性低剂量照射对公众健康影响的研究。 本研究对几类建筑装饰材料的辐射剂量学模式及其放射性核素限量进行了研究，并找到一种可用于已建住房装饰建筑材料放射性水平检测判断的检测筛选方法。得到如下结论。 1．给出了各类装饰建筑材料的辐射剂量模式 由于各种装饰材料的厚度、密度和核素活度浓度都不一样，它们的核素放射性比活度—空气吸收剂量率转换因子应有很大差别；同时，土壤作为半无限大的体源，其空气吸收剂量率转换因子较装饰材料这种有限大的体源要大得多。显然，建筑装饰材料不能近似采用室外土壤的转换因子。要较准确地反应各类装饰建材对室内空气吸收剂量率的贡献，必须考虑各类材料本身的特性。本研究用蒙特卡罗方法的应用程序EGSnrc计算出几类饰材的核素比活度—室内空气吸收剂量转换系数。得到各类饰材的Y外照射剂量学计算模式如下： 花岗石 （?）=0.0648C_Ra+0.0750C_th+0.0516C_K 抛光砖 （?）=0.0273C_Ra+0.0376C_th+0.0227C_K 彩釉砖 （?）=0.0190C_Ra+0.0215C_th+0.0171C_K 式中，（?）为空气吸收剂量率，nGyh^-1；C_Ra、C_th、C_K分别为各类材料中²²⁶Ra、四川大学博士学位论文”勺h和气的放射性比活度，Bqkg一，;式中的常数分别为各类材料中鞠系、脚h系和，0K的核素放射性比活度一空气吸收剂量率转换因子（nGyh-l/Bqkg一，）. 用该模式算出的空气吸收剂量率与实测值一致。而用UNSCEAR（联合国原子辐射效应科学委员会）报告给出的土壤Y外照射剂量计算模式算出的装饰材料的空气吸收剂量率与实测值相差很大。说明该模式更符合实际。2.推导出各类装饰建材的放射核素限t 由于装饰材料不能使用土壤的剂量模式。同时，Ic即（国际放射防护委员会）和U王A（国际原子能机构）都已明确我国《放射卫生防护基本标准》GB 4792一1984对公众的剂量限值不适用于天然放射性，而我们的国家标准仍使用土壤的剂量转换因子和公众的年剂量限值来推导建筑材料的核素限量。显然，要较合理地限制装饰材料对公众的照射，必须使用装饰材料本身的剂量模式，以及可用于天然源的年剂量限值。本论文根据三类不同装饰材料核素比活度一空气吸收剂量转换因子，对花岗石和抛光砖使用ICRP第82号报告“在持续照射情况下公众的防护一委员会辐射防护体系应用于由天然源和长寿命放射性残存物引起的可控制的辐射照射”:用于单一源的辐射防护最优化的年剂量约束不大于每年0.3msv，对彩釉砖使用“含放射性物质消费品”的年有效剂量限制O.05msv。得到各类装饰材料的天然放射性核素限制式为: 花岗石: Y外照射限制:Cth/570+C、/660+C‘/830蕊1 内照射限制:C、/200簇l 抛光砖: Y外照射限制:Cth/1140+C、/1570+Q/1890蕊1 内照射限制:CRa/200续1彩釉砖:Y外照射限制:Ctn/332 内照射限制:釉面料中+C、/375+2肠Ra的比活度CK/417蕊1 C澎1000蕊1 虽然本论文推导Y外照射限制采用的年剂量限值较现行国家标准的小，本论文给出的花岗石和抛光砖的外照射限制都较现行国家标准要宽，这是因为本四川大学博士学位论文论文算出的这些饰材天然放射性核素比活度一空气吸收剂t转换因子要比现行国家标准采用的土坡剂t转换因子小得多。彩釉砖由于采用“含放射性物质消费品”的附加年剂t限值，加上表层釉面的放射性水平较高，它的外照射限制较现行国家标准要严格一些;内照射限制也与现行国家标准完全不同。3.建立起装饰建材的无损检测筛选方法并给出了结果判断筛选值 根据核素衰变纲图，对天然放射性核素均匀分布的材料来说，幻勺h、226Ra、气的Y比活度就与单位质t材料中的。、p辐射水平有固定的关系，这时，由于单位质盘材料中的Q、p辐射水平与其表面的。、p水平有确定的关系，而表面。、p辐射水平可以在其表面无损侧出。因此，只要通过上述关系，找到比活度超限值时对应的表面Q、p放射性水平，以后就可以通过测得的。、p水平来判断样品的丫放射性是否超限值。这样就将丫射线强度的测量问题转化为表面Q、B射线的强度测量问题，从而实现建材较准确的无损检测筛选。由于天然放射系中最大能t的p射线在建筑装饰材料中的最大射程大于单块饰材的厚度，在对已装饰室内测盆时，测得的p辐射水平还包括饰材下面主体建材的贡献，此时用测得的p辐射水平来判断就会产生错误。然而a粒子在材料中的射程只有几微米，因此可用材料的表面Q水平与国家标准内、外照射指数分类临界值对应的值，来进行无损检测筛选结果的判断。由于用于表面Q辐射水平侧量的仪器（进口仅万元人民币左右）相对高纯锗Y谱仪（进口需要近六十万人民币）来说便宜许多，而且携带方便，可用于现场检测;表面a水平也不用像Y谱分析那样更多还原

【Abstract】 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更多还原