The determination of the activity concentration of naturally occurring radionuclides in construction materials is based on the principles of gamma-spectrometry. Gamma spectrometry is a comparative method and therefore includes many parameters that are specific to the test sample and measurement circumstances. Consequently, several of the testing conditions must be verified prior to testing and/or require correction to obtain accurate results. Besides problems encountered during the measurement, the interpretation of the results and calculation of the activity indices, needed for material classification, may lead to significant mistakes. Current regulation in the European Union requires to calculate an activity concentration index (index I) using the activity concentration of ²²⁶Ra, ²³²Th and ⁴⁰K. Not all of these radionuclides are directly measurable by gamma spectrometry and, to determine the index, additional assumptions have to be made about secular equilibrium in uranium and thorium decay series. These assumptions are often not valid in case of NORM (Naturally Occurring Radioactive Materials) where long term lack of secular equilibrium in the uranium and/or thorium decay series is often observed. As a consequence, this may result in an underestimation or overestimation of the index. The article discusses specific disequilibrium situations in building materials. Sources for potential inaccurate determinations and misinterpretation are identified and practical mitigation options are proposed.

建筑材料中天然存在的放射性核素活度浓度的确定是基于伽马能谱法的。伽马能谱法是一种比较方法，因此包括许多特定于测试样品和测量环境的参数。因此，必须在测试之前验证几个测试条件和/或需要进行校正才能获得准确的结果。除了在测量过程中遇到的问题外，材料分类所需的结果解释和活性指数的计算可能会导致重大错误。欧盟目前的法规要求使用²²⁶ Ra，²³²的活动浓度来计算活动浓度指数（指数I）。Th和^40K。不是所有这些放射性核素都可以通过伽马能谱法直接测量，并且要确定该指数，还必须对铀和or衰变系列中的长期平衡做出其他假设。在NORM（天然放射性物质）的情况下，这些假设通常是无效的，在NORM中，经常观察到铀和/或decay衰变系列长期缺乏长期平衡。结果，这可能导致索引的低估或高估。本文讨论了建筑材料中的特定不平衡情况。确定潜在的不准确确定和误解的来源，并提出实际的缓解措施。