Assessment of building materials for compliance with regulations of ROC

There are five countries which have set radioactivity standards for natural building materials. Three countries use a 1 mSv a−1 annual dose limit and the other two use 2 mSv a−1 to derive the radioactivity concentration regulation formula. In recent years, large amounts of building materials, averaging 724 Gg a−1 have been imported into Taiwan from many countries. Owing to the impact of the cobalt-60 contaminated reinforcing steel incident in Taiwan, people are deeply concerned with the natural radioactivity level of building materials. In this study, 180 kinds of marble and granite from 20 countries were sampled and their natural radioactivity was measured by gamma spectrometry. The results show that the radioactivity level is low in marble but high in some granite samples. The 232Th and 226Ra contents in granite have a close relation with each other but no correlation with the 40K content. Fourteen granite samples contain radioactivity higher than the criterion based on the 1 mSv a−1 dose limit. Granite is usually used as a flooring material. Its typical content by weight is only 2.2% in concrete buildings. Thus, decorative granite is unlikely to contribute more than 1 mSv a−1, as confirmed by in situ measurements. Limiting granite as decorative materials on floors and walls of buildings is not necessary.