Do you know that building materials naturally contain radionuclides?

Most building materials of mineral origin could contain small amounts of Natural Occurring Radioactive Materials (NORM), mainly radionuclides from the ²³⁸U and ²³²Th decay chains and the radioactive isotope of potassium, ⁴⁰K.
Therefore, building materials can cause significant gamma dose⁽¹⁾ indoors, due to their natural radionuclide content. During the last three decades, there has been an increasing interest in the study of the radioactivity of different building materials.
Several national surveys were conducted to establish the radioactivity concentrations in such materials.
For example, Trevisi et al. (J. Environ. Radioact., 105 (2012) 11-20) conducted a literature review on building materials used in the European Union. This enabled the compilation of a database of the activity concentrations of ²³⁸U, ²³²Th and ⁴⁰K in such materials used in Member States. Tables 6 and 7 show the European averages of activity concentrations in brick, concrete, cement and natural gypsum compared with those in European soil (calculated with the data from the 2008 UNSCEAR Report - UNSCEAR, 2010).

Table 6 and Table 7

A regulatory control of building material in terms of radioactivity is already in force in several countries. It is aimed, generally, at limiting the radiation exposure from materials with enhanced or elevated levels of natural radionuclides.

In view of future legislative initiatives, European Commission published a reference document, the European technical guidance RP112 (European Commission, 1999), in which it suggests to base radioactivity controls of building materials on a defined dose criterion for controls (index I) and an exemption level. In particular, RP112 proposes that a dose criterion be chosen on a national basis in the range 0.3-1 mSv y^-1 of excess gamma dose to that received outdoors, and to exempt from all restrictions building materials that increase the annual effective dose to a member of the public by 0.3 mSv at the most. In addition, index I is defined as:

$I= \frac{C_{Ra-226}}{300Bq\ kg^{[-1]}} + \frac{C_{Th-232}}{200Bq\ kg^{{[ -1]}}} +\\ \frac{C_{K-40}}{3000Bq\ kg^{-1}}$

and it assumes different limit values for dose criterion varying between 0.3 to 1 mSv/y. In the formula C indicates the activity concentration of each radionuclide. Depending on the dose

criterion adopted (0.3 or 1 mSv/y) and the use of the material, the index I should comply with the values reported in Table 8:

Table 8

In order to test the applicability of this technical guidance, the Index I was assessed for the sets of data of activity concentration of bulk building materials in the database. See Table 9. This enabled us to approximate the percentage of bricks, concrete and phosphogypsum samples which are possibly subjected to restriction.

Table 9