Geoecological assessment methods of the radiation hazard of the use of rocks in the building materials industry

The production of human activity has led to the formation of technogenic radiation background, which is formed in its habitat due to initially distributed in the structures of the earth, particularly in rocks, “eternal” natural radionuclides (NRN). In its turn, rocks are the main raw material for building materials and products from them. Natural radionuclides are a source of radiation hazard to humans and their habitats throughout the entire chain of production and use of building materials for the construction of residential, administrative and industrial buildings. In order to reduce the factors of the negative impact of man-made radiation background on a person it is possible on the basis of studies of the radiation characteristics of building materials and raw materials for their manufacture, to identify sources of NRN in the chain from rocks to industrial production. In turn, the completeness and validity of the results is possible only on the basis of a comprehensive geo-environmental assessment of the radiation hazard characteristics of building materials and raw materials for their manufacture, which will reduce the negative impact on the ecology of the human environment through the use of “radiationfriendly” materials.


Introduction
As a result of anthropogenic environmental factors studies, scientists established the significance of the radiation factor due to the natural background, radiation background from natural radionuclides and artificial background [1][2][3]. The influence of this factor is intensifying in the light of global changes in the human environment, including through the increasing use of natural resources, changing landscapes, urbanization, etc. etc., which in turn requires finding a reasonable compromise in terms of preserving the well-being of the population, nature and industrial production [1][2][3][4].
The man-made radiation factor has the greatest impact on humans and their habitats due to the content of the NRN in the rocks, which are the main raw materials for the production of building materials. The radioactivity of rocks is due to the presence in them of long-lived radionuclides belonging to the families of uranium-238 (238U), and thorium-232 (232Th) with daughter decay products and potassium-40 (40K). Radiation hazards to humans in these chains have mainly radiation from the decay products: radionuclides -226 (226Ra), radon-222 (222Rn) and radon (toron) -220 (220Rn) [4.5-10].
Studies of the radioactivity of various building materials show a significant variation in the numerical values of the NRN [10][11][12][13][14][15][16][17]. The illustration is the data given in table 1. Therefore, from the point of view of science and practice, the data on the content of NRN in nature have the great importance, i.e. data on the abundance of elements whose isotopes determine the natural radioactivity of rocks, and as a result, the NRN content in building materials and raw materials. The most detailed data is considered in practice [18] and is given as an example in Table 2. The data presented clearly shows a significant variation in 2, 3, 4 orders of magnitude in the weight content of elements for different types, classes and origins of rocks. These facts, on the one hand, explain the difference in the NRN content in building materials and, on the other hand, allow us to establish a relationship between the origin of raw materials and the specific activity of the NRN in building materials, which in turn allows us to purposefully create "radiation-friendly" building materials.

Techniques and objects of a research
The results of previous studies have shown that the content of various radionuclides in rocks differs significantly depending on their type, origin and structure of formation of rocks. In addition, industry, additives and artificial materials are used for the production of some building materials. Recently, a huge amount of building materials, origin and raw materials for manufacturing, which are not always determined, have appeared on the Russian market. The raw materials may contain radionuclides of technogenic origin, formed due to accidents at facilities and uncontrolled release of technogenic radionuclides (TRN) into the environment.
Known methods do not allow a comprehensive assessment of the radiation hazard of the use of rocks in the production of building materials. At the same time, a geoecological assessment of natural and man-made radionuclides entering building materials throughout the production chain from rocks to industrial production will reduce the negative impact on the human environment ecology through the use of "radiation-friendly" materials.
"Radiation-friendly" materials include materials with the lowest radionuclide content (radium 226, thorium 222, potassium 40, cesium 137) [19,20]. This is feasible in the development of an integrated methodology for assessing radiation parameters in the production and use of building materials, which will lead to the creation of an environmentally safe and comfortable environment in the places where people live.
The main purpose of the method is to obtain complete and scientifically based information on radiation factors affecting humans and the environment during the extraction of raw materials, the manufacture and use of materials based on rocks. The technique considers not only the process of justifying and selecting radiation-friendly materials using new extraction of natural resources -the main branch (RESOURCES), but also the use of previously secondary resources -a side branch (WASTE). The catastrophic accumulation of industrial waste, including construction waste, also requires their involvement in the production of building materials. This reduces the burden on the natural environment, since previously extracted and used natural resources are included in the turnover. Block diagram, sequence and stages content are shown on the picture 1.
The method of geoecological assessment of the radiation hazard of using rocks in the production of building materials consists of the following steps: 1 st stage RESOURCES: Extraction of new resources from the natural environment. Pre-selection and evaluation of components of raw materials based on theoretical data for the design of new building materials, taking into account the types of rocks. Raw materials for the construction industry.
WASTE: The use of industrial waste, waste rock in the extraction of minerals, the reuse of materials from the construction industry, including the demolition of buildings and structures.
2 nd stage -Potential danger (safety) RESOURCES: Estimates of potential hazard, taking into account radiation factors for various applications in civil and industrial construction.
WASTE: Analysis of possible use of secondary resources.  WASTE: Radiation monitoring in full volume. 9 th stage -Recommendations RESOURCES: Using of information for scientific and technical justification of adjusting regulatory and technical documentation to reduce the negative impact on the environment of the human environment through the use of radiation-friendly building materials and products from them. WASTE: Use of information for a scientific and technical justification for limiting the use of certain types of secondary raw materials in the construction industry.
The developed methodology is based on the Russian concept and criteria, as well as international evaluation criteria, recommendations in the field of limiting the exposure of the population from natural sources, the parameters used for these purposes and experimental methods.

Analysis and summery
The use of the technique in practice is illustrated by the examples below. Materials such as brick, concrete, which form the basis of each building, and finishing materials that are used for interior decoration were investigated. That is, the materials directly affecting the environmental and radiation component of the dwelling. Among the finishing materials were considered tiles, dry mixes, putties and various adhesives. In total, several dozen samples of building materials were prepared for research. Figure 2 shows the maximum values of the data obtained by type of building materials. Analysis of the obtained results showed that the presented materials do not exceed allowed value of the specific effective activity, and they belong to the 1st class of radiation safety [21], i.e. they can be used without restrictions. Ceramic materials, brick and ash have the highest NRN content. Comparison of experimental data with calculated ones based on the European approach [1][2] on the so-called radiation factor for the materials considered leads to similar conclusions. Table 3 shows the corresponding results. At the same time, for other materials and with different EPN content in the materials, the results show limitations in the application of the European approach [19][20]. Conducted theoretical and experimental studies revealed the relationship of controlled radiation parameters, such as specific and total effective activity of the ERN (Aeff), equivalent dose rate (DER) and radon flux density (RFD) between the origin and types of basic building materials and raw materials for their manufacture. It has been found that for most materials there is a relationship with data on the prevalence of U -226 Ra and K -40 K. In the case of Th -232 Th, there is no unambiguous connection. In these cases, this indicates the need for experimental studies of raw materials and the technology of making ceramic materials and ash in which the raw materials are fired, and, therefore, the concentration of radioactive elements increases. Table 4 presents the averaged experimental data on the magnitude of the monitored parameters for building materials and products from them. From the presented data, we see that there is a relationship between the content of natural radionuclides and the equivalent dose rate: the higher specific effective activity, the greater dose rate. Between the criterion of natural radioactivity and radon flux density, dependence is mainly observed in bulk materials and with a high content of 226 Ra, since the inert radioactive gasradon-222 ( 222 Rn) is a daughter product of 226 Ra.