Advances in Materials Science and Engineering Assessment of Gamma Radiation Hazards Related to Geologic Materials: Comparison of Results by Field Gamma Spectrometry and Laboratory Methods

Received Jan 31, 2018; Accepted Apr 7, 2018

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1. Introduction

Natural ionizing radiation includes external and internal sources. While internal sources comprise naturally occurring radioisotopes that are taken into the human body, external ones are mainly cosmic rays and gamma radiation emissions from both terrains and building materials [1]. Isotopes present different activity values (radioactive decay rate, which is expressed in SI units as Becquerel, Bq, with 1 Bq = 1 s⁻¹), and the ratio of the activity of the isotope to the total mass can be considered as an expression of its concentration, referred as activity concentration or specific activity (Bq/kg). The external gamma radiation related to terrestrial sources is mainly due to primordial radionuclides with radioactive decay half-lives that are approximately Earth’s age or older [2]. They are mainly ⁴⁰K and radioisotopes of the radioactive decay series of ²³⁸U and ²³²Th (daughter isotopes of these radioisotopes) present in minerals and rocks used in building materials, being the main cause of indoor radiation exposure, which is about 40% greater than outdoor exposures in middle and high latitudes [3].

Different approaches have been considered to assess the dose that a person will receive from building materials in a given indoor space. The 2013/59/EURATOM directive of the Council of Europe (CEU [4]), which is directed to setting “basic safety standards for protection against the dangers arising from exposure to ionising radiation,” indicates the use of an activity concentration index (1) which is based on the sum of factors obtained by dividing the activity concentrations (or specific activities) of isotopes by constants that correspond to certain reference conditions in terms of room characteristics, materials application, and bulk density and exposition time.$$\begin{array}{}\text{(1)}& I=\left(\frac{C_{\mathrm{Ra}‐226}}{300}\right)+\left(\frac{C_{\mathrm{Th}‐232}}{200}\right)+\left(\frac{C_{\mathrm{K}‐40}}{3000}\right),\end{array}$$where C_Ra-226 is the activity concentration of ²²⁶Ra in Bq/kg, C_Th-232 is the activity concentration of ²³²Th in Bq/kg, and C_K-40 is the activity concentration of ⁴⁰K in Bq/kg.

A value of one for this activity concentration...