Estimating the Radioactive Heat Production of a Granitic Rock in the University of A Coruna (Galicia, Northwest Spain) by Gamma-ray Spectrometry  
[PERSON]  
1 University Institute of Geology, University of A Coruna, Campus de Elvi  
policy, a good assessment of the geothermal potential is essential to provide present and future projections of its potential use. In this work, we focus on a local case study in northwest Spain in an attempt to reflect the high potential of this energy in some areas of the country and the need for establishing both development and investment plans for its exploration.  
Even though the European Geothermal Energy Council [10] has stated that its objectives until the year 2050 include the establishment of a European geothermal industry base (2020) or obtaining a substantial part of the electricity supply from geothermal energy (2050), these objectives are far from being fulfilled in Spain. Studies of geothermal potential carried out in Spain in the last 45 years have been few and have often been reduced to conservative estimates obtained from theoretical or tabulated parameters [7; 11]. In most of the territory of Spain, based on the VDI 4640 (2001) standard [12], it has been estimated that there is a very low heat flux, with medium enthalpy resources (temperatures between 100 \({}^{\circ}\)C and 150 \({}^{\circ}\)C) and very low enthalpy (T \(<\) 30 \({}^{\circ}\)C), with some exceptions--such as the Canary Islands [7]. This standard establishes estimated values to assess the geothermal potential, without considering how the variability in the mineral composition of rocks affects their thermal conductivity and, above all, the variable heat generation in them due to their contents of primordial radioisotopes of uranium, thorium, and potassium. The most ambitious study carried out by the Institute for the Diversification and Saving of Energy [7] acknowledges, in fact, that its own estimates are conservative. Currently, there are more precise studies to estimate the real geothermal potential, although with poor spatial resolution [8]. For the northwest of Spain, it has been proposed that the geological characteristics may be of particular interest for the use of geothermal energy through GSHPs [13].  
In recent years, published studies have provided data on terrestrial gamma radiation [14], potential radon emissions [15], and even data on the geochemical composition of radioisotopes on the surface, in the first Geochemical Atlas of Spain [16]. These new data, separately, have made it possible to observe that in northwest Spain, both U and Th isotopes are especially abundant in certain rocks (such as granites), exceeding the average values for this type of rock [17; 18; 19]. These radioisotopes are responsible for 85% of the heat production in rocks by radioisotopes [17], so they are the main cause of the geothermal gradient at the surface of the crust being higher than the average gradient. Due to this abundance of U and Th, very high values of terrestrial gamma radiation and potential emission of radon in rocks are observed in the autonomous community of Galicia [14; 15]. In this region, granitic rocks originating during the Variscan Orogeny are especially abundant, in which high concentrations of U, Th, and K have been observed [13; 20], exceeding the average concentrations expected in granites, as occurs in some Palaeozoic granites [17; 18; 19]. Despite this, the geothermal potential of this area has not yet been studied in detail.