Micron 70 (2015) 1–6 Contents lists available at ScienceDirect Micron j ourna l ho me page: www.elsevier.com/locate/micron Effective atomic number and density determination of rocks by X-ray microtomography Eduardo Inocente Jussiani ∗ , Carlos Roberto Appoloni Applied Nuclear Physics Laboratory (LFNA), Physics Department, State University of Londrina, Londrina, Paraná, Brazil a r t i c l e i n f o Article history: Received 9 June 2014 Received in revised form 13 November 2014 Accepted 14 November 2014 Available online 22 November 2014 Keywords: Microtomography Density Effective atomic number Rocks a b s t r a c t Microtomography, as a non-destructive technique, has become an important tool in studies of internal properties of materials. Recently, interest using this methodology in characterizing the samples with respect to their compositions, especially rocks, has grown. Two physical properties, density and effective atomic number, are important in determining the composition of rocks. In this work, six samples of materials with densities that varied from 2.42 to 6.84 g/cm 3 and effective atomic numbers from 15.0 to 77.3 were studied. The measurements were made using a SkyScan-Bruker 1172 microtomography apparatus operating in voltages at 50, 60, 70, 80, 90 and 100 kV with a resolution of 13.1 m. Through micro-CT images, an average gray scale was calculated for the samples and correlation studies of this value with the density and the effective atomic number of samples were made. Linear fits were obtained for each energy value. The obtained functions were tested with samples of Amazonite, Gabbro, Sandstone and Sodalite. © 2014 Elsevier Ltd. All rights reserved. 1. Introduction X-ray tomography was developed in the 1970s for medical applications (Landis and Keane, 2010). A few years later, this methodology was being applied in studies of rocks (Atanasio et al., 2010; Baker et al., 2012), reservoir rocks (Appoloni et al., 2007; Marques et al., 2011; Fernandes et al., 2012), materials structures (Moreira et al., 2010; Nagata et al., 2011) and biological samples (Mizutani and Suzuki, 2012). In the area of applications in stud- ies of rocks, microtomography is a methodology able to get 2D images of the internal structures of the rocks, pore size and the distribution of pore size (Oliveira et al., 2012). Also 3D images of samples can be rendered to study the connectivity between the pores and analyze the spatial distribution of the different phases of a rock, if this occurs. In recent years, interest has increased in the characterization of rocks by their chemical composition (Remeysen and Swennen, 2008; Koroteev et al., 2011). There are many studies that seek to characterize rocks by their density and effective atomic number using the technique of dual energy (Yasdi and Esmaeilnia, 2003; Duliu et al., 2009; Miller et al., 2013; Tsuchiyama et al., 2013). This technique consists of making two scans at two different ∗ Corresponding author. Tel.: +55 43 33714736; fax: +55 43 3371 4166. E-mail addresses: duinocente@hotmail.com (E.I. Jussiani), appoloni@uel.br (C.R. Appoloni). voltages and the results are analyzed simultaneously. This is not the methodology employed in this work. Another possible tech- nique such as X-ray Fluorescence Computed Tomography (XFCT) is more complex and very expensive compared with the methodology proposed in this paper. We have been working since 2010 deter- mining the chemical composition of samples making only one scan (Jussiani, 2012; Jussiani and Appoloni, 2013). Microtomography is based on attenuation of X-rays which pass through a sample. This attenuation is detected by a CCD camera (detector) and from projections at different angles and through mathematical models (Feldkamp et al., 1984) it is possible to deter- mine the attenuation of the radiation in the smallest area of the sample element (pixel) or in 3D images, the smallest sample volume (voxel). The attenuation coefficients are shown in images with 256 gray scale, which are distributed among the elements of pixel/voxel with the highest and lowest radiation attenuation. 2. Theory When a polychromatic radiation goes through an inhomoge- neous material, the relationship between the incident and the transmitted radiation is given by the equation: I =  Emax 0 I 0 (E) exp  -  x 0  ′ (E, x) dx  dE (1) http://dx.doi.org/10.1016/j.micron.2014.11.005 0968-4328/© 2014 Elsevier Ltd. All rights reserved.