Investigation of gamma radiation shielding properties in materials containing Fe-FeB-Cu-C

In recent years, the need for alternative materials in radiation shielding has driven researchers to focus on iron-based composites modified with elements like boron, copper, and carbon. These elements are known to influence key physical and chemical properties. For instance, boron increases the hardness and thermal resistance of the structure through the formation of borides. Copper is commonly used to enhance corrosion resistance, while carbon significantly strengthens the material and contributes to phase development. Despite these advantages, such additions can also introduce microstructural inhomogeneity and internal stresses, which may compromise the overall mechanical performance. This thesis presents a study on Fe-based composites produced via the powder metallurgy technique, focusing on their microstructure and gamma radiation shielding behavior. Four different samples were prepared: Sample A was composed of pure iron; Sample B contained 50% Fe and 50% FeB; Sample C included 49% Fe, 49% FeB, and 2% Cu; and Sample D consisted of 48.75% Fe, 48.75% FeB, 2% Cu, and 0.5% C. The powders were mixed for 24 hours using a ceramic ball mill, followed by compaction at 600 MPa. All samples were sintered at 1200°C for 30 minutes under a nitrogen atmosphere. The morphological properties of the samples were investigated using a X-ray diffractometer (XRD), a field emission scanning electron microscope (FEG-SEM), an energy dispersive X-ray spectrometer (EDS), and a Raman spectrometer. Afterwards, the gamma shielding properties (mass reduction coefficient (MAC), linear reduction coefficient (LAC), half value thickness (HVL), tenth value thickness (TVL) and mean free path (MFP)) of the samples at 1.173 MeV and 1.332 MeV energies were experimentally investigated using NaI(Tl) detector and the obtained results were compared with the calculated results in the XCOM theoretical database. XRD analyses of the samples were carried out using a Rigaku D-Max 2100 PC brand device in the Department of Metallurgical and Materials Engineering, Faculty of Engineering, Sakarya University, in the 5-90° 2θ range and at a scanning speed of 2°/min. According to the XRD analysis results, the highest intensity peak in all samples was obtained around 2θ=44°, and all of these peaks belong to the (110) iron plane. In addition, the presence of (200) and (211) planes of iron can be seen at angles around 2θ=64° and 82°, respectively. In the FeB-doped B sample, the peaks at angles around 2θ=26.46°, 42.37°, 44.80°, and 49.54° match the (111), (004), (212), and (114) planes of the FeB phase. In sample D, which contains low amounts of copper and carbon and high amounts of FeB, (002), (110), (111), (200), (004) and (220) planes belonging to the FeB phase were observed at the angles of 2θ=20.81°, 24.34°, 26.42°, 34.64°, 42.13° and 50.16°, respectively; and (111) and (200) planes belonging to the Cu phase were observed at the angles of 2θ=43.34° and 50.46°. Additionally, (100), (222), (211), (221), (110) and (333) planes of the carbon phase were determined at the angles of 2θ=46.42°, 54.28°, 59.14°, 65.90°, 84.51° and 86.20°. The FEG-SEM and EDS analyses of the samples were performed using the FEI/Quanta FEG 450 model FEG-SEM device within the Sakarya University Research Deanship Research-Development Application and Research Center (SARGEM). The images of the samples were taken at 10 µm, 5 µm, and 3 µm scales, and the EDS analyses were taken from 3 different regions in 10 µm scale images. The FEG-SEM images of the samples show distinct cracked structures in the various areas. These structures show that the material has an irregular distribution in its microstructural properties and contains areas resistant to mechanical loading. It can be said that the high boron content, especially in samples B, C, and D, increases the hardness of these samples and their wear resistance, while also significantly increasing the fragility of the structure. In the obtained FEG-SEM images, it can be seen that cracks form and progress as a direct result of this effect. EDS analyses from different regions show that the samples contain high amounts of Fe and FeB and considerable amounts of C and Cu. Raman spectroscopy analyses of the samples were performed using the Kaiser RAMANRXN1 Microprobe device within the Sakarya University Research Deanship Research-Development Application and Research Center (SARGEM). Two distinct peaks were detected in the Raman spectra of the samples, the D band around 1350 cm-1 and the G band around 1580 cm-1. The fact that the height of the D band in the samples is more dominant than the G band indicates that the sample structures contain more amorphous carbon and the crystal structure is irregular. Gamma shielding capabilities were tested using a 3″×3″ NaI(Tl) detector and a 60Co point source, targeting photon energies of 1.173 MeV and 1.332 MeV. Each sample was measured three times for 20 minutes. Based on these measurements, mass attenuation coefficients (MAC), linear attenuation coefficients (LAC), half-value layers (HVL), tenth-value layers (TVL), and mean free paths (MFP) were calculated. The radiation shielding performance of the samples was quantitatively evaluated at photon energies of 1.173 MeV and 1.332 MeV using key shielding parameters such as the mass attenuation coefficient (MAC), linear attenuation coefficient (LAC), half-value layer (HVL), tenth-value layer (TVL), and mean free path (MFP). At 1.173 MeV, the experimentally determined MAC values were 0.057±0.002 cm2/g for Sample A, 0.054±0.002 cm2/g for Sample B, 0.050±0.002 cm2/g for Sample C and 0.054±0.001 cm2/g for Sample D. The corresponding error rates compared to theoretical values from the XCOM database were 3.26% for Sample A, 1.99% for Sample B, 9.25% for Sample C, and 1.99% for Sample D. At 1.332 MeV, the experimental MAC values were 0.059±0.003 cm2/g, 0.056±0.004 cm2/g, 0.051 ± 0.002 cm2/g, and 0.056±0.001 cm2/g for Sample A, B, C, and D, respectively. The respective error rates at this energy were 13.89% (A), 8.31% (B), 9.25% (C), and 8.31% (D). Notably, the minimum error rate (1.35%) was observed for Sample C at 1.332 MeV, and the maximum error (13.89%) for Sample A at the same energy. Overall, the experimental and theoretical MAC values demonstrated reasonable agreement, with all error margins remaining below 14%. The experimental LAC values obtained in this study were compared to those reported in the literature for conventional and Fe-based shielding materials. At 1.173 MeV, the LAC values of the fabricated samples were higher than those of traditional materials such as concrete (0.139 cm-1) and several Fe-based polymer-infiltrated foams like Poly-IF20 (0.187 cm-1), Poly-IF30 (0.245 cm-1), and Poly-IF40 (0.327 cm-1). Moreover, the shielding efficiency of the samples was comparable to advanced materials like Poly-IF50 (0.420 cm-1) and Fe/Cr18/Ni10 (0.435 cm-1). At 1.332 MeV, the LAC values of all samples again outperformed those of Poly-IF20, Poly-IF30, and standard concrete. The results were comparable to high-alloy steels such as Fe/Cr8/Ni10. However, the fabricated composites still fell short of the performance shown by high-density materials such as Fe/Cr25/Ni20 (0.464 cm-1), Fe/Cr16/Ni72 (0.580 cm-1), and especially lead (Pb), which displayed an LAC of 0.637 cm-1. Morphological analysis for samples A, B, C, and D confirmed the presence of different phases in their structures. It was observed that carbon and boron additives, in particular, caused incompatibility between phases and structural stress-induced defects. These additives may cause primary and secondary cracks on the surfaces and negatively affect the mechanical strength of the samples. Findings regarding gamma shielding performances show that FeB, Cu, and C additives reduce this property to a limited extent. On the other hand, alloys containing FeB stand out with their high wear and corrosion resistance. In addition, the high temperature stability of boron phases can potentially increase thermal strength. However, FeB, Cu, and C additives disrupt the homogeneity of the phase distribution and increase the risk of crack formation (due to boride/carbide formation). This situation was also clearly demonstrated by morphological observations. As a result, the samples can be considered potential candidates for gamma shielding applications under certain engineering conditions, with their high corrosion resistance and structural stability.