Gamma Radiation Shielding Analysis of Clay doped with Fe2O3 -rich additive complemented with Alucobond panels: A study of Am241, Cs137 and Co-60

Abstract

Clay from six known clay deposits in Ghana, namely Oframase and Amperkrom in the Eastern region, Okyreko and Assin Fosu in the Central region, and Abokobi and Kinbu in the Greater Accra Region have been studied for their gamma shielding properties against Am-241, Cs-137 and Co-60 representing lower, middle and large photon energy ranges respectively. Their shielding performance was investigated when they were undoped (X0 series), and then doped at 5% wt (X1 series) and 10% wt (X2 series) of an Fe2O3-rich additive and subsequently coupled to Aluminium composite panels (Alucobond) to evaluate the overall performance. The samples, both doped and undoped exhibited a range of densities, with values spanning from 1.651 g/cm³ (FOS-X0) to 2.069 g/cm³ (ABK-X2). It was noted that the additive, as well as the clay materials own elemental composition and the grain size distribution contributed to the density of the test pieces. With 5% by wt doping the increase in density of the samples ranged from 0.94% - 2.97%, while at 10% wt doping it improved by 3.62% - 8.76%. For Am-241, the linear attenuation coefficients (LAC) show variability, with values ranging from 0.372 ± 0.0012 cm-1 (FOS-X0) to 0.596 ± 0.0022 cm-1 (ABK X2), reflecting differences in the clays’ ability to attenuate radiation. The mass attenuation coefficient (MAC), which accounts for both the material density and the attenuation properties, follows a similar trend, ranging from 0.225 cm2g 1 (FOS-X0) to 0.296 cm2g-1 (OKY-X2). In the case of Cs-137, the LAC ranged from 0.116 ±0.0009 cm-1 (FOS-X0) to 0.145 ±0.0016 cm-1 (ABK-X2) while the MAC ranged from 0.0675 cm2g-1(AMK-X0) to 0.0707 cm2g-1 (OKY-X2). Similarly, considering Co-60, the LAC ranged from 0.08±0.0018 cm-1 (FOS-X0) to 0.107±0.0029 cm-1 (ABK-X2) while the MAC ranged from 0.0484 cm2g-1(FOS X0) to 0.0517 cm2g-1 (ABK-X2). The results show that for Am-241, the dopant addition at 10% wt contributes to the 22.13% to 37.10% in LAC improvement. In the case of Cs-137 it results in 16.60% to 26.05% in LAC increase, while a 5.07% to 11.81% increase in LAC is observed for Co -60. Conversely, the increase in LAC when the clays are doped with 5% wt additive is less pronounced, not exceeding 3.5% for all the clays and photon energies investigated. LAC values in this study for the various samples were also corroborated by MCNP simulation. The variability in LAC and MAC across the samples can be attributed to differences in their elemental and mineralogical composition, particularly the presence of elements like iron, aluminum, and silica, which influence their radiation absorption capabilities. For instance, the Al content ranges from 36,643 mg/kg (OKY-X0) to 136,386 mg/kg (FOS -X0), while Fe concentrations span from 10,166 mg/kg (FOS-X0) to 78,290 mg/kg (AMK -X2). Silicon (Si) concentrations also exhibit variation, ranging from 183,669 mg/kg (FOS-X2) to 276,740 mg/kg (ABK-X2). Other elements such as potassium (K) and titanium (Ti) are also present but in smaller quantities, although they impact the density of the clays. K concentration levels ranged from 1,406 mg/kg (OFM-X0) to 5,173 mg/kg (FOS-X1), and Ti concentrations varied between 1,524 mg/kg (FOS-X2) to 4,636 mg/kg (OFM-X0). These elements play a crucial role, especially in ceramic and material science. These results confirm theory that density strongly correlate with linear attenuation coefficient for photon shielding which is energy dependent. Overall, the research’s finding highlights the prospect of clay doped with Fe2O3 for shielding low energy photons particularly for medical applications relying on ABK-X2 clay which is the densest composite clay material investigated as a case in point. If Alucobond panels which is used as wall finishing is incorporated as an extra layer, ABK-X2 clays’ LAC performance will over-perform that of ordinary concrete at lower energies. This is particularly true, for the medical range of X-ray energies (30 keV to 150 keV) for purposes of diagnostic imaging such as mammography, general radiography and computed tomography (CT) scans. Consequently, all things being equal, the walls of a medical diagnostics facility can be built by using locally sourced clay particularly OKY-X2 or ABK-X2 clay which is the densest and doped at 10% wt of the Fe203 oxide (71% purity) additive used in this study. The clay can safely be used in place of ordinary concrete to shield expected photon energies in such a facility which would be less than 150keV. Furthermore, adding an Alucobond panel to a fixed thickness of clay would improve the required 5 and 7 HVLs shielding performance by 7.3% and 14.1% for one surface paneling and two surface paneling respectively. The clays together with any of the Aluminum composite panels (Alucobond) defined in this study ensure that more than 99% of the initial radiation is attenuated. Further studies on clay densification like firing at higher temperatures and the effects of addition of other dopants such as Titanium oxide to enhance shielding performance of clay is recommended.