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<p>Accurate evaluation of gamma attenuation in jointed rock masses is essential for radiation shielding and nuclear waste management, yet the combined effects of joint infill type and thickness remain poorly understood. Joints, as common discontinuities in rock masses, strongly influence the radiological behavior of rocks. This study investigates the effects of joint infill type and thickness on the effective mass attenuation coefficient (eMAC) in jointed rocks using a combined approach integrating experimental measurements, Monte Carlo simulations with MCNPX, and theoretical validation via the XCOM database. Five common rock types—granite, magnetite, hornblende, salt, and travertine—were examined, each containing artificial joints filled with one of five materials (clay, lime, hematite, lead oxide, and pure lead) at thicknesses ranging from 2 to 8 mm. A series of gamma attenuation tests were conducted using a <sup>137</sup>Cs source and a Geiger–Müller detector. The results revealed that increasing the infill thickness—particularly for high-Z, high-density materials—produces a substantial quantitative enhancement in gamma attenuation. Specifically, Pb infill increased the effective mass attenuation coefficient by approximately 41–59% at an 8-mm joint thickness relative to the 0-mm condition, while hematite infill produced an increase of about 10–24% over the same thickness range. MCNPX simulations complemented the experimental data, enabling the evaluation of joint apertures below 1 mm—conditions challenging to assess experimentally. These simulations confirmed a significant decrease in eMAC with increasing aperture, especially for joints filled with low-density materials. Furthermore, the theoretical eMAC values obtained from the XCOM database differed from the experimental and MCNPX-modeled results by approximately 6–10% under homogeneous rock conditions. This level of deviation is consistent with typical ranges reported in the literature and further supports the validity of the overall methodological approach. Statistical analysis using multiple linear regression (R<sup>2</sup> = 0.775) confirmed the dominant influence of infill thickness and material type over host rock properties. The findings underscore the critical role of joint characteristics in shielding design and demonstrate the value of integrating experimental, numerical, and theoretical methods to optimize radiation attenuation strategies in geotechnical and nuclear engineering applications.</p>

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Effects of type and thickness of joint infill materials on gamma radiation attenuation in rock masses: experimental and numerical investigations

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年4月18日

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  • Sahand Golmohammadi,
  • Majid Noorian-Bidgoli,
  • Ahmad Ramezani Moghaddam-Arani

摘要

Accurate evaluation of gamma attenuation in jointed rock masses is essential for radiation shielding and nuclear waste management, yet the combined effects of joint infill type and thickness remain poorly understood. Joints, as common discontinuities in rock masses, strongly influence the radiological behavior of rocks. This study investigates the effects of joint infill type and thickness on the effective mass attenuation coefficient (eMAC) in jointed rocks using a combined approach integrating experimental measurements, Monte Carlo simulations with MCNPX, and theoretical validation via the XCOM database. Five common rock types—granite, magnetite, hornblende, salt, and travertine—were examined, each containing artificial joints filled with one of five materials (clay, lime, hematite, lead oxide, and pure lead) at thicknesses ranging from 2 to 8 mm. A series of gamma attenuation tests were conducted using a 137Cs source and a Geiger–Müller detector. The results revealed that increasing the infill thickness—particularly for high-Z, high-density materials—produces a substantial quantitative enhancement in gamma attenuation. Specifically, Pb infill increased the effective mass attenuation coefficient by approximately 41–59% at an 8-mm joint thickness relative to the 0-mm condition, while hematite infill produced an increase of about 10–24% over the same thickness range. MCNPX simulations complemented the experimental data, enabling the evaluation of joint apertures below 1 mm—conditions challenging to assess experimentally. These simulations confirmed a significant decrease in eMAC with increasing aperture, especially for joints filled with low-density materials. Furthermore, the theoretical eMAC values obtained from the XCOM database differed from the experimental and MCNPX-modeled results by approximately 6–10% under homogeneous rock conditions. This level of deviation is consistent with typical ranges reported in the literature and further supports the validity of the overall methodological approach. Statistical analysis using multiple linear regression (R2 = 0.775) confirmed the dominant influence of infill thickness and material type over host rock properties. The findings underscore the critical role of joint characteristics in shielding design and demonstrate the value of integrating experimental, numerical, and theoretical methods to optimize radiation attenuation strategies in geotechnical and nuclear engineering applications.