Magnetic-resonance relaxation-time distributions are commonly used to characterize the pore spaces of fluid-saturated porous media such as concrete, soils, and petroleum-reservoir rocks. The pore size is a critical determinant of the relaxation behavior observed in a fluid-saturated porous medium. It is experimentally challenging to explore the pore size in isolation because changing the sample to change the pore size usually leads to a concurrent change in surface relaxivity. To explore the effect of changing the pore size in isolation, we employ bead packs of different bead sizes. In this way, the matrix and therefore surface relaxivity should be constant as the pore size changes. The measured relaxation lifetimes vary systematically in paramagnetic and diamagnetic glass-bead systems. Direct proportionality between the relaxation lifetime and pore size is observed across the fast-exchange and intermediate regimes of Brownstein-Tarr theory. Although the relaxation-diffusion regime is often incorrectly assigned, the proportionality between lifetime and pore size ensures that the use of the $T_2$ distribution as a proxy for pore size in applied studies is sound.

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• Diffusion
• Flows in porous media
• Temperature
• Glasses
• Porous materials
• Porous media
• Wet granular materials
• Nuclear magnetic resonance