A Possible Difference in the Surface Relaxivity of Costal and Inland Sands

Abstract

The 1 H nuclear magnetic resonance (NMR) spin-lattice relaxation rate of hydrated sands is related to the sur- face-to-volume ratio of the voids or pores between the hydrated sand grains and the surface relaxivity of the grains. The electron spin resonance (ESR) signal is often used to predict the relative surface relaxivity as the surface relaxivity is thought to be proportional to the concentration of paramagnetic species in the sand grains. We have identified a discrep- ancy in the surface relaxivity and ESR signal of an ocean beach sand compared to two sands of similar diameter from in- land deposits. This difference can either be due to more surface weathering of the inland sand or more paramagnetic mate- rial from seawater adhering to the ocean sand. tion of these metals on the surface layer to differ from that within the grain. The comparison made to exemplify this difference is between an active beach sand from Asilomar, CA USA, and two inland sands from Illinois USA. We pre- sent the details of these findings in this paper. In the previous paper, we reported R1 values at proton resonance frequencies ( ) between 30 MHz and 10 kHz. This data was used to extrapolate a value for R1 and  at  = 2.5 kHz, the approximate resonance frequency of protons in the magnetic field of the Earth. This extrapolation was risky because the dispersion in R1 with  could either continue at  < 10 kHz or stop and R1 level off. In the current presentation, we have added a datum point at 1.9 kHz using an Earth's field NMR spectrometer that eliminated the need to extrapo- late. BACKGROUND