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We have performed a series of experiments to understand the effects of quartz overgrowths on nanometer to centimeter scale pore structures of sandstones. Blocks from two samples of St. Peter Sandstone with different initial porosities (5.8 and 18.3 %) were reacted from 3 days to 7.5 months at 100 and 200°C in aqueous solutions supersaturated with respect to quartz by reaction with amorphous silica. Porosity in the resultant samples was analyzed using small and ultrasmall angle neutron scattering and scanning electron microscope/backscattered electron (SEM/BSE)based image-scale processing techniques. Significant changes were observed in the multiscale pore structures. By three days much of the overgrowth in the low-porosity sample dissolved away. The reason for this is uncertain, but the overgrowths can be clearly distinguished from the original core grains in the BSE images. At longer times the larger pores are observed to fill with plate-like precipitates. As with the unreacted sandstones, porosity is a step function of size. Grain boundaries are typically fractal, but no evidence of mass fractal or fuzzy interface behavior was observed suggesting a structural difference between chemical and clastic sediments. After the initial loss of the overgrowths, image scale porosity (> ~ 1 cm) decreases with time. Submicron porosity (typically ~25 % of the total) is relatively constant or slightly decreasing in absolute terms, but the percent change is significant. Fractal dimensions decrease at larger scales, and increase at smaller scales with increased precipitation.

The thermal, mechanical, and chemical evolution of a sedimentary basin exerts important controls on porosity and permeability of reservoir rocks. Oxygen isotope ratios of individual diagenetic cements record evidence of this history, but cannot be analyzed accurately by conventional techniques. Recent improvements for in situ analysis by ion microprobe provide high precision and accuracy at a scale of 5-10 μm. In combination with cathodoluminescence imaging, in situ analysis of δ 18 O (quartz) from the Cambrian Mount Simon Sandstone in the Illinois Basin (USA) reveals gradients within single overgrowths of as much as 7.7‰/50 μm. While the inner portions of overgrowths remain approximately constant in δ 18 O across the basin, the δ 18 O of the rim becomes lower with depth. These data suggest that overgrowths formed during burial and heating, possibly with minimal changes in δ 18 O of pore fl uids. If δ 18 O(H 2 O) = −3‰, the highest temperature calculated for the rim of an overgrowth is 107 °C at a paleodepth of 3.5 km. The variability both in average δ 18 O of overgrowths and patterns from individual overgrowths corresponds with a geotherm of 30 °C/km, and there is no evidence of quartz precipitation from higher temperature hydrothermal fl uids.

Calorimetric decay energy spectroscopy of electron-capturedecaying isotopes is a promising method to achieve the sensitivity required for electron neutrino mass measurement. The very low total nuclear decay energy (Q EC < 3 keV) and short half-life (4570 y) of 163 Ho make it attractive for high-precision electron capture spectroscopy (ECS) near the kinematic endpoint, where the neutrino momentum goes to zero. In the ECS approach, an electron-capture-decaying isotope is embedded inside a microcalorimeter designed to capture and measure the energy of all the decay radiation except that of the escaping neutrino. We have developed a complete process for proton-irradiation-based isotope production, isolation, and purification of 163 Ho. We have developed transition-edge sensors for this measurement and methods for incorporating 163 Ho into high-resolution microcalorimeters, and have measured the electron-capture spectrum of 163 Ho. We present our work in these areas and discuss the measured spectrum and its comparison to current theory.