Eric Pili

Radon emanation from brittle fracturing in granites under upper crustal conditions

Radon-222, a radioactive gas naturally produced in the Earths crust, informs us about the migration of fluids and is sometimes considered as a potential earthquake precursor. Here we investigate the effects of mechanical and thermal damage on the radon emanation from various granites representative of the upper crust. Radon concentration measurements performed under triaxial stress and pore fluid pressure show that mechanical damage resulting from cycles of differential stress intensifies radon release up to 170 ± 22% when the sample ruptures. This radon peak is transient and results from the connection of isolated micropores to the permeable network rather than new crack surface creation per se. Heating to 850°C shows that thermal fracturing irreversibly decreases emanation by 59–97% due to the amorphization of biotites hosting radon sources. This study, and the developed protocols, shed light on the relation between radon emanation of crustal rocks, deformation, and pressure-temperature conditions.

An enhanced method for molybdenum separation and isotopic determination in uranium-rich materials and geological samples

The precise and accurate determination of Mo isotope ratios in geological and U-rich samples requires a thorough separation of Mo from elements that could cause matrix effects and isobaric interference. This interference can be attributed to the presence of residual Fe, Ru, Zr and W naturally present in the samples as well as PO4 contributed by the resin used during chemical separation. Using three-stage ion-exchange chromatography, we have obtained a high degree of purification with Mo yields ranging between 42 and 80%. Mo isotopic compositions were measured at a concentration of 30 ng ml−1 using a Neptune Plus MC-ICP-MS equipped with Jet cones. The sensitivity is ∼1200–1600 V ppm−1 Mo with an aspiration rate of approximately 150 μl per minute. Chemical and instrumental mass dependent fractionations were both corrected using the double-spike method. The total amount of Mo necessary for a single analysis is approximately 45 ng and the typical precision for terrestrial samples is 0.02‰ (2 SE, n = 8). This precise and accurate determination of Mo isotope ratios in U-rich samples has the potential for tracing the origin of uranium ores. Another application could be in nuclear forensics, for identifying the separation processes in the nuclear fuel cycle or the provenance of nuclear materials.