SPORT: A new sub-nanosecond time-resolved instrument to study swift heavy ion-beam induced luminescence - Application to luminescence degradation of a fast plastic scintillator

We developed a new sub-nanosecond time-resolved instrument to study the dynamics of UV-visible luminescence under high stopping power heavy ion irradiation. We applied our instrument, called SPORT, on a fast plastic scintillator (BC-400) irradiated with 27-MeV Ar ions having high mean electronic stopping power of 2.6 MeV/\mu m. As a consequence of increasing permanent radiation damages with increasing ion fluence, our investigations reveal a degradation of scintillation intensity together with, thanks to the time-resolved measurement, a decrease in the decay constant of the scintillator. This combination indicates that luminescence degradation processes by both dynamic and static quenching, the latter mechanism being predominant. Under such high density excitation, the scintillation deterioration of BC-400 is significantly enhanced compared to that observed in previous investigations, mainly performed using light ions. The observed non-linear behaviour implies that the dose at which luminescence starts deteriorating is not independent on particles' stopping power, thus illustrating that the radiation hardness of plastic scintillators can be strongly weakened under high excitation density in heavy ion environments.Comment: 5 figures, accepted in Nucl. Instrum. Methods

Nanoscale resetting of the Th/Pb system in an isotopically-closed monazite grain: A combined atom probe and transmission electron microscopy study

© 2018 China University of Geosciences (Beijing) and Peking University Understanding the mechanisms of parent-daughter isotopic mobility at the nanoscale is key to rigorous interpretation of U–Th–Pb data and associated dating. Until now, all nanoscale geochronological studies on geological samples have relied on either Transmission Electron Microscope (TEM) or Atom Probe Microscopy (APM) characterizations alone, thus suffering from the respective weaknesses of each technique. Here we focus on monazite crystals from a ~1 Ga, ultrahigh temperature granulite from Rogaland (Norway). This sample has recorded concordant U–Pb dates (measured by LA-ICP-MS) that range over 100 My, with the three domains yielding distinct isotopic U–Pb ages of 1034 ± 6 Ma (D1; S-rich core), 1005 ± 7 Ma (D2), and 935 ± 7 Ma (D3), respectively. Combined APM and TEM characterization of these monazite crystals reveal phase separation that led to the isolation of two different radiogenic Pb (Pb*) reservoirs at the nanoscale. The S-rich core of these monazite crystals contains Ca–S-rich clusters, 5–10 nm in size, homogenously distributed within the monazite matrix with a mean inter-particle distance of 40–60 nm. The clusters acted as a sink for radiogenic Pb (Pb*) produced in the monazite matrix, which was reset at the nanoscale via Pb diffusion while the grain remained closed at the micro-scale. Compared to the concordant ages given by conventional micro-scale dating of the grain, the apparent nano-scale age of the monazite matrix in between clusters is about 100 Myr younger, which compares remarkably well to the duration of the metamorphic event. This study highlights the capabilities of combined APM-TEM nano-structural and nano-isotopic characterizations in dating and timing of geological events, allowing the detection of processes untraceable with conventional dating methods

Unraveling static olivine grain growth properties in the Earth's upper mantle

International audienceGrain size in the Earth's upper mantle is a fundamental parameter that has crucial implications on large-scale processes, such as the permeability and the rheology of rocks. However, grain size is constantly evolving with time, where static grain growth implies an increase of the average grain size whereas dynamic recrystallization contributes to its decrease. Static grain growth is most dominant in grain size-sensitive deformation regimes and is classically defined by a grain growth law of the form:rfn - rin = k twith rf and ri, the final and initial grain radii, n the grain size exponent, t the duration, k the grain growth rate. These growth parameters are highly dependent on the value of n, which has considerable implications when extrapolating from laboratory to geological length and time scales. Here, we will show that there is no clear n value that can be extracted from grain growth experiments and that this value must be fixed based on the appropriate theoretical background. We have therefore investigated static grain growth of olivine aggregates where the intergranular medium is dry, wet or contains melt. Grain growth experiments were performed and modeled by considering different growth mechanisms (i.e. diffusion-limited and interface reaction-limited). We have established the dry grain growth law from previously published experiments at 1-atm and high-temperature conditions. Grain growth rates for these samples are limited by Si diffusion at grain boundaries (GB), implying n = 2. On the contrary, experiments on melt- and H2O-bearing aggregates indicate faster growth rates than for dry samples, regardless of the liquid fraction (i.e. >0%). We propose a general grain growth law, which takes into account dry GB as well as wetted grain-grain interfaces, by using the wetting properties of the liquid phase as shown by our high-resolution images. We show that our unified grain growth law considerably deviates from the classical grain growth law, with critical differences at geological time scales. We expect that our law will help unravel physical properties that are dependent on processes happening at the GB scale, such as rheology, diffusion or permeability

Unraveling static olivine grain growth properties in the Earth's upper mantle

International audienceGrain size in the Earth's upper mantle is a fundamental parameter that has crucial implications on large-scale processes, such as the permeability and the rheology of rocks. However, grain size is constantly evolving with time, where static grain growth implies an increase of the average grain size whereas dynamic recrystallization contributes to its decrease. Static grain growth is most dominant in grain size-sensitive deformation regimes and is classically defined by a grain growth law of the form:rfn - rin = k twith rf and ri, the final and initial grain radii, n the grain size exponent, t the duration, k the grain growth rate. These growth parameters are highly dependent on the value of n, which has considerable implications when extrapolating from laboratory to geological length and time scales. Here, we will show that there is no clear n value that can be extracted from grain growth experiments and that this value must be fixed based on the appropriate theoretical background. We have therefore investigated static grain growth of olivine aggregates where the intergranular medium is dry, wet or contains melt. Grain growth experiments were performed and modeled by considering different growth mechanisms (i.e. diffusion-limited and interface reaction-limited). We have established the dry grain growth law from previously published experiments at 1-atm and high-temperature conditions. Grain growth rates for these samples are limited by Si diffusion at grain boundaries (GB), implying n = 2. On the contrary, experiments on melt- and H2O-bearing aggregates indicate faster growth rates than for dry samples, regardless of the liquid fraction (i.e. >0%). We propose a general grain growth law, which takes into account dry GB as well as wetted grain-grain interfaces, by using the wetting properties of the liquid phase as shown by our high-resolution images. We show that our unified grain growth law considerably deviates from the classical grain growth law, with critical differences at geological time scales. We expect that our law will help unravel physical properties that are dependent on processes happening at the GB scale, such as rheology, diffusion or permeability

Unraveling static olivine grain growth properties in the Earth's upper mantle

International audienceGrain size in the Earth's upper mantle is a fundamental parameter that has crucial implications on large-scale processes, such as the permeability and the rheology of rocks. However, grain size is constantly evolving with time, where static grain growth implies an increase of the average grain size whereas dynamic recrystallization contributes to its decrease. Static grain growth is most dominant in grain size-sensitive deformation regimes and is classically defined by a grain growth law of the form:rfn - rin = k twith rf and ri, the final and initial grain radii, n the grain size exponent, t the duration, k the grain growth rate. These growth parameters are highly dependent on the value of n, which has considerable implications when extrapolating from laboratory to geological length and time scales. Here, we will show that there is no clear n value that can be extracted from grain growth experiments and that this value must be fixed based on the appropriate theoretical background. We have therefore investigated static grain growth of olivine aggregates where the intergranular medium is dry, wet or contains melt. Grain growth experiments were performed and modeled by considering different growth mechanisms (i.e. diffusion-limited and interface reaction-limited). We have established the dry grain growth law from previously published experiments at 1-atm and high-temperature conditions. Grain growth rates for these samples are limited by Si diffusion at grain boundaries (GB), implying n = 2. On the contrary, experiments on melt- and H2O-bearing aggregates indicate faster growth rates than for dry samples, regardless of the liquid fraction (i.e. >0%). We propose a general grain growth law, which takes into account dry GB as well as wetted grain-grain interfaces, by using the wetting properties of the liquid phase as shown by our high-resolution images. We show that our unified grain growth law considerably deviates from the classical grain growth law, with critical differences at geological time scales. We expect that our law will help unravel physical properties that are dependent on processes happening at the GB scale, such as rheology, diffusion or permeability

Unraveling static olivine grain growth properties in the Earth's upper mantle

International audienceGrain size in the Earth's upper mantle is a fundamental parameter that has crucial implications on large-scale processes, such as the permeability and the rheology of rocks. However, grain size is constantly evolving with time, where static grain growth implies an increase of the average grain size whereas dynamic recrystallization contributes to its decrease. Static grain growth is most dominant in grain size-sensitive deformation regimes and is classically defined by a grain growth law of the form:rfn - rin = k twith rf and ri, the final and initial grain radii, n the grain size exponent, t the duration, k the grain growth rate. These growth parameters are highly dependent on the value of n, which has considerable implications when extrapolating from laboratory to geological length and time scales. Here, we will show that there is no clear n value that can be extracted from grain growth experiments and that this value must be fixed based on the appropriate theoretical background. We have therefore investigated static grain growth of olivine aggregates where the intergranular medium is dry, wet or contains melt. Grain growth experiments were performed and modeled by considering different growth mechanisms (i.e. diffusion-limited and interface reaction-limited). We have established the dry grain growth law from previously published experiments at 1-atm and high-temperature conditions. Grain growth rates for these samples are limited by Si diffusion at grain boundaries (GB), implying n = 2. On the contrary, experiments on melt- and H2O-bearing aggregates indicate faster growth rates than for dry samples, regardless of the liquid fraction (i.e. >0%). We propose a general grain growth law, which takes into account dry GB as well as wetted grain-grain interfaces, by using the wetting properties of the liquid phase as shown by our high-resolution images. We show that our unified grain growth law considerably deviates from the classical grain growth law, with critical differences at geological time scales. We expect that our law will help unravel physical properties that are dependent on processes happening at the GB scale, such as rheology, diffusion or permeability

The fate of Si and Fe while nuclear glass alters with steel and clay

International audienceThe French concept developed to dispose high-level radioactive waste in geological repository relies on glassy waste forms, isolated from the claystone host rock by steel containers. Understanding interactions between glass and surrounding materials is key for assessing the performance of a such system. Here, isotopically tagged SON68 glass, steel and claystone were studied through an integrated mockup conducted at 50°C for 2.5 years. Post-mortem analyses were performed from nanometric to millimetric scales using TEM, STXM, ToF-SIMS and SEM techniques. The glass alteration layer consisted of a crystallized Fe-rich smectite mineral, close to nontronite, supporting a dissolution/reprecipitation controlling mechanism for glass alteration. The mean glass dissolution rate ranged between 1.6 × 10$_{−2}$ g m$_{−2}$ d$_{−1}$ to 3.0 × 10$_{−2}$ g m$_{−2}$ d$_{−1}$ , a value only 3-5 times lower than the initial dissolution rate. Thermodynamic calculations highlighted a competition between nontronite and protective gel, explaining why in the present conditions the formation of a protective layer is prevented

A new setup for localized implantation and live-characterization of keV energy multiply charged ions at the nanoscale

International audienceAn innovative experimental setup, PELIICAEN, allowing the modification of materials and the study of the effects induced by multiply charged ion beams at the nanoscale is presented. This ultra-high vacuum (below 5 × 10−10 mbar) apparatus is equipped with a focused ion beam column using multiply charged ions and a scanning electron microscope developed by Orsay Physics, as well as a scanning probe microscope. The dual beam approach coupled to the scanning probe microscope achieves nanometer scale in situ topological analysis of the surface modifications induced by the ion beams. Preliminary results using the different on-line characterization techniques to study the formation of nano-hillocks on silicon and mica substrates are presented to illustrate the performances of the setu