Philippe Blanc

Cathodoluminescence in geosciences

1 Cathodoluminescence in Geosciences: An Introduction.- 2 Physical Parameters for the Identification of Luminescence Centres in Minerals.- 3 Information Encoded in Cathodoluminescence Emission Spectra.- 4 Importance of Instrumental and Experimental Factors on the Interpretation of Cathodoluminescence Data from Wide Band Gap Materials.- 5 Systematic Cathodoluminescence Spectral Analysis of Synthetic Doped Minerals: Anhydrite, Apatite, Calcite, Fluorite, Scheelite and Zircon.- 6 The Status of the Standards Program of the Society for Luminescence Microscopy and Spectroscopy.- 7 Geologic Application of Cathodoluminescence of Silicates.- 8 Cathodoluminescence Microcharacterisation of Silicon Dioxide Polymorphs.- 9 Brittle Deformation in Sandstone Diagenesis as Revealed by Scanned Cathodoluminescence Imaging with Application to Characterization of Fractured Reservoirs.- 10 High-Resolution Cathodoluminescence Studies of Feldspar Minerals.- 11 Application of Cathodoluminescence to Carbonate Diagenesis.- 12 Cathodoluminescence of Carbonate Shells: Biochemical vs Diagenetic Process.- 13 Quantitative High Resolution Spectral Analysis of Mn2+ in Sedimentary Calcite.- 14 Systems of Interacting Luminescence Centers in Natural Diamonds: Laser-Induced Time-Resolved and Cathodoluminescence Spectroscopy.- 15 Use of Cathodoluminescence for U-Pb Zircon Dating by Ion Microprobe: Some Examples from the Western Alps.- 16 A Combination of Single Zircon Dating by TIMS and Cathodoluminescence Investigations on the Same Grain: The CLC-Method - U-Pb Geochronology For Metamorphic Rocks.- 17 Relevance of Cathodoluminescence for the Interpretation of U-Pb Zircon Ages, with an Example of an Application to a Study of Zircons from the Saxonian Granulite Complex, Germany.- 18 Cathodoluminescence in Applied Geosciences.- 19 Cathodoluminescence as a Tool in Gemstone Identification.

Natural fission reactors in the Franceville basin, Gabon: A review of the conditions and results of a “critical event” in a geologic system

Abstract Natural nuclear fission reactors are only known in two uranium deposits in the world, the Oklo and Bangombedeposits of the Franceville basin: Gabon. Since 1982, five new reactor zones have been discovered in these deposits and studied since 1989 in a cooperative European program. New geological, mineralogical, and geochemical studies have been carried out in order to understand the behavior of the actinides and fission products which have been stored in a geological environment for more than 2.0 Ga years. The Franceville basin and the uranium deposits remained geologically stable over a long period of time. Therefore, the sites of Oklo and Bangombeare well preserved. For the reactors, two main periods of actinide and radionuclides migration have been observed: during the criticality, under P-T conditions of 300 bars and 400–500°C, respectively, and during a distention event which affected the Franceville basin 800 to 900 Ma ago and which was responsible for the intrusion of dolerite dikes close to the reactors. New isotopic analyses on uranium dioxides, clays, and phosphates allow us to determine their respective importance for the retention of fission products. The UO 2 matrix appears to be efficient at retaining most actinides and fission products such as REEs, Y, and Zr but not the volatile fission products (Cd, Cs, Xe, and Kr) nor Rb, Sr, and Ba. Some fissiogenic elements such as Mo, Tc, Ru, Rh, Pd, and Te could have formed metallic and oxide inclusion in the UO 2 matrix which are similar to those observed in artificial spent fuel. Clays and phosphate minerals also appear to have played a role in the retention of fissiogenic REEs and also of Pu.

Annealing radiation damage and the recovery of cathodoluminescence

The structural recovery upon heat treatment of a highly metamict, actinide-rich zircon (U~6000 ppm) has been studied in detail using a range of techniques including X-ray powder diffraction, Raman spectroscopy, SHRIMP ion probe, electron microprobe, transmission electron microscopy and cathodoluminescence analysis. The structural regeneration of the amorphous starting material depends on random nucleation. It starts between 800 and 950°C when amorphous ZrSiO4 decomposes to form crystalline ZrO2 and amorphous SiO2. At around 1100°C, well-crystallised ZrSiO4 grows at the expense of the oxides. U has been retained in the newly grown zircon whereas Pb was evaporated during the heat treatment. This process is in marked opposition to the reconstitution of moderately metamict minerals, which experience a gradual recovery controlled by the epitaxial growth at the crystalline–amorphous boundaries. Both of these recovery processes are not the direct inverse of metamictisation. The structural regeneration was found to be connected with a significant increase in the emission of CL. In all cases (annealing heavily damaged zircon and moderately damaged zircon and monazite), we observe that the final, wellcrystallised annealing products emit more intense CL than their radiation-damaged starting minerals, although having almost identical elemental composition. Our observations are taken as evidence that the CL is not only determined by the chemical composition of the sample but is also strongly controlled by structural parameters such as crystallinity or the presence of defect centres.

Tunnel afterglow, fading and infrared emission in thermoluminescence of feldspars

Abstract Anomalous fading of TL, OSL and IRSL has been observed in many samples of feldspars and attributed to the tunnel effect. Investigations do show expected tunnel afterglow except for samples with no fading. Its intensitym quite noticeable at LNT, is in proportion with reported rate of fading. The emission is entirely in the red and infrared part of the spectrum. An important thermal quenching is observed. Low temperature storage results in fading of TL. Cathodoluminescence emission spectra, monitored from 200 to 900 nm, do confirm TL observations. They show two well-separated ranges: one, “blue”, from UV to yellow (the only one observed in usual TL dating), displays various emission bands; the other, “IR”, red and infrared, shows a well-characterized narrow Gaussian emission band, with a maximum around 720 nm. Models are proposed, relating fading with disorder in crystals. Tunnel afterglow appears as a good criterion of fading in feldspars.

Marbles from Roman Hispania: stable isotope and cathodoluminescence characterization

Abstract Pure white marble has been considered a valuable ornamental and architectural material since ancient times. Many scientific techniques have been used to create an extensive data base of “finger-prints” characterizing white marbles from the major classical quarries. However, determining the provenance of white marbles is a difficult task due to their similarity in physical and chemical parameters. Three techniques (petrography, cathodoluminescence and stable C and O isotopes) have been used to characterize white marbles from the ancient quarries of the Iberian Peninsula. Maximum grain size, texture and isotopic composition can be used to identify the different quarries. Each area is generally represented by several cathodomicrofacies, but quantitative CL analysis is also helpful in distinguishing those quarries for which the data provided by other techniques are not sufficiently diagnostic. The database and the discriminating criteria presented in this study have been tentatively applied to some ancient sculptures from the National Museum of Roman Art in Merida (Spain).

Experimental study of argon sorption in quartz: Evidence for argon incompatibility

Abstract We have conducted Ar sorption experiments on two varieties of natural quartz minerals (Q112, Q113) and a synthetic one (QHE37). Runs were performed in an internally heated pressure vessel at 1300°C and pressures of up to 8000 bar for run times between 1 and 12 d, on grain sizes ranging from 11–20 to 60–80 μm. Run products were analysed by gas chromatography (GC), Knudsen cell mass spectroscopy (KMS), electron microprobe (EMP), and scanning electron microscopy (SEM). Release spectra of Ar desorption were monitored by KMS. For sample Q112 and QHE37 two release signals are observed (500–1000°C and 1200–1600°C). When two grain sizes of the same specimen (QHE37) are analysed, the high temperature peak does not vary whereas the low temperature peak is significantly increased with decreasing grain size, suggesting desorption of surface bonded Ar. Argon contents from the high temperature peak indicate an Ar sorption of 28 ppm (QHE37) and 48 ppm (Q112) at 4070 bar. Specimen Q113 does not exhibit low temperature release, nevertheless, its Ar content is higher in smaller grains (11–20 μm: 431 ppm, 60–80 pm: 128 ppm), while increasing the duration of the experiments from ∼ 1 d to ∼ 10 d does not change the Ar content. This apparently erratic behaviour suggests an extrinsic control for Ar sorption. EMP analysis of all samples at the μm scale reveals heterogeneous Ar distribution. A few enriched spots with Ar up to 4000 ppm are observed (e.g., Q113) compared to a background concentration below the detection limit of ∼30 ppm. The average concentration measured by EMP is fairly similar to the high temperature step of bulk analytical methods (KMS or GC). We can conclude that bulk measurements of the sorption of Ar do not document equilibrium dissolution. Assuming the Ar diffusivity to be fast enough to permit saturation of at least the 11–20 μm grain fraction after ∼ 10 d, at 8000 bar and 1300°C, an upper bound of Ar solubility can be given as 30 ppm. In contrast, bulk methods yield variable average Ar concentrations which depend on experimental conditions. This indicates that solubilities measured by bulk methods grossly overestimate the true solubility. A quartz /melt partition coefficient of less than 0.006 can be derived.

Carbonation-decarbonation of concretes studied by the way of carbon and oxygen stable isotopes

Abstract Cements cylinders were submitted for three years to a CO 2 aggressive solution (pH 4). The comparison of carbonate content, and 13 C and 18 O isotope variations of CO 3 = with depth and time, leads to a carbonation/decarbonation model the constraints of which are strenghtened by the isotopic data. This implies to consider secondary carbonation processes during the elimination of calcium towards the aggressive external solution in order to simulate isotopic evolution.

ISOTOPE GEOCHEMISTRY (13C, 18O) OF CARBONATION PROCESSES IN CONCRETES

Abstract From laboratory experiments on C3S, CSH and OPC cement submitted to carbonation and measurements of the 13C-18O stable isotope concentration of the evolved CO2 are found some clues to the mechanism of carbonation. Isotope data are compared with mineral carbon content and XRD and SEM examinations. A provisional model explaining the features of isotope evolution during carbonation is presented.

Effect of Thermal Preannealing on Fluorescence, Thermostimulated Luminescence and Cathodoluminescence of CaSO4 Doped with Europium

This study addresses the important influence of air thermal preannealings (500–1150 °C) on the emissions of Eu2+ and Eu3+ ions in CaSO4 samples doped with various Eu concentrations (10–2000 ppm) and synthesized under oxidizing conditions. The characteristics of optical excitation, optical absorption, fluorescence and cathodoluminescence spectra are given before and after the annealings. The role of UV, X-ray or electron irradiation is discussed. An irreversible conversion Eu3+ Eu2+ is obtained beyond 600–900 °C, even for low Eu concentrations (<50 ppm). There exists an intense change in the ratio of Eu2+/Eu3+ emissions at about 25–100 ppm. Moreover, the present paper shows again how careful one must be with the interpretation of the presence of Eu2+ in CaSO4:Eu when considering cathodoluminescence results only. Two types of Eu2+ centres seem to be obtained in CaSO4:Eu3+ by thermal preannealings and/or under ionizing (X-ray, cathode-ray) irradiations. n n n nCette etude revele limportance des recuits thermiques (500–1150 °C) sous air du CaSO4:Eu sur les emissions des ions Eu2+ et Eu3+, pour des echantillons synthetises dans des conditions oxydantes et pour differents dopages compris entre 10 et 2000 ppm. Les spectres dexcitation optique, dabsorption optique, de fluorescence et de cathodoluminescence sont donnes avant et apres recuit. Le role des excitations UV, X ou electronique est souligne. On confirme une conversion irreversible Eu3+ Eu2+ en fonction de la temperature du recuit (sous air), principalement dans lintervalle 600–900 °C, et cela meme pour de tres faibles dopages (< 50 ppm). Il existe une forte variation du rapport des emissions Eu2+/Eu3+ autour de 25–100 ppm. De plus ce travail indique de nouveau quil faut etre prudent dans linterpretation de la presence dions Eu2+ dans CaSO4:Eu au vu des seuls spectres de cathodoluminescence. Deux types de centres Eu2+ semblent se former dans CaSO4:Eu3+ apres prerecuit thermique et/ou irradiation ionisante (X, rayonnement cathodique).

Cathodoluminescence in Geosciences: An Introduction

A wide variety of processes induces different kinds of luminescence, which is an emission of photons mainly in the visible domain (Marfunin 1979; Machel et al. 1991): n n nRadioluminescence is excited by X-ray photons, γ-rays, and α and β nuclear particles bombardment. n n nChemiluminescence is the result of chemical reactions (chemical radicals, oxidation of phosphorus, etc.). n n nElectroluminescence is generated by application of an electric field. n n nTriboluminescence is due to mechanical deformation (breaking of crystals bonds). n n nIonoluminescence is generated under energetic ion beam, for example in an ion microprobe. n n nBioluminescence is generated by biological processes. n n nThermoluminescence is light emission due to an activator in a mineral when the mineral is heated and is also referred to as thermally stimulated relaxations (McKeever 1985). n n nPhotoluminescence involves the selective energy of photons to excite electronic levels of luminescent centers. n n nCathodoluminescence is produced by energetic electrons.