Thermal Reconversion of Oxidised Lead White in Mural Paintings via a Massicot Intermediate

Lead white is the most ancient and common white pigment used in mural paintings. However, it tends to blacken with time due to its oxidation to plattnerite (\b{eta}-PbO2). Chemical treatments were used but they can put the pictorial layers supports at risks. Hereby we address the possibility of thermally reconverting black plattnerite to white lead carbonates via a massicot (\b{eta}-PbO) intermediate, with a view to developing a restoration procedure using continuous wave laser heating. We first investigated the conditions (temperature, time, and environment) in which pure powders react, before studying mural painting samples. Experiments were made in ovens and TGA and XRD and SEM characterization were achieved. Litharge ({\alpha}-PbO) and massicot were obtained from plattnerite respectively between 564 and 567 {\deg}C and at 650 {\deg}C. Lead carbonates (cerussite, hydrocerussite and plumbonacrite) formed from massicot in wet CO2 below 100 {\deg}C in a few hours. Lastly, when heating plattnerite based mural painting samples, lead species reacted with binders and mortar, yielding massicot, plumbonacrite but also lead silicate and calcium lead oxides. This demonstrates the viability of thermal reconversion of darkened lead in mural, while raising concerns about the formation of several lead species by reaction with mural painting constituents

Ultrafast Laser-Based Spectroscopy and Sensing: Applications in LIBS, CARS, and THz Spectroscopy

Ultrafast pulsed lasers find application in a range of spectroscopy and sensing techniques including laser induced breakdown spectroscopy (LIBS), coherent Raman spectroscopy, and terahertz (THz) spectroscopy. Whether based on absorption or emission processes, the characteristics of these techniques are heavily influenced by the use of ultrafast pulses in the signal generation process. Depending on the energy of the pulses used, the essential laser interaction process can primarily involve lattice vibrations, molecular rotations, or a combination of excited states produced by laser heating. While some of these techniques are currently confined to sensing at close ranges, others can be implemented for remote spectroscopic sensing owing principally to the laser pulse duration. We present a review of ultrafast laser-based spectroscopy techniques and discuss the use of these techniques to current and potential chemical and environmental sensing applications

Velocity-space sensitivity of the time-of-flight neutron spectrometer at JET

The velocity-space sensitivities of fast-ion diagnostics are often described by so-called weight functions. Recently, we formulated weight functions showing the velocity-space sensitivity of the often dominant beam-target part of neutron energy spectra. These weight functions for neutron emission spectrometry (NES) are independent of the particular NES diagnostic. Here we apply these NES weight functions to the time-of-flight spectrometer TOFOR at JET. By taking the instrumental response function of TOFOR into account, we calculate time-of-flight NES weight functions that enable us to directly determine the velocity-space sensitivity of a given part of a measured time-of-flight spectrum from TOFOR

Relationship of edge localized mode burst times with divertor flux loop signal phase in JET

A phase relationship is identified between sequential edge localized modes (ELMs) occurrence times in a set of H-mode tokamak plasmas to the voltage measured in full flux azimuthal loops in the divertor region. We focus on plasmas in the Joint European Torus where a steady H-mode is sustained over several seconds, during which ELMs are observed in the Be II emission at the divertor. The ELMs analysed arise from intrinsic ELMing, in that there is no deliberate intent to control the ELMing process by external means. We use ELM timings derived from the Be II signal to perform direct time domain analysis of the full flux loop VLD2 and VLD3 signals, which provide a high cadence global measurement proportional to the voltage induced by changes in poloidal magnetic flux. Specifically, we examine how the time interval between pairs of successive ELMs is linked to the time-evolving phase of the full flux loop signals. Each ELM produces a clear early pulse in the full flux loop signals, whose peak time is used to condition our analysis. The arrival time of the following ELM, relative to this pulse, is found to fall into one of two categories: (i) prompt ELMs, which are directly paced by the initial response seen in the flux loop signals; and (ii) all other ELMs, which occur after the initial response of the full flux loop signals has decayed in amplitude. The times at which ELMs in category (ii) occur, relative to the first ELM of the pair, are clustered at times when the instantaneous phase of the full flux loop signal is close to its value at the time of the first ELM

Lasers for nuclear technologies

International audienceA wide spectrum of laser applications for nuclear technologies and industry on the basis of the latest RandD in CEA (France) will be presented. In particular, the problems of paint and metal decontamination, tokamak plasma facing walls detritiation, remote characterisation and testing (radiometry and thermography, laser induced breakdown spectroscopy, plasma diagnostics) will be discussed. The experiments were made along with the fundamental studies on laser beam/matter interaction (laser ablation with ns, ps, fs and double-pulses) and the modelling of these processes. Other laser applications (art and cultural heritage, Mars curiosity mission, optical elements, micro-fabrication, additive manufacturing) will be under discussion as well

Laser methods development for nuclear technologies

International audienceLaser methods and their applications for nuclear industry are regarded as very attractive and promising as they may provide remote measurements and surface processing without undesirable production of additional nuclear wastes. Laser methods for chemical analysis, non-destructive testing and control, surface decontamination and processing are under intensive development and study. Different laser methods, Laser Induced Breakdown Spectroscopy (LIBS- method) for elemental and isotopic analysis, laser active radiometry and pyrometry for surface non-destructive characterization, laser decontamination of metal surfaces and paint removal from concrete, laser detritiation and cleaning of tokamak walls and optics will be presented and discussed. The presentation is based on both the experimental and theoretical results obtained in our Department [1-6] in a wide collaboration with French national laboratories and other international teams (Russia, UK, Germany, and Japan). Special attention will be given to physical interpretation of laser methods performances in correlation with the development of adequate theoretical models and simulations. Future possible applications of laser methods for characterization and detritiation of ITER plasma facing walls and components, for surface micro-processing for micro-fluidic applications, and also for nano-analysis by a tip enhanced near-field ablation will be presented

Laser cleaning of paints and metals problems and possible solutions

International audienceLaser cleaning of complex surfaces (paints and metals with a micrometric oxide layer) should beregarded as a complicated multi parametric physical-chemical process and a tough technicalprocedure. To ensure surface laser cleaning with a required quality, high efficiency and minimumof undesirable effects and to avoid possible thermo-chemical changes in the surface undercleaning, one should take into consideration numerous laser parameters, optical and physicalchemicalfeatures of a surface under cleaning, laser beam/surface interaction regime,environmental conditions, etc.A summarized review of the experimental results on the laser cleaning of paints on concrete,metal mirrors and stainless steel surfaces with a micrometric oxide layer performed with highrepetition rate (1-20 kHz) nanosecond lasers (5-100 ns) will be presented along with the results ofmulti parametric studies. Theoretical modeling (3D+t) for an adequate explanation of theobtained results and physical-chemical processes associated with laser cleaning will be underdiscussion. The problems of cleaning regime optimization, the appropriate choice of the laserwavelength (infrared, visible or ultraviolet) and the pulse duration (nanosecond, picosecond orfemtosecond) for complex surfaces and art objects, in particular, will be under special discussion

Nano-sampling of metals with ultra-short laser pulses

International audienceIn sample microanalysis by laser ablation (LA), spatial resolution is determined by laser beam diffraction limits (of the order of a laser wavelength) and thermal diffusion of a deposited heating energy during laser pulse (proportional to the square root of pulse duration and matter diffusivity). Being limited by these laser beam features and those of heating energy, spatial resolution (a crater diameter) of $\sim$1 $\mu$m was obtained with 4 ns laser pulses on 266 nm wavelength. To improve spatial resolution of microanalysis, the application of lasers with the pulses of shorter durations (ps and fs) may be advised. As another way to improve spatial resolution of microanalysis up to $\sim$100 nm, one may advise LA with a highly localized laser field created by a tip near-field enhancement. The experiments with ns laser pulses were made along with multi-parametric theoretical studies based on one-temperature heating model. In this work, the theoretical studies were extended on ultra-short laser pulses (ps or fs) to analyze the effect of pulse duration and matter properties (absorption coefficient, thermal conductivity and capacity) on the resulting temperature field spatial distribution T (t, x, y, z). A two-temperature model was applied for T (t, x, y, z) calculations. The results of these simulations are compared to temperature distributions for ns laser pulses. Discussion on advantages of ultra-short pulses application for LA with a tip near-field enhancement for consecutive chemical analysis with nanometric resolution will be presented