The development of ultra-intense electron pulse for applications needs to be accompanied by the implementation of a practical dosimetry system. In this study four different systems were investigated as dosimeters for low doses with a very high-dose-rate source. First, the effects of ultra-short pulses were investigated for the yields of the Fricke dosimeter based on acidic solutions of ferrous sulfate; it was established that the yields were not significantly affected by the high dose rates, so the Fricke dosimeter system was used as a reference. Then, aqueous solutions of three compounds as fluorescence chemical dosimeters were utilized, each operated at a different solution pH: terephthalic acid - basic, trimesic acid - acidic, and coumarin-3-carboxylic acid (C3CA) - neutral. Fluorescence chemical dosimeters offer an attractive alternative to chemical dosimeters based on optical absorption for measuring biologically relevant low doses because of their higher sensitivity. The effects of very intense dose rate (TGy/ s) from pulses of fast electrons generated by a picosecond linear accelerator on the chemical yields of fluorescence chemical dosimeters were investigated at low peak doses (<20 Gy) and compared with yields determined under low-dose-rate irradiation from a 60 Co gamma-ray source (mGy/s). For the terephthalate and the trimesic acid dosimeters changes in the yields were not detected within the estimated (∼10%) precision of the experiments, but, due to the complexity of the mechanism of the hydroxyl radical initiated reactions in solutions of the relevant aromatic compounds, significant reductions of the chemical yield (–60%) were observed when the C3CA dosimeter was irradiated with the ultra-short pulses.

The in-line, rapid and precise control of semi-finished products and complex technical parts is a major challenge for the aerospace value chain. This is particularly true for composite parts, assemblies and coatings. Similar control needs are also found during the maintenance phases of the products. These controls often require new contactless, nonhazardous Non-Destructive Testing and Evaluation (NDT&E) methods to go beyond the capabilities of the existing ones. To address these issues, we use an innovative solution based on ultrashort electromagnetic pulses in the terahertz (THz) wave band: their ultrafast single-shot detection in the time domain enables raster scanning of objects in short times for an imaging analysis with depth resolution. Our STRIPP Control product range unleashes thus the potential of THz Time-Domain Spectroscopy to control, amongst others, Glass Fiber Reinforced Polymer (GFRP) parts, coatings and Carbon Fiber Reinforced Polymer (CFRP) unidirectional (UD) tapes. In composites, the pulsed THz raster imaging reveals defects like fiber clusters, air gaps, and impregnation heterogeneities that can be characterized and precisely localized. For coatings, the major advantage of our approach is its ability to rapidly provide a full map of thickness and presence of defects. Thanks to the ultrashort duration and high repetition rate of acquisition, the single shot technology is suited for the control of composites within cycle time of industrial production and for maintenance operations with

Picosecond pulse radiolysis measurements were performed in neat D2O and H2O in order to study the isotopic effect on the time-resolved yield of the hydrated electron and hydroxyl radical. First, the absorption band of the hydrated electron in D2O, eD2O-, is measured between 250 and 1500 nm. The molar absorption coefficient of the solvated electron spectrum in D2O was determined using the isosbestic point method by scavenging the solvated electron using methyl viologen. The amplitude and shape of the absorption spectrum of the hydrated electron in D2O are different from those previously reported in the literature. The maximum of the hydrated electron in the D2O absorption band is ca. 704 nm with a molar absorption coefficient of (22 900 ± 500) L mol-1 cm-1. Based on this extinction coefficient, the radiolytic yield of eD2O- just after the 7 ps electron pulse was determined to be (4.4 ± 0.2) × 10-7 mol J-1, which coincides with the one for eH2O- in H2O. The time-dependent radiolytic yield of eD2O- was determined from a few ps to 8 ns. To determine the OD˙ radical yield, the contribution of the solvated electron and of the transient species produced by the electron pulse in the windows of the fused silica optical cell was taken into account for the analysis of the transient absorption measurements at 260 nm. Therefore, an appropriate experimental methodology is used for measuring low absorbance at two different wavelengths in ps pulse radiolysis. The yield of the OD˙ radical just after the 7 ps electron pulse was found to be (5.0 ± 0.2) × 10-7 mol J-1. In the spurs of ionization, the decay rate of eD2O- is slower than eH2O-, whereas the decay rate of OD˙ is similar to the one of OH˙. Here, the established time-dependent yield of the solvated electron and the hydroxyl radical provide the foundation for improving the models used for spur reaction simulations in heavy water mainly for the chemistry of CANDU reactors.

Processes induced by ionizing radiation concern fields such as nuclear energy, radiobiology and radiotherapy. For these applications, a thorough knowledge of the caused physical and chemical processes of radiation effects is needed to optimize the performance and operation of equipment, to ensure the safety and to master the absorbed dose. Radiation-induced phenomena as defect formation and oxidation processes typically involve a number of relaxation steps on several magnitudes of time and space. A direct observation is therefore challenging but necessary for the understanding of the complex mechanisms that exhibit often a multitude of (parallel and consecutive) reaction pathways whose efficiency and branching is dependent on conditions as temperature, concentration and surrounding. Particular ultra-fast fundamental reactions such as solvation dynamics, electron and proton transfer are still not studied in many relevant systems as existing experimental installations do not provide the necessary time resolution. After a general description of radiation chemistry and its applications fields, we present a few examples of research studies which call for new tools that overcome the actual limitations; we give the state of the art of the radiolysis installations in use and describe finally the challenges of the next generation of time-resolved radiolysis, and how in our opinion the laser driven accelerator technology in combination with optical detection schemes can face them. It is not taking a risk to predict that performance of the new radiolysis installations, based on laser-driven electron and ion bunch sources, will markedly improve our knowledge on radiation chemistry both for fundamental science and practical application.

It is generally considered that the pre-solvated electron and the solvated electron reacting with a solute yield the same product. Silver cyanide complex, Ag(CN)2-, is used as a simple probe to demonstrate unambiguously the existence of a different reduction mechanism for pre-hydrated electrons. Using systematic multichannel transient absorption measurements at different solute concentrations from millimolar to decimolar, global data analysis and theoretical calculations, we present the dissociative electron attachment on Ag(CN)2-. The short-lived silver complex, Ag0(CN)22-, formed by hydrated electron with nanosecond pulse radiolysis, can be observed at room temperature. However, at higher temperatures only the free silver atom, Ag0, is detected, suggesting that Ag0(CN)22- dissociation is fast. Surprisingly, pulse radiolysis measurements on Ag(CN)2- reduction, performed by a 7 ps electron pulse at room temperature, show clearly that a new reduced form of silver complex, AgCN-, is produced within the pulse. This species, absorbing at 560 nm, is not formed by the hydrated electron but exclusively by its precursor. DFT calculations show that the different reactivity of the hydrated and pre-hydrated electrons can be due to the formation of different electronic states of Ag0(CN)22-: the prehydrated electron can form an excited state of this complex, which mainly dissociates into Ag0CN- + CN-.

NMR measurements show that diethyl carbonate (DEC, a solvent with a low dielectric constant) solutions of LiClO4 contain (LiClO4)n oligomers. The reduction of these species by solvated and presolvated electrons is followed by picosecond pulse radiolysis measurements. The data analysis shows that several anions absorbing in the near-infrared (NIR) and visible range are formed after the 7 ps electron pulse. In contrast with tetrahydrofuran (THF) solutions of LiClO4, the anionic monomer (LiClO4)- is not observed in DEC solutions. This is due to the fact that DEC is a nonpolar solvent favoring the clustering of monomers in the nonirradiated solution, as shown by NMR results, and also due to the instability of the anionic monomer. The absorption spectra of the anionic dimer (LiClO4)2-, trimer (LiClO4)3-, and tetramer (LiClO4)4- are clearly observed in NIR and visible ranges. Compared to the results obtained for the same system in THF and in agreement with simulated absorption spectra, the experimental results show that the absorption bands are shifted to the blue end of the spectrum when n increases. The kinetics recorded for the molar LiClO4 solution indicates that the solute is only in the form of oligomers (LiClO4)n with a large n value and that the reduced species absorb weakly in the visible region. Lastly, and contrary to what is known for well-separated ions in polar solvents, it is shown that the (LiClO4)n- anions are not stable with respect to self-reduction, leading to the decomposition of perchlorate anions. In this reaction, the perchlorate anion ClO4- is reduced by the Li atom into a chlorate anion ClO3-. This is proved by the presence of ClO3- and chlorinated species detected by mass spectrometry measurements in irradiated DEC solutions containing LiClO4.

Oxidation by the ultra-short lived radical cation of water, H2O˙+, can potentially take place at the interface of water and numerous heterogeneous systems involved in radiation therapy, energy and environmental industries. The oxidation processes induced by H2O˙+ can be mimicked in highly concentrated solutions where the nearest neighbors of H2O˙+ may be molecules other than water. The reactivity of H2O˙+ and D2O˙+ is probed in hydrogenated and deuterated sulfuric acid solutions of various concentrations. The oxidized solute, sulfate radical, is observed at 7 ps and remarkably higher yields are found in deuterated solutions. The isotopic effects reveal the competition between two ultrafast reactions: proton transfer toward H2O (D2O) and electron transfer from HSO4- to H2O˙+ (D2O˙+). Density functional theory simulations decipher the electron transfer mechanism: it proceeds via sub-femtosecond charge migration and is not affected by isotopic substitution. This work definitively demonstrates why direct oxidation triggered by H2O˙+ can be competitive with proton transfer.

Picosecond pulse radiolysis measurements of tetrahydrofuran (THF) solutions containing LiClO4 over a wide range of concentration are performed to investigate the formation of transient species. The (35)Cl NMR measurements of these solutions prior to irradiation show that the salt is in the form of (LiClO4)n oligomers. Kinetics and transient absorption spectra of intermediates in each solution are obtained on the time scale from 10 to 3800 ps. A global spectro-kinetic matrix of the data is analyzed by the multicurve resolution alternated least-squares (MCR-ALS) method. It shows the presence of 3 transient species induced by electron pulse, in addition to the solvated electron. A hybrid Monte Carlo/DFT molecular simulation method is elaborated, using the MPW1K functional for the configuration sampling and B3LYP for the spectra calculations. The maximum of the absorption band of the monomer (LiClO4)(-), dimer (LiClO4)2(-), trimer (LiClO4)3(-), and tetramer (LiClO4)4(-) anions are deduced from the simulations. They enable one to label the MCR-ALS spectra (differences are below 0.1 eV) and to interpret the kinetic data. The simulations show also that Li(I) ion catalyzes the reduction of perchlorate by excess electrons. Only the dimer anion, due to its unique structure with a stable Li2(+) core and two nonbridging perchlorates, presents higher stability toward ClO4(-) reduction into ClO3(-). It corresponds to the long-lived species observed in the experiments.

Picosecond pulse radiolysis measurements have been performed in several highly concentrated HClO4 and H3PO4 aqueous solutions containing silver ions at different concentrations. Silver ion reduction is used to unravel the ultrafast reduction reactions observed at the end of a 7 ps electron pulse. Solvated electrons and silver atoms are observed by the pulse (electron beam)-probe (supercontinuum light) method. In highly acidic solutions, ultrafast reduction of silver ions is observed, a finding that is not compatible with a reaction between the H(•) atom and silver ions, which is known to be thermally activated. In addition, silver ion reduction is found to be even more efficient in phosphoric acid solution than that in neutral solution. In the acidic solutions investigated here, the species responsible for the reduction of silver atoms is considered to be the precursor of the H(•) atom. This precursor, denoted (e(-), H3O(+)), is a pair constituting an electron (not fully solvated) and H3O(+). Its structure differs from that of the pair of a solvated electron and a hydronium ion (es(-), H3O(+)), which absorbs in the visible region. The (e(-), H3O(+)) pair , called the pre-H(•) atom here, undergoes ultrafast electron transfer and can, like the presolvated electron, reduce silver ions much faster than the H(•) atom. Moreover, it is found that with the same concentration of H3O(+) the reduction reaction is favored in the phosphoric acid solution compared to that in the perchloric acid solution because of the less-efficient electron solvation process. The kinetics show that among the three reducing species, (e(-), H3O(+)), (es(-), H3O(+)), and H(•) atom, the first one is the most efficient.

Highly concentrated potassium carbonate aqueous solutions are studied by picosecond pulse radiolysis with the purpose of exploring the formation processes of carbonate radical CO3(•-). The transient absorption band of solvated electron produced by ionizing is markedly shifted from 715 to 600 nm when the solute concentration of K2CO3 is 5 mol L(-1). This spectral shift is even more important than that observed for the solvated electron in 10 mol L(-1) KOH solutions. The broad absorption band of solvated electron in K2CO3 solutions overlaps with that of carbonate radical CO3(•-) formed at ultrashort time. Nitrate ion is used to scavenge the solvated electron and to observe the contribution of carbonate radical CO3(•-). The analysis of the amplitude and the kinetics of carbonate radical formation in highly concentrated solutions shows that CO3(•-) is formed within the electron pulse (7 ps) by two parallel mechanisms: a direct effect on the solute and the oxidation of the solute by water radical hole H2O(•+). These two mechanisms are followed by an additional one, by reaction between the solute and OH(•) radical especially in lower concentration. The radiolytic yield of each process is discussed.

We present a ground breaking Terahertz Time-Domain spectrometer (THz-TDS) and illustrate its performance by the non-destructive evaluation of fibre reinforced plastics and adhesively joined assemblies. Operated as imaging dev ce this technology gives in a direct way access to the inner structu re of dielectric materials and reveals manufacturing defects or fatigue damage in short acq uisition time. Electromagnetic radiation of THz frequencies allows the contact-free testing of dielectric volumes and buried or coated metallic surfaces without ionizing eff ect. THz-TDS is a particular powerful tool for NDT as it provides a multitude of information useful at the same time for imaging, material characterisation a nd spectroscopic analysis. Amplitude and time of flight of the ultrashort THz pulse in the time domain, as well as the spectrally resolved amplitude and phase information available by Fourier-Transformation, enable the analysis of complex objects. In many cases, three dimensional monitoring is possible with one-sided acc ss to the object. THz-TDS has been applied to aircraft composites, and its ability to detect mechanical and heat damage, voids, delamination, water or moisture conta mination has been shown. The single shot THz pulsed sensor “STRIPP” developed in our group reduces the acquisition time drastically relative to the repetitive solutions: the ultrashort detection window of some tens of picoseconds is recorded within o ne single laser shot. The measurements are performed at high stability and acquisition of kHz rates, without moving parts. With this leap in technology, the potential of terahertz radiation can be further exploited in industrial environments. We recent ly a alysed an object and the integrity of its structural sub-units during fr ee fall. The here presented applications illustrate further the performance of the technology, particular its ability to determine the thickness of substructures with micro et e precision, to localize precisely defects as delamination and inclusions. So , the high contrast of ultrafast THz pulses on dielectrics enables the localization and analysis of polymers that are buried in another polymer. In general, “STRIPP” can be used for the design, quality control and inspection of aerospace components. Electromagnetic waves with Terahertz (THz) frequencies or corresponding submillimetre wavelengths are situated in the range between the infrared and microwaves. They combine advantages of these neighboured spectral regions as high penetration depth in dielectrics and low scattering on micro-structured media. With optical generation schemes, free space propagation with good beam quality and accordingly diffraction M or e In fo a t O pe n A cc es s D at ab as e w w w .n dt .n et /? id = 18 93 9

Ageing of electrolytes used in batteries is a major issue for researchers and industry, as it represents an important cost in the development of new batteries. Past failures to adequately characterize the degradation processes of the electrolyte have led to potentially disastrous safety issues. It is, therefore, paramount to have an in-depth understanding of the underlying ageing phenomena. On the Inside Back Cover picture, we show that radiolysis techniques can induce similar mechanisms in the electrolyte, allowing for an accelerated assessment of the ageing phenomena within hours. More details can be found in the Full paper by Ortiz et al. on page 3605 in Issue 21, 2015 (DOI: 10.1002/cssc.201500641).

We apply single shot THz Time Domain Spectroscopy to control glass fiber reinforced plastics that were machined during their production. The THz imaging reveals that the mechanical processing as hole punching introduced significant modifications to the composite structures, also beyond the directly impacted region. These changes can be precisely localized and further characterized in order to classify the types of defect. The results show that the time of flight information is particularly sensitive to changes in the complex fiber and polymer matrix network. They can be visualized and quantified with B- and C-scans. Thanks to the ultrashort duration and high repetition rate of acquisition, the single shot technology is suited for the control of composites within cycle time of industrial production.

Picosecond pulse radiolysis measurements have been performed in neutral and highly acidic aqueous solutions containing silver ions at different concentrations. Silver ion reduction is used to understand the ultrafast chemistry of irradiated water and aqueous solutions. The absorption band measured at the end of the 7-ps electron pulses has an intense band with a maximum at 360 nm due to the formation of silver atoms. Kinetics shows that the amount of silver atom formed at the end of the electron pulse in phosphoric acid solutions is greater than that in neutral water. This unexpectedly high yield of silver atom formation cannot be explained solely by the reaction between silver ions and solvated electrons in neutral solutions nor by the reaction with hydrogen atoms in phosphoric acid solutions. To explain the observed ultrafast reduction of silver ions, the presolvated electron, be it free or paired to the hydronium cation, must react very quickly with a silver ion, potentially competing with geminate recombination of the electron and its sibling radical cation.

The ageing phenomena occurring in various diethyl carbonate/LiPF6 solutions are studied using gamma and pulse radiolysis as a tool to generate similar species as the ones occurring in electrolysis of Li-ion batteries (LIBs). According to picosecond pulse radiolysis experiments, the reaction of the electron with (Li+, PF6-) is ultrafast, leading to the formation of fluoride anions that can then precipitate into LiF(s). Moreover, direct radiation-matter interaction with the salt produces reactive fluorine atoms forming HF(g) and C2H5F(g). The strong Lewis acid PF5 is also formed. This species then forms various (RRRP)-R-1-R-2-P-3=O molecules, where R is mainly -F, -OH, and -OC2H5. Substitution reactions take place and oligomers are slowly formed. Similar results were obtained in the ageing of an electrochemical cell filled with the same model solution. This study demonstrates that radiolysis enables a description of the reactivity in LIBs from the picosecond timescale until a few days.

The behavior of carbonates is critical for a detailed understanding of aging phenomena in Li-ion batteries. Here we study the first reaction stages of propylene carbonate (PC), a cyclical carbonate, by picosecond pulse radiolysis. An absorption band with a maximum around 1360 nm is observed at 20 ps after the electron pulse and is shifted to 1310 nm after 50 ps. This band presents the features of a solvated electron absorption band, the solvation lasting up to 50 ps. Surprisingly, in this polar solvent, the solvated electron follows an ultrafast decay and disappears with a half time of 360 ps. This is attributed to the formation of a radical anion PC(-•). The yield of the solvated electron is low, suggesting that the radical anions are mainly directly produced from presolvated electrons. These results demonstrate that the initial electron transfers mechanisms are strongly different in linear compared with cyclical carbonates.

We present a new development for pump probe absorption spectroscopy that allows the simultaneous measurement from the green part of the visible spectrum (510 nm) over the whole near-infrared range to >1600 nm, corresponding to 0.77-2.40 eV. The system is based on a sub-picosecond supercontinuum generated in bulk material used as a broadband probe that is dispersed with a custom-made prism spectrometer and detected by an InGaAs array with extended sensitivity to the visible. Two versions, with and without probe referencing, are implemented for operation at laser repetition rates of a few hertz and kilohertz, respectively. After presentation of the optical configuration of the spectrometer, its performance is characterized and further illustrated on two time scales, with the ultrafast radiolysis of isopropanol induced by a picosecond electron pulse and with the instantaneous response of a BK7 plate to a femtosecond light pulse. The photophysics of the dye IR-140 is resolved from the femto- to picosecond regime. Stable and easy day-to-day routine use of the spectrometer also can be achieved in non-optical laboratory surroundings. For operation in a hazardous environment, the optical probe beams can be transported to the detector unit by optical fibers.

The electron transfer from oxide into water is studied in nanoparticle suspensions of various oxides (SiO2, ZnO, Al2O3, Nd2O3, Sm2O3, and Er2O3) by means of pulse and gamma radiolysis. The time-resolved and steady-state investigations of the present study demonstrate independently that whatever the band gap and the electron affinity of the oxide, the electron transfer always takes place in these nanometric systems: Irradiation generates hot electrons which have enough energy to cross the semiconductor-liquid interface. Moreover, picosecond measurements evidence that the spectrum of the solvated electron is the same as in water. Lastly, the decay of the solvated electron is similar on the picosecond to nanosecond time scale in water and in these suspensions, but it is clearly different on the nanosecond to microsecond time scale.

Many potential applications of THz-Time Domain Spectroscopy in science or industry call for highest acquisition speed and stability. Our approach of single-shot detection provides the full temporal information on the ultrashort THz electric field with variable window of several 10 picoseconds at kHz repetition rates. We use this technique to image moving objects and to study transient phenomena.