Developing more efficient catalytic processes using abundant and low toxicity transition metals is key to enable their mainstream use in synthetic chemistry. We have rationally designed a new Mn(
i
...)-catalyst for hydroarylation reactions that displays much improved catalytic activity over the commonly used MnBr(CO)
5
. Our catalyst, MnBr(CO)
3
(MeCN)
2
, avoids the formation of the off-cycle manganacycle-(CO)
4
species responsible for low catalyst activity, allowing near room temperature hydroarylation of alkenes and alkynes with broad functional group tolerance including late stage functionalisation and diversification of bioactive molecules.
A Mn(
i
)-catalyst for hydroarylation reactions, MnBr(CO)
3
(MeCN)
2
, avoids the formation of the off-cycle manganacycle-(CO)
4
species responsible for low catalyst activity typical of MnBr(CO)
5
, leading to mild and broad scope hydroarylation.
The radiation response of a phosphorus-doped multimode optical fiber is investigated under both transient (pulsed X-rays) and steady-state (γ- and X-rays) irradiations. The influence of a H 2 ...preloading on the fiber radiation-induced attenuation (RIA) in the 300-2000-nm wavelength range has been characterized. To better understand the impact of this treatment, online behaviors of fiber samples containing different amounts of gas are compared from glass saturation (100%) to less than 1%. In addition to these in situ experiments, additional postirradiation spectroscopic techniques have been performed such as electron paramagnetic resonance or luminescence measurements to identify the different point defects responsible for the induced losses and their H 2 dependence. All our data at room temperature (RT) highlight a strong positive impact of H 2 , even at very low concentrations, on the RIA. Hydrogen quickly passivates (t <; 1 s) most of the defects responsible for the visible-near-IR RIA, mainly phosphorus oxygen hole centers (POHC) and P1 defects. However, 1 year after the H 2 loading at RT or when operating at liquid nitrogen temperature, the RIA levels of the not-treated and H 2 -loaded fiber become comparable. The obtained results provide a better understanding of the potential and limitations of H 2 -loading treatment to design radiation-hardened fiber links.
The effects induced on the blue luminescence centered around 2.8eV, characteristic of silica nanoparticles, were investigated by monitoring its intensity during and after exposure to the third and ...the fourth harmonic of a Nd:YAG pulsed laser. The luminescence trend is found to be dependent on the UV photon energy: 3.50eV photons induce a partial bleaching followed by a recovery in the post-irradiation stage; 4.66eV photons cause a total bleaching permanent after the irradiation. These results are interpreted as the conversion of luminescent defects towards stable and metastable configurations.
► Blue luminescence band due to surface defects of silica nanoparticles. ► Bleaching of luminescent defects induced by UV laser radiation. ► Conversion of luminescent defects towards stable or metastable states. ► Reaction-limited process of surface defects with atomic/molecular species of ambient atmosphere.
Raman Distributed Temperature Sensors (RDTSs) offer exceptional advantages to monitor the envisioned French deep geological repository for nuclear wastes, called Cigéo. Both γ-ray and hydrogen ...release from nuclear wastes can strongly affect the temperature measurements made with RDTS. We present experimental studies on how the performances of RDTS evolve in harsh environments like those associated with γ-rays or combined radiations and H 2 release. The response of two standard and one radiation tolerant multimode fibers (MMFs) are investigated. In all fibers the differential induced attenuation between Stokes and anti-Stokes signal, (α AS - α S ) causes a temperature errors, up to 30 ° C with standard multimode fibers (100 m) irradiated at 10 MGy dose. This degradation mechanism that is more detrimental than the radiation induced attenuation (RIA) limiting only the sensing range. The attenuation in the 800-1600 nm spectral range at room temperature is explored for the three fibers γ-irradiated and/or hydrogen loaded to understand the origin of the differential RIA. We show that by adapting the characteristics of the used fiber for the sensing, we could limit its degradation but that additional hardening by system procedure is necessary to correct the T error in view of the integration of our RDTS technology in Cigéo. The current version of our correction technique allows today to limit the temperature error to ~ 2 ° C for 10 MGy irradiated samples.
We report an experimental investigation on the radiation-induced attenuation (RIA) in the ultraviolet-visible domain for Ge-doped optical fibers, during X-ray (10 keV) exposure at different ...temperatures. The objective is to characterize the impact of the irradiation temperature on the RIA levels and kinetics. Our data highlight that for dose exceeding 1 kGy(SiO2) the RIA spectrum changes with the irradiation temperature. In particular, for wavelengths below 470 nm the RIA depends both on the dose and on the irradiation temperature, whereas at higher wavelengths the RIA depends only on the dose. From the microscopic point of view the origin of this behavior is explained by a larger impact of the irradiation temperature on the Ge(1) defects generation mechanism with respect to the one of GeX defects, which appears as poorly temperature sensitive in the tested range. This finding prevents us from easily establishing a conclusive relation between the generation mechanisms of these two types of defects. The lower content of radiation induced Ge(1), in fiber irradiated at higher temperature, is supported by the electron paramagnetic resonance (EPR) results acquired after the irradiation. In situ RIA and postmortem EPR data show a significant correspondence of the Ge(1) growth as a function of the dose. Confocal microscopy luminescence experiments indicate that the non-bridging oxygen hole center concentration is higher at 473 K in comparison with those observed at 300 and 373 K.
We studied the responses of fiber-based temperature and strain sensors related to optical frequency domain reflectometry (OFDR) and exposed to high <inline-formula><tex-math notation="LaTeX">\gamma ...</tex-math></inline-formula>-ray doses up to 10 MGy. Three different commercial fiber classes are used to investigate the evolution of OFDR parameters with dose, thermal treatment and fiber core/cladding composition. We find that the fiber coating is affected by both thermal and radiation treatments and this modification results in an evolution of the internal stress distribution inside the fiber that influences its temperature and strain Rayleigh coefficients. These two environmental parameters introduce a relative error up to 5% on temperature and strain measures. This uncertainty can be reduced down to 0.5% if a prethermal treatment at 80 °C and/or a preirradiation up to 3 MGy are performed before insertion of the fiber in the harsh environment of interest. These preliminary results demonstrate that OFDR fiber-based distributed sensors look as promising devices to be integrated in radiation environments with associated large ionizing doses.
We report distributed temperature measurements based on Raman scattering performed during steady state γ-ray irradiation at a dose rate of 1 kGy(SiO 2 )/h and up to a total ionizing dose (TID) of ~ ...0.1 MGy. We characterize on-line the evolution of the performances of a single-ended Raman distributed temperature sensor (RDTS) during the γ-ray exposure of different classes of commercial multimode fibers (MMFs) acting as the sensing element. RDTS is influenced by the radiation-induced attenuation (RIA) phenomena leading to both large errors in the temperature measurements and a diminution of the useful sensing length. The amplitude of the radiation-induced temperature error strongly depends on the fiber choice and on the irradiation conditions. For the single-ended RDTS operation in the targeted Cigéo application the selection of a radiation tolerant sensing fiber will be mandatory, but not sufficient, to overcome the expected severe ambient conditions around radioactive wastes. For efficient temperature sensing up to an accumulated dose of 0.1 MGy, preirradiation of the selected radiation resistant (RR) fibers appears also necessary to improve the sensor performances.
We investigated the combined effects of temperature and X-rays exposures on the nature of point defects generated in Ge-doped multimode optical fibers. Electron paramagnetic resonance (EPR) results ...on samples X-ray irradiated at 5 kGy(SiO
2
), employing different temperatures and dose rates, are reported and discussed. The data highlight the generation of the Ge(1), Ge(2), E′Ge and E′Si defects. For the Ge(1) and Ge(2), we observed a decrease in the induced defect concentrations for irradiation temperatures higher than ~450 K, whereas the E′ defects feature an opposite tendency. The comparison with previous post-irradiation thermal treatments reveals peculiar effects of the temperature increase during the irradiation. Such difference, confirmed also by online radiation-induced attenuation measurements, has to be considered for practical use of these fibers in a mixed environment. Importantly, even if post-irradiation fading should be considered, the Ge(1) and Ge(2) concentrations measured by postmortem EPR experiments in room-temperature-irradiated samples are quite representative of the concentrations induced in the temperature range 230–450 K regardless of the investigated dose rate. The enhancement of the E′ content can be related to the simultaneous generation of this defect with non-bridging oxygen hole center from strained bonds implying a relevant modification of the defects generation/formation processes in the host glass matrix.
Two variants of the surface-nonbridging oxygen hole center, (
Si–O)
3Si–O
• and (
Si–O)
2(H–O)Si–O
•, stabilized in porous films of silica nano-particles were investigated by time resolved ...luminescence excited in the visible and UV spectral range by a tunable laser system. Both defects emit a photoluminescence around 2.0
eV with an excitation spectrum evidencing two maxima at 2.0 and 4.8
eV, this emission decreases by a factor ∼2 on increasing the temperature from 8 up to 290
K. However, the different local structure influences the emission lineshape, the quantum yield and the decay lifetime. Such peculiarities are discussed on the basis of the symmetry properties of these defects.
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