15 research outputs found
The way to Open Access : French strategies to move forward
No full textIn France, the movement in favour of open access to scientific research output is getting increasingly coordinated and supported at the political level. The CNRS, leading research organization in Europe and signatory of the Berlin Declaration, has an evident strategic role to play in this development. Various initiatives that have emerged in the French academic world in recent years have led, for example, in early 2005 to the joint announcement, by four major research institutions, of a common policy to promote open access to published material and other types of digital resources, and to set up institutional archives. The article highlights some key issues of this policy, gives an overview of the current and past CNRS involvement in Open Access and describes the principal functions, as well as the related challenges, of the future institutional repositories
BEAM PROFILE MEASUREMENT WITH OPTICAL FIBER SENSORS AT FLASH
No full textAbstract The system is intended to determine the beam profile at the DESY-FLASH undulator section as well as measuring beam losses with high spatial resolution. The measurement setup is based on wire scanners, optical fibers which are symmetrically mounted around the beam line over the full length (30 m) of the undulator section, a signal conditioning unit and a data acquisition system. The optical fibers are used as beam loss sensors, and depending on the software configuration, the setup is working either as a beam loss position monito
Organic reactivity of alcohols in superheated aqueous salt solutions: an overview
No full textThe low dielectric constant and high self-dissociation constant of water in a temperature range between 150 and 250 degrees C make it a very appealing solvent for synthesis. Surprisingly, while organic chemistry in water at low temperature or around its critical point has been investigated in detail, very little seems to be known about the behaviour of organic molecules under hydrothermal conditions. The present work thus aims at shading some light on this field. As a start, we decided to investigate the reactions in which alcohols can undergo in water in the above-mentioned temperature range. Knowing that very strong salt effects on organic reactions have already been observed in super critical water, the impact of salt on the outcome of our tests was also investigated in detail
Beam loss Monitors for FEL using optical Fiber
No full textBeam losses and beam profiles at particle accelerators can be determined by measuring the ionizing radiation outside the vacuum chamber. The next generations of free elec tron lasers require novel solutions for beam loss monitor and radiation detection systems. A new concept at the Free Electron Laser Hamburg FLASH and Photo Injector Test Facility Zeuthen PITZ was developed and put into operation. The concept based on optical fibers used as radiation detection sensor. Slow beam loss monitors determine the total ionization dose at selected positions or along the beam line and undulator sections in a response time of a few milliseconds by measuring the radiation induced attenuation of the fiber. Fast beam loss monitors detect the Cerenkov light generated by relativistic electrons penetrating radiation hard fiber. The new beam loss position and beam profile monitor systems utilize this effect. The time response is below milliseconds with a time resolution of some nanoseconds. These monitors provide a technique to improve the beam performance and trace the stability of the over all setting parameters. This paper presents the new diagnostic methods and the operation experience of the systems with a focus on the fast beam loss monitor
Beam Loss Position Monitor using Cerenkov radiation in optical fibers
No full textThe VUV FEL in TESLA technology at DESY provides Giga Watt output power in laser pulses. The SASE single pass Free Electron Laser FEL has been developed for high brightness user applications. At the design parameters the average power of the electron beam is about 72 kW. To avoid vacuum breakdown and high radiation levels caused by electron losses a machine protection system is required. Collimators are installed upstream of the radiation sensitive undulators. How ever, the proper operation of the collimator system needs to be measured with a beam loss monitor. Conventional radiation sensor systems are not suited for the VUV FEL undulators, because of the restricted free space in the undulator gap. A Beam Loss Position Monitor BLPM based on Cerenkov light in optical fibers allows real time monitoring of loss location and loss intensity. Electrons with energies above 175 keV generate Cerenkov light during their penetration of the optical fiber. The fast response of the Cerenkov signal is detected with photomultipliers at the end of the irradiated fibers. The reconstruction of the particle loss trace in 3 space dimensions became possible with four sensor
Synthesis of Early-Transition-Metal Carbide and Nitride Nanoparticles through the Urea Route and Their Use as Alkylation Catalysts
No full textDensification of mesoporous silicas by radiation damage – New perspectives for the treatment of radioactive effluents
No full textInternational audienceIn recent years, mesoporous silicas (SBA15, MCM41) discovered in the 1990s, synthetized by sol-gel process [1-2] have been the subject of numerous studies for various applications in the fields of catalysis, CO2 encapsulation, or treatment of radioactive effluents [3]. More precisely, a new strategy for this treatment is based on the use of a mesoporous silica functionalized by an organic ligand selective of the RadioNuclides (RN). This hybrid material would allow at the same time the separation of the RN and their encapsulation after collapsing the porosity. This new concept would result in obtaining a primary wasteform matrix. Several ways are being considered to close the mesoporosity: chemical reactions (sol-gel in particular), thermomechanical treatments, and irradiation effects. The collapse of silica mesoporosity by external irradiation (ion and electron) has been demonstrated in several works [4-5]. More recently, the possibility of closing the porosity of a mesoporous silica through self-irradiation damage produced by the presence of the short-lived actinide 238Pu has been studied in our laboratory. The results of this work will be presented in the talk. 238/239Pu sorption experiments have shown that hybrid silicas grafted with Ac-Phos and Prop-Phos ligands (Figure 1) have a loading capacity of around 10% by weight, enabling significant self-irradiation damage, comparable to an external irradiation experiment, to be achieved in around two years. Our findings are in line with previous results [6]. Small-angle Xray scattering (SAXS), which is accessible on the SOLEIL synchrotron’s MARS beamline, was employed for characterization of these Pu-doped materials. After 17 months of ageing, these measurements show a decrease in the interplanar (100) distance of the hexagonal pore network of mesoporous silica, indicating a densification of around 10% of the pore volume.[1] Beck, J. S., J. C. Vartuli, W. J. Roth, M. E. Leonowicz, C. T. Kresge, K. D. Schmitt, C. T. W. Chu, D. H. Olson, E. W. Sheppard, S. B.Mccullen, J. B. Higgins and J. L. Schlenker, A New Family of Mesoporous Molecular-Sieves Prepared with Liquid-CrystalTemplates, American Chemical Society, Vol. 114, 1992, pp. 10834-10843.[2] Zhao, D., J. Feng, Q. Huo, N. Melosh, G. H. Fredrickson, B. F. Chmelka and G. D. Stucky, Triblock copolymer syntheses ofmesoporous silica with periodic 50 to 300 angstrom pores, Vol. 279, 1998, pp. 548-552.[3] P. Makowski, X. Deschanels, A. Grandjean, D. Meyer, G. Toquer and F. Goettmann, New J. Chem., 36 (2012) 531.[4] Y. Lou, S. Dourdain, C. Rey, Y. Serruys, D. Siméone, N. Mollard, X. Deschanels, Micropor. Mesopor. Mater., 251 (2017) 146.[5] J. Lin, G. Toquer, C. Grygiel, S. Dourdain, Y. Guari, C. Rey, J. Causse, X. Deschanels, « Behavior of mesoporous silica under2 MeV electron beam irradiation » Microporous Mesoporous Mater. 328 (2021) 111454.[6] Fryxell, G. E., H. Wu, Y. Lin, W. J. Shaw, J. C. Birnbaum, J. C. Linehan, Z. Nie, K. Kemner and S. Kelly, Lanthanide selective sorbents: self-assembled monolayers on mesoporous supports (SAMMS), Vol. 14, 2004
Densification of mesoporous silicas by radiation damage – New perspectives for the treatment of radioactive effluents
No full textInternational audienceIn recent years, mesoporous silicas (SBA15, MCM41) discovered in the 1990s, synthetized by sol-gel process [1-2] have been the subject of numerous studies for various applications in the fields of catalysis, CO2 encapsulation, or treatment of radioactive effluents [3]. More precisely, a new strategy for this treatment is based on the use of a mesoporous silica functionalized by an organic ligand selective of the RadioNuclides (RN). This hybrid material would allow at the same time the separation of the RN and their encapsulation after collapsing the porosity. This new concept would result in obtaining a primary wasteform matrix. Several ways are being considered to close the mesoporosity: chemical reactions (sol-gel in particular), thermomechanical treatments, and irradiation effects. The collapse of silica mesoporosity by external irradiation (ion and electron) has been demonstrated in several works [4-5]. More recently, the possibility of closing the porosity of a mesoporous silica through self-irradiation damage produced by the presence of the short-lived actinide 238Pu has been studied in our laboratory. The results of this work will be presented in the talk. 238/239Pu sorption experiments have shown that hybrid silicas grafted with Ac-Phos and Prop-Phos ligands (Figure 1) have a loading capacity of around 10% by weight, enabling significant self-irradiation damage, comparable to an external irradiation experiment, to be achieved in around two years. Our findings are in line with previous results [6]. Small-angle Xray scattering (SAXS), which is accessible on the SOLEIL synchrotron’s MARS beamline, was employed for characterization of these Pu-doped materials. After 17 months of ageing, these measurements show a decrease in the interplanar (100) distance of the hexagonal pore network of mesoporous silica, indicating a densification of around 10% of the pore volume.[1] Beck, J. S., J. C. Vartuli, W. J. Roth, M. E. Leonowicz, C. T. Kresge, K. D. Schmitt, C. T. W. Chu, D. H. Olson, E. W. Sheppard, S. B.Mccullen, J. B. Higgins and J. L. Schlenker, A New Family of Mesoporous Molecular-Sieves Prepared with Liquid-CrystalTemplates, American Chemical Society, Vol. 114, 1992, pp. 10834-10843.[2] Zhao, D., J. Feng, Q. Huo, N. Melosh, G. H. Fredrickson, B. F. Chmelka and G. D. Stucky, Triblock copolymer syntheses ofmesoporous silica with periodic 50 to 300 angstrom pores, Vol. 279, 1998, pp. 548-552.[3] P. Makowski, X. Deschanels, A. Grandjean, D. Meyer, G. Toquer and F. Goettmann, New J. Chem., 36 (2012) 531.[4] Y. Lou, S. Dourdain, C. Rey, Y. Serruys, D. Siméone, N. Mollard, X. Deschanels, Micropor. Mesopor. Mater., 251 (2017) 146.[5] J. Lin, G. Toquer, C. Grygiel, S. Dourdain, Y. Guari, C. Rey, J. Causse, X. Deschanels, « Behavior of mesoporous silica under2 MeV electron beam irradiation » Microporous Mesoporous Mater. 328 (2021) 111454.[6] Fryxell, G. E., H. Wu, Y. Lin, W. J. Shaw, J. C. Birnbaum, J. C. Linehan, Z. Nie, K. Kemner and S. Kelly, Lanthanide selective sorbents: self-assembled monolayers on mesoporous supports (SAMMS), Vol. 14, 2004
