Competitive Adsorption and Diffusion of Gases in a Microporous Solid

The experimental and theoretical study of the co-adsorption and co-diffusion of several gases through a microporous solid and the instantaneous (out of equilibrium) distribution of the adsorbed phases is particularly important in many fields, such as gas separation, heterogeneous catalysis, purification of confined atmospheres, reduction of exhaust emissions contributing to global warming, etc. The original NMR imaging technique used gives a signal characteristic of each adsorbed gas at each instant and at each level of the solid and therefore the distribution of several gases in competitive diffusion and adsorption. But it does not allow to determine separately the inter- and intra-crystallite quantities. A new fast and accurate analytical method for the calculation of the coefficients of co-diffusing gases in the intra- and inter-crystallite spaces of microporous solid (here ZSM 5 zeolite) is developed, using high-performance methods (iterative gradient methods of residual functional minimization and analytical methods of influence functions) and mathematical co-adsorption models, as well as the NMR spectra of each adsorbed gas in the bed. These diffusion coefficients and the gas concentrations in the inter- and intra-crystallite spaces are obtained for each position in the bed and for different adsorption times

The STAR-RICH Detector

The STAR-RICH detector extends the particle idenfication capabilities of the STAR spectrometer for charged hadrons at mid-rapidity. It allows identification of pions and kaons up to ~3 GeV/c and protons up to ~5 GeV/c. The characteristics and performance of the device in the inaugural RHIC run are described

The ALICE experiment at the CERN LHC

ALICE (A Large Ion Collider Experiment) is a general-purpose, heavy-ion detector at the CERN LHC which focuses on QCD, the strong-interaction sector of the Standard Model. It is designed to address the physics of strongly interacting matter and the quark-gluon plasma at extreme values of energy density and temperature in nucleus-nucleus collisions. Besides running with Pb ions, the physics programme includes collisions with lighter ions, lower energy running and dedicated proton-nucleus runs. ALICE will also take data with proton beams at the top LHC energy to collect reference data for the heavy-ion programme and to address several QCD topics for which ALICE is complementary to the other LHC detectors. The ALICE detector has been built by a collaboration including currently over 1000 physicists and engineers from 105 Institutes in 30 countries. Its overall dimensions are 161626 m3 with a total weight of approximately 10 000 t. The experiment consists of 18 different detector systems each with its own specific technology choice and design constraints, driven both by the physics requirements and the experimental conditions expected at LHC. The most stringent design constraint is to cope with the extreme particle multiplicity anticipated in central Pb-Pb collisions. The different subsystems were optimized to provide high-momentum resolution as well as excellent Particle Identification (PID) over a broad range in momentum, up to the highest multiplicities predicted for LHC. This will allow for comprehensive studies of hadrons, electrons, muons, and photons produced in the collision of heavy nuclei. Most detector systems are scheduled to be installed and ready for data taking by mid-2008 when the LHC is scheduled to start operation, with the exception of parts of the Photon Spectrometer (PHOS), Transition Radiation Detector (TRD) and Electro Magnetic Calorimeter (EMCal). These detectors will be completed for the high-luminosity ion run expected in 2010. This paper describes in detail the detector components as installed for the first data taking in the summer of 2008

Mathematical modelling and visualization of gas transport in a zeolite bed using a slice selection procedure

International audienceWe present the analytical solution of the equations of gas diffusion in a heterogeneous zeolite bed. The problem is handled by assuming that the bed consists of a large number of very thin layers of solid, perpendicular to the direction of propagation of the gas. Mass transfer by diffusion in such a material is determined by a system of differential equations with boundary and interface conditions. The results allow the theoretical determination of the time dependence of the concentration profiles and the inter- and intra-crystallite diffusion coefficients of a gas in each layer of the bed. A numerical application concerns the diffusion of benzene in a cylindrical bed of ZSM5 displaced vertically and rapidly, step by step, inside the NMR probe. Thus we can obtain the time dependence of the concentration of gas absorbed at the level of each slice. These coupled investigations give a better understanding of the diffusion process in this multilayer material

Physical State of di-Nitrogen in the Presence of SBA and Various Zeolites Probed by 15 N Spin–Lattice Relaxation of Pure 15 N 2 in the 30–300 K Temperature Range

International audience15N NMR spin–lattice relaxation times of N2 in the presence of mesoporous SBA-80 and selected zeolites (Y, OMEGA, MORDENITE, ZSM-5, ZSM-11, AlPO-5, RHO) have been measured at 30 MHz and at temperatures ranging from ambient temperature to about 30 K. The interpretation of these experimental data rests on two relaxation mechanisms: spin-rotation (mainly active when N2 molecules reorient rapidly) and dipolar interaction with surface protons (depending essentially on the N2 translational diffusion mobility). Both mechanisms have to be taken into account for all samples except SBA-80 (for which the interpretation of experimental data requires two different spin-rotation interactions), and RHO (for which two different dipolar interactions are required). For all zeolites investigated here it has been indispensable to define a cutoff temperature below which spin-rotation is no longer active, indicating the quasi-disappearance of the gaseous state to the benefit of a condensed state. This cutoff temperature is 77 K for Y, OMEGA, and possibly MORDENITE, whereas it is higher for those zeolites with pore diameters approaching the dinitrogen molecular length. It is thus concluded that these NMR relaxation measurements are able to reveal the physical state of dinitrogen in the presence of SBA-80 and zeolites possessing very different structures

The CSI-based RICH detector array for the identification of high momentum particles in ALICE

After ten years of R&D activities, an array of seven proximity focusing RICH modules is being built to identify &#960;-K in the range 1<p<2.7 GeV/c and K-p in the range 1.5<p<5 GeV/c in the ALICE experiment at LHC. This device, named High Momentum Particle Identification Detector (HMPID), with a total active area of 11 m2, represents the largest scale application of MWPCs with high Quantum Efficiency (QE) CsI segmented photo-cathodes for the Cherenkov photon conversion. An overview of the RICH layout, the technique of photocathode production, the front-end (FE) and readout (R/O) electronics and finaaly the detector control system (DCS), are presented

Cleaning and recirculation of perfluorohexane (C6F14C_{6} F_{14}) in the STAR-RICH detector

A RICH detector with a CsI photo-cathode and liquid perfluorohexane radiator has been installed in the STAR experiment at RHIC. The liquid is continuously cleaned and distributed to a quartz containment vessel within the detector by a closed recirculation system. A VUV spectrometer is connected to the system which monitors the optical transparency of the liquid. This measurement provides one of the pieces of information necessary to model the number of Cherenkov photons which reach the pad plane. A description of the liquid recirculation system and the cleaning procedure for the liquid as well as the spectrometer is presented along with results of their performance. (23 refs)