Neutron imaging and tomography with MCPs

A neutron imaging detector based on neutron-sensitive microchannel plates (MCPs) was constructed and tested at beamlines of thermal and cold neutrons. The MCPs are made of a glass mixture containing B-10 and natural Gd, which makes the bulk of the MCP an efficient neutron converter. Contrary to the neutron sensitive scintillator screens normally used in neutron imaging, spatial resolution is not traded off with detection efficiency. While the best neutron imaging scintillators have a detection efficiency around a percent, a detection efficiency of around 50% for thermal neutrons and 70% for cold neutrons has been demonstrated with these MCPs earlier. Our tests show a performance similar to conventional neutron imaging detectors, apart from the orders of magnitude better sensitivity. We demonstrate a spatial resolution better than 150 um. The sensitivity of this detector allows fast tomography and neutron video recording, and will make smaller reactor sites and even portable sources suitable for neutron imaging.Comment: Submitted to the proceedings of the 19th International Workshop on Radiation Imaging Detectors (iWoRiD) 2-6 July 2017, Krakow, Polan

In-situ high-temperature EXAFS measurements on radioactive and air-sensitive molten salt materials

The development at the Delft University of Technology (TU Delft, The Netherlands) of an experimental set-up dedicated to high-temperature in situ EXAFS measurements of radioactive, air-sensitive and corrosive fluoride salts is reported. A detailed description of the sample containment cell, of the furnace design, and of the measurement geometry allowing simultaneous transmission and fluorescence measurements is given herein. The performance of the equipment is tested with the room-temperature measurement of thorium tetrafluoride, and the Th—F and Th—Th bond distances obtained by fitting of the EXAFS data are compared with the ones extracted from a refinement of neutron diffraction data collected at the PEARL beamline at TU Delft. The adequacy of the sample confinement is checked with a mapping of the thorium concentration profile of molten salt material. Finally, a few selected salt mixtures (LiF:ThF4) = (0.9:0.1), (0.75:0.25), (0.5:0.5) and (NaF:ThF4) = (0.67:0.33), (0.5:0.5) are measured in the molten state. Qualitative trends along the series are discussed, and the experimental data for the (LiF:ThF4) = (0.5:0.5) composition are compared with the EXAFS spectrum generated from molecular dynamics simulations

In situ high-temperature EXAFS measurements on radioactive and air-sensitive molten salt materials

The development at the Delft University of Technology (TU Delft, The Netherlands) of an experimental set-up dedicated to high-temperature in situ EXAFS measurements of radioactive, air-sensitive and corrosive fluoride salts is reported. A detailed description of the sample containment cell, of the furnace design, and of the measurement geometry allowing simultaneous transmission and fluorescence measurements is given herein. The performance of the equipment is tested with the room-temperature measurement of thorium tetrafluoride, and the Th-F and Th-Th bond distances obtained by fitting of the EXAFS data are compared with the ones extracted from a refinement of neutron diffraction data collected at the PEARL beamline at TU Delft. The adequacy of the sample confinement is checked with a mapping of the thorium concentration profile of molten salt material. Finally, a few selected salt mixtures (LiF:ThF4) = (0.9:0.1), (0.75:0.25), (0.5:0.5) and (NaF:ThF4) = (0.67:0.33), (0.5:0.5) are measured in the molten state. Qualitative trends along the series are discussed, and the experimental data for the (LiF:ThF4) = (0.5:0.5) composition are compared with the EXAFS spectrum generated from molecular dynamics simulations

Quasielastic and elastic scattering studies of aligned DMPC multilayers at different hydrations

Lipid model membranes such as 1,2-Dimyristoyl-sn-Glycero-3-Phosphocholine (DMPC) serve as role models for their more complex counterparts in biological systems. Quasielastic neutron scattering (QENS) [1-3], inelastic neutron scattering (INS) [4] and neutron spin echo spectroscopy (NSE) [5] have been employed to study local as well as collective dynamics of these membranes on a ps-ns time scale. Most of these studies lack a systematic investigation of the behavior of the model membranes in dependence on their hydration. We now started a detailed investigation of hydration effect on model membrane systems. The complexity of the dynamics can be further reduced by selective deuteration, which allows to distinguish between dynamics of different part of the lipid molecules. In the here presented work we have used chain deuterated DMPC-d54 to study the dynamics of the lipid head group. To probe both dynamics in the plane of the membrane and perpendicular to it, the samples were prepared on cleaned silicon wafers. The hydration for the two samples was adjusted by hydrating them for pure D2O and from a saturated salt solution respectively, resulting in two different states of hydration (repeat distance d=62.5 Å with 15 water molecules per lipid and d = 54.9 Å with 9 water molecules per lipid, respectively). The alignment and mosaicity were checked prior to the measurements for all samples by neutron diffraction and was found to be below 1°. QENS experiments were performed at the time-of-flight spectrometer TOFTOF at the research reactor FRMII in Munich (energy resolution: 56 μeV FWHM) in the temperature range from 5°C to 30°C to cover the main phase transition from the Pβ gel phase to the liquid crystalline Lα phase of DMPC which occurs around 23°C. Elastic incoherent neutron scattering (EINS) measurements were performed at the high momentum transfer backscattering spectrometer IN13 (energy resolution 8 μeV FWHM) and the cold neutron backscattering spectrometer IN16 (energy resolution 0.9 μeV FWHM) both at the Institut Laue-Langevin (ILL), Grenoble. For the QENS experiment elastic incoherent structure factors (EISF) and diffusion constants were extracted, which indicate that hydration has a clear influence on the mobility of this system [6]. The integrated intensities from the EINS experiments showed a shift of the main phase transition as a function of hydration which coincides with a change of the slopes of the mean square displacements [7]. In addition to earlier QENS [1-3] and backscattering [8] investigations, these experiments extend our knowledge of model membrane systems. References [1] S. König et al., J.Phys.II France, 2 (1992) 1589-1615 [2] M.C. Rheinstädter et al., Phys. Rev. E 75 (2007) 011907 [3] S. Busch et al., JACS 132, (2010), 3232-3233 [4] M.C. Rheinstädter et al., Phys Rev. Lett. 93 (2004) 108107 [5] M.C. Rheinstädter et al., Phys. Rev. Lett. 97 (2006) 048103 [6] M. Trapp et al., in preperation [7] M. Trapp et al., Spectrosc.-int. J., accepted (2010) [8] M.C. Rheinstädter et al., Phys. Rev. E 71 (2005) 061908 (2002

Cold working consequence on the magnetocaloric effect of Ni 50 Mn 34 In 16 Heusler alloy

The negative effect of cold working on the magnetocaloric effect across the Curie transition of Mnbased Heusler alloys is highlighted. The results of manual crushing and subsequent heat treatment on the magnetic and magnetocaloric properties of a Ni50Mn34In16 sample are reported. Plausible explanations of the degradation of the magnetocaloric effect by cold working are discussed, on the basis of magnetic and structural measurements performed on a reference sample. The study of the connection between microstructure and magnetic properties of these materials represents a key point for the improvement of Heusler-based magnetic refrigeration

Understanding the Activation of ZSM-5 by Phosphorus: Localizing Phosphate Groups in the Pores of Phosphate-Stabilized ZSM-5

Fluid catalytic cracking (FCC) produces (the feedstock for) a major part of the world’s fuels, as well as chemical building blocks for, for example, polymers, pharmaceuticals, and specialty materials. ZSM-5 is the active ingredient in propylene-selective FCC catalyst systems and is stabilized or activated with phosphorus compounds. Despite this process being one of the largest-scale industrially applied catalytic processes, there is still considerable debate on the mechanism of activation, as well as on the interaction between phosphate and zeolite aluminum species. In this work, we use synchrotron-based powder XRD, neutron diffraction, and subsequent pair distribution function analysis to unequivocally corroborate the activation mechanism of phosphorus-based promotion in FCC catalysis and localize the phosphate groups inside the pore system of P-activated ZSM-5. We find local disorder in the zeolite T–O coordination, which could not be observed with traditional XRD analyses. Furthermore, we support these experimental findings with full periodic quantum-mechanical modeling (QMM) of the highly relevant, but often overlooked, combination of dealumination by hydrolysis (steaming) and phosphatation of the zeolite framework. We thereby show that phosphate can react with partially dislodged aluminum species that remain stable and are still tethered to their original framework position. Finally, by assessing all available literature postulations by the same periodic QMM and comparing them energetically with our obtained results, we can conclude that by accounting for the highly relevant inclusion of steaming prior to phosphatation, the two models resulting from this work rank among the three most relevant remaining models. This combined experimental and theoretical work fundamentally explains the activation and promotion mechanism of one of the world’s most applied chemical processes—propylene-selective FCC

A lithium argyrodite Li6PS5Cl0.5Br0.5 electrolyte with improved bulk and interfacial conductivity

Contains fulltext : 200899.pdf (postprint version ) (Open Access

PDFgetN3: atomic pair distribution functions from neutron powder diffraction data using ad hoc corrections

PDFgetN3, a new software tool for the extraction of pair distribution functions (PDFs) from neutron powder diffraction intensity data, is described. Its use is demonstrated with constant-wavelength neutron data measured at the new powder diffractometer PEARL at the Delft University of Technology. PDFgetN3 uses an ad hoc data collection protocol similar to PDFgetX3. The quality of the resulting PDFs is assessed by structure refinement and by comparison with established results from synchrotron X-ray scattering