Institut Laue-Langevin Research Articles

Demonstration of focusing by a neutron accelerator

Space-time focusing was demonstrated by a neutron accelerator. Test experiments were performed by using very slow neutrons at High-Flux Reactor at Institut Laue-Langevin. Focusing of neutrons at the detector position through the accelerator was observed. Focusing neutrons enables us to transport the neutrons while maintaining density from source to experimental position. This will be a powerful technique for measurement of the permanent electric dipole moment of neutrons, which require a high density of neutrons.

Innovative Wavelet Protocols in Analyzing Elastic Incoherent Neutron Scattering

Wavelet analysis has recently found a wide range of applications in Physics, Mathematics, and signal processing. This is mainly due to its ability to locally resolve a nonstationary signal in terms of functional forms, called mother wavelets, and to firmly locate trend anomalies in the signal. In the present paper, some examples of the application of wavelet analysis to elastic incoherent neutron scattering (EINS) data collected by the IN13 spectrometer at the Institute Laue Langevin (ILL) on water mixtures of the three homologous disaccharides, trehalose, maltose, and sucrose, and on literature data of dry and hydrated lysozyme and myoglobine as a function of temperature and of exchanged wave vector are presented. The experimental findings have been analyzed by means of a wavelet analysis that allows one to characterize the scattered elastic intensity behavior on different scales and to locate the discontinuities and the trend anomalies in the registered signal. This latter procedure is made possible thanks to the multiscale analysis, which allows, by decreasing the scale, one to localize the peculiar trend features. The entire body of the experimental findings reveals different transition temperatures for the three investigated disaccharides together with a stronger temperature dependence of the maltose/H(2)O and sucrose/H(2)O systems in comparison with the trehalose/H(2)O mixture, which signals a stronger character of this latter in comparison with the other two homologous disaccharides. These results justify the better ability of trehalose, with respect to maltose and sucrose, to encapsulate biostructures in a more rigid matrix.

Dynamics and Thermodynamics of Crystalline Polymorphs: α-Glycine, Analysis of Variable-Temperature Atomic Displacement Parameters

Multitemperature synchrotron diffraction data to 0.5 Å resolution in the temperature range 10-298 K and neutron data at 18 K of the α-glycine polymorph have been collected at the KEK photon factory (PF), SPring-8 and the Institut Laue Langevin (ILL) for the study of molecular motion in the crystal and of the associated thermodynamic functions. Atomic displacement parameters (ADPs) of non-H atoms are obtained from refinements based on nonspherical atomic scattering factors (invariom model) to minimize correlation between parameters describing thermal motion and valence electron density. The ADPs in the temperature range 50-298 K from SPring-8 connect smoothly with those from neutron diffraction at 18 K and 288-323 K. The combined ADPs from both sources covering the temperature range 18-323 K are used for a normal-mode analysis in the molecular mean field approximation. The lattice vibration frequencies from the ADP analysis and the internal vibration frequencies from an ONIOM (B3LYP/6-311+G(2d,p):PM3) calculation together with the Einstein, Debye, and Nernst-Lindemann models of heat capacity are used to calculate Cp, Hvib, and Svib values that are in good agreement with those from calorimetry.

GRAVITATIONAL QUANTUM STATES OF NEUTRONS AND THE NEW GRANIT SPECTROMETER

The review covers recent developments on gravitational quantum states of neutrons and the new GRANIT spectrometer, discussed during the Workshop GRANIT-2010 in Les Houches.1The GRANIT facility2includes the spectrometer and the infrastructure needed for its operation. It is constructed at Institut Laue-Langevin (ILL)3in Grenoble for studies of/with gravitational quantum states of neutrons, and for related topics. New methodical developments4are discussed for future upgrades of this facility. An important motivation for this activity consists in constraining fundamental short-range forces.5Other quantum phenomena in gravitational field,6and centrifugal quantum states of neutrons,7were discussed as well. A detailed presentation of all these topics could be found in Workshop-2010 presentations.8We will focus here on instrumental developments and on options for studying neutron gravitational states.

A low-pass velocity filter for ultracold neutrons

We have built a device to filter ultracold neutrons with axial velocities vn≤8.0m/s from faster neutrons. The apparatus has been successfully tested at the Institut Laue-Langevin in Grenoble and is used in specific experiments, e.g., the measurement of ultracold neutron transmission through various types of neutron guides.

Low-spin structure of85Se and theβnbranching of85As

Fission fragments from neutron-induced fission of ${}^{235}$U produced at the high-flux reactor of the Institut Laue-Langevin, Grenoble, were separated with the Lohengrin separator to provide a beam of neutron-rich ${}^{85}\phantom{\rule{-0.16em}{0ex}}$As nuclei. The ${\ensuremath{\beta}}^{\ensuremath{-}}$ decay of ${}^{85}\phantom{\rule{-0.16em}{0ex}}$As to ${}^{85}$Se was studied using $\ensuremath{\gamma}$-$\ensuremath{\gamma}$ and $\ensuremath{\beta}$-$\ensuremath{\gamma}$ coincidence techniques. ${}^{85}$Se was also studied using the prompt-$\ensuremath{\gamma}$ coincidence data from spontaneous fission of ${}^{248}$Cm and ${}^{252}$Cf measured with the Eurogam2 and Gammasphere Ge arrays, respectively. The combination of $\ensuremath{\beta}$ decay and prompt-$\ensuremath{\gamma}$ data enabled the determination of spins and parities of low-energy excited states in ${}^{85}$Se. There are new arguments supporting the $5/{2}^{\ensuremath{-}}$ assignment for the ground state of ${}^{85}\phantom{\rule{-0.16em}{0ex}}$As.

High precision depolarisation measurements with an opaque test bench

We present a tool to investigate neutron depolarisation effects with 10−4 precision. The test bench consists of two opaque 3He cells with in-situ adiabatic fast passage flipping of the helium spin. The cells polarise a neutron beam to more than 99.99 % and analyse its polarisation with high accuracy. For depolarisation studies, a sample can be inserted between the two cells and its effect on a primarily highly polarised beam is analysed. The test bench has been validated at the cold neutron beam PF1B at Institut Laue-Langevin, France. We present here preliminary results for the wavelength range from 5Å to 7Å. Polarisation with super mirrors is limited to about 99.7%. Direct evidence of depolarisation in the order of 10−3 in polarising super mirrors was found by the test bench.

Inelastic scattering measured on a neutron reflectometer

It is possible to use the D17 neutron reflectometer at the Institut Laue-Langevin as a direct geometry time-of-flight spectrometer. The kinematic constraints for the measurement of incoherent scattering and inelastic scattering from highly oriented samples are presented, along with an initial discussion of the energy resolution of the instrument. Inelastic scattering from water and polycarbonate are measured and contrasted with scattering from vanadium. The implications and possibilities for the future measurement of inelastic scattering are discussed.

Crystal structures of ethylene glycol and ethylene glycol monohydrate

We have carried out a neutron powder diffraction study of deuterated ethylene glycol (1,2-ethanediol), and deuterated ethylene glycol monohydrate with the D2B high-resolution diffractometer at the Institut Laue-Langevin. Using these data, we have refined the complete structure, including all hydrogen atoms, of the anhydrous phase at 220 K. In addition, we have determined the structure of ethylene glycol monohydrate at 210 K using direct space methods. Anhydrous ethylene glycol crystallizes in space-group P2(1)2(1)2(1) with four formula units in a unit-cell of dimensions a = 5.0553(1) Å, b = 6.9627(1) Å, c = 9.2709(2) Å, and V = 326.319(8) Å(3) [ρ(calc)(deuterated) = 1386.26(3) kg m(-3)] at 220 K. Ethylene glycol monohydrate crystallizes in space-group P2(1)/c with four formula units in a unit-cell of dimensions a = 7.6858(3) Å, b = 7.2201(3) Å, c = 7.7356(4) Å, β = 92.868(3)°, and V = 428.73(2) Å(3) [ρ(calc)(deuterated) = 1365.40(7) kg m(-3)] at 210 K. Both the structures are characterized by the gauche conformation of the ethylene glycol molecule; however, the anhydrous phase contains the tGg' rotamer (or its mirror, g'Gt), whereas the monohydrate contains the gGg' rotamer. In the monohydrate, each water molecule is tetrahedrally coordinated, donating two hydrogen bonds to, and accepting two hydrogen bonds from the hydroxyl groups of neighboring ethylene glycol molecules. There are substantial differences in the degree of weak C-D···O hydrogen bonding between the two crystals, which calls into question the role of these interactions in determining the conformation of the ethylene glycol molecule.

FIGARO: The new horizontal neutron reflectometer at the ILL

Fluid Interfaces Grazing Angles ReflectOmeter (FIGARO) is the new horizontal neutron reflectometer at the Institut Laue-Langevin, Grenoble, France. It is a versatile, high-flux time-of-flight instrument with features suitable for a range of studies in soft condensed matter, chemistry, physics and biology both at free air/liquid interfaces and buried liquid/liquid and solid/liquid interfaces. Most of the experiments exploit isotopic contrast variation to determine the structure and composition of surface layers. Multiple chopper discs allow variable wavelength resolution, with the loose-resolution options increasing the available neutron flux for fast kinetic studies of thin films and improving the data acquisition efficiency from complex samples requiring multiple contrast measurements. It is possible to approach the interface with neutrons from below or above the horizon. The instrument is equipped with a range of sample environments including free liquid adsorption troughs, a Langmuir trough, an overflowing cylinder and a range of solid/liquid sample cells. FIGARO was launched as a user instrument in April 2009 and its success has been steadily increasing since. This article includes an introduction to the scientific case, detailed sections on the instrument components and performance, and descriptions of standard sample environments developed to date as well as some selected early scientific highlights.

Experimental investigation of a low-cost solid state detector with high spatial resolution for ultracold neutrons

An ultracold-neutron detector based on a commercial CMOS webcam was investigated for the first time at the instrument PF2 of the Institut Laue-Langevin. In this feasibility study two different neutron converters, 10B and 6Li, were compared. For a standard high-definition videochip with an active area of 3.2 mm × 4.8 mm, a spatial resolution of ≈ 0.3 μm is possible to obtain. For a 430 nm thin 6Li converter, positioned in front of the webcam, a detection efficiency of (47.1 ± 0.6)% was found.

γγangular-correlation analysis of200Hg after cold-neutron capture

We report on a $\ensuremath{\gamma}\ensuremath{\gamma}$ angular-correlation experiment investigating ${}^{200}$Hg after cold-neutron capture. The experiment was performed using eight high-purity germanium detectors mounted on an array installed at the PF1B neutron beam line of the research reactor of the Institut Laue-Langevin in Grenoble, France. The geometry of the array allows $\ensuremath{\gamma}\ensuremath{\gamma}$ angular-correlation analyses that can be used for the determination of level spins and multipole mixing ratios in ${}^{200}$Hg. We present multipole mixing ratios for secondary $\ensuremath{\gamma}$ rays and investigate the nature of the ${}^{200}$Hg neutron-capture state by analyzing the observed primary $\ensuremath{\gamma}$ rays of this nucleus.

Preliminary neutron crystallographic study of human transthyretin.

Preliminary studies of perdeuterated crystals of human transthyretin (TTR) have been carried out using the LADI-III and D19 diffractometers at the Institut Laue-Langevin in Grenoble. The results demonstrate the feasibility of a full crystallographic analysis to a resolution of 2.0 Å using Laue diffraction and also illustrate the potential of using monochromatic instruments such as D19 for higher resolution studies where larger crystals having smaller unit cells are available. This study will yield important information on hydrogen bonding, amino-acid protonation states and hydration in the protein. Such information will be of general interest for an understanding of the factors that stabilize/destabilize TTR and for the design of ligands that may be used to counter TTR amyloid fibrillogenesis.

The Laboratoire Léon Brillouin and the Orphée Reactor: The French National Neutron Facility

The Laboratoire Léon Brillouin is a French Research Infrastructure jointly supported by the Commissariat à l'Energie Atomique et aux Energies Alternatives (CEA) and the Centre National de la Recherche Scientifique (CNRS); it constructs and operates spectrometers around Orphée, a 14MW reactor operated by the CEA since 1980. The LLB is rather unique among neutron centers worldwide because it was specified from the outset to operate as both a large-scale facility open to a user community as well as a research institute in charge of developing its own research programs. In view of the duality of its mission, the objectives of the LLB are to perform research in its own scientific programs, to promote the use of diffraction and neutron spectroscopy, to welcome and assist experimentalists, subsequently ensuring training and education, and providing access for industrial partners. These activities are enduring and complementary to international centers, such as the Institute Laue-Langevin or the future European Spallation Source in Sweden, and cooperation programs with other national centers.

Isotopic yield measurement in the heavy mass region for239Pu thermal neutron induced fission

Despite the huge number of fission yield data available in the different evaluated nuclear data libraries, such as JEFF-3.1.1, ENDF/B-VII.0, and JENDL-4.0, more accurate data are still needed both for nuclear energy applications and for our understanding of the fission process itself. It is within the framework of this that measurements on the recoil mass spectrometer Lohengrin (at the Institut Laue-Langevin, Grenoble, France) was undertaken, to determine isotopic yields for the heavy fission products from the ${}^{239}$Pu(n${}_{th}$,f) reaction. In order to do this, a new experimental method based on $\ensuremath{\gamma}$-ray spectrometry was developed and validated by comparing our results with those performed in the light mass region with completely different setups. Hence, about 65 fission product yields were measured with an uncertainty that has been reduced on average by a factor of 2 compared to that previously available in the nuclear data libraries. In addition, for some fission products, a strongly deformed ionic charge distribution compared to a normal Gaussian shape was found, which was interpreted as being caused by the presence of a nanosecond isomeric state. Finally, a nuclear charge polarization has been observed in agreement, with the one described on other close fissioning systems.

Population Characteristics for Spin and Excitation Energy of Fragments in Thermal Neutron Induced Fission

The characterisation of fragments from nuclear fission in terms of excitation energy and spin population is still a debated subject. We show that data on excitation energy, kinetic energy and spin of the fragments in thermal neutron induced fission of the actinides can be consistently described by the statistical model in nuclear physics. We present an empirical relationship which allows calculating the temperature of fission products at the scission point. From the temperature we derive the distribution functions for excitation, kinetic energy and fragment spin. We compare the results from the statistical model with experimental data from the LOHENGRIN spectrometer at the Institut Laue-Langevin in Grenoble/France.

The GRANIT spectrometer

Abstract The existence of quantum states of matter in a gravitational field was demonstrated recently in the Institut Laue–Langevin (ILL), Grenoble, in a series of experiments with ultra cold neutrons (UCN). UCN in low quantum states is an excellent probe for fundamental physics, in particular for constraining extra short-range forces; as well as a tool in quantum optics and surface physics. The GRANIT is a follow-up project based on a second-generation spectrometer with ultra-high energy resolution, permanently installed in ILL. It has been constructed in framework of an ANR grant; and will become operational in 2011.

Gravitational and centrifugal quantum states of neutrons

Two related physical phenomena have recently been observed: quantum states of neutrons in the gravitational field above a flat mirror, and quantum states of neutrons in an effective centrifugal potential in the vicinity of a concave mirror. It is curious that the measurement of the near-surface quantum states of these two types is the first direct demonstration of the weak equivalence principle for a massive object in a quantum state. These two phenomena and their application to various domains of science will be explored using a new GRANIT spectrometer, which is under commissioning in the Institut Laue-Langevin, Grenoble, France. Most recent advances in these domains are mentioned.

Effects of high intensity neutron flux on in-situ spin-exchange optical pumping of 3He

Prior studies revealed neutron beam-induced alkali-metal spin relaxation in 3He cells polarized in-situ by spin-exchange optical pumping. These effects are minor for neutron beams of low to moderate intensity, but become important at the highest neutron flux levels available in the full spectrum beams of high flux neutron sources. It was found that the relaxation consisted of a fast and a slow component, but the origin of neither is understood. This work further explored the mechanisms of this effect by measuring the magnitude and time dependence of alkali-metal spin-relaxation rates as a function of N2 and 3He composition. The experiments were performed on a thermal neutron beam line at the Institut Laue-Langevin with a maximum neutron flux of 2.4 × 109 cm−2 s−1.

Phase and Microphase Separation of Polymer Thin Films Dewetted from Silicon—A Spin–Echo Resolved Grazing Incidence Neutron Scattering Study

An understanding of the structure of ultrathin polymer films on solid substrates has scientific importance in applications as well as in fundamental studies of polymer diffusion or adsorption. We present studies of the organization of dewetted droplets of polymers on a silicon surface using a new neutron scattering technique, spin-echo resolved grazing incidence scattering (SERGIS), that has the potential to address at the same time the droplet-droplet correlations and the chemical configuration inside each droplet. For the seminal experiments, the polarized neutron reflectometer EVA at the Institut Laue-Langevin, Grenoble, France, was equipped with a spin-echo setup, and measurements were taken on surface structures previously characterized by different techniques. The dewetted polymers used in our studies were pure polystyrene, a mixture of polystyrene and polyparamethylstyrene, and a diblock copolymer of the two homopolymers. Even with a provisional setup SERGIS, we were able to determine the correlation between the droplets, providing results in excellent agreement with those obtained by atomic force microscopy and grazing incidence small-angle X-ray and neutron scattering. In addition, it was confirmed that the correlation function for diblock copolymer droplets is more complex than for polymer mixtures, exhibiting partial ordering of the copolymer within each droplet.