Matthias Baron

Violation of a Bell-like inequality in single-neutron interferometry.

Non-local correlations between spatially separated systems have been extensively discussed in the context of the Einstein, Podolsky and Rosen (EPR) paradox and Bells inequalities. Many proposals and experiments designed to test hidden variable theories and the violation of Bells inequalities have been reported; usually, these involve correlated photons, although recently an experiment was performed with 9Be+ ions. Nevertheless, it is of considerable interest to show that such correlations (arising from quantum mechanical entanglement) are not simply a peculiarity of photons. Here we measure correlations between two degrees of freedom (comprising spatial and spin components) of single neutrons; this removes the need for a source of entangled neutron pairs, which would present a considerable technical challenge. A Bell-like inequality is introduced to clarify the correlations that can arise between observables of otherwise independent degrees of freedom. We demonstrate the violation of this Bell-like inequality: our measured value is 2.051 ± 0.019, clearly above the value of 2 predicted by classical hidden variable theories.

The new high resolution ultra small-angle neutron scattering instrument at the High Flux Reactor in Grenoble

In 1998, the combined Interferometer and Ultra Small Angle Neutron Scattering (USANS) instrument S18 at the 58 MW High Flux Reactor at the Institute Laue-Langevin in Grenoble (France) started operation. The instrument has been upgraded to allow more advanced neutron optics experiments for fundamental, nuclear and condensed matter physics. The new supermirror guide along with the two channel cut silicon perfect crystals, configured as an advanced high resolution Bonse-Hart camera, provides optimal intensity conditions. A large range of wavelengths is accessible by variations of the Bragg angle and by using different reflecting planes of a properly cut silicon monochromator block in combination with different channel-cut analyzer crystals. The fine adjustment analyzer system is achieved by an advanced piezo drive, which has an accuracy of 0.036 seconds of arc. The basic features of the USANS camera, which takes advantage of a new tail suppression method, and the results of various test measurements concerning intensities, long term stability and the accessible wavelength range will be presented. A high resolution position sensitive detector can either be used to analyze beam profiles or to perform neutron radiography experiments.

First phase-contrast tomography with thermal neutrons

Attenuation-contrast tomography with monochro-matic thermal neutrons becomes a standard tool at many places in the world. A new tomographic neutron technique-the inter-ferometric imaging or neutron phase-contrast tomography (nPCT)-is introduced. nPCT is similar to x-ray phase-contrast tomography (xPCT) and offers a complete three-dimensional (3-D) investigation of the attenuation, the small angle scattering, and the phase-shifting properties of isotope distributions in the sample. As a first demonstration of the feasibility of nPCT, an aluminum screw has been imaged in an aluminum block of slightly different composition. A spatial resolution of 100 /spl mu/m has been achieved and the high sensitivity of phase-contrast measurements with thermal neutrons was verified.

Measurement of a confinement induced neutron phase.

Particle physicists see neutrons as tiny massive particles with a confinement radius of about 0.7 fm and a distinct internal quark–gluon structure. In quantum mechanics, neutrons are described by wave packets whose spatial extent may become ten orders of magnitude larger than the confinement radius, and can even reach macroscopic dimensions, depending on the degree of monochromaticity. For neutrons passing through narrow slits, it has been predicted that quantization of the transverse momentum component changes the longitudinal momentum component, resulting in a phase shift that should be measurable using interferometric methods. Here we use neutron interferometry to measure the phase shift arising from lateral confinement of a neutron beam passing through a narrow slit system. The phase shift arises mainly from neutrons whose classical trajectories do not touch the walls of the slits. In this respect, the non-locality of quantum physics is apparent.

Ultra-small-angle neutron scattering studies of artificial lattices

Ultra-small-angle neutron scattering (USANS) with the use of perfect silicon crystals provides a resolution of the order of 10-5 A-1 in reciprocal space, which corresponds to rad in scattering angles and m structures in real space. From small-angle scattering by artificial lattices follows a unique test procedure for the related devices and techniques. Corresponding measurements were performed at the USANS facilities of the Atominstitut in Vienna and of the S18 instrument at the ILL. We observed diffraction patterns from samples being periodically structured in one and two dimensions. These measurements take advantage of the extended coherence function of the set-up and the high quality of the manufactured silicon sample lattices. Due to these characteristics up to 50 interference orders were obtained at the S18 instrument. Scattering from two-dimensional periodic structures was observed for different orientations of the sample which shows characteristic diffraction maps in reciprocal space.

Optimisation of a crystal design for a Bonse- Hart camera

Bonse-Hart double-crystal diffractometers (DCDs) with multi-bounce channel-cut crystals show rocking curves that depart dramatically from dynamical diffraction theory in their wings. The intrinsic background is many orders of magnitude higher than the predictions of dynamical diffraction theory. This effect was studied at the ultra-small-angle neutron scattering facility at the Atominstitut in Wien and at facilities in Grenoble, Julich and Villigen. The scattering intensity contains Bragg reflections from the front and the back faces, and thermal diffuse scattering from the internal volume. The aim of this study was to eliminate this contamination and develop a new crystal design which provides optimal resolution. Therefore different ways were tested. In the first step the contamination was eliminated by cutting a groove in the middle of the back plate of the channel-cut crystals and inserting a cadmium absorber in this groove. With this modification an additional suppression of the wings of the rocking curve of about one order of magnitude was achieved. After this, we developed a new design for a DCD. The concept for this new crystal design was to avoid the back reflection and the thermal diffuse scattering. The different steps on the way to produce these crystals are presented in a detailed way. The crystal preparation and the different instruments where these crystals have been tested are also described.

First attempt of neutron quantum state reconstruction

The neutron interferometer set-up S18 at the ILL reactor has been used for the first neutron quantum state reconstruction experiment. By a simultaneous measurement of the coherence function and of the modulated momentum distribution behind the interferometer, the Wigner function of various quantum states can be reconstructed. This is equivalent to knowledge of the particle wavefunction. Its spatial dimension follows from the measurement of the coherence function, which is the autocorrelation function of the wavefunction and the shape in momentum space follows from momentum post-selection experiments. Non-orthogonal traces through the (x, k)-phase space have to be measured for an unambiguous reconstruction. Nearly classical (coherent) and non-classical states in the form of Schrodinger cat-like states have been identified. Comparisons of calculated and measured Wigner functions will be shown.

Scattering studies of large scale structures at the ultra small angle neutron scattering instrument S18

In recent years ultra small angle neutron scattering (USANS) has developed into a powerful standard method for large scale structure investigations. The upgraded instrument S18 at the ILLs 58MW high flux reactor is operated routinely with increasing beam time demand. The performance of the instrument and its abilities will be discussed in this paper. A peak to background ratio better than 105 is reached using Agamalians tail reduction method. A q-range from 2.10−5 up to 5.10−2A−1 can be covered. This allows a clear overlap with standard pinhole SANS instruments. The new way collecting scattering data logarithmically equidistant in q-space saves measuring time. This allows measuring times of about 1.5h for strong scattering specimens with reasonable statistics. We will present an overview of recent experiments which have been performed in co-operation with different groups from the international user community. This work comprises of structure investigations of petroliferous sedimentary rocks showing fractal scattering behaviour and time resolved USANS studies of the dynamics of hydration of cement paste. Concerning soft matter structures, Pirelli rubber nanocomposites have been investigated. In addition, time resolved measurement on a D2O solution of a PPO–PEO–PPO block copolymer (Reverse Pluronic 25R5) and the dynamics of phase separation of methyl-hydroxy-propyl cellulose (MHPC) have been studied using a sample temperature control system.

Mesoscopic structure of marble determined by combined USANS and SANS

Marbles, carbonatic (i.e. calcitic–dolomitic) rocks deriving from the metamorphic evolution of previous carbonates, are often rather similar to each other in many respects (i.e. mineralogical, physical–structural and chemical), and thus difficult to identify. In search for a diagnostic method to provenance marbles, we have selected a limited number of Italian white marbles representing a wide array of metamorphic (i.e. thermal) levels. The mesoscale structural arrangement of these samples was derived by means of combined Ultra Small Angle and Small Angle Neutron Scattering experiments. The parameters of the model used to fit the data have been correlated with the metamorphic history of the samples. These interesting preliminary results, to be confirmed with new analyses, throw new light on the strict relationship between the formation history of a marble and its intermediate mesoscopic structure, which is of potential interest for other applications, such as the source identification and authentication of...

Tomography using monochromatic thermal neutrons with attenuation and phase contrast

Attenuation-contrast tomography with monochromatic thermal neutrons was developed and operated at guide station S18 of the institute Laue-Langevin in Grenoble. From the S18 spectrum the neutron wavelength (lambda) equals 0.18 nm was selected by employing a fore crystal with the silicon 220 reflection at a Bragg angle (Theta) equals 30 degrees. Projections were registered by a position sensitive detector (PSD) consisting of a neutron-to-visible-light converter coupled to a CCD detector. Neutron tomography and its comparison with X-ray tomography is studied. This is of special interest since the cross section for neutron attenuation ((sigma) atom) and the cross section for neutron phase shift (bc) are isotope specific and, in addition, by no means mostly monotonous functions of atomic number Z as are attenuation coefficient ((mu) x) and atomic scattering amplitude (f) in the case of X-rays. Results obtained with n-attenuation tomography will be presented. Possibilities and the setup of an instrument for neutron phase-contrast tomography based on single-crystal neutron interferometry will be described.