H. Rauch

Test of a single crystal neutron interferometer

Abstract The interference of two widely separated coherent neutron beams produced by dynamical diffraction in a perfect Si-crystal has been observed. Phase shifting material inserted in the beams results in a marked intensity modulation behind the interferometer. Neutron interferometry introduces several new feasible experiments in nuclear and solid state physics.

Verification of coherent spinor rotation of fermions

Abstract The perfect crystal neutron interferometer was used to test the spinor rotation of spin- 1 2 -systems. Coherently splitted unpolarized slow neutrons exposed partially to a variable magnetic field show interference oscillations which are consistent with the predicted 4π-value.

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.

Experimental Test of Quantum Contextuality in Neutron Interferometry

We performed an experimental test of the Kochen-Specker theorem based on an inequality derived from the Peres-Mermin proof, using spin-path (momentum) entanglement in a single neutron system. Following the strategy proposed by Cabello et al. [Phys. Rev. Lett. 100, 130404 (2008)10.1103/PhysRevLett.100.130404], a Bell-like state was generated, and three expectation values were determined. The observed violation 2.291 +/- 0.008 not less, dbl equals1 clearly shows that quantum mechanical predictions cannot be reproduced by noncontextual hidden-variable theories.

Monte Carlo calculation of the magnetization of superparamagnetic particles

Abstract The thermodynamics of single superparamagnetic particles is studied by means of a Monte Carlo technique which we recently derived for the calculation of compact ferromagnets [1, 2]. Using this method, an exact (numerical) calculation of the magnetization and of the internal energy of the particle is obtained. The particle consists of several hundred to thousand spins arranged in a body-centered cubic lattice, interacting with nearest neighbours according to the Heisenberg model of ferromagnetism. It is shown that in the phase transition region the effect of the finiteness of the system cannot be explained by any shift of the Curie point, because the finite system does not exhibit any pronounced phase transition. A marked temperature dependence of the magnetization on the size and shape of the particle is found. With these calculations it is possible to interprete the experiments in a new way.

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.

Test of channel-cut perfect crystals for neutron small angle scattering experiments

Abstract Channel-cut crystals have been tested to reduce the tails of double crystal rocking curves. Such devices are useful tools for small angle scattering experiments in the Q -range between 10 −5 and 10 −3 A −1 and for real time experiments at short time scales. Therefore, large objects and large distance interparticle correlations can be investigated advantageously by this method. Test measurements with Latex sphere, polymer blends and lamellar structures have shown the capacity of perfect crystal small angle scattering cameras. The radius of gyration and the characteristic dimension of the lamellar structure have been determined.

Static versus time-dependent absorption in neutron interferometry

Abstract Neutron absorption in one of the two beam paths of a neutron interferometer gives different interference pattern with static and with time-dependent absorption even when the time-averaged absorption is the same. This has been demonstrated by experiment.

Observation of the neutron magnetic resonance energy shift

Using a high resolution backscattering instrument the energy shift caused by the Zeeman splitting and the inelasticity of the interaction of neutrons with a neutron magnetic resonance system could be observed. Various applications concerning the realization of a dynamical neutron polarization system, the pumping of neutrons into a certain energy interval and the production and handling of ultra cold neutrons are discussed.

Der Gd-neutronenzähler

Abstract In continuation of research carried out earlier 1 ), systematic measurements of the attainable efficiency and the background sensitivity of a new thermal neutron detector are reported. The neutron detection is due to the measurement of conversion electrons produced by the prompt neutron capture γ-rays in Gd (natural Gd and 157 Gd). For the detection of conversion electrons surface barrier detectors are used. A detection efficiency exceeding 40% can be obtained. A further advantage is the extremely small size of these detectors and their low sensitivity for background radiation (fast neutrons and γ-rays).