M. Zawisky

Basic features of the upgraded S18 neutron interferometer set-up at ILL

Abstract The perfect crystal interferometer instrument S18 at the Institute Laue-Langevin (ILL) in Grenoble has been upgraded to allow more advanced neutron optics experiments for fundamental, nuclear and condensed matter physics. The new supermirror guide together with the multipurpose monochromator provides considerably higher intensities in a wide wavelength region. The optimal use of neutrons is obtained by a nondispersive arrangement of the monochromator and the interferometer crystals. This also allows to obtain completely polarised beams using permanent magnetic prism deflection. An additional third analyzer axis permits novel postselection experiments concerning momentum distribution and polarisation analysis of the interfering beams. Several types of large perfect crystal interferometers are available for different applications. The system can be configured as an advanced high-resolution Bonse–Hart small angle scattering camera. The results of various test measurements concerning intensities, interference contrast, long-term stability, the accessible wavelength range and the basic features as a SANS camera will be presented. Various proposals for experiments will be discussed as well.

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.

TESTING OF QUANTUM PHASE IN MATTER-WAVE OPTICS

Various phase concepts may be treated as special cases of the maximum likelihood estimation. For example the discrete Fourier estimation that actually coincides with the operational phase of Noh, Fouge`res and Mandel is obtained for continuous Gaussian signals with phase modulated mean.Since signals in quantum theory are discrete, a prediction different from that given by the Gaussian hypothesis should be obtained as the best fit assuming a discrete Poissonian statistics of the signal. Although the Gaussian estimation gives a satisfactory approximation for fitting the phase distribution of almost any state the optimal phase estimation offers in certain cases a measurable better performance. This has been demonstrated in neutron--optical experiment.

Phase estimation in interferometry

An objective theory of phase shift estimation is formulated within quantum mechanics and quantum estimation theory. The general validity of Bayesian analysis even in the limit of very low particle numbers is demonstrated using the information of measured phase-sensitive data. The formalism was applied to the estimation of an unknown phase in neutron interferometry operating near the quantum limit, when only a few particles are registered, and also in the regime of large particle numbers.

Maximum-likelihood absorption tomography

Maximum-likelihood methods are applied to the problem of absorption tomography. The reconstruction is done with the help of an iterative algorithm. We show how the statistics of the illuminating beam can be incorporated into the reconstruction. The proposed reconstruction method can be considered as a useful alternative in the extreme cases where the standard ill-posed direct-inversion methods fail.

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.

Neutron Interferometer with very thin Lamellae

We describe the manufacturing and testing of a monolithic perfect crystal interferometer with very thin lamellae, optimized for neutron phase contrast imaging where high spatial phase resolution is required. The two main characteristics of our new interferometer design are thin lamellae (t = 0.56 mm) for beam splitter S and analyzer A, and mirrors Ml, M2 of twice the thickness (t M = 1.12 mm) of S and A. The different stages of crystal preparation and the successful test with X-rays are reported.

The coherent scattering length of 86Kr determined by neutron interferometry

Abstract We determined the coherent neutron scattering length of gaseous natural krypton and 86 Kr using neutron interferometry. Measurements were performed at a 250 kW TRIGA reactor. The result for 86 Kr, b c = 8.07(26) fm is new; the result for n Kr is in excellent agreement with literature. The accuracy of the results is restricted by the stability of the setup and not by the limited neutron flux. The results obtained at the small reactor prove that neutron interferometry is feasible even at small neutron sources, provided that a stable setup is used.

Advanced Neutron Imaging and Sensing

Publisher Summary This chapter provides an overview of important improvements in imaging techniques for thermal neutron beams. The chapter presents some minimal theoretical tools necessary for the understanding of the subtle and fundamental effects associated with neutrons optics. The chapter discusses the neutrons experiments that reveal the quantum mechanical nature of neutrons. Several neutron optical measurement techniques are discussed in the chapter. It focuses on the wave-particle duality and decoherence in neutron interferometry as well asthe utilization of quantum effects for improving classical imaging.

Coherent Scattering Length Measurements on Krypton with Neutron Interferometry at a Small Reactor

Abstract We carried out neutron interferometry measurements to determine the coherent neutron Scattering lengths of gaseous natural krypton and 86Kr. Measurements were performed at a 250 kW TRIG A reactor. The accuracy of the results is restricted by the stability of the set-up and not by the limited neutron flux. The results obtained at this reactor prove that neutron interferometry is feasible even at small neutron sources, provided that a stable set-up is used.