U. Bonse

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.

3D computed X-ray tomography of human cancellous bone at 8 μm spatial and 10−4 energy resolution

Human cancellous bone was imaged and its absorptive density accurately measured in three dimensions (3D), nondestructively and at high spatial resolution by means of computerized microtomography (microCT). Essential for achieving the resolution and accuracy was the use of monoenergetic synchrotron radiation (SR) which avoided beam hardening effects, secured excellent contrast conditions including the option of energy-modulated contrast, and yet provided high intensity. To verify the resolution, we selected objects of approximately 8 micron size that could be observed on tomograms and correlated them in a unique manner to their counter images seen in histological sections prepared from the same specimen volume. Thus we have shown that the resolution expected from the voxel size of 8 microns used in the microCT process is in effect also attained in our results. In achieving the present results no X-ray-optical magnification was used. From microCT studies of composites (Bonse et al., X-ray tomographic microscopy (XTM) applied to carbon-fibre composites. In: Materlik G, ed. HASYLAB Jahresbericht 1990. Hamburg: DESY, 1990; 567-568) we know that by including X-ray magnification a resolution below 2 microns is obtained. Therefore, with foreseeable development of our microCT method, the 3D and nondestructive investigation of structures in mineralized bone on the 2 micron level is feasible. For example, it should be possible to study tomographically the 3D distribution and amount of osteoclastic resorption in the surrounding bone structure.

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.

Imaging of ferromagnetic domains by neutron interferometry

Abstract Ferromagnetic domains in Fe-3% Si were observed by neutron phase-contrast imaging, using a perfect crystal Bragg-diffraction interferometer and unpolarized neutrons. Domain contrast is observed when full interference, with a magnetic reference field, is used, while wall contrast is encountered without field.

The prototype neutron interferometer at the Grenoble high flux reactor

Abstract The basic characteristics and the instrumentation of the experimental interferometer setup at the Institut Max von Laue - Paul Langevin (I.L.L.), Grenoble are outlined. The instrument incorporates a triple Laue-case (“LLL-type”) Bragg diffraction interferometer. The interference contrast of a real interferometer crystal as compared to the ideal model is discussed. The diffractometer used for the experiment as well as the environmental requirements are described. As an example, the application of the instrument to the determination of coherent scattering lengths is presented along with experimental results.

Test measurements with a perfect crystal neutron interferometer

Two widely separated coherent neutron beams from dynamical diffraction in a perfect Si-crystal are used for neutron interferometric measurements. Al and Bi samples cause phase shifts within the individual beams which result in a marked intensity oscillation of the interfering beams behind theE-shaped interferometer crystal. With this interferometer interesting features of various physical quantities can be investigated in a new way, e.g. refracting index, scattering amplitudes, magnetic domain structures, density inhomogeneities, and coherence properties of the neutron beams.

Measurement of coherent neutron scattering lengths of gases

With the neutron interferometer, measurements of the coherent neutron scattering lengths by various gases have been performed. We get the following numbers for the bound coherent scattering lengths for atoms (in fm):bc(H) =−3.64(3),bc(D)=6.55(8),bc(He−3)=5.74(7),bc(He)=3.26(3),bc(N)=9.30(8),bc(O)=5.83(5),bc(Ne) =4.63(4),bc(Ar)=2.07(2),bc(Kr)=7.52(6),bc(Xe)=4.69(4). In some cases greater accuracy is achieved in comparison with recommended values from the literature. The absolute values for hydrogen and deuterium measured with gaseous samples, are about 2% smaller than the values measured with liquids and other reference values.

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.

New developments in attenuation and phase-contrast microtomography using synchrotron radiation with low and high photon energies

Microtomography using synchrotron radiation is widely used in fields of e.g. medicine, biology and material science. Using attenuation contrast at photon energies in the range of 8 to 25 keV and phase contrast at photon energies of 12 keV, 20 keV and 24 keV the method of microtomography is applied to a large number of samples. A comparison of the two different contrast mechanism is presented. Feasibility, advantage and limits of these methods are shown in theory and by experiment. New developments in high-energy microtomography using synchrotron radiation in the energy range of 60 to 100 keV are described. Using attenuation contrast, several samples are investigated. For the investigation of larger specimens with diameters on the order of 1 - 2 cm, the use of a new (mu) CT-technique based on scanning a 2-dim. X-ray detector is demonstrated. At 70 keV photon energy an X-ray LLL-interferometer is tested and used to measure phase projections. For the first time, phase- contrast microtomography could be applied to weakly and normally absorbing material at a high photon energy.

Precise interferometric measurement of the NiK-edge forward scattering amplitude with synchrotron X-rays

We present the first high precision measurement of the complete wavelength dependence of theK-edge dispersion including the whole range of the Kossel and Kronig structure. Synchrotron X-rays of DESY, Hamburg, have been used providing a highly collimated and intense beam with continuous spectral distribution for interferometric measurement. In comparing the result with other experimental and theoreticalf′ values and also with the absorption spectrum, quite good agreement is obtained.