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Neutrons are highly sensitive to magnetic fields owing to their magnetic moment, whereas their charge neutrality enables them to penetrate even massive samples. The combination of these properties with radiographic and tomographic imaging [1][2][3][4] enables a technique that is unique for investigations of macroscopic magnetic phenomena inside solid materials. Here, we introduce a new experimental method yielding twoand three-dimensional images that represent changes of the quantum-mechanical spin state of neutrons caused by magnetic fields in and around bulk objects. It opens up a way to the detection and imaging of previously inaccessible magnetic field distributions, hence closing the gap between high-resolution two-dimensional techniques for surface magnetism 5,6 and scattering techniques for the investigation of bulk magnetism 7-9 . The technique was used to investigate quantum effects inside a massive sample of lead (a type-I superconductor).The specific interaction of neutrons with matter enables neutron radiography to complement X-ray imaging methods for analysing materials 1 . Conventional radiography is a geometrical projection technique based on the attenuation of a beam by a sample along a given ray. Quantum mechanically, neutrons are described by de Broglie wave packets 10 whose spatial extent may be large enough to produce interference effects similar to those known from visible laser light or highly brilliant synchrotron X-rays. Measurements of the neutron wave packet's phase shift induced by the interaction with matter have a long and distinguished history [11][12][13][14] and were recently combined with neutron imaging approaches, where two-and three-dimensionally resolved spatial information about the quantum mechanical interactions of neutrons with matter was obtained 2,3,15 . In addition, neutrons, which from the particle-physicist's point of view are small massive particles with a confinement radius of about 0.7 fm, possess another outstanding property: a magnetic moment µ (µ = −9.66 × 10 −27 J T −1 ). The magnetic moment is antiparallel to the internal angular momentum of the neutron described by a spin S with the quantum number s = 1/2. Consequently, the high sensitivity of neutrons to magnetic interactions has extensively been and is still being exploited in numerous experiments to study fundamental magnetic properties and to understand basic phenomena in condensed matter 7-9 . Here, we present an experimental method that combines spin analysis with neutron imaging and yields a new contrast mechanism for neutron radiography that enables two-and three-dimensional investigations of magnetic fields in matter. This method is unique not only in that it provides spatial information about the interaction of the spin with magnetic fields but also in its ability to measure these fields within the bulk of materials, which is not possible by any other conventional technique.Our concept is based on the fact that any spin wavefunction corresponds to a definite spin direction and by using the Schrödin...

A special double monochromator system was tested for a conventional operating tomography setup in order to use a broad wavelength band of monochromatic neutrons for radiography and tomography. Scanning through the wavelength region of Bragg edges, it is possible to make series of radiographs and tomographs at different wavelengths from 2.0 until 6.5Å. So no beam hardening influences the measurements and is not to be corrected. With this instrument for cold neutron radiography and tomography, energy selecting quantitative radiography, stress and strain mapping, and phase radiography were performed.

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