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Methoden und Instrumentierung Vortrag: Do., 11:30–11:50 D-V39
Neutron phase contrast imaging using a grating interferometer
Christian Grünzweig 1,2 , Franz Pfeiffer 1 , Oliver Bunk 1 , Ian Johnson 1 ,
Xavier Donath 1 , Gabriel Frei 1 , Eberhard Lehmann 1 , Hennrik Rønnow 1,2 ,
Christian David
1 Paul Scherrer Institut, 5232 Villigen PSI, Switzerland – 2 ETH-Zürich, Switzerland
Today the majority of radiographic imaging applications is based on the attenuation
of the radiation inside the object. However, the imaging of the phase shift induced by
the object can provide substantially new and otherwise not accessible information. In
the case of x-rays, phase contrast imaging yields an increased contrast for biological
samples, and thus is of potential interest for medical applications [1,2]. Neutron phase
measurements, on the other hand, have a long and distinguished history in the exploration
of the fundamental properties of quantum mechanics [3]. Thus, a combination
of phase sensitive measurements with a neutron imaging approach has the potential of
providing two- or even three-dimensionally resolved spatial information on the quantum
mechanical interactions of massive particles with matter.
Here we report how a setup consisting of three transmission gratings can yield quantitative
differential neutron phase contrast images [4]. As opposed to existing techniques,
the method requires only little spatial and chromatic coherence. Since separate phase
and attenuation images are obtained simultaneously, our method provides additional
information through neutron phase-sensitive imaging, but yet is fully compatible with
conventional neutron radiography. The high efficiency of our method, compared to the
other existing methods (pinhole geometry, crystal interferometer and analyzer crystal),
reduces the measurement time for 3D neutron phase contrast tomography by more than
two orders of magnitude and opens up the way for imaging the phase shifts induced
by other than the nuclear interaction as shown in Fig. 1.
[1] R. Fitzgerald, Physics Today 53, 7, 23-27 (2000).
[2] F. Pfeiffer, O. Bunk, T. Weitkamp, and C. David, Nature Physics 2, 258-261 (2006).
[3] H. Rauch and S.A. Werner, Neutron Interferometry, Oxford University Press, Oxford
(2000).
[4] F. Pfeiffer, C. Grünzweig, O. Bunk, G. Frei, E. Lehmann, and C. David, accepted
for publication in Phys. Rev. Lett. (2006).
Fig. 1: Conventional neutron radiograph (a) and retrieved
phase image (b) of Cupper and Titanium metal rods. The
white scale bar corresponds to 5 mm. Due to similar neutron
capture cross sections and incoherent scattering lengths, a
difference in attenuation of the neutron beam in the rods is
hardly recognized (a). In the phase image it is interesting
that Ti has a brighter colour compared to the background
whereas Cu appears darker. This is due to the negative neutron
scattering length density of Ti and consequently a negative
phase shift [π] is measured in the material.