THE DEVELOPMENT OF INSTRUMENTS FOR SMALL ANGLE SCATTERING OF NEUTRONS DURING THE LAST DECADES. T. Springer, B. Alefeld and D. Schwahn, Forschungszentrum Jülich GmbH, Institut für Festkörperforschung, D-52425 Jülich, Germany.
Neutron small angle scattering is an efficient method to investigate mesoscopic structures in condensed matter physics, material science and biology, for dimensions between 1 and 103 nm, or Q-values between 10-2 and 10-5 Å-1. The most common instrument is the slit hole camera [1] with very long distances between entrance slit, sample and detector, e.g. up to 80 m for the well-known D11 at the ILL in Grenoble. For very high resolution, the Bonse Hart camera covers a Q-range between 10-4 and 10-5 Å-1 using a pair of parallel ideal silicon crystals as collimator [2]. By multi-slit crystals the analyser can be multiplexed. Recently, we succeeded to build a prototype of a focusing camera [3] with a 4 m long copper-covered glass mirror of very high quality; the entrance slit is imaged in the detector plane. For the first time, Q-values down to a few 10-4 Å-1 were reached, with a very low parasitic background. This instrument is well suited for pulsed sources because the detector is off the primary beam, and the length is relatively small.
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[3] B. Alefeld, D. Schwahn and T. Springer, Nucl. Instr. and Methods in Physics Research A274 (1989) 210; C. Lartigue, J. Copley, F. Mezei and T. Springer, Proc. ILL-Workshop: "New Tools for Neutron Instrumentation" (1995); J. Neutron Research in print