COMPOSITE GERMANIUM CRYSTALS WITH ANISOTROPIC MOSAIC AS A FOCUSSING MONOCHROMATOR FOR NEUTRON POWDER DIFFRACTION. T. Vogt, Physics Department, Brookhaven National Laboratory New York, 11973-5000, USA

The High Resolution Neutron Powder Diffractometer has now been operating for over 2 years at the High Flux Beam Reactor at Brookhaven National Laboratories. Its unique and innovative feature is a neutron monochromator made out of stacks of deformed Ge(115) wafers. A process to create a spatially homogeneous but anisotropic mosaic structure in thin germanium wafers was developed. The individual wafers were then recombined to wafer stacks which allow the construction of large focusing monochromators which yield symmetric reflection profiles. The presentation will describe the construction of this wafer stack monochromator and its performance when used in high-resolution neutron powder diffraction.

[1] T. Vogt, L.Passell, S. Cheung, J.D. Axe. Nucl. Instr. Meth. A338, 71-77 (1994)

[2] J.D. Axe, S. Cheung, D.E. Cox, L.Passell, T. Vogt, S. Bar-Ziv. Journal of Neutron Research 2(3) , 85-95 (1994)

[3] T. Vogt, U. Wildgruber, L. Passell, S. Cheung. Journal of Neutron Research in press