Precise Back Tracing of the ⁵⁷Fe Mößbauer Wavelength

by Birk Andreas and U. Kuetgens, Physikalisch-Technische Bundesanstalt Braunschweig

Friday 5 Sept 2008, 14:15 → 15:15 Europe/Berlin

Bldg. 25f, room 456

In order to define a novel length standard in the nanometer regime we aim to trace the wavelength of ⁵⁷Fe Moessbauer radiation λM = 0.086 nm (photon energy E_M = 14.4125 keV) back to the international unit system (SI) by use of a combined scanning Fabry-Perot interferometer (FPI) for the Moessbauer radiation and the light of an iodine-stabilized Nd:YAG laser. As mirrors sapphire crystals are proposed which offer the (1 3 -4 28) lattice plane for 90°-backreflection of ⁵⁷Fe-Moessbauer radiation at approx. 115 °C [1]. Since sapphire crystals contain multitudinous dislocations, X-ray topography is used to identify suitable samples. Since large quantities of sapphire crystals have to be analyzed, a Berg-Barrett setup is developed which is optimized for large area topography recording of many crystals in short time with crystallo-graphic X-ray tubes. The presentation will give a short overview about the “Physikalisch-Technische Bundesanstalt” (PTB) and an introduction of our working group “x-ray optics”. Then, with emphasis on the X-ray topography, the entitled project is described. [1] Yu. V. Shvyd’ko, “X-Ray Optics: High energy-resolution Applications”, Berlin, Heidelberg, New York: Springer, (2004).