Accession Number : ADP008064

Title :   Observation of Nuclear Diffraction from Multilayers Containing 57Fe,

Corporate Author : HAMBURG UNIV (GERMANY F R) INST FUER EXPERIMENTALPHYSIK

Personal Author(s) : Rohlsberger, R. ; Witthoff, E. ; Luken, E. ; Gerdau, E.

Report Date : 05 MAR 1992

Pagination or Media Count : 4

Abstract : The small resonance width gamma o of Mossbauer transitions allows monochromatization of synchrotron radiation down to a bandwidth of 10 to the minus 7th power - 10 to the minus 9th power by nuclear resonant diffraction. Up to now, the Mossbauer isotopes 57 Fe ( Eo = 14.4 keV, gamma o = 4.7 - 10 to the minus 9th power eV) and 169 Tm ( Eo = 8.4 keV, gamma o = 1.2-10-7 eV) have been used in this field. In order to observe nuclear resonant diffraction, the competing contribution of electronic scattering with a bandpass of at least a few meV has to be strongly reduced. Precise determinations of hyperfine interactions can be made by observation of quantum beats in the collective decay of the nuclei excited by synchrotron pulses. Most of the experiments have been done with single crystals which have a pure nuclear reflection. In these cases the structure factor for the electronic reflection is zero because of the symmetry of the crystal. The structure factor for the nuclear reflection is nonzero, because subgroups of the Mossbauer nuclei are distinguished by a symmetry breaking hyperfine interaction or by isotopic arrangement. In a layered crystal of 56 Fe and 57 Fe atoms obviously the electronic and nuclear lattice constant differ by a factor of two, so that a superstructure appears with a pure nuclear reflection. Such a crystal has not been grown up to now, since the preparational requirements are very hard to meet. However, an isotopic superstructure can easily be realized in a multilayer, which need not be a single crystal. Alternating layers containing 56 Fe and 57 Fe give rise to a multilayer Bragg peak of pure nuclear origin. Such a multilayer will be described here.

Descriptors :   *DIFFRACTION, *LAYERS, *IRON, *RESONANCE, *NUCLEAR RESONANCE, ATOMS, BANDWIDTH, CONSTANTS, CRYSTALS, DECAY, DETERMINATION, NUCLEI, ELECTRONICS, INTERACTIONS, ISOTOPES, NUCLEAR PROPERTIES, OBSERVATION, PULSES, RADIATION, REFLECTION, REQUIREMENTS, SCATTERING, SINGLE CRYSTALS, STRUCTURES, SUPERSTRUCTURES, SYMMETRY, SYNCHROTRON RADIATION, SYNCHROTRONS, TRANSITIONS, WIDTH, MOSSBAUER EFFECT.

Subject Categories : Atomic and Molecular Physics and Spectroscopy
      Nuclear Physics & Elementary Particle Physics
      Crystallography
      Inorganic Chemistry

Distribution Statement : APPROVED FOR PUBLIC RELEASE