Fabrication of 57Fe/Fe multilayers (abstract)

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Abstract
Synchrotron radiation can furnish Mössbauer radiation sources with higher brightness compared with conventional radioactive γ‐ray sources when nuclear resonant Bragg scattering of synchrotron radiation is utilized. So far the observation of nuclear resonant Bragg scattering has been successfully carried out using single crystals containing 57Fe isotope at INP, HASYLAB, and BNL. We intend to use 57Fe/Fe multilayers instead of the crystals as a nuclear scatterer. In order to observe nuclear resonant scattering it is necessary to suppress Thomson electronic scattering which makes a huge background noise. In the case of the multilayer containing 57Fe and 56Fe only, nuclear resonant Bragg scattering can be observed in the absence of electronic Bragg scattering. Computation of the reflected intensities from a multilayer was made by the method analogous to that used in the design of a multilayer interference filter for a visible ray. Multilayers were fabricated by depositing alternate layers of 57Fe and 56Fe with designed layer thicknesses of 8 and 12 Å, respectively. As substrates, quartz glass plates and quartz crystal plates were used. The substrates were cooled by liquid nitrogen. The structure of the multilayer was characterized by Mössbauer γ‐ray diffraction. The 14.4‐keV γ‐rays from 57Co source were used. A rocking curve has a peak, when measured under the resonance condition. The Bragg angle of the peak coincide well with that calculated from the designed spacings. From these facts it is concluded that the peak corresponds to nuclear resonant Bragg scattering.

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