Resonant diffraction of synchrotron radiation by a nuclear multilayer.

We report the observation of nuclear resonant diffraction of synchrotron radiation by a synthetic multilayer. The nuclear period of the [57Fe(22&/Sc( 1 lA]/Fe(228i)/Sc(l l&l x 25 multilayer was chosen~ to be twice the electronic period to obtain a pure nuclear Bragg reflection. Strong enhancement of the radiative scattering channel provided a fast time response for the 57Fe resonant scattering at the Bragg peak, with a decay time of 4 ns. The nuclear multilayer will be useful as a narrow bandpass monochromator for synchrotron radiation. Much of the progress in studying nuclear resonant diffraction of x-radiation has been accomplished with perfect single crystals having a naturally occurring structure [ 1, 21. Quite recently, artificial layered structures fabricated of Mossbauer isotopes have begun to be studied [361. Synthetic layered structures are attractive tools for studying nuclear diffraction because their structure and composition may be varied within broad limits, and tailored to the experimental goals. They permit control of important parameters of the coherent x-radiation . fields, including spatial arrangement, energy spectrum, time evolution, and polarization. In particular, nuclear layered structures. have an important application for the generation of highly monochromatic beams of xradiation. X-ray monochromators utilizing Bragg reflections from silicon crystals can (by using high-order reflections) produce beams with energy bandwidths of a few meV [7]. Much narrower bandwidths (~1 KeV) can be achieved using resonant nuclear scattering from single crystals, but the magnetic crystal structure required to give a pure nuclear reflection introduces hyperfine splitting of the nuclear resonance, and gives a scattered beam with a complicated energy structure [2]. Artificial layered structures can be prepared with differing nuclear and electronic structures [8, 91, giving rise to pure nuclear diffraction of synchrotron radiation without magnetic hyperfine splitting. The very small scattering angles typical of reflections from