NRS

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Introduction

Nuclear Resonant Scattering (NRS) is a spectroscopic technique that utilizes the Mössbauer effect to investigate hyperfine interactions. This is done by irradiating high-brilliance synchrotron X-ray pulses on a sample material containing Mossbauer-active nuclei. The X-rays are tuned to specific energies corresponding to the various nuclear transitions of the nuclei.

Experimental setup

An NRS experiment is usually conducted in a synchrotron facility. High-brilliance X-ray pulses are generated by passing relativistic electrons, coming from the booster ring, through an undulator in a synchrotron storage ring. The X-rays are monochromatised, but with a bandwidth that is still larger than the hyperfine splitting of the nuclear levels. This is done to ensure that all available energy levels corresponding to a single nuclear energy level are excited simultaneously. The beam then irradiates the sample containing Mössbauer-active isotopes, such as ^57Fe. Detectors, like avalanche photodiodes, capture the delayed photons emitted from the excited nuclei, allowing for time-resolved measurements.

Time domain and quantum beats

Because the X-rays come in short pulses, the temporal evolution of the emitted photons by the excited nuclei in the sample material can be observed. The interference between photons emitted by different hyperfine-split nuclear levels leads to so-called quantum beats in the time spectra. Analyzing these beats, using Fourier transformation, provides detailed information about hyperfine interactions, such as the magnetic hyperfine field, quadrupole moment and isomer shift.

Applications

NRS has a wide range of applications across various scientific fields: spin dynamics in condensed matter physics, studying surface coatings and ultra-thin films in nanoscience, studying the behaviour of iron-containing biomolecules in biology and medicinal research.

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