A NOVEL APPROACH TO NUCLEAR RESONANCE SPECTROSCOPY: NEW APPLICATIONS TO CHEM

University Of Chicago, Chicago IL

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Abstract

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. We propose to demonstrate a novel approach to perform nuclear forward scattering (NFS) in which a mechanical chopper suppresses the prompt x-ray pulse that forms the nuclear exciton and allows the delayed NFS signal to reach the detector without any background radiation. The experiment will be performed at ID-14 beamline where a suitable tunnel chopper for this demonstration is available. The experiment will be performed using well know 14.4125 keV nuclear state in 57-Fe without the need for a high-resolution monochromator with 1-2 meV energy-resolution traditionally used at the nuclear resonance beamlines at all the third-generation high-energy SR facilities. The new approach allows one to investigate nuclear exciton decay that manifests over many lifetimes of the nuclear excited state. The NFS signal is perturbed either by an inherent stochastic motion of the nuclei or by that of the environment (diffusion, charge- and spin-relaxation or transformation) or by external stimuli such as rf magnetic, laser or ultrasound fields. Such studies, which manifest in NFS spectrum over many nuclear lifetimes, were hitherto difficult to perform with the available bunch-filling patterns at the storage-rings. The new technique, with suggested optimization, will also open new opportunities to perform nuclear resonance studies in isotopes with higher exciton energy states. In this proposal, we will establish the feasibility through a successful demonstration of the new technique in the SMO1 operation of the APS. The attached pdf contains a brief science case motivating the development of the new approach and future technical opportunities expected from the method. A full description of the new approach along with a schematic layout of the experiment and a complete analysis of its expected performance is also provided.