Category Archives: Polarized Targets

A prototype system for dynamically polarized neutron protein crystallography #DNPNMR

Pierce, J., L. Crow, M. Cuneo, M. Edwards, K.W. Herwig, A. Jennings, A. Jones, et al. “A Prototype System for Dynamically Polarized Neutron Protein Crystallography.” Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 940 (October 2019): 430–34.

https://doi.org/10.1016/j.nima.2019.06.023

The sensitivity of Neutron Macromolecular Crystallography to the presence of hydrogen makes it a powerful tool to complement X-ray crystallographic studies using protein crystals. The power of this technique is currently limited by the relative low neutron flux provided by even the most powerful neutron sources. The strong polarization dependence of the neutron scattering cross section of hydrogen will allow us to use Dynamic Nuclear Polarization to dramatically improve the signal to noise ratio of neutron diffraction data, delivering order of magnitude gains in performance, and enabling measurements of radically smaller crystals of larger protein systems than are possible today. We present a prototype frozen spin system, built at Oak Ridge National Laboratory to polarize single protein crystals on the IMAGINE beamline at the High Flux Isotope Reactor (HFIR). Details of the design and construction will be described, as will the performance of the system offline and during preliminary tests at HFIR.

Dynamic Nuclear Polarization Enhanced Neutron Crystallography: Amplifying Hydrogen in Biological Crystals #DNPNMR

Pierce, Joshua, Matthew J. Cuneo, Anna Jennings, Le Li, Flora Meilleur, Jinkui Zhao, and Dean A.A. Myles. “Dynamic Nuclear Polarization Enhanced Neutron Crystallography: Amplifying Hydrogen in Biological Crystals.” In Methods in Enzymology, 634:153–75. Elsevier, 2020. 

https://doi.org/10.1016/bs.mie.2019.11.018

Dynamic nuclear polarization (DNP) can provide a powerful means to amplify neutron diffraction from biological crystals by 10–100-fold, while simultaneously enhancing the visibility of hydrogen by an order of magnitude. Polarizing the neutron beam and aligning the proton spins in a polarized sample modulates the coherent and incoherent neutron scattering cross-sections of hydrogen, in ideal cases amplifying the coherent scattering by almost an order of magnitude and suppressing the incoherent background to zero. This chapter describes current efforts to develop and apply DNP techniques for spin polarized neutron protein crystallography, highlighting concepts, experimental design, labeling strategies and recent results, as well as considering new strategies for data collection and analysis that these techniques could enable.

Quantum mechanical aspects of dynamical neutron polarization

I came across this article about DNP, apparently the acronym is not just used as in DNP-NMR but also for Dynamic Neutron Polarization, Dinitrophenol, Doctor of Nursing Practice etc. …

Betz, T., G. Badurek, and E. Jericha, Quantum mechanical aspects of dynamical neutron polarization. Physica B: Condensed Matter, 2007. 397(1-2): p. 195-197.

http://www.sciencedirect.com/science/article/pii/S0921452607001639

Dynamic Neutron Polarization (DNP) is a concept which allows to achieve complete polarization of slow neutrons, virtually without any loss of intensity. There the neutrons pass through a combination of a static and a rotating magnetic field in resonance, like in a standard NMR apparatus. Depending on their initial spin state, they end up with different kinetic energies and therefore different velocity. In a succeeding magnetic precession field this distinction causes a different total precession angle. Tuning the field strength can lead to a final state where two original anti-parallel spin states are aligned parallel and hence to polarization. The goal of this work is to describe the quantum mechanical aspects of DNP and to work out the differences to the semi-classical treatment. We show by quantum mechanical means, that the concept works and DNP is feasible, indeed. Therefore, we have to take a closer look to the behavior of neutron wave functions in magnetic fields. In the first Section we consider a monochromatic continuous beam. The more realistic case of a pulsed, polychromatic beam requires a time-dependent field configuration and will be treated in the second Section. In particular the spatial separation of the spin up- and down-states is considered, because it causes an effect of polarization damping so that one cannot achieve a fully polarized final state. This effect is not predicted by the semi-classical treatment of DNP. However, this reduction of polarization is very small and can be neglected in realistic DNP-setups.

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