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Related Concept Videos

Potential Due to a Polarized Object01:29

Potential Due to a Polarized Object

A neutral atom consists of a positively charged nucleus surrounded by a negatively charged electron cloud. When placed in an external electric field, the external electric force pulls the electrons and nucleus apart, opposite to the intrinsic attraction between the nucleus and the electrons. The opposing forces balance each other with a slight shift between the center of masses of the nucleus and the electron cloud, resulting in a polarized atom. On the other hand, a few molecules, like water,...
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In the absence of an external magnetic field, nuclear spin states are degenerate and randomly oriented. When a magnetic field is applied, the spins begin to precess and orient themselves along (lower energy) or against (higher energy) the direction of the field. At equilibrium, a slight excess population of spins exists in the lower energy state. Because the direction of the magnetic field is fixed as the z-axis,  the precessing magnetic moments are randomly oriented around the z-axis. This...
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Two NMR-active nuclei bonded to a central atom can be involved in geminal or two-bond coupling. Geminal coupling is commonly seen between diastereotopic protons in chiral molecules and unsymmetrical alkenes, among others.
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Atomic Nuclei: Nuclear Spin State Overview01:03

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Atomic Nuclei: Nuclear Spin State Population Distribution01:14

Atomic Nuclei: Nuclear Spin State Population Distribution

Near absolute zero temperatures, in the presence of a magnetic field, the majority of nuclei prefer the lower energy spin-up state to the higher energy spin-down state. As temperatures increase, the energy from thermal collisions distributes the spins more equally between the two states. The Boltzmann distribution equation gives the ratio of the number of spins predicted in the spin −½ (N−) and spin +½ (N+) states.

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Related Experiment Video

Updated: Jul 4, 2026

All-electronic Nanosecond-resolved Scanning Tunneling Microscopy: Facilitating the Investigation of Single Dopant Charge Dynamics
11:33

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Published on: January 19, 2018

Dynamic nuclear polarization in silicon microparticles.

A E Dementyev1, D G Cory, C Ramanathan

  • 1Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA. anatolyd@physics.harvard.edu

Physical Review Letters
|June 4, 2008
PubMed
Summary
This summary is machine-generated.

Researchers achieved record high 29Si spin polarization in microcrystalline silicon powder using dynamic nuclear polarization. This breakthrough could enable hyperpolarized silicon microparticles as magnetic resonance imaging tracers.

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Area of Science:

  • Solid-state physics
  • Materials science
  • Nuclear magnetic resonance

Background:

  • Microcrystalline silicon is a heterogeneous material with both amorphous and crystalline regions.
  • Dangling bonds in the amorphous regions provide unpaired electrons crucial for polarization.
  • Dynamic nuclear polarization (DNP) is a technique to enhance nuclear spin polarization.

Purpose of the Study:

  • To achieve record high 29Si spin polarization in microcrystalline silicon.
  • To investigate the mechanisms of nuclear spin polarization in heterogeneous silicon samples.
  • To explore the potential of hyperpolarized silicon for magnetic resonance imaging (MRI).

Main Methods:

  • Utilized dynamic nuclear polarization (DNP) on microcrystalline silicon powder.
  • Employed off-resonant microwave radiation to drive electron-nuclear spin flips.
  • Investigated spin diffusion across crystalline boundaries for polarization transfer.

Main Results:

  • Achieved record high 29Si spin polarization levels.
  • Demonstrated distinct polarization mechanisms in amorphous and crystalline regions.
  • Observed long T1 relaxation times for hyperpolarized silicon microparticles.

Conclusions:

  • Dynamic nuclear polarization is effective for enhancing 29Si spin polarization in microcrystalline silicon.
  • Heterogeneous nature of silicon allows for efficient polarization via electron-nuclear spin flips and spin diffusion.
  • Hyperpolarized silicon microparticles show promise as contrast agents for MRI due to long relaxation times.