19. Electron paramagnetic Resonance: NMR, MRI.
* Zeeman Effect:
A static magnetic field spits the spectral lines into two or more
components. In the absence of an external magnetic field the
orientations of the magnetic moments of the electrons are random;
this state corresponds to energy Eo. The magnetic field aligns the
magnetic moments of the electrons either parallel to the field of
antiparallel to the field.
* Transition between sublevels: Most electrons are in the lower energy
state. Transitions to the upper energy state are possible when
electromagnetic quanta with appropriate energy are absorbed by the
electrons.
* Electron Paramagnetic Resonance: EPR/ESR
EPR is the selective absorption of electromagnetic waves by the
electrons of paramagnetic particles in a static magnetic field. The
resonant frequency is in the microwave region (about 10 GHz)
* Energy condition for EPR: The frequency νo of the electromagnetic
wave and the induction Bo of the external magnetic field must satisfy
the condition: hvo = gμB B0. For Maximum absorption the magnetic field
vector of the wave must be orthogonal to the external magnetic field.
* EPR Spectrometer Parts:
- Constant Magnet
- Microwave generator
- Waveguides and resonator
- Absorption detection and registration
- Sample
