Precession Probes

In the probe area, where the sample is placed, resonance is obtained by superimposing a weak oscillating field B on the field B0 generated by a coil that is fed by an AC radiofrequency. In order for B to have the proper space orientation, the propagation axis of the radiofrequency has to be perpendicular to the Oz axis (Fig. 9.8). The transfer of energy from the source to the nuclei occurs when the radio-frequency of the source and the frequency of precession are the same. When this occurs, nuclei in energy state E can pass to energy state E2 the relative populations become modified. 

PAC atomic probes (e.g., mIn or mHf) possess a nuclear quadrupole moment and a magnetic dipole. Even if no field acts on the PAC nucleus, the successive emission of the y-photons through an intermediate state exhibits an appreciable angular anisotropy between the emission directions. If the (isolated) nucleus is then brought into a perturbing field (e.g., on a specific lattice site which is next to a vacancy), the angular anisotropy becomes time-dependent due to the precession of the nuclear spin. For example, if the PAC nucleus in the crystal is exposed to a (static) electric... 

Ito, K., Kobayashi, S., and Tokuda, M., "Mixing Characteristics of a Submerged Jet Measured Using an Isokinetic Sampling Probe", Metallurgical Transactions B (Precess Metallurgy), 22, 439 (1991). 

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