Abstract
Abstract : The objective of the program was to evaluate feasibility of non- destructive electronic measurement (and logging) of rock stress in situ, using atomic resonances that are pressure-sensitive. Nuclear quadrupole resonance (NQR) appeared clearly applicable, since no magnetic aligning field is needed, there are several common NQR-active nuclear species in major rock-forming minerals, and rf magnetic fields between 0.3 and 3 megahertz (the resonant frequencies) propagate well through many rocks. There are also alternative resonance methods which may be applicable, including NMR, EPR, and EFR. A comprehensive literature search has been completed on NQR in minerals, which shows that aluminum-27 and a few other elements in feldspars are promising for NQR measurement of rock stress. Efforts to detect these resonances in mineral specimens were mostly unsuccessful because of their extreme weakness. The outlook for NQR is now considered marginal. Short studies of other rf spectrographic methods showed that ferromagnetic effects cannot be used, but that electron paramagnetic resonance (EPR) holds some promise as a means of measuring rock stress, since strong EPR signals are readily obtained from most rocks.
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