In a classic paper, Solomon showed that the presence of inhomogeneous, first-order quadrupolar interactions leads to the formation of extra "allowed" spin echoes in nuclei for which the spin I-%. We demonstrate (both theoretically and experimentally) that shifting the rf phase of the second pulse by 90° (in a spin-f system) enhances the extra allowed echoes by a factor of almost 5 in amplitude over the unshifted case. Using the density-matrix formulation (and assuming no magnetic inhomogeneities), we have derived, for a 90° phase shift, the amplitude and shape dependence on the second-pulse turning angle of the |r, 2r, and 3T echoes. Experimental echo amplitudes and shapes (for both 0° and 90° phase shifts) were obtained, at room temperature, on 127 I in a fused sample of KI, and these show good agreement with the calculations. Because of the enhancement, this technique affords a much easier separation of the respective distributions arising from the f <-> f and from the J <-> | satellite transitions than is possible in the unshifted case. Another feature of the phase-shifted case is that, in favorable circumstances, the 3r echo may be observed although the 2T echo is obscured by the receiver recovery time. Preliminary data on quadrupole distributions at Al sites in NiAl and AuAl 2 intermetallic compounds are presented. Spin-spin relaxation of the satellite transitions is noted. Results expected for systems which have spin values other than 7=f (both integral and half-integral) are mentioned.
Pulsed nuclear magnetic resonance has been used to differentiate in vivo between normal mouse tail tissue and a malignant transplanted melanoma, S91, located on the tail. The tumor displayed a nuclear (proton) spin-lattice relaxation time of approximately 0.7 second contrasted with the simultaneously measured normal tail tissue relaxation time of approximately 0.3 second.
The nuclear-magnetic-resonance (NMR) and susceptibility behavior of the intermetallic compound AuGa2 differs anomalously from the isoelectric and isostructural compounds Auln& and AuAlq. In an effort to test and extend the explanation offered by Jaccarino et al. and by Switendick and Narath, spin-lattice relaxation times and Knight shifts have been measured as a function of temperature and composition for the AuAlp-AuGa2, AuA12-AuIn2, and AuGa2-AuIn2 pseudobinary alloy systems. At high temperature, the solute X (Al, In, Ga) resonance properties are dominated by the host. Satellite resonances are observed with temperature dependences differing from the main resonance. The results are partially explainable on the basis of an average-band model and partially on a local atom model. The role of the Au d bands is discussed. Metallurgical results on alloying are obtained using the NMR data.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.