Long single pulse NQR for broad resonance lines.

This paper describes the experimental application of long single pulses to strongly inhomogeneously broadened NQR spectral lines, where the pulse length significantly exceeds the transverse relaxation time. A63Cu NQR resonance in the mineral covellite (CuS) was used as an exemplar for study in this specific regime, which was motivated by the requirement to obtain useful signals in very large volume applications having radiofrequency power limitations. In this study, signal transients that followed the application of the long single pulses were measured over a large range of radiofrequency field strength and pulse width. The results indicate effective generation of signal amplitudes. This is in contrast to previously reported studies involving long pulses applied to relatively narrow resonances. The results are found to be well described by simulations of the modified Bloch equations.

(121,123)Sb and (75)As NMR and NQR investigation of the tetrahedrite (Cu12Sb4S13)--Tennantite (Cu12As4S13) system and other metal arsenides.

This work is motivated by the recent developments in online minerals analysis in the mining and minerals processing industry via nuclear quadrupole resonance (NQR). Here we describe a nuclear magnetic resonance (NMR) and NQR study of the minerals tennantite (Cu12As4S13) and tetrahedrite (Cu12 Sb4S13). In the first part NQR lines associated with (75)As in tennantite and (121,123)Sb isotopes in tetrahedrite are reported. The spectroscopy has been restricted to an ambient temperature studies in accord with typical industrial conditions. The second part of this contribution reports nuclear quadrupole-perturbed NMR findings on further, only partially characterised, metal arsenides. The findings enhance the detection capabilities of NQR based analysers for online measurement applications and may aid to control arsenic and antimony concentrations in metal processing stages.

(75)As NQR studies on FeAs2.

(75)As NQR spectra and relaxation times of synthetic and natural FeAs2 samples have been studied at variable static magnetic field and temperature. FeAs2 is a well understood diamagnetic semiconductor and occurs as the natural mineral lollingite in selected ore deposits. We observed a spin-spin relaxation time enhancement of up to five in synthetic powders in the presence of a weak external static magnetic field. The effect is of interest with regard to signal-to-noise ratio improvement for materials characterization applications where broad NQR absorption lines are excited with wideband pulse sequences.

75As, 63Cu NMR and NQR characterization of selected arsenic minerals.

The direct measurement and identification of solid state arsenic phases using (75)As NMR is made difficult by the simultaneous conditions of large quadrupole moment and low coordination symmetry in many compounds. However, specific arsenic minerals can efficiently be detected and discriminated via nuclear quadrupolar resonance (NQR). We report on the first NMR and NQR measurements in the natural minerals enargite (Cu3AsS4), niccolite (NiAs), arsenopyrite (FeAsS) and loellingite (FeAs2). The NQR frequencies have been determined from both high-field NMR powder patterns and via zero-field frequency sweeps. Density functional theory (DFT) based ab initio calculations support the experimental results. The compounds studied here are common in terms of the known set of As-containing minerals. They are sometimes encountered in the context of base metal or gold mining. The study represents a significant addition to the list of arsenic minerals that can now be detected with NQR techniques.