An automated instrument for polarization-enhanced broadband nuclear quadrupole resonance (NQR) spectroscopy

An automated instrument for improving the sensitivity of nuclear quadrupole resonance (NQR) spectroscopy is presented. The device is capable of pre-polarizing samples within a custom Halbach-type permanent magnet and then moving them into an external probe for zero-field NQR detection. Polarization transfer between protons and nitrogen (¹⁴N) nuclei in the sample occurs during demagnetization, thus increasing the amplitude of the detected NQR signals. The sample motion profile is completely programmable, thus providing a high level of control over the sample position and velocity for optimizing the polarization transfer process for various samples. Moreover, the magnet and motion controller are combined with a shielded sample probe and ultra-broadband front-end electronics (both designed in-house) to realize a complete scientific instrument for ¹⁴N NQR experiments. Compared with previous work in the field, the system is designed to be programmable, robust, and easy to use. Experimental results from several samples are also presented.