A cryostatic, fast scanning, wideband NQR spectrometer for the VHF range

TL;DR

This paper introduces a cryostatic, wideband NQR spectrometer with electronic tuning for rapid, explorative scans across 20-120 MHz, significantly improving speed and sensitivity especially at low temperatures and for compounds with long T1 times.

Contribution

The paper presents a novel electronically tuned, cryogenic wideband NQR probehead and an interleaved subspectrum sampling strategy that enable fast, broad-range NQR spectroscopy in the VHF range.

Findings

Achieved over 100-fold acceleration in NQR scans compared to classical methods.

Successfully demonstrated the system with triphenylbismuth at room temperature and 77K.

Enabled efficient exploration of low-SNR, long T1 compounds in the VHF range.

Abstract

In the search for a novel MRI contrast agent which relies on T1 shortening due to quadrupolar interaction between Bi nuclei and protons, a fast scanning wideband system for zero-field nuclear quadrupole resonance (NQR) spectroscopy is required. Established NQR probeheads with motor-driven tune-match stages are usually bulky and slow, which can be prohibitive if it comes to Bi compounds with low SNR (excessive averaging) and long quadrupolar T1 times. Moreover many experiments yield better results at low temperatures such as 77K (liquid nitrogen, LN) thus requiring easy to use cryo-probeheads. In this paper we present electronically tuned wideband probeheads for bands in the frequency range 20 - 120 MHz which can be immersed in LN and which enable very fast explorative scans over the whole range. To this end we apply an interleaved subspectrum sampling strategy (ISS) which relies on the electronic tuning capability. The superiority of the new concept is demonstrated with an experimental scan of triphenylbismuth from 24-116 MHz both at room temperature and in LN. Especially for the first transition which exhibits extremely long T1 times (64ms) and low signal the new approach allows an acceleration factor by more than 100 when compared to classical methods.