Aplicability of TNT "super-Q detection" to multipulse sequences

Area of Science:

• Nuclear Quadrupole Resonance (NQR) Spectroscopy
• Analytical Chemistry
• Spectroscopic Techniques

Background:

• High-quality factor (Q) probes enhance sensitivity in Nuclear Magnetic Resonance (NMR) and NQR.
• Very high Q values can introduce limitations, necessitating careful optimization.
• Understanding the Q factor's impact on NQR detection is crucial for improving analytical sensitivity.

Purpose of the Study:

• To explore the signal-to-noise ratio (SNR) of (14)N NQR multipulse detection of trinitrotoluene (TNT).
• To investigate the influence of the pickup coil's Q factor, particularly in the "super-Q" regime.
• To establish a Q-dependent sensitivity map for TNT detection.

Main Methods:

• A mixed experimental-theoretical approach was employed to determine TNT SNR as a function of Q factor.
• The study focused on the "super-Q" regime where probe bandwidth is narrower than NQR linewidths.
• A 2D sensitivity map was generated by repeating measurements across various excitation/detection frequencies.

Main Results:

• Maximum sensitivity for TNT detection was observed and found to be practically Q-independent for Q values between 400 and 4000.
• Conflicting requirements between Short-Living Species Excitation (SLSE) and "super-Q" detection were identified.
• A modest gain of approximately 6 dB was achieved compared to a conventional Q ≈ 100 coil.

Conclusions:

• Sensitivity for TNT detection using (14)N NQR is robust within a moderate range of Q factors (400-4000).
• The "super-Q" regime offers limited practical advantages due to excitation-detection conflicts.
• Further optimization is needed to fully leverage high-Q probes for enhanced TNT detection sensitivity.