Gregorovic Alan, Apih Tomaz
Institute Jozef Stefan, Solid State Physics, Jamova 39, 1000 Ljubljana, Slovenia.
J Magn Reson. 2009 Jun;198(2):215-21. doi: 10.1016/j.jmr.2009.02.011. Epub 2009 Feb 28.
Nuclear quadrupole resonance (NQR) has a distinct potential to verify the presence of nitrogen bearing substances based on the unequivocal signatures of their spectra. Therefore, this technique is especially suitable for remote detection of illicit substances and explosives. Unfortunately, the inherent signal-to-noise of the most abundant explosive trinitrotoluene (TNT) is very low. Here we present an NQR method with improved sensitivity for estimation of the probability of TNT presence in the investigated object. The method consists of a spin-lock spin-echo (SLSE) multipulse sequence for signal excitation and a time domain matched filter for signal detection. We find that the signal-to-noise increases by shortening the pulse spacings, even though this means a decrease in spectral resolution. In our case, the decrease of the pulse spacings from the typical 2 ms to 540 micros resulted in an increase of the signal-to-noise by 14 dB. A theory describing this enhancement is presented and compared to experimental results on TNT. Issues related to temperature and polymorphism variations are also discussed.
核四极共振（NQR）基于含氮物质光谱的明确特征，在验证其存在方面具有独特潜力。因此，该技术特别适用于非法物质和爆炸物的远程检测。不幸的是，最常见的炸药三硝基甲苯（TNT）的固有信噪比非常低。在此，我们提出一种用于估计被调查对象中TNT存在概率的具有更高灵敏度的NQR方法。该方法由用于信号激发的自旋锁定自旋回波（SLSE）多脉冲序列和用于信号检测的时域匹配滤波器组成。我们发现，通过缩短脉冲间隔，信噪比会提高，尽管这意味着光谱分辨率降低。在我们的案例中，脉冲间隔从典型的2毫秒缩短至540微秒，使信噪比提高了14分贝。本文提出了一种描述这种增强效果的理论，并将其与TNT的实验结果进行了比较。还讨论了与温度和多晶型变化相关的问题。
