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Nuclear quadrupole resonance (NQR) enhancement by polarization transfer and its limitation due to relaxation

Aiming for polarization transfer enhancement of 14N nuclear quadrupole resonance (NQR) for the detection of explosives with low NQR frequencies, we examine the potential and limitations of this method. As illustrative sample materials two non-explosive compounds, urotropine (C6H12N4) and urea (CON2H...

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Bibliographic Details
Published in:Journal of physics. D, Applied physics Applied physics, 2007-12, Vol.40 (23), p.7555-7559
Main Authors: Privalov, A F, Kruk, D, Gädke, A, Stork, H, Fujara, F
Format: Article
Language:English
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Summary:Aiming for polarization transfer enhancement of 14N nuclear quadrupole resonance (NQR) for the detection of explosives with low NQR frequencies, we examine the potential and limitations of this method. As illustrative sample materials two non-explosive compounds, urotropine (C6H12N4) and urea (CON2H4) with NQR frequencies of 3.3 MHz and 2.8 MHz, respectively, have been chosen. In both substances the NQR signal can be easily seen. In urotropine no signal enhancement has been detected. The reason is a 14N spin-lattice relaxation time being much shorter than the 1H-14N polarization transfer time. Although in urea the signal enhancement is significant there is, because of the long 1H polarization time, still no effective gain as compared with the pure NQR signal accumulated during the same time interval. To estimate the expected NQR signal enhancement, a polarization enhancement factor has been derived in terms of a simplified theoretical treatment, neglecting spin-lattice relaxation. The substantial influence of relaxation effects on the signal enhancement has been discussed in a qualitative manner in connection with the experiments performed for urea and urotropine.
ISSN:0022-3727
1361-6463
DOI:10.1088/0022-3727/40/23/047