On the NQR detection of nitrogenated substances by multi‐pulse sequences

Abstract

PACS 76.60.GvTheoretical and practical aspects of using multi-pulse spin-locking and the "strong off-resonant comb" (SORC) sequence for detecting nitrogenated substances by the nuclear quadrupole resonance method were studied. A number of optimum correlations between the parameters of multi-pulse sequences and the relaxation characteristics of the substances under investigation were determined. The obtained relations were used for the fast detection of α-trinitrotoluene (TNT). Relaxation parameters and temperature coefficients for twelve 14 N lines of the orthorhombic phase of TNT measured at room temperature are also presented.

14N NQR, relaxation and molecular dynamics of the explosive TNT

“…There is good overall agreement between the two sets of values of b for monoclinic TNT with a mean difference of about 6% and largest difference of 12%, for the 844 kHz line. Table 2 also compares our b values for orthorhombic TNT with previously published values [36] and the overall agreement is good with a mean difference of about 8%, however here the largest difference is higher at 22%, for the 837 kHz line. For TNT detection applications, since sensitivity increases with frequency, the obvious choice is to work with the ν + NQR lines and usually the highest frequency lines at 870 kHz for monoclinic TNT and 868 kHz for orthorhombic TNT.…”

“…The T 1 values obtained here for monoclinic TNT at 22°C (295 K) and orthorhombic TNT at 20°C (293 K) are presented in Table 2 where they are compared to the previously published values for orthorhombic TNT [36] at 23°C and monoclinic TNT [3] presumably at room temperature. Our T 1 values for nineteen of the NQR lines in Table 2 NQR spin-lattice relaxation times T 1 can be strongly influenced by slow molecular rotations and T 1 often becomes shorter to higher temperatures as such processes become more important, the temperature dependence of T 1 can then be used to gain some insight into such molecular dynamics [34,35,15].…”

Revealing dipolar coupling with NQR off-resonant pulsed spin locking

“…9,10,15,20 Within this periodicity we observe extremes in the signal behavior at ∆f = m 2τ , for integer m, corresponding to θ totntot = θ 2î ; and at ∆f = The evolution of the signal under D and P for a given net rotation is performed numerically, but under certain conditions, namelyn tot =î, an analytical solution is readily available.…”

Study of 14N NQR response to SORC pulse sequence

“…Figure 1 shows the signal amplitude as a function of the frequency offset f observed at fixed 2τ = 1.6 ms. According to Mikhaltsevitch and Rudakov [4] and taking powder average [9] with respect to crystalline orientation, the signal amplitude S obtained by the SORC pulse sequence (τ -ϕ-τ ) N will be given for polycrystalline sample as…”

“…Thorough understanding of this phenomenon is very important for the successful practical application of remote NQR for the explosive detector. Recently, Mikhaltsevitch and Rudakov reported theoretical and experimental studies on the NQR response to multi-pulse sequence [4,5], which stimulate us to study this phenomenon more seriously with our own sample.…”