RU1824559C - Method of detecting explosives based on application of nuclear quadrupole resonance - Google Patents

Abstract

SUMMARY OF THE INVENTION: an object to be examined is irradiated with two multipulse sequences which differ in the frequency of filling of the radio pulses, and subsequent signal accumulation and processing are carried out.

Description

The method is designed to detect hidden bookmarks of explosives (BB) and can be used in customs screening, in forensics and in other cases where it is required to determine the presence of B inside objects without violating the integrity of the shell.

The purpose of the invention is to reduce examination time while maintaining high reliability of the results.

The method for detecting B B includes irradiating the examined object at the NQR frequency with a multipulse sequence, coherent accumulation of the NQR signal, processing the accumulated signal and comparing the obtained processing result with a threshold value, additional irradiating the object with a multipulse sequence, the frequency of filling of radio pulses in which differs from the frequency of filling of radio pulses during the first exposure, by a value of 1 / (2 t), (where r is the repetition period of the radio pulses in the sequences), whence accumulated signal and the additional comparison

the result of the second accumulation with the initially selected threshold.

The conclusion about the presence of B B is made when the obtained result is exceeded by the value of the threshold value in one of the exposures.

Figure 1 shows the structural diagram of the layout of a device that implements the proposed method.

The layout of the device in FIG. 1 works as follows. A frequency synthesizer (MF) 1 (for example, type 46-31) generates oscillations with a frequency fi close to the NQR frequency of the explosives arriving at the input of the radio pulse generator 2, which, according to the signals from the signal control and processing device (UOS), was used as A computer type 1N-1200 (France), forms a series of coherent radio pulses with a duration of tw and a repetition period of. Power amplifier 3 amplifies the radio pulses to the level necessary to create a magnetic field strength of about 10-20 G in the volume under study. step on sensor 4 usually

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An inductor included in the resonant circuit is used to create a magnetic field. From the sensor circuit 4, the received NQR signal is fed to the receiving device (PD) 5, which amplifies and quadrature detects it, for which reference voltages are applied to the PU 5 from the MF 1, the phase of one of which is shifted by tg / 2 relative to the phases of the other using a phase shifter 6. After filtering, the low-frequency signals of the quadrature channels are fed to the ASM 7, which performs analog-to-digital conversion and coherent summation of the signals. At the end of the sequence, the pulse SLD 7 processes the accumulated signal and compares the result of the processing with a threshold, the value of which is set based on the required probabilities of skipping the false alarm AND, when the threshold value is exceeded, SLR 7 generates a signal indicating the presence of explosives in the subject for alarm unit 8 . If the threshold is not exceeded, then the SLMF 7 gives on the midrange 1 a command to set the frequency equal to hf 1 ± 1 / (2 t and re-irradiates the subject with a multipulse sequence In particular, the accumulation and re-comparison of the result of processing the accumulated NQR signal obtained during the second irradiation If the result of the second irradiation exceeds the threshold, a decision is made about the presence of explosives in the subject under investigation, otherwise the SLM 7 generates a signal for BS 8, indicating the absence specific type of explosives

When checking for the presence of several types of explosives, the indicated sequence of operations is repeated for each explosive, while MF1 and the sensor circuit 4 are tuned to the frequency corresponding to the resonant frequency of the explosive to be detected

Comparative tests of this method and the prototype method consisted of conducting two series of 100 examinations in each method, while in one of the examination series a package measuring 350x350x50 mm contained a 10 g hexogen tab and there was no tab in the second series. The f 3410 kHz line was used to identify hexogen. In the examination according to this method, the examination cycle contained the following steps: placing the package in the sensor, irradiating it with a sequence of 9000 pulses with a repetition period of g - 630 μs and a frequency of fi --3410 kHz, coherent accumulation of NQR -from clicks. Fourier transform (FP) of the accumulated signal, calculation of the integral of the FP module and comparison of the obtained value with a threshold value. The threshold value was chosen based on the assumption of probabilities of 0.05. If the threshold value was not exceeded during the first exposure, then after 1 second the second sequence was irradiated with the same number of pulses and the repetition period, but with the filling frequency of radio pulses fa 3410.8 kHz. If V after the second exposure, the threshold was not exceeded, a decision was made that there was no bookmark. The decision to have a bookmark was made if the threshold was exceeded in at least one of two dimensions. When conducting a series of 100 examinations with a package containing RDX bookmark, in 43 cases the explosive bookmark was detected during the first measurement, in the remaining 57 cases, two measurements were required, and the average time for examining one package was

Tobsl Wed - (43 x 5.67 s + 57 x (11.34 s +

1 1 s) / 100-9.47 s

When conducting surveys according to the known method (prototype), in order to ensure the same probabilities of false detection of a 0.05 and skipping the bookmark / 0 05, it was necessary to increase the number of pulses in the sequence to 170,000 with the same repetition period of 630 μs and the inspection time per package amounted to:

to6cn 107.1 C

those. This method reduces the examination time for RDX by more than 10 times.

Similar tests carried out on HMX and Tetrile showed that the method reduces the examination time by 3.6 times for HMX and 4.5 times for Tetrile.

Claims (1)

SUMMARY OF THE INVENTION A method for detecting explosives using nuclear quadrupole resonance (NQR), comprising irradiating an examined object at a NQR frequency with a multipulse sequence, coherent accumulation of a NQR signal, processing the accumulated signal, and comparing the obtained processing result with a threshold value, characterized in that that the goal of increasing expressiveness while maintaining 5 18245596 the reliability of detection is 1/2 t. where t is the repetition period of the radioimplementary irradiation of the multi-pulse object in sequences, and the conclusion about pulse sequence, the frequency of the presence of explosives make filling radio pulses in which due to exceeding the result differs from the frequency of filling radioim-5 the value of the threshold value in one of . pulses at the first exposure to the value of the irradiation.