A contactless method for detecting explosives and narcotics.
Vadim Antonovich Shelkov
A CONTACTLESS METHOD FOR DETECTING EXPLOSIVES AND NARCOTIC SUBSTANCES
In the summer of 2000, the All-Russian Exhibition Center hosted another exhibition, Forensics, this time 2000”, the last one in the outgoing century.
We had to wait almost 3 months for its opening, but, ultimately, the delay turned out to be quite justified: in terms of the number of participants and the interest that individual exhibits generated made it stand out from the previous one.
We will not dwell on the remarkable, both in terms of quality of execution and ease of use, thermal imagers of the American company Raytheon.
This class of devices was described in sufficient detail in Nos. 3, 4 of «Special Equipment for 1999.»
We will only note a portable device the size of a household video camera («camcorder»), which allows you to see the trace of your palm on the wall even a minute after you removed it. On a dark night, it is able to clearly distinguish by its light, i.e. warm hood the car that some time ago carefully parked near the protected object.
Specialists racking their brains in search of the most effective means of preventing terrorism and covert information collection will appreciate the opportunities that are opening up, unless of course they are stopped by the cost of the simplest model at $25,000.
The State Enterprise V.V. Tikhomirov Research Institute of Instrument Engineering demonstrated an amazing new product, which is called “on the topic of the day”: a detector of explosives and narcotics based on nuclear quadrupole resonance.
The devices are “safe” type devices for checking mail, hand luggage, etc. with a working chamber volume of 10 — 25 liters.
The problem of contactless detection of hermetically sealed explosives and drugs does not allow employees of special services in all developed countries of the world to sleep peacefully.
Research shows that one of the most promising remote methods for detecting these substances is the nuclear quadrupole resonance (NQR) method. Compared to others, it is distinguished by exceptional selectivity.
The nuclear quadrupole resonance method is based on a physical phenomenon characteristic of the so-called quadrupole nuclei in crystalline structures.
In an ordered crystalline structure, all quadrupole nuclei have a certain resonance frequency, i.e. the frequency at which resonant absorption of electromagnetic energy occurs.
For each chemical compound containing such nuclei, there are one or more characteristic resonance frequencies, which are determined by the structure of the specified compound.
For this reason, NQR resonance is an exclusively selective method for detecting certain substances containing quadrupole nuclei.
As is known, all explosives and narcotic substances contain nitrogen nuclei N 14, which have quadrupole properties.
The frequencies of the quadrupole resonance of nitrogen nuclei in different compounds are concentrated in the range from 0.8 to 6 MHz.
This circumstance significantly simplifies the problem: to create a device for detecting explosives and narcotic substances, it is possible to use parts and units developed for tomography in low magnetic fields based on nuclear magnetic resonance.
However, to detect the received signal, it is necessary to use precision low-noise amplifiers of the corresponding frequency range.
Let's add to this other necessary equipment: a pulse transmitter (1 kW, 500 Hz — 10 MHz), a precision receiver, a frequency synthesizer, a control computer complex, etc.
Now it becomes clear why the estimated cost of a NQR installation for remote detection of drugs in passenger luggage, as well as inside and on the surface of the human body, will be at least 500-600 thousand US dollars.
Nevertheless, the nuclear quadrupole resonance method allows detecting hexogen, octogen, PETN, as well as mixtures of these substances, in addition, to detect heroin, cocaine and narcotic substances on their salts.
By the NQR resonance frequency, it is possible to determine not only the type of explosive or narcotic substance, but also its mass.
For example, the figures show NQR signals, as well as the spectra of hexogen and cocaine, respectively.
Time realization and spectrum of the free induction signal of hexogen: Fig. 1
Time realization and spectrum of the free induction signal of cocaine: Fig. 2
According to the assurances of specialists from the V.V. Tikhomirov Institute of Instrument Engineering, the NQR detectors created or under development allow detecting explosives and narcotics weighing more than 3-5 grams in postal items and hand luggage with a volume of up to 25 liters in 10-25 seconds.
We could put an end to this and wait for these amazing devices to drop significantly in price and appear in every airport and post office.
However, one circumstance related to the operating principle of the NQR detector raises certain doubts.
During the examination, the controlled object is irradiated with electromagnetic energy of a fairly low frequency (hundreds of kilohertz, units of megahertz).
Elementary shielding can create an insurmountable barrier to the detection of explosives and narcotics using this method.
This remark should also be applied to various metal transport containers.
Thus, equipment based on backscattered X-rays still remains the most universal means for detecting various dangerous attachments in hand luggage, baggage, vehicles, and even on the human body (see “Special Equipment” No. 3, 1999)