CN1162993A - Detector for explosive substances - Google Patents

Abstract

The presence of Semtex plastic explosive in a sample such as a fingerprint is detected by Raman spectroscopy. RDX and PETN, the active chemical ingredients of Semtex, have strong Raman peaks at 885 cm<-1> and 874 cm<-1> respectively. Consequently, both these peaks can be detected in a Raman spectroscopic system by employing a filter (28) having a narrow passband centred on 880 cm<-1> and with a bandwidth of 20 cm<-1>. Such a filter is used in a Raman system used to scan airport boarding cards, or in a Raman microscope which produces images of fingerprints etc.

Description

The detecting device of explosive

Invention field

The present invention relates to be used for the checkout equipment of explosive detection.In certain embodiments, the present invention relates to the detection problem to the explosive composition of plastic explosive Semtex at least.

The prior art problem.

European patent application EP 455516 (Britain's space flight) has illustrated a kind of safety practice that is used for places such as airport.Every passenger who boards was given a boarding card usually before climbing up aircraft, he or she submits this card in the wicket then.If the once contacted explosive of this passenger or other contraband material, he or she is contacted so will stay the vestige of this material after it on boarding card.At the ticket checking point, will analyze boarding card, detect these vestiges.EP455516 has disclosed the chemico-analytic possibility method of several these vestiges of detection.They comprise mass spectroscopy, vapor-phase chromatography, and ion mobility spectroscopic measurement method.But because a variety of causes, said method does not have a kind of feasible.For example, the vapour pressure of the explosive composition of plastic explosive semtex is extremely low, and this makes their utmost points be difficult to utilize " air-breathing detector " technology for detection to arrive.In addition, proposed various technology all can be destroyed sample, like this boarding card can not be re-used as can with the evidence of suspicion passenger confrontation.

Raman spectroscopy is to analyze and discern a kind of known technology of material.This type of example can be referring to International Patent Application WO 90/07108 (Renishaw) and european patent application EP543, No. 578 (Renishaw).

Plastic explosive Semtex has two kinds of chemical activity compositions: ring trimethylene-trintriamine or RDX and pentaerythritol tetranitrate or PETN.RDX and PETN are the transparent crystal of millimeter magnitude in explosive, and they are sticked together by a kind of amorphous wax material.Power name worker has made report to the Raman spectrum of RDX and PETN before this, the Raman spectrum that for example utilizes Fourier Ramman spectroscopy to obtain.The visible J.Akhavan of this type of example is published in the 47A volume of Spectrochimica Acta, " analysis of the explosive sample of Fourier Ramman spectroscopy commute " on the 9/10th the 1247th～1250 page in 1991.But such research is carried out under laboratory condition, and the feasibility of a kind of like this equipment of not mentioned production, this equipment can detect the situation that exists such as the plastic explosive of Semtex in the quite short time, this plastic explosive also may be polluted by other material, and this device is needed in this area just.

Brief summary of the invention

The present invention is the continuation of our work carried out, adopts the Raman analysis device analysis Semtex sample of explanation in European patent 543 578.What should give attention is that RDX and the PETN composition ratio in the Semtex sample that market is bought of Semtex is different.In addition, many peaks are relevant with polarization in the Raman spectrum of RDX and PETN.Because the microscopic particles of the most of Semtex that find in sample such as the impression of the hand is made up of single monocrystalline at the scene, we find that the intensity of the Raman bands of a spectrum that polarize is relevant with the differential seat angle between the crystal orientation with the plane of polarization of laser lighting.But our frequency that studies show that still remains unchanged.

Particularly, find that from our research RDX is at 885cm ^-1There is the last one peak at the place.PETN is at 874cm ^-1There is the last two peak at the place, and these are relevant with polarization.

According to the present invention, the method that detects explosive in the on-the-spot sample comprises this sample of irradiation, produce the scattering Raman spectrum thus, and use has covered 885cm ^-1And 874cm ^-1A kind of narrow bandpass color filter the Raman spectrum that is produced is filtered, and detect light through filtering.By above-mentioned discussion, should be understood that this method can detect at 885cm so if analyze the sample that comprises Semtex ^-1The place the RDX bands of a spectrum and/or at 874cm ^-1One of the PETN bands of a spectrum of the place or all, and irrelevant with the ratio of these materials in Semtex.

The present invention also provides several different being used to implement the structure of the equipment of this method.

The accompanying drawing summary

The preferred embodiments of the invention are illustrated with reference to the accompanying drawings, in the accompanying drawing:

Fig. 1 a) and 1b) be given in the Raman spectrum of RDX and PETN on the silicon wafer respectively;

Fig. 2 a)-2f) is given in the polarization Raman spectrum of the RDX crystal of different orientation;

Fig. 3 is a kind of boarding card reader, for example can be used for the reader structural representation on airport;

Fig. 4 is the structural representation of improved scanister that is used for the card reader of Fig. 3;

Fig. 5 analyzes for example structural representation of another equipment of impression of the hand of on-the-spot sample.

The preferred embodiment explanation

Fig. 1 provides and is deposited on the silicon wafer, is of a size of several microns the RDX and the typical Raman spectrum of PETN crystal in a side, in the drawings a) corresponding to the situation of RDX, b) corresponding to PETN.Measurement result is to use the equipment of EP543578, the laser that allows the helium-neon laser of 25mw launch 632.8 sodium rice to produce.Use the micro objective of X20, a NA=0.45.The watt level that arrives sample approximately is 5 milliwatts, and this is equivalent to energy density 2 * 10 ⁹Watt/meter ²

Be 5 seconds the access time of above-mentioned two spectrum.The raman scattering cross section of RDX and PETN appears bigger, makes to be easy to obtain Raman spectrum.We also test same sample with the Art laser instrument of one 514.5 nanometer, have obtained essentially identical result.This spectrum is similar with the spectrum that obtains the writing time of length with bigger laser power to employing FT Raman technology.

We showed a plastic explosive such as Semtex etc. can be simply by obtaining Raman spectrum or Raman bands of a spectrum image is discerned.Table 1 has listed all Raman bands of a spectrum that appear in the spectrum shown in Figure 1.The relative intensity at peak is represented with letter character: the S representative is strong, and the M representative is medium, a little less than the W representative; The V prefix designates meaning very.P shows that this peak polarizes.Just at a glance, the Raman spectrum of different RDX particles is some difference always, and this is because the great majority of these particles are single monocrystalline.For single crystal samples, the intensity of polarization Raman bands of a spectrum is relevant with the differential seat angle between the crystal orientation with the plane of polarization of laser instrument.But frequency remains unchanged.

Table 1

?RDX??(cm -1)	????PETN??(cm -1)
		????129????S ????152????S ? ????207????S ????226????W ? ? ????304????VW ? ????345????VS，P ????413????M ????463????S ????487????M ? ????589????W ????606????M ? ????668????M ? ????737????W ? ????787????M ????849????M ? ????885????S ????922????W ????944????W ? ????1031????S，P ? ? ????1217????VS，P ????1235????M，P ? ????1272????S，P ? ????1312????S，P ????1350????M，P ????1390????M，P ? ????1426????M，P ? ????1509????VW ????1573????VW ????1595????W，P ? ? ? ????2909????W ????2953????M ? ????3006????M ? ????3079????M	? ????147?????S ????194?????W ? ????229?????S ????260?????M ????280?????M ? ????321?????W ? ? ????458?????M ? ????539?????MS ????589?????MS ? ????625?????VS ????677?????M ????705?????M ? ????751?????W ? ????840?????M ????874?????VS ? ? ????941?????M ????1005????VW ????1033????VW ????1045????M ????1195????W ? ? ????1253????M ????1279????M ????1294????VS ? ? ? ????1405????W ? ????1471????M ????1512????VW ? ? ????1631???VW ????1662????M ????1675????M ????2917????W ? ????2990????M ? ????3024????M ?

Shown in Figure 2 is the polarization Raman spectrum of obtaining from the RDX monocrystalline.This crystal is grown in the laboratory, and is rectangular, and size is about 1 * 2 * 5mm ³We correspondingly are defined as X, Y and Z axle; Therefore the nose degree of crystal is along two plane surfaces in Z-direction and the YZ plane.Theoretical analysis demonstrate the Raman scattering light intensity be proportional to the dipole moment of inducing by incident radiation in the sample square.This dipole moment is expressed as:

U=aE (1) or

u _x=a _xxE _x+a _xyE _y+a _xzE _z

u _y=a _yxE _x+a _yyE _y+a _yzE _z

u _z=a _ZxE _y+ a _ZyE _y+ a _ZzE _z(2) here

Be the electric field of incident laser rate, and

It is polarizability tnesor.By using the microscope example objective table directed RDX crystal prototype of electricity and before spectroscope, placing an analyser, can obtain nine Raman spectrums.One of nine unit of each spectrum reflection polarizability tnesor, i.e. the influence of XX, YY, ZZ, XY, YX, XZ, ZX, YZ or ZY etc.Because a _Xy=a _Yx, a _Xz=a _Zx, a _Yz=a _Zy, only provide six independent spectrum here.This class research gives about the symmetric details of vibration mode except that having confirmed that the RDX particle is the monocrystalline.

As can be by seeing in Fig. 1 and 2 and the table 1, RDX be at 885cm ^-1There are strong bands of a spectrum at the place, and PETN is at 874cm ^-1The last one bands of a spectrum are arranged.These bands of a spectrum no matter polarize and crystalline orientation as what intensity is all bigger.The conclusion of these researchs is, the composition that we find the Semtex material for example Semtex-H can detect with a narrow band pass filter, and the passband center of this optical filter is at 880cm ^-1, bands of a spectrum are wide to be (for example) 20cm ^-1, be positioned at 885cm so that cover ^-1And 874cm ^-1The bands of a spectrum at place.

Fig. 3 has represented schematically how conventional boarding card reader is improved the block diagram with this class detecting device of packing into.As passenger during, be awarded a boarding card usually in the airport ticket checking.If his or she contacted before this Semtex explosive will leave the vestige particle in the so his or her hand, these particles can be transferred on the boarding card 10 when normal contact.Then, before boarding in a suitable checkpoint airport Men Chu for example, this passenger must be inserted into card reader shown in Figure 3 with boarding card 10.

As simply signal among Fig. 3, the boarding card reader comprises a shell 12, is furnished with the card reading device 14 of a routine in it.Card reader has the connecting gear of a routine to be used for card is sent to card reading device 14 by the inlet 18 of arrow 20 directions along transfer path 16 from shell.The function that card reading device 14 is carried out such as every passenger of identification is not shown up so that determined whether the passenger.It can return the sub-fraction of passenger's card, and this part has comprised such as details such as seat numbers, but it preferably keeps the major part of card.This means that when detecting Semtex, this card keeps makes further to analyze usefulness, so that can confirm, and can be used as evidence if desired.

When boarding card 10 when transfer path 16 transmits, it is by the photoscanning of laser instrument 22.Can adopt the laser instrument of many types, comprise the gas laser such as He-Ne, perhaps suitable stabilization and semiconductor laser diode through filtering.Through 90 ° of reflections, and reflected light focuses on the card 10 through lens or lens combination 26 dichroic filter when through path 16 with the light of optical maser wavelength.Since scanning area preferably block 10 whole or most of, so Optical Maser System can comprise a cylindrical lens, when card these lens when arrow 20 directions are moved are providing a line focusing at the Width across card.Same lens combination 26 is compiled the scattered light from illuminated line.It turns back to dichroic filter 24, and this optical filter is removed reflected light and the Rayleigh scattering light that has with excitation laser 22 identical wavelength, but transmits the Raman light of any scattering.This scattering Raman light is by way of a narrow band pass filter 28, and focused on the detecting device 32 by lens 30, and detecting device 32 can be an avalanche photodide.

Light filter 28 has one to be about 20cm ^-1Narrow passband, its center is at about 880cm ^-1So as discussed, if arbitrarily RDX or PETN particle appear on the boarding card 10, detecting device 32 will be reacted, because light filter will allow 874cm ^-1And 885cm ^-1The graceful bands of a spectrum of haling at place pass through.But detecting device 32 will be not react to the scattered light at any other wave number place.At Fig. 3, optical filter 28 is expressed as vertical with light path, but if desired this optical filter is adjusted to 880cm ^-1, so also can be angled with normal.

The output result of detecting device 32 is sent to control device 34, and this control device 34 can comprise the computing machine of this equipment components of control, and if receive greater than the signal of certain given threshold value from detecting device 32 then send an appropriate signals.Control device 34 preferably can carry out the background subtraction, promptly determines 880cm ^-1Optical filter 28 detected any peak heights are in the height of background.This is very important when boarding card is easy to carry about with one the material of broadband aura or fluorescence, and no matter this material is the material of boarding card itself, still dust or the grease that obtains in hand-held process.In order to carry out background rejection, can be by placing beam splitter 36 before the optical filter 28 with the part reflection of scattered light, to another narrow band pass filter 38, lens 40 and detecting device 42.Remove optical filter 38 and be tuned to 880cm ^-1With the arrowband of a side, for example 810cm ^-1All the other are all identical in addition, do not have Raman scattering or seldom at the Semtex of this place, arrowband.Control device 34 is sent in the output of detecting device 42, and it is deducted from the signal of detecting device 32 by means of proper procedure in the computing machine or the special electronic circuit such as comparer herein.Control device provides suitable mark at the signal of deduction background above under the situation of predetermined threshold then.

At Fig. 3, beam splitter 36 can be simple 50: 50 beam splitters.But for fear of the loss of the scattered light that can be used for detecting, it is a sword type optical filter preferably, between the bands of a spectrum of optical filter 28,38 sharp cut-off is arranged.This guarantees 880cm ^-1All light in the bands of a spectrum reflex to optical filter 28, and all light in the adjacent bands of a spectrum are reflected onto optical filter 38 simultaneously.In fact, optical filter 36 can need not to be sword type optical filter, is centered close to 880cm and be designed to only make ^-120cm ^-1Wide bands of a spectrum by and directly it is sent to detecting device 32 (and need not adopt an independent optical filter 28), and other light reflexes to background optical filter 38 with all.Perhaps, optical filter 36 can be a notch filter, and it allows except that seeing through as all scattered lights the arrowband of background deduction and arriving optical filter 28, and the light of using do background rejection directly reflexes to detecting device 32 (need not adopt optical filter 38).

Our test shows such as aforesaid Raman equipment can successfully detect minimum Semtex particle in the several seconds, for example about 1 μ m ³, the particle of 1 pico-gram that weighs.Our test simulation all situations of real-life, wherein we have made some " impure " samples with finger tip, these samples are by Semtex and other grease material cross pollution.But, according to desired sensitivity, and acceptable false alarm rate, preferably boarding card 10 is compared with conventional boarding card reader along the speed of transfer path 16 processes and is decreased.Another kind of possible measure is that card material is coated with the skim material, such as silver, gold or copper, makes its surface suitably more coarse.Because adopted a so suitable surface, the RDX or the PETN material molecule that are adsorbed onto rough surface can demonstrate Surface enhanced raman spectroscopy (SERS) performance, this performance has increased Raman scattering by means of a very large factor.

Same wish to guarantee that boarding card made by non-fluorescence card stock.Can replace using the another kind of mode of non-fluorescence card is to adopt the laser instrument 22 of the light of the spectrum that can produce red sector far away or infrared region.The excitation of this class wavelength has reduced or eliminated fluorescence problem considerablely.

Certainly, also can adopt other optical devices except that shown in Figure 3.For example, suitable optical devices can shine simultaneously and collect from blocking the Raman diffused light of both sides.

Fig. 4 provides the improvement project of the Scan Architecture that is used for Fig. 3 boarding card reader.Here, be that arrow 20 directions along Fig. 3 are observed boarding card in vertical cross-section.In lens combination 26, be used for producing the necessary cylindrical lens of line focus and may be not the effective and efficient manner of the Raman diffused light of collecting maximum.Therefore, Fig. 4 provides an improved lens combination 26 ', and this system produces point focusing on card 10, and Raman diffused light is had higher collection rate.After by 46 reflections of polygon device, light focuses on the card 10, and each face of polygon device 46 all is a minute surface.Device 46 points to along arrow 44 and is rotated continuously by (unshowned) motor driven.This makes the horizontal inswept card 10 of laser spots, and its speed is greater than by the length direction sweep velocity of moving and being provided along the card of transfer path 16 directions.

The scattered light of card returns through the minute surface and the lens combination 26 ' of device 46, enters and similar optical detection system shown in Figure 3.Fig. 3 and 4 systems of describing only detect the situation that exists of blocking some some Semtex of place on 10.A special feature of Raman analysis technology is its non-destructive.Therefore, if detect the existence of Semtex, just this card can keep with for further analysis and can be used as evidence so.Obviously, can improve this type systematic, make it to be used to detect the Semtex on other surface such as bill, I.D., the passport etc., this system also can be used for other occasion except that the boarding card reader of airport, for example the porch of public building, government house etc.The non-destruction characteristic of Raman analysis makes it can be applicable to this class occasion, and this is because ticket, card etc. can be sent back to after analyzing.

In addition, can be in conjunction with such as at United States Patent (USP) 5,377 when the relevant assembly 32-42 of detecting device and Fig. 3 uses, a kind of hand-held fibre-optical probe of describing among 044 (Owen) and 5,112,127 (Carrabba).The light of laser 22 is given probe through optical fiber downwards, and Raman diffused light feeds back to assembly 32-42 through another root optical fiber.So then hand-held fibre-optical probe can be used for surveying the situation that exists of Semtex on many kinds of objects, and comprises directly suspect's hand is surveyed, or treat the luggage that is written on the aircraft and survey.In fact, after suitable miniaturization was handled, detector module 32-42 and various wave filter and lens can be with suitable object lens and semiconductor laser diode handheld probe unit of packing into.For making probe object under test location relatively, probe can dispose suitable backed or other location aid device.

In some occasion, hope can be done the further analysis that allowed than Fig. 3 and 4 apparatus shown to sample.At this moment can adopt all equipment as shown in Figure 5 to finish, disclosed similar of this equipment and European patent EP 543578, this European patent will be hereinafter with for referencial use.A sample is positioned on the microscope stage 54, projects on this sample through lens combination 56, catoptron 62 and micro objective 64 from the light of laser instrument 50.If wish certain regional imaging, regulate lens 56 so and make the laser-beam divergence on the sample 52 and be radiated on the desired zone this sample.Micro objective 64 is collected Raman diffused light, makes it to return through dichroic filter 60 (it will have reflection and Raman diffused light removal with the identical wavelength of laser instrument as preamble).Optical filter 70 is foregoing narrow common optical filters, is centered close to 880cm ^-1, bandwidth 20cm ^-1, so that detect RDX and the PETN composition of Semtex.The two dimensional image in the illuminated district of sample is 880cm according to the center ^-1Band, focus on again on the suitable two-dimensional detector 72 by lens 74 such as charge-coupled device (CCD).This image is shown that by computing machine 76 computing machine 76 is also controlled other parts of this equipment on request after obtaining.For example, because same as described above, by optical filter 70 is tilted to make it to retune to contiguous passband slightly, computing machine 76 can carry out background subtraction.Then, computing machine 76 obtains another background image, with the data of each pixel of background image from 880cm ^-1Detain in the corresponding data in the image of band and go.

Fig. 5 shows that also this equipment can have an independently operator scheme, and its details are found in EP543578, and this independent manipulation mode is used in the situation that the image any part detects RDX or PETN and confirms its existence.Lens 56 can focus on again so that rayed on a single point of being concerned about of image, makes microscope stage move in case of necessity.Catoptron 66 is removed from light path, and Raman diffused light promptly reflexes to diffraction grating 78 through prism 79 like this.This makes institute be concerned about that the raman scattering spectrum of a little locating intersperses among on the surface of CCD72, and is feasible by confirming that it is RDX and/or PETN with composing to make comparisons shown in Fig. 1 and 2.

Certainly, equipment shown in Figure 5 can improve to be suitable for various different application.Whole system shown in Figure 5 is applicable to that more technician there can distinguish the spectrum that diffraction grating 78 produces in court check (forensic) laboratory.Perhaps, in order to make the system that can be used for police bureau, can omit diffraction grating 78, prism 79 and catoptron 66,68, optical filter 70 directly places the path of dichroic filter 60 and lens 74.Unfamiliar then operating personnel can be created in 880cm easily ^-1About 20cm ^-1Impression of the hand image in the band, this image can indicate the situation that exists of Semtex particle in the impression of the hand.

Except that being undertaken the background subtraction, can also do another and have suitable passband and reach same purpose by optical filter 70 is changed for the optical filter that background detects usefulness by control the tuning of optical filter 70.In addition, dirigibility also shows can remove optical filter 70, can form the image of impression of the hand or other sample like this on CCD, and this CCD has absorbed the white light of introducing in the microscope.Can be with the White-light image of impression of the hand and at 880cm ^-1It is particularly advantageous that the image of being got in the bands of a spectrum is compared nature, because any explosive vestige and the actual of impression of the hand that it makes people find are as can be seen got in touch.Perhaps, this has also eliminated impression of the hand is possibility at the substrate of having been crossed by explosive polluting before this, and improves the value of the court evidence that this technology produces.

As can be seen from Figure 2, although the 885cm of RDX ^-1Band always exists, but it is relevant with polarization to a certain extent.PETN at 874cm ^-1The peak irrelevant with polarization.These facts can be used to distinguish RDX and PETN where necessary.A polarizing filter is positioned in the light path of Raman scattering light, after the dichroic filter 24,60, and regulates this polarizing filter to judge 880cm ^-1Recording intensity and whether change in the band.

Another remodeling of Fig. 5 equipment (being with or without diffraction grating 78) is to make the light filter 70 that can be changed to another light filter be tuned to one of other peak shown in Fig. 1 and 2, for example the 533cm of RDX ^-1The peak.Perhaps an optical filter 70 can be tuned to two peaks simultaneously.533cm for RDX ^-1And 885cm ^-1The Raman diffused light of each of peak all produces an image, and each image has all been deducted the factor of background and (used respectively at for example 500cm ^-1And 810cm ^-1The image that the place obtains).Resulting two images by computing machine 76 utilization " with " logic generates a final image, this image has only provided those and has produced 533 and 885cm simultaneously ^-1The zone at peak.This makes that the recognition result of the RDX of adversary India and China is more credible.This a kind of technology also can be used in the non-imaging system, for example by some light filters and beam splitter are provided in the system of Fig. 3 again.Similarly, other material beyond the Semtex also must be discerned from two or more raman characteristic peaks.

Fig. 3,4 and 5 dichroic filter 24,60 can be the dichroic filters of multilayer.Perhaps, also can adopt holographic notch or sword type optical filter, described in EP543578, incident angle was lower when this class light filter used, and for example 10 ° or 11 °, to improve its irrelevance to polarization intensity.The Rugate light filter can change holographic filter into.Light filter 28,38,70 also can be any in these patterns.

People's such as C.Cheng article, " the Raman microtechnic is to the on-the-spot detection and Identification of micro explosive ", incorporated herein by reference, this article is stepped in JFSCA, detection science magazine (Journalof Forensic Sciences) the 40th volume, the 31st～37 page of first phase January nineteen ninety-five.Delivering of this article is after the priority date of present patent application.

Claims (8)

1. the equipment of explosive materials in the test sample comprises:

A light source is used for this sample is shone to produce Raman diffused light;

A detecting device is used to detect the Raman diffused light from sample reception; With

Narrowband light filter between sample and detecting device, this light filter only allow and comprise 874cm ^-1And 885cm ^-1Certain arrowband in light by and arrive detecting device.

2. according to the equipment of claim 1, it is characterized in that the form of sample has card or other document, its certain zone is scanned by light source, detecting device and light filter.

3. equipment according to claim 2 is characterized in that in this equipment card or other document are transmitted through light source, detecting device and light filter.

4. according to claim 2 or 3 described equipment, it is characterized in that this equipment comprises that lens are used to stride the line focusing that card or other document produce the light that light source sends.

5. according to claim 2 or 3 described equipment, it is characterized in that this equipment comprises that a device is used to stride card or other document the light of light source is carried out spot scan.

6. equipment according to claim 1 is characterized in that the two dimensional image that the detecting device test sample is regional.

7. according to the described equipment of one of aforementioned claim, it is characterized in that this equipment comprises that device is used to detect raman scattering spectrum, this device separates with said narrowband light filter.

8. according to the described equipment of one of aforementioned claim, the bandwidth that it is characterized in that narrowband light filter is about 20cm ^-1, the center is at about 880cm ^-1

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