EXPLOSIVE TAGGING

Field

The present invention relates to the field of explosives and more particularly to the field of tagging and tracking of explosives.

Background

The use of explosives is very extensive across the mining, building and pyrotechnical sectors and in recent years use in terrorists bombs has dramatically increased. The bombing of the World Trade Centre in 1994, the US Embassies in Africa, USS Cole, 9/11, Bali 1, Bali 2 and many incidents in Iraq, Israel and London are just some of the incidences which have prompt renewed vigor in tracking and identifying the origins of explosives . All governments worldwide are also mindful of the theft of commercial and military explosives and the potential for their use in terrorist activities . Indeed it was in response to the bombing of Pan Am Flight 103 over Lockerbie, Scotland in December 1988 that the MARPLEX (Marking of Plastic Explosives) convention arose. This treaty obligates all manufacturers of sheet and plastic explosive to "tag" these materials with one of three or four mandated additives that all have a high vapour pressure and are detectable by gas chromatographic or other standard detection means . Sanctions can be very severe for any sale or transfer of untagged explosives of these types,- in the United States it may lead to the death penalty.

The most effective current tagging agent, and now mandated, for sheet or plastic explosives is 2, 3 -dimethyl- 2, 3-dinitrobutane (DMNB) . A quantity of 1% by mass of DMNB must be added to any quantity of sheet or plastic

explosive as a minimum concentration; there are current global regulatory meetings with the aim of increasing the concentration of DMNB to 1.5 % in the near future.

The MARPLEX Treaty additives are only really effective and practical to mix with plastic and sheet explosives which represent only a small percentage of the explosives, manufactured and used world wide per annum. These mandated additives are all intended solely for pre detonation explosives detection since they are completely consumed during detonation. Used in this way they do not provide any clear indication once the explosives have been detonated whether it was made by a terrorist or not.

MARPLEX mandated tags employed in plastic and sheet explosives are also expensive to manufacture and completely unsuitable for addition to the common reagents used in explosives such as ammonium nitrate. Addition of volatile organic additives to hot ammonium nitrate liquor is potentially reactive and can also result in sensitizing the ammonium nitrate .

Other chemical taggants have also been described in the literature but not found use commercially. One such class is that of rare earth elements, which purport to impart a certain unique identity to the explosive which facilitates pre or post blasting identification so as to trace the originator of the explosives (US5677187) . Detection is carried out by elemental analysis. These rare earth elements are expensive to use in the manufacture of explosives and specialized equipment is needed to perform the post blast elemental analysis.

US 4,013,490 describes use of small inorganic phosphors added to explosive materials in the form of conglomerates . The phosphor is detected post blast by ultraviolet light. Potential disadvantages of adding

these water-insoluble tagging materials to ammonium nitrate based explosives include (i) non-uniform dispersal, and (ii) safety problems due to accretions (which may create potentially hazardous friction and impact sensitivity during manufacture, handling, storage and use of the explosive product) .

Another class of post detection taggant consists of tiny multi-layered plastic fragments, in which a colour and magnetic code is present in the multilayering. Many trials have been performed with this material mixed in small concentrations with ammonium nitrate based explosives and dynamites, particularly in the United States. Switzerland utilizes a version of this technology to track commercial explosives use and supply. Explosives manufacturers in the United States have, however, consistently resisted any attempts by the US Government to compel manufacturers to add this material to their products, on grounds of safety, stability and relative ineffectiveness, as well as high cost.

It is therefore an object of the present invention to address or at least ameliorate some of the above shortcomings of the currently described taggants, or to provide an alternative material for explosive tagging.

Summary

According to the present invention, there is provided a tagged explosive comprising an explosive composition and a precursor tag, the precursor tag comprising a transformable material that can transform during detonation of the explosive composition into a luminescent tag.

The luminescent tag can be detected in post detonation debris.

The precursor tag is non-luminescent prior to detonation, and is detectable in the explosive prior to detonation. The precise composition of the precursor tag, and thus the luminescent tag into which it is transformed, is intended to be unique to a particular manufacturer, and may also be unique to a particular explosive composition class or type, batch number, and/or date of manufacture. The precursor tag will generally comprise at least two components, usually in a specific ratio, that will be uniquely used to identify the manufacturer or origin of the explosive composition.

When an (undetonated) explosive of unknown origin containing such a precursor tag is located, its origin can be identified, using standard analytical techniques such as X-ray fluorescence, ICP-AES or atomic absorption spectroscopy. When an explosive of unknown origin containing such a precursor tag has been detonated, for example in a terrorist incident, the origin of the explosive can be detected and identified using a spectroscopic technique that makes use of the characteristic luminescence signature for the luminescent tag.

The identification and use of a tag that is transformed into another material that is luminescent during detonation gives at least two particular benefits: (1) examining the undetonated explosive does not reveal a luminescent signature, so it is not apparent that the material has been tagged and (2) detection of the precursor tag components is non-trivial, and without detailed analysis, does not inform the user as to the exact nature of the material responsible for the luminescent signature post-detonation.

There is a very significant public benefit in

being able to apply a unique post-detonation luminescence signature to any batch of an explosive composition that facilitates the rapid identification of persons involved in the illegal use of explosives. There are also significant commercial benefits for manufacturers of explosives in being able to track and trace explosives products through the use of transformable additives to explosives that become photoactive on detonation.

The present invention also provides a precursor tag for use in an explosive composition, said precursor tag comprising a transformable material that can transform during detonation of an explosive composition to which it is added, into a luminescent tag.

The luminescent tag can be detected in post detonation debris.

The present invention also provides a method for the preparation of a tagged explosive, the method comprising adding a precursor tag to the explosive composition or to any process stream during the production of the explosive composition, wherein the precursor tag comprises a transformable material that can transform during detonation of the explosive composition into a luminescent tag.

The present invention also provides a method for the identification of the origin of an explosive post detonation of the explosive, the method comprising:

obtaining spectral information for a luminescent tag in the post detonation debris, and

comparing the spectral information obtained against spectral information for tagged

— O "~ explosives of a plurality of origins .

Usually, the spectral information will comprise a luminescence spectrum or information relating to a luminescence spectrum, although other spectroscopic techniques can be used. The spectral information for tagged explosives of a plurality of origins will typically be stored in a database. The device used for obtaining the spectral information for the luminescent tag may also incorporate the database information to enable the identification of the origin of the explosive to be assessed in the one device.

The present invention also provides a method for the identification of the origin of an undetonated explosive, the method comprising:

analysing the explosive for the presence of a precursor tag comprising a transformable material that can transform during detonation of the explosive into a luminescent tag, and

comparing the precursor tag identified through the analysis to information on precursor tags present in explosives of a plurality of origins.

The present invention further provides a system for enabling the identification of the origin or manufacturer of an explosive composition, comprising:

assigning one or more unique precursor tags to manufacturers or originators of explosive compositions, to enable the manufacturer or originator to include precursor tags of that unique identity into

the subject explosive composition to be identified by that precursor tag, wherein the precursor tag is a transformable material that can transform during detonation of the explosive into a luminescent tag; maintaining one or more databases containing information on the precursor tag and spectral information on the corresponding luminescent tag, for explosives to which precursor tags have been assigned, and providing access to the database to enable a comparison to be made between the information on the database, against (a) information on the precursor tag obtained from an explosive of unknown manufacturer or origin and/or (b) spectral information obtained following the analysis of post detonation debris of an explosive containing a precursor tag, to enable the manufacturer or origin of the explosive to be identified.

Brief Description of Drawings

Figure 1 is a schematic diagram of a tagged explosive set up under typical experimental conditions to test detonation and detection of the luminescent tag; and

Figure 2 is a fluorescence spectrum for two test shots A and B showing typical detector output and presence of peaks identifying a particular luminescent tag in the explosive debris post detonation.

Detailed Description

The present invention relies on the use of precursor tags in explosive compositions, which transform during detonation of the explosive composition into luminescent tags.

Any chemical material that has the ability to transform under the conditions of an explosive composition into a different material that is luminescent and is detectable through spectroscopic techniques, preferably luminescence spectroscopy, can be used as a precursor tag. The conditions of the explosion are very high heat, and the presence of components of explosive composition such as fuel elements (oils, waxes, finely divided aluminium metal and the like) . Under these conditions, a range of materials have the ability to be transformed into luminescent materials .

Generally the precursor tag, and the luminescent tag will be inorganic materials. According to one embodiment, the precursor tag comprises a rare earth metal salt. Preferably, the precursor tag comprises a combination of two or more rare earth metal salts. The precursor tag may be constituted by the rare earth metal salts in pure form. Alternately, the rare earth metal salt can be in the form of a doping element in an alkali metal salt, and alkaline earth metal salt, an aluminium salt, ammonium salt, or in a combination of such salts.

Examples of salts of rare earth metals that suitable for use as precursor tags include oxide salts; nitrate salts, perchlorate salts, persulphate salts and combinations thereof.

The rare earth elements are the lanthanides (being lanthanum and the 14 elements that follow lanthanum

in the periodic table) , plus yttrium. Specifically, the rare earth elements are lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium and yttrium.

It will be understood that by selecting a unique combination of two or more rare earth metal salts as components of the precursor tag, a unique combination can be obtained which, when transformed during detonation of the explosive composition, will give rise to a unique luminescence spectra or another detectable indicia which relates back to the unique combination of those rare earth metal salts in the precursor tag, and in the transformed luminescent tag. The identity and/or ratio of rare earth metal salts in the transformed luminescent tag determines the coding of the original explosive by the manufacturer. That is, each manufacturer is identifiable by a specific identity and/or ratio of components in the precursor tag, such as rare earth metal salts, for use in their explosive compositions. It is also possible for a manufacturer to be assigned a range of ratios of rare earth metal salts, with specific combinations that link to other identifying features of the explosive compositions manufactured by them, such as explosive type, lot number, date of manufacture and/or place of manufacture . The reference to "origin" refers to any one or more of these features of an explosive, being manufacturer, place/country of origin, explosive type, lot number and/or date of manufacture.

Accordingly, it is to be understood that the precise identity of the rare earth metal salts present in the precursor tags is not critical to the way in which the invention works. Rather, a particular rare earth metal salt, combination of salts and/or ratio of salts for inclusion in the precursor tags will be selected for each manufacturer by a regulating authority or body. What is

required is that the precursor tag is in a form which transforms on detonation of the explosive into a luminescent tag, and is not itself luminescent at the time of manufacture .

In the context of ammonium nitrate-based explosive compositions, the use of precursor tags which comprise rare earth metal salts as components are of particular interest . The rare earth metal salts may be added in a pure form, or in the form of doping in a carrier salt. The carrier salt may be for instance an alkali or alkaline earth metal salt, such as a nitrate or an aluminium salt, such as aluminium nitrate, or a combination of such nitrates . Because the great bulk of explosives used in the mining industry worldwide are ammonium nitrate-based, it is believed that this form of precursor tag will be of greatest interest due to its availability and compatibility with ammonium nitrate during processing. The precursor tags can be safely incorporated with ammonium liquor for the purpose of tracking. Preferably, the precursor tag salts will not substantially disrupt the crystal phase change, crystallographic properties, porosity, surface hardness or friability of the ammonium nitrate prill or the ammonium nitrate in the liquor stages of slurry or emulsion explosive production. Further details on methods for preparation of explosive compositions containing the precursor tags are described below.

The precursor tags may be water soluble or water- insoluble . The water soluble precursor tags have the added advantage that they are difficult to remove from explosive compositions containing them. In the case ammonium nitrate-based explosives, one technique used by third parties to attempt to remove tags is to dissolve the ammonium nitrate of the explosive composition in water. Water soluble precursor tags provide the advantage that

they are themselves dissolved together with ammonium nitrate, and make it difficult for third parties to remove these tags from the explosive compositions. Whilst water- insoluble precursor tags do not share this advantage, they do nevertheless provide advantages in terms of their conversion into luminescent tags upon detonation of the explosive composition, and the luminescent tags are much faster and easier to detect in the post detonation debris compared to other types of tag materials . Detecting non- luminescent tags is a more complicated issue, because the presence/absence of a number of materials needs to be determined, as well as their relative concentrations.

Explosive Compositions

The precursor tags may be combined with any explosive compositions known in the art. Suitable classes of explosives include ammonium nitrate-based explosives including ANFO explosives, emulsion explosives, slurry explosives, TNT-based explosives, RDX-based explosives, plastic explosives and so forth. Such explosive compositions may contain any of the usual components and additives known in the art for explosive compositions .

As noted previously, the MARPLEX tags are employed in plastic and sheet explosives, and are unsuitable for addition to ammonium nitrate explosives . Thus, one class of explosives of particular interest to the present invention are the ammonium nitrate-based explosives.

Transformation to Luminescent Tags

The precursor tag is a transformable material that can transform during detonation of the explosive composition into a luminescent tag. According to one embodiment, the transformation involves reaction of the

precursor tag with other components of the explosive composition during detonation, and/or under the influence of the high temperatures achieved in the detonation of the explosive. These temperatures typically reach 2,000 ⁰ C - 3,000 ⁰ C. The precursor tags can undergo reactive transformations with components of the explosive compositions, typically the fuel elements (such as oils, waxes, finely divided aluminium metal and the like) present in the explosive composition at detonation. Reactive transformation refers to the transformation of the transformable material or chemical agent from the state in which it is undetectable by luminescence spectroscopy to a state in which it is detectable through luminescence. The luminescent tags created are refractory inorganic materials .

In the case of a reaction with a fuel element in the explosive composition such as fuel oil, the precursor tag can transform into a luminescent oxide. Luminescent rare earth metal oxides commonly comprise a "base" rare earth metal oxide, with one or more dopant rare earth metals . Thus the precursor tag in this case would generally contain the required rare earth metals in salt forms, usually as separate salts (present in the required ratios) which transform into a mixed rare earth metal oxide. The mixed rare earth metal oxide is based on one of the rare earths, with doping by the second (and further) rare earth metal dopants. The mixture of two or more rare earth metal salt precursors present in the explosive composition are in this case transformed into doped rare earth metal oxides having luminescent properties .

Other forms of luminescent tags into which the precursor tags can be transformed include luminescent rare earth metal sulphates and rare earth metal chlorides .

The oxide, sulphate or chloride luminescent products produced on detonation of the explosive containing a precursor which comprises one or a mixture of rare earth oxides (specifically non-luminescent rare earth oxides), nitrates, persulphates or perchlorides in the presence of the fuels in the explosive, are themselves refractory materials, and traces of these oxides sulphates or chlorides will tend to be imprinted on and/or coat any debris left as an aftermath of detonation of the explosive. Post detonation, the luminescent tag produced can be detected by a suitable spectroscopic technique making use of its luminescence, such as molecular fluorescence or phosphorescence spectroscopy.

Detection Techniques

Post detonation of the explosive, the origin of the explosive can be identified by obtaining spectral information for a luminescent tag in the post detonation debris, and comparing the spectral information obtained against the spectral information for tagged explosives of a plurality origins. These may be stored as a collection, library or database. This may be stored in the detection device or spectrometer itself, for immediate identification of the origin of the explosive.

Suitably, the spectral information obtained will be gathered through fluorescence or phosphorescence spectroscopy.

Any type of spectrometer capable of detecting luminescence can be used for this purpose . Examples include portable pulsed diode spectrofluorometers, and spectrofluorometers containing a xenon lamp source. The spectrometer may additionally contain a processor to compare the luminescent response detected by spectrometer against a database of unique luminescent responses for a

library of luminescent tags corresponding to precursor tags which enable identification of the origin of the explosives. References to the origin of an explosive refer to any one or more of a manufacturer, particular explosive composition class or type, batch number and/or date of manufacture. Preferably, the origin information will include at least the identification of the manufacturer .

The light source used in such luminescence spectroscopic techniques may include x-ray radiation, laser radiation, ultra-violet radiation, or even visible radiation.

One particular advantage of an embodiment of the present invention is that the luminescence of the post- detonation debris and thus the origin of the explosive can be assessed in situ or at the detonation site, making use of a portable luminescence reader. To this end, the portable luminescence reader described in WO 2006/119561 can be utilized. The disclosure of this international application is incorporated herein by reference.

The spectral information for the luminescent tag can alternatively comprise Raman spectrometry (with laser emission excitation) or x-ray and visible light spectrometry. The detection techniques are suitable for detecting rare earth metal oxides in the post detonation debris. Alternatively, any other analytical techniques that may be employed to detect trace quantities of rare earth metal can be used. However, standard elemental analytical techniques such as X-ray fluorescence, ICP-AES or atomic absorption spectroscopy that do not make use of luminescence spectrum information, are not preferred.

The origin of an undetonated explosive can also be identified in accordance with another aspect of the

present invention. According to this aspect, the explosive is analyzed for the presence of a precursor tag, in which the precursor tag comprises a transformable material that can transform during detonation of the explosive into a luminescent tag. Suitable techniques for analysing the explosive composition for such precursor tags include standard elemental analytical techniques such as X-ray fluorescence, ICP-AES or atomic absorption spectroscopy

Method of Manufacture

According to one aspect of the present invention, there is provided a method for the preparation of a tagged explosive which comprises adding the precursor tag to the explosive composition, or to any process during the production of the explosive composition.

In the case of ammonium nitrate-based explosive compositions, the precursor tag is preferably added into a process stream during the manufacture of the explosive material. The process stream may be a liquor process stream, to enable either complete dissolution or dispersing of the precursor tag in that stream to achieve a uniformed distribution of the precursor tag throughout the explosive composition at a very small concentration. The process stream may be a process stream during ammonium nitrate prill formation or a process stream for manufacturing ammonium nitrate emulsion explosive and/or ammonium nitrate based water gel slurry explosive. The precursor tag may be added either in liquid solute form or as a dry crystalline material.

In the case of molecular explosives, compound explosives (including plastic and sheet explosives) , TNT- based explosives, or RDX-based explosives, the precursor tag can be:

i) added during casting ii) added during mixing of bulk formulations intended to form plastic and sheet explosives, or iii) added to powdered molecular or compound explosive materials that will subsequently pressed or cold cast into pellets or into complex shapes .

Examples of complex shapes include rocket propellant grains for rocket motors or presses shaped charged warheads .

Examples of bulk formulations are mixtures of the explosive (eg RDX) , polymer (eg polyisobutylene) and plasticiser .

In the case of plastic and sheet explosive, the precursor tags can be added to RDX or PETN prior to heating and addition of plasticisers . RDX refers to cyclotrimethylenetrinitramine, a nitroamine, and PETN to pentaerythritol tetranitrate. As water is driven off, the precursor tag (preferably non hygroscopic and non reactive with any other ingredient prior to detonation) is incorporated through a doughy/rubbery mass of explosive, prior to sheeting or cartridging.

The amount of the precursor tag incorporated into explosive composition should be such as to enable post detonation detection of the corresponding luminescent tag through luminescence spectroscopy. In general, an amount of about 2% by weight or less of the precursor tag is added to the explosive composition. Preferably, the amount is 1% by weight or less of the composition. More preferably, the precursor tag is present at a minimum amount of 0.01% by weight, although the minimum amount may

more suitably be more than 0.1% by weight. Preferably, the amount present is a "trace detectable" amount. This amount refers to an amount of precursor tag which, when converted into a luminescent material on detonation of the explosive, is not optically detectable in the presence of ambient light, but is detectable in luminescence spectroscopy.

Examples

The present invention will now be described in further detail with reference to the following examples of two embodiments of the invention.

Example A and Control

A 20Og mass of "Powergel Magnum" explosive (an ammonium nitrate-based commercial emulsion explosive manufactured by Orica Explosives Pty Ltd) was dosed with 1% by mass of a precursor tag consisting of a selected combination of rare earth metals in a selected ratio, in oxide form. The precursor tag has no inherent fluorescence (luminescence), but transforms, or is activated, into a luminescent (fluorescent) tag having a characteristic fluorescence spectrum on detonation, as demonstrated in the results that follow.

The precursor tag and Powergel Magnum were mixed by hand. This tagged explosive was packed into a plastic shaped charge container SC65 of 200g capacity.

Glass micro-spheres were mixed into the explosive in an attempt to reinstate some of the sensitising "hot spots" which are lost when the explosive was kneaded to incorporate the precursor tag. A 25 gram plastic explosive (PE4) booster was placed above the explosive.

The control was also a Powergel Magnum explosive, but this contained no tag. The control explosive was packed into a plastic shaped charge container - SC85 - of 40Og capacity. Other than the size and absence of a tag, the control was the same as Example A.

Example B

In Example B, 15Og of cyclotrimethylene trinitramine (RDX) (approx. 87.5% V.O.D. unconfined 7600 to 7800 m/s) , a plastic explosive ("PE4"), was used as the explosive composition. A 1% amount (1.5g) of the same precursor tag used in Example A was hand mixed with the explosive. The tagged explosive was packed into cylindrical plastic container.

Preparation Details for Witness Plates and Sampling Materials

Figure 1 illustrates the experimental set up to test the detection of the tags in the explosives.

Each tagged explosive was placed on an assembly of post-blast sampling materials, which included the following set-up, as illustrated in Figure 1:

[1] Plastic sheet (1 m ² )

[2] Hessian sandbag. The sand provides a large surface area to trap post detonation samples and decouples the explosive from the ground.

[3] Stainless steel wool placed in the sandbag. The steel wool provides a robust material to trap post detonation samples.

[4] Aluminium witness plate. The witness plate provides verification of detonation. The upper surface of the witness plate was stippled with a needle gun to provide a roughened surface and an increased

surface area for collection of post detonation samples .

[5] A shaped charge (in the case of

Examples A and the control example) or a cylindrical charge container (in the case of Example B) . - [6] Explosive fuel, which is tagged in the case of Examples A and B, and contains no tag in the case of the control example.

[7] Top.

[8] Nonel detonator.

Control

The control shot was fired at the commencement of the trial to verify detonation characteristics of PG Magnum when packed in shaped charge containers . Post detonation materials were collected for the control example.

Detonation of Examples A and B, and Sampling Post Detonation Materials

Post detonation products from charges containing the tagged explosive of Examples A and B, and the control example, were sampled on a base station detection unit.

After the shots were fired, the debris from the shot was examined to determine the "quality" of the explosive and a preliminary examination of the witness plate was carried out. The debris was bagged for subsequent examination in the field laboratory using a spectrofluorometer with a xenon lamp source, referred to as the Dl detector. The witness plate was placed in a separate bag to the other debris (plastic sheet, sand, steel wool and Hessian sandbag) . The Dl detector used in the field laboratory was operated in a continuous

"spectrofluorimeter-mode" to detect taggants in the debris .

Results

The results are presented in Table 1 and in Figure 2.

Table 1

CO

C CO CO

NJ m

CO

I m m

TJ ι- m

IO

Example A

A fluorescence spectrum of the witness plate following detonation of Example A was recorded using the Dl detector. The results of the spectrum appears in Figure 2A. The peak at 618nm and the satellites at approximately 590nm and approximately 700nm clearly indicate the formation of the luminescent tag that corresponds to the precursor added to the explosive composition.

Example B

On-site detection of the post-detonation debris following detonation of Example B did not give a clear reading for the presence of the luminescent tag. However, under laboratory conditions, the luminescent tag corresponding to the precursor tag used in Example B could be detected on both the witness plate and the sand from the sandbag. The fluorescence spectrum obtained using the Dl detector in the laboratory is shown in Figure 2B. In this spectrum the main peak can be clearly identified. The noise level precluded an unequivocal identification of the satellites in this spectrum.

Further explosive compositions that can be produced containing precursor tags are set out in Table 2 below.

Table 2

Conclusion

The results of the trial demonstrate that luminescent tags can be generated in situ during detonation of an explosive containing a precursor tag composition that is not luminescent.

Various modifications may be made to the Examples without departing from the spirit and scope of the invention.