Use of Nuclear and Non-nuclear Techniques for Humanitarian Demining and Explosives Detection
Technologies and systems for non-intrusive analysis of materials are vital tools for all Member States in their fight against terrorism and the smuggling of contraband. Because threats to national security are dynamic in type and scope, there must be continuous efforts to improve existing tools and to develop new ones for the detection of explosives and other threats. The focus of this meeting is on the use of nuclear based techniques for the detection of conventional explosives and other illicit substances, notwithstanding its relevance for the detection of nuclear/radiological materials.
It is estimated that more than 110 million active mines are a permanent threat in some 70 countries, resulting in about 2000 casualties per month, most of them being civilians. Using conventional technologies (metal detectors, dogs, prodding) the process of identifying landmines is a time consuming, expensive and extremely dangerous procedure. Mined areas are generally close to the battlefields, and are consequently heavily polluted by metal pieces from the explosions of different types of ordnance (an exploded ordnance results in more than 1000 small metal fragments). The presence of metal clutter produces a large number of false alarms in the metal detectors (MD) commonly used in de-mining. As a consequence, it is thought that there is a need for a technological breakthrough in this field to definitively solve the landmine problem.
Two major aspects of nuclear security concern the smuggling of explosives into a nuclear power plant, research reactor, or nuclear facility for purposes of sabotage, leading to significant releases and the exploration of novel techniques in detecting the illicit movement (across borders, from a facility or into a major public event) of nuclear material (Pu and U) which is difficult to detect from its gamma/neutron signal. The R&D in nuclear technology may be able to propose new approaches toward increasing nuclear security.
The illegal transport of special nuclear materials (SNMs) is generally regarded as a major terrorist risk. This is because a nuclear weapon set off in a populated area will have an extremely devastating, humanitarian, psychological as well as material effect. Special nuclear materials are difficult to detect because the gamma emissions are weak and the neutron emissions fall below the natural background beyond practical stand off distances. The consequences of a terrorist organization assembling and using such a weapon are enormous and cannot be overlooked. It is therefore important to be able to check the transport chain for SNMs.
Explosives detection and demining through the use of atomic/nuclear techniques has been the object of a number of studies over the last decade. Both fields of application include rapid data acquisition that utilizes high speed sensors which necessarily have a high false alarm rate. There is thus need for effective confirmation sensors. This is the area where nuclear technology can play an important role. A set of field tests on neutron based equipment has been recently performed under realistic conditions and the first results are available to the community. Nuclear based equipment dedicated to border monitoring has also been recently tested and preliminary results have been discussed.
Since the mid 1990s considerable funding and effort has been invested worldwide in order to develop new technologies for humanitarian demining with the aim of improving the productivity of present humanitarian demining methods while maintaining or increasing deminers’ safety. During this time there has also been considerable investment of military funds in new sensing technologies that in some cases could also be applied to mine action. In military demining the objective is to clear a minefield as fast as possible, and usually a clearance rate of 80% to 90% is accepted. Humanitarian demining, on the other hand, is more difficult and dangerous, as it requires the complete removal of all mines and the return of the cleared minefield to normal use. The change in the emphasis of the expected operational use of detection technology by military personnel from, for example, combat minefield breaching to peace-keeping and peace-building operations, has also seen military detection requirements move to some extent towards those expected for humanitarian demining. Metal detectors find objects containing metal by utilizing a time-varying electromagnetic field to induce eddy-currents in the object, which in turn generate a detectable magnetic field. Old landmines contain metal parts (e.g. the firing pin), but modern landmines contain very small amounts or no metal at all. Increasing the sensitivity of the detector to detect smaller amounts of metal also makes it very sensitive to metal scrap often found in areas where mines may be located. Furthermore, metal detectors, however sophisticated, can only succeed in finding anomalies in the ground without providing information about whether an explosive agent is present or not. One major problem in humanitarian demining is to discriminate between the environmental clutter and a landmine. Identifying and removing a harmless object is a time-consuming and costly process.
In fact one of the main problems of using a metal detector in a minefield is due to the very high “positive false alarm” rate that affects the overall effectiveness of mine clearance operations. This situation calls for more attention to be given to the development of appropriate technology for improving the performance in all areas of mine survey and clearance. Nuclear techniques based on neutron irradiation of mined areas can possibly fill the technological gap and give a contribution to greatly reduce the number of positive false alarms thus reducing the time needed for inspection and rendering the operations safer and faster.
There is perhaps a general disappointment that only a few of the new technologies have progressed quickly from research and development (R&D) to field use, although this understandable expectation was to be somewhat unrealistic. This could be explained by the fact that most of the R&D focused on the technology development and less on the complexity of the environmental and field use conditions. Moreover, the development costs, following the R&D chain from basic research towards prototyping, testing and production, have been underestimated. The need for substantially greater funding to take a functional prototype of humanitarian demining technology to field readiness (i.e. beyond the cost of developing the prototype in the first place) has been the reason why the largest majority of such projects came to a dead end at the laboratory stage and are not yet in the aim of an industrial development. Nevertheless in a number of laboratories and universities around the world efforts have been continued even in precarious funding conditions. The results of laboratory mockups of some sensors are now satisfactory and, in fact, a few nuclear probes have gone a step forward to a field demonstrator which represents the last step towards industrialization.
The use of advanced technology to track the movement of cargo and entry and exit of individuals is essential to the task of managing the movement of hundreds of millions of individuals, conveyances, and vehicles across international borders.
The threat of terrorist use of explosive devices, chemical, biological and radioactive agents has become realistic since the Sarin attack in the Tokyo subway system on March 20, 1995 and after the tragic events of September 11, 2001. The possibility of further attacks against civil populations is one of the most important issues on the international political agenda. In classifying terror actions, it is normally accepted to separate attacks against specific human targets from those against extended targets as Hotels, Embassies, Consulates or other public buildings. In attacks against well identified people, relatively small quantities of High Explosive (HE) material are effective. As an example few kilograms of RDX have been used at the Sheraton Hotel bombing in Karachi. In other cases, the quantity of explosives used can reach several hundreds of kilograms (400 kg in Istanbul, 800 kg in Nassirya (Iraq) against the Italian military base).
Consequently, it seems that a system effective in identifying Improvised Explosive Devices (IED) in order to protect critical infrastructures from vehicle born explosive attacks should be capable of identifying at least 10 kg of explosive, supposed to be concentrated in a single volume.
A scenario often evocated implies the use of the so called “dirty bombs”: a sizeable quantity of radioactive material detonated by conventional explosive and dispersed in the environment. Illicit trafficking of explosives and fissile material through the conventional commercial networks (air, maritime and terrestrial) therefore represents a real challenge to security for the future.
Manual and visual inspection of a large commercial payload at terrestrial borders (trucks), airports and seaports (containers) would not be a viable solution both from efficiency considerations and for legal reasons. The standoff inspection of cargo by means of imaging and analytical methods in an integrated system based on a sound technology to identify threat materials is then needed. A positive indication of an explosives threat from a sensor does not mean that an explosive is present. Standoff explosives detection must take into account more than the single sensor indication, because a system that depends on a single signal yields excessive false alarms. The intent of a system of orthogonal detectors is detection of an explosive when one is present and extremely few indications of an explosive when one is not present. In order to achieve this goal, careful system design is needed to resolve ambiguous sensor information. In addition, a system allows one to consider additional aspects such as mass of explosive, available sampling time, available response actions and times, and the role of human judgment in assessing effectiveness.
To design an effective standoff explosives detection system (explosives detection where physical separation puts individuals and valuable assets outside the zone of severe damage from the potential detonation of an explosive device) the following issues must be considered:
Neutron interrogation offers the possibility of measuring the elemental density of most elements in materials. Fast neutrons can be produced efficiently and economically by small accelerators or compact electronic neutron generators, making possible the use of neutron based techniques in field applications. With the use of "tagged" neutrons it is possible to determine the local distribution of elements inside the sample volume, or to inspect a precise element of volume (voxel) that has been identified as suspect. Secondary neutrons produced by the irradiation of the sample can be used, by means of multiplicity measurements or spectral analysis, to identify the presence of fissile materials in the inspected volume. Neutron based sensors operated in combination with imaging devices would yield information to be embedded into the conventional intelligence stream against smuggling. Such complex systems would satisfy the criteria described above for an effective contribution of technology to the needs of the fight against illegal and criminal activities across borders.
Several methods based on neutron induced reactions have been developed and a number of them have reached a good level of efficiency:
As for the issue of detecting explosives in the context of civil security, nuclear based technologies under development make the object of large R&D projects involving wide collaborations among academic as well as industrial partners. In a few cases neutron based devices have been thoroughly tested under realistic conditions in both portable and fixed installations. Some of the R&D on these components is the object of a CRP funded by the IAEA.
Role and Involvements of the IAEA
Being aware of the world wide landmine and explosives detection problem, the International Atomic Energy Agency has since 1997 been looking into the potential of nuclear techniques, mainly neutron-based, to tackle this issue.
At first a Coordinated Research Project (CRP) on “Application of Nuclear Techniques to Anti-Personnel Landmines Identification” was implemented during the period 1999-2003, the complete findings of which were published in 2004 in a special issue of the “Applied Radiation and Isotopes” Journal, Volume 61, Issue 1 (2004). In line with the recommendations at the CRP and its final RCM and taking into account the emerging potentials of utilizing neutron generators, a Technical Meeting on “Neutron Generators for the Detection of Explosives and Illicit Materials” was held in Vienna in June 13-16, 2005 (Working Material). The Technical Meeting report strongly recommended that the IAEA initiate a new CRP on “Neutron based Techniques for the Detection of Illicit Materials and Explosives”. This was started in 2005 with the focus on detection of quantities of explosives larger than 100 g and will be completed in 2010. A Technical Meeting on “Combined Devices for Humanitarian Demining and Explosives Detection” was held in Padova, Italy in November 2006 (IAEA Proceedings Series STI/PUB/1300). The focus of which was how to combining various nuclear and non-nuclear techniques. Experts recommended that the IAEA complete the ongoing efforts and encourage the realization of field tests to be autonomously organized by the participant Member States teams. Following the field tests, this Technical Meeting took place and gave the opportunity to Member States to present and share their results.