333 10 Unmasking the Illicit Trafficking of Nuclear and Other Radioactive Materials Stuart Thomson, Mark Reinhard, Mike Colella, and Claudio Tuniz CONTENTS 10.1 Introduction 334 10.1.1 The Nuclear and Radiological Terrorist Threat 334 10.1.2 Radioactive and Nuclear Materials 334 10.1.3 Categorization of Nuclear and Radiological Materials 335 10.1.4 Radiological Scenarios 336 10.1.5 The Illicit Trafficking of Radioactive Materials 338 10.1.6 The Role of Scientific Practitioners 339 10.2 Radiation Detection Strategies 339 10.2.1 Introduction 339 10.2.2 Radionuclides of Interest to Border Monitoring 340 10.2.3 Radiation Detection at Border Control Points 341 10.2.3.1 Gamma Ray Detectors 342 10.2.3.2 Stage One: Fixed Portal Monitors 344 10.2.3.3 Stage Two: Locating and Isolating the Source of Radioactivity 345 10.2.3.4 Stage Three: Isotopic Analysis 345 10.2.4 Masking of Illicit Materials 346 10.2.5 Other Types of Detectors 346 10.2.5.1 Neutron Detectors 346 10.2.5.2 Radiation Pagers 346 10.3 Nuclear and Radiological Forensics 347 10.3.1 Introduction 347 10.3.2 At the Scene 348 10.3.2.1 The Investigation Team 348 10.3.2.2 Sample Collection 349 DK594X_book.fm Page 333 Tuesday, June 6, 2006 9:53 AM © 2007 by Taylor & Francis Group, LLC 334 Radionuclide Concentrations in Food and the Environment 10.3.2.3 Sample Storage and Transportation 349 10.3.3 The Nuclear Forensics Laboratory 350 10.3.3.1 Introduction 350 10.3.3.2 Imaging Techniques 352 10.3.3.3 Bulk Analysis 355 10.3.3.4 Particle Analysis 359 10.4 Conclusion 360 References 361 10.1 INTRODUCTION 10.1.1 T HE N UCLEAR AND R ADIOLOGICAL T ERRORIST T HREAT In the last 15 years we have seen vast changes in the worldwide political land- scape. The end of the Cold War and the subsequent dissolution of the Soviet Union saw a reshuffling of international alliances and the disintegration of former political ties. With the end of the Cold War, many envisaged a new world order and hoped security would be rooted within the United Nations. Clearly, this has not occurred. The reawakening of ethnic and religious tensions and the exacerbation of global socioeconomic issues are causing conflicts in a number of critical regions of the world. One phenomenon of particular concern is the upsurge in global terrorist activity. The appalling events of the Tokyo subway attack (1995), Okla- homa City bombing (1995), September 11 attacks (2001), Bali bombings (2002), and recent attacks in Madrid, Russia, and Jakarta (2004) exemplify the consid- erable threat small, well-organized groups can pose to the safety of a civilian population. Moreover, these events show that terrorism is fast becoming a con- siderable threat to global security. While terrorist groups continue to use primarily conventional weapons to conduct their operations, there is concern that several may be considering the use of radiological weapons [1,2]. Relevant to this discussion are both nuclear (fis- sionable) and other radioactive materials, which although disparate in terms of their potential to cause destruction, are both of increasing concern to the world- wide community. 10.1.2 R ADIOACTIVE AND N UCLEAR M ATERIALS Radioactive materials may be either naturally occurring or anthropogenic (man- made). Naturally occurring radioactive materials (NORMs) include isotopes pro- duced via the uranium series, the actinium series, and the thorium series, and the low-abundance isotope of potassium, 40 K. Besides the NORMs of primordial origin, there is a very weak (but measurable) concentration of natural radio- nuclides, such as 3 H, 14 C, and 10 Be, produced by nuclear reactions of highly energetic cosmic rays. Anthropogenic radioactive materials are produced via appropriate nuclear reactions. Examples include the production of 60 Co via neutron capture in a DK594X_book.fm Page 334 Tuesday, June 6, 2006 9:53 AM © 2007 by Taylor & Francis Group, LLC Illicit Trafficking of Nuclear and Other Radioactive Materials 335 nuclear reactor and the production of 18 F in a medical cyclotron via the (p,n) reaction. Many anthropogenic short-lived isotopes are commonly used in indus- trial and medical applications. Nuclear materials form a special subset of radioactive materials. In addition to being radioactive, nuclear materials can undergo nuclear fission. The two most important nuclear materials from the point of view of weapons manufacture, and therefore nuclear safeguard controls, are enriched uranium and plutonium. 10.1.3 C ATEGORIZATION OF N UCLEAR AND R ADIOLOGICAL M ATERIALS The International Atomic Energy Agency (IAEA) classifies radioactive materials into five separate categories: unirradiated direct use nuclear materials, irradiated direct use nuclear materials, alternative nuclear materials, indirect use nuclear materials, and radioactive sources [3]. Unirradiated direct use nuclear material does not contain substantial quantities of fission products and can be readily used to construct a nuclear weapon or improvised nuclear device (IND) [3]. This is primarily because these materials require little or no further processing. Examples of such materials are highly enriched uranium (HEU), containing the isotope 235 U at a concentration greater than 20%, or plutonium containing less than 7% 240 Pu [3]. Irradiated direct use nuclear materials contain substantial quantities of fission products and require further processing to produce materials capable of being used to fabricate a nuclear device. Irradiated direct use nuclear materials can be found in spent reactor fuels [3]. Alternative nuclear materials include radionuclides such as 241 Am and 237 Np, which are fissionable and may have the potential to be used in a nuclear device [3]. Indirect use materials are those that require significant processing to enable them to be used in a nuclear weapon. Examples of indirect use materials include uranium containing 235 U in quantities less than 20% and plutonium containing 238 Pu in quantities greater than 80% [3]. The processing of such material is technically challenging and requires specific facilities and expertise. Hence indi- rect use nuclear materials pose less of a threat than direct use materials. Radioactive sources is the classification given to nonfissionable radioactive materials. These sources are used in industry, medicine, agriculture, research and education. The IAEA classifies radioactive sources based on the risk they pose to health [4]. Table 10.1 details the nomenclature typically used to categorize nuclear and radioactive materials. There is no separate international classification system to categorize materials according to the potential for malevolent use, however, parameters to consider include those based on the radiological hazards, in addition to issues related to portability, dispersability, and the potential for theft. Table 10.2 details the results of a Monterey Institute of International Studies report commissioned to determine the radioactive materials that pose the greatest risk to public health and safety, focusing on the potential consequences of their malevolent use [5]. More detailed guidance on the categorization of nuclear material is available from the IAEA [3,4]. DK594X_book.fm Page 335 Tuesday, June 6, 2006 9:53 AM © 2007 by Taylor & Francis Group, LLC 336 Radionuclide Concentrations in Food and the Environment 10.1.4 R ADIOLOGICAL S CENARIOS In recent publications, four mechanisms by which terrorists can exploit current nuclear and radioactive stockpiles and obtain suitable weapons have been dis- cussed [1,6]. The mechanisms are • The theft and detonation of an existing nuclear weapon. • The theft or purchase of fissile material for the purpose of manufac- turing and detonating an IND. • Attacks on nuclear facilities leading to widespread release of radioactive material. • The illegal acquisition of radioactive materials for the manufacture of either a radiological dispersal device (RDD) or a radiation emission device (RED). TABLE 10.1 The Categorization of Nuclear and Other Radioactive Materials: Examples of Materials and Their Application (Adapted from IAEA [28]) Category Type of Material Examples of Radioactive Isotopes Unirradiated direct use nuclear material Highly enriched uranium (HEU) >20% 235 U Plutonium and mixed uranium/plutonium oxides (MOX) <80% 238 Pu 233 U Irradiated direct use nuclear material Irradiated nuclear fuel material In irradiated nuclear fuel Indirect use nuclear material Depleted uranium (DU) <0.7% 235 U Natural uranium (NU) 0.7% 235 U Low enriched uranium (LEU) >0.7% 235 U and <20% 235 U Plutonium ( 238 Pu) >80% 238 Pu Radioactive sources Category 1 (most dangerous) Thermoelectric generators 238 Pu and 90 Sr Irradiators/sterilizers 60 Co and 137 Cs Teletherapy sources 60 Co and 137 Cs Radioactive sources Category 2 Industrial γ radiography 192 Ir High/medium dose rate brachytherapy 103 Pd, 60 Co, 137 Cs, and 125 I Radioactive sources Category 3 Fixed industrial gauges 60 Co, 137 Cs, 241 Am Well logging gauges 241 Am, 137 Cs, and 252 Cf Radioactive sources Category 4 Thickness/fill level gauges 241 Am Portable gauges (e.g., moisture, density) 137 Cs and 60 Co Radioactive sources Category 5 (least dangerous) Medical diagnostic sources 131 I Fire detectors 241 Am, 238 Pu DK594X_book.fm Page 336 Tuesday, June 6, 2006 9:53 AM © 2007 by Taylor & Francis Group, LLC Illicit Trafficking of Nuclear and Other Radioactive Materials 337 The first two scenarios relate to the detonation of a nuclear device, while the latter scenarios relate to the use of radioactive materials to impart a radiation dose to a civilian population and contaminate an area and its inhabitants with radioactive material. The detonation of a nuclear warhead or an IND within a city would result in a significant loss of life, loss of buildings and infrastructure, and would have an enormous environmental and economic impact. Civilians who survive the blast would endure both short- and long-term health effects due to radiation exposure [1]. Although this scenario is the most devastating, it is considered the most unlikely due to the high security most states use to guard their nuclear stockpiles [1]. The technical requirements in manufacturing a nuclear device are significant and require considerable infrastructure, expertise, and financial resources. While some commentators do not see these hurdles as insurmountable to terrorists, it is generally accepted that the most likely method by which terrorists could obtain nuclear material and technical information would be via existing state-owned facilities [1]. For this reason, the proliferation of nuclear materials, particularly in the last 15 years, has been a great concern to the international community, as it may increase the probability of such technology falling into the wrong hands [7,8]. An attack on a nuclear facility is a means by which terrorists could expose the public to radiation and cause contamination of the surrounding area. However, all states require strict security for such facilities, particularly larger establish- ments such as nuclear power plants. The large structural mass surrounding a reactor core would facilitate the need for a large catastrophic event to cause a reactor core breach. With this in mind, it would be extremely difficult for terrorists to achieve such a feat. Nonetheless, some of the latest reactor construction TABLE 10.2 Radioactive Sources of Greatest Concern (Adapted from Ferguson et al. [5]) Isotope Common Use Form Half-Life Emissions 137 Cs Teletherapy, blood irradiations, and sterilization facilities Solid, chloride powder 30.1 yr β and γ radiation 60 Co Teletherapy, industrial radiography, and sterilization facilities Solid, metal 5.3 yr β and γ radiation 192 Ir Industrial radiography and low dose brachytherapy Solid, metal 74 days β and γ radiation 226 Ra Low dose brachytherapy Solid, metal 1600 yr α and γ radiation 90 Sr Thermoelectric generators Solid, oxide powder 28.8 yr β radiation 241 Am Well logging, thickness, moisture and conveyor gauges Solid, oxide powder 433 yr α radiation 238 Pu Heat sources for pacemakers and research sources Solid, oxide powder 88 yr α radiation DK594X_book.fm Page 337 Tuesday, June 6, 2006 9:53 AM © 2007 by Taylor & Francis Group, LLC 338 Radionuclide Concentrations in Food and the Environment techniques are incorporating extra security measures to further limit the possi- bility of a successful terrorist attack. The final terrorist scenario listed involves the use of an RDD or RED. This scenario is deemed the most probable form of terrorist attack. This is because many radionuclides are widely used in medicine, industry, and science and are accessible to criminals and terrorists [9]. An RDD requires radioactive material that is capable of dispersal into the surrounding environment. The resulting contamination would present a potential health hazard and would require signif- icant decontamination to be undertaken. An RED works primarily by stealth and utilizes a radioactive source to expose potential victims to radiation. A source placed in a location where it can impart a dose to a target may go undetected for long periods. While the use of either an RDD or RED is considered the most plausible terrorist act, the consensus is that such acts would generally result in a small number of immediate deaths [9]. The benefit to terrorists using such a device is the disruption it is likely to cause. A device used in a city is likely to result in hysteria from the public, based on the fear that they may have been exposed to radiation [1]. In the case of an RDD, the consequent contamination from such a device would take considerable time to clean up, resulting in long- term evacuation of the area, which is likely to have significant economic and social impacts [1,9]. Protecting and accounting for both nuclear and other radioactive materials is a major concern of the international community and there have been significant efforts to modernize physical protection and accounting systems throughout the world [9]. Individual states and international organizations have also been pro- viding both technical and financial support to less wealthy nations. One example is the recent commitment of the G8 group of nations to provide US$20 billion over 10 years to help former Soviet Union states manage and secure their radio- active materials [6]. However, the problem of securing radioactive materials is a worldwide dilemma. In the past, many security measures applied to nonfissionable radioactive sources aimed to prevent accidental access or petty theft of the sources [10]. Any thought of terrorists using radionuclides as weapons were not persuasive enough to enforce a move to more regulated systems. While many states are now acting to address this issue, there still exist many thousands of unaccounted for sources worldwide. These sources are termed “orphaned sources,” an expression used by the IAEA to denote radioactive sources that are outside official regulatory control, which may have been lost, discarded, or stolen [4]. Therefore orphaned sources represent potential weapons for terrorists. 10.1.5 T HE I LLICIT T RAFFICKING OF R ADIOACTIVE M ATERIALS Since 1993 there have been 540 confirmed cases (Table 10.3) of illicit trafficking of nuclear and radioactive materials registered on the IAEA’s illicit trafficking database [11]. The majority of the confirmed incidents involved some form of criminal intent. This figure most probably represents a conservative estimate of the true problem, and there are growing concerns that more organized and sophisticated DK594X_book.fm Page 338 Tuesday, June 6, 2006 9:53 AM © 2007 by Taylor & Francis Group, LLC Illicit Trafficking of Nuclear and Other Radioactive Materials 339 trafficking of radioactive materials may be occurring undetected [12]. These figures illustrate the need for comprehensive programs worldwide to both secure existing sources and to recover orphaned sources. 10.1.6 T HE R OLE OF S CIENTIFIC P RACTITIONERS The need to develop strategic programs aimed at preventing, recovering, and responding to terrorist acts involving nuclear and other radiological materials requires a high level of involvement from the scientific community. The utilization of existing technology and the development of improved methods of detection and characterization are required to ensure the security of all radioactive materials. For the purposes of this discussion, the primary focus will be on some of the scientific methods and procedures currently used to track illicit radioactive mate- rials. Of particular relevance are the fields of radiation detection and analytical techniques used for nuclear and radiological forensic science. 10.2 RADIATION DETECTION STRATEGIES 10.2.1 I NTRODUCTION The use of radiation detectors to identify the presence of radioactive materials is essential to any program aimed at minimizing the potential threat that such materials may pose. In recent years there has been significant interest in the development of new radiation detector strategies for uncovering radioactive mate- rials. These strategies range from the development of “simple to use” radiation detection devices for emergency responders to the development of new detector systems that give detailed information on relevant radionuclides and their quantities. In developing these new capabilities, the scientific community has become more closely involved with agencies such as law enforcement, fire, medical, and customs [13–15]. Clearly the operational needs of each agency involve the use of different instrumentation and strategies, requiring both instrument companies TABLE 10.3 Confirmed Incidents Involving Illicit Trafficking of Nuclear Materials and Radioactive Sources By Participating Member States Illicitly Trafficked Material Confirmed Incidents (1993 to 2003) Nuclear material 182 Other radioactive material 300 Nuclear and other radioactive material 23 Radioactively contaminated material 30 Other 5 DK594X_book.fm Page 339 Tuesday, June 6, 2006 9:53 AM © 2007 by Taylor & Francis Group, LLC 340 Radionuclide Concentrations in Food and the Environment and scientists to become more conscious of the challenges that each of these agencies face. Another requirement is the need for distributing information about new detector technologies to user groups in a form that is easily interpreted and not overwhelmingly technical. The global need for solutions in this area also necessitates the sharing of any new capabilities or techniques between states. To this end, the IAEA has supported international technical initiatives to explore suitable technologies and novel solu- tions for user groups. (The relevant programs include the coordinated research project (CRP) “Improvement of Technical Measures to Detect and Respond to Illicit Trafficking of Nuclear and Other Radioactive Materials” and the “Illicit Trafficking Radiation Detection Assessment Program” (ITRAP), and the Inter- national Technical Working Group’s (ITWG) Nuclear Forensic Laboratories (INFL) program. These programs have enabled cooperative research to be under- taken, allowing the pooling of available knowledge and resources. Much of the focus of recent detector research has been on the development and implementation of instrumentation for international border monitoring. Exam- ples include [13] fixed, automated portal monitors; personal radiation detectors (PRDs); handheld /neutron detectors; and multipurpose handheld radioisotope identifiers. Much of today’s detection equipment is based on well-established technology developed to meet the needs of the scientific and industrial commu- nities. Evidently the ability to use existing “off-the-shelf” technology is attractive, as it has enabled the relatively quick distribution of hardware in response to the heightened security threats following the terrorist attacks of recent years. Two drawbacks to this approach are evident. The first is that many of the off-the-shelf instruments are not optimized to address the needs of border monitoring agencies. Second, a rush to deploy existing radiation detection instruments has failed to address more strategic questions concerning the detection of radioactive materials at border control points. Part of the solution to providing the best instrumentation and detector strategies is to design equipment to suit the required applications of user agencies. 10.2.2 R ADIONUCLIDES OF I NTEREST TO B ORDER M ONITORING Of the thousands of radionuclides associated with NORMs or anthropogenic production, only a few are liable to be encountered by border monitoring staff. These materials include isotopes produced in significant quantities for designated applications in medicine or industry, and NORMs that are prevalent in many substances commonly traded (e.g., ceramics, stoneware, and fertilizers). The radionuclides of greatest interest, as determined by various agencies associated with the IAEA [13], are listed below: • Medical radionuclides: 18 F, 32 P, 51 Cr, 67 Ga, 90 Y, 99 Mo, 99m Tc, 111 In, 123 I, 125 I, 131 I, 133 Xe, 153 Sm, 198 Au, and 201 Tl. • Industrial or scientific radionuclides: 22 Na, 57 Co, 60 Co, 75 Se, 90 Sr, 133 Ba, 137 Cs, 152 Eu, 192 Ir, 198 Au, 207 Bi, 226 Ra, 238 Pu, and 241 Am. DK594X_book.fm Page 340 Tuesday, June 6, 2006 9:53 AM © 2007 by Taylor & Francis Group, LLC Illicit Trafficking of Nuclear and Other Radioactive Materials 341 • NORMs: 40 K, 226 Ra, 232 Th, and 238 U. • Nuclear materials: 233 U, 235 U, 237 Np, and 239 Pu. Neutron sources based on mixed radionuclides may also be encountered due to the widespread use of neutron emitters in mining and other underground gauging applications. These include mixed radionuclide neutron sources like 241 AmBe and 238 PuBe, in which the 241 Am and 238 Pu produce α particles that interact with beryllium via a (α,n) reaction to form neutrons. Visual identification is not a reliable means of identifying the presence of radioactive material. The most suitable method for measurement of emitted radi- ation is the use of dedicated radiation detection instrumentation employed in an appropriate manner. The majority of the radionuclides listed above have γ-ray emissions with energies between 50 keV and 3 MeV, which are measurable by most γ-ray spectroscopy instruments (notable exceptions are the pure β emitters such as 32 P, 90 Sr, and 90 Y). The measurement of γ-ray emissions relies on the transmission of photons through any packaging or shielding material (i.e., lead) placed around the radioactive material. Therefore the ability to detect the material depends on the type and quantity of shielding material surrounding the radioactive material, the type of radionuclides present, and the activity of the source. 10.2.3 RADIATION DETECTION AT BORDER CONTROL POINTS Border control points are strategic positions along regulatory control boundaries where customs agents can potentially monitor the movements of all people, trans- port vehicles, and goods through a defined transport corridor. Such points are there- fore ideal for monitoring and controlling the movement of radioactive materials. The techniques and strategies aimed at detecting the presence of radioactive materials in this context differ considerably from those found in the laboratory. Apart from the obvious requirement that the inspection procedures must reliably detect the presence of illicit radioactive materials, there are additional require- ments, including • The inspection system should not unnecessarily impede or disrupt the flow of general traffic. • The analysis is performed in real time in order to enable customs and law enforcement officers to act rapidly. • There should be the ability to deal with the wide variety of traffic that may pass through the corridor. In establishing a system that satisfies this somewhat competing set of criteria, a “staged” or “layered” approach is used. The first stage will typically employ a system for the gross detection of radioactive material. This would consist of an autonomously operated radiation detector system fixed in position along the transport corridor. All traffic passes by the fixed monitor, thereby allowing non- invasive testing for radioactive material. The detector would monitor changes in DK594X_book.fm Page 341 Tuesday, June 6, 2006 9:53 AM © 2007 by Taylor & Francis Group, LLC 342 Radionuclide Concentrations in Food and the Environment the ambient radiation level from that attributed to the local background. The system would alarm when levels exceeded a set threshold. An alarm would then initiate a personnel response that would confirm the alarm state. If confirmed, stage two would commence. The second stage of the detection strategy is to assess the radiological hazards and potential health risks to which an operator may be exposed and then locate the radioactive material. The assessment of radiological hazards is discussed extensively in a number of publications such as those prepared by the International Commission on Radiological Protection (ICRP) [16], the International Commis- sion on Radiological Units and Measurements (ICRU) [17], and the U.S based National Commission on Radiation Protection (NCRP) [18]. Locating the radio- active materials is the domain of handheld instrumentation. By scanning the instrument over the vehicle, cargo, or person, the location of the radiation can be determined. Once this has been performed, stage three would commence. The purpose of stage three is to identity the isotopes that are present in the sample. By measuring the γ-ray spectrum of the suspect sample and comparing it to a library of radionuclide spectra, the identity of the sample can be determined. Border monitoring staff can then determine if the source of the radiation is an innocent event, such as the sanctioned movement of an industrial radiography source, an inadvertent event, such as the presence of residual radioactivity within an individual having recently undergone a medical treatment with a radiophar- maceutical agent, or an illicit event, such as the intentional smuggling of radio- active material. At present, no single instrument is able to perform all the measurements required for stages one to three. Therefore, instrument selection is crucial to implementing an effective detection strategy within each stage. 10.2.3.1 Gamma Ray Detectors Advice for the selection and use of detector instrumentation, specifically for border monitoring applications, is detailed in a recent IAEA publication jointly sponsored by the World Customs Organization (WCO), European Police Office (Europol), and International Criminal Police Organization (Interpol) [13]. Similar information regarding detector instrumentation for measuring nuclear materials is also available from the IAEA [19]. The two most important properties of γ radiation detection instrumentation are the “detection efficiency” and the “energy resolution.” The detection efficiency relates to the sensitivity of the instrument at detecting radiation emitted by a source, while the energy resolution relates to the ability of the detector to accu- rately measure the energy of the detected radiation. The border control setting also introduces operational considerations that are not relevant in the industrial or scientific context. These additional considerations include factors such as the ease of use, as perceived by the nonexpert user, and instrument reliability criteria such as ruggedness and the ability to operate in adverse environmental conditions. DK594X_book.fm Page 342 Tuesday, June 6, 2006 9:53 AM © 2007 by Taylor & Francis Group, LLC [...]... of time of the measurement, and, in the case of a moving item, the speed of the item relative to the detector In general, the intensity of radiation at the surface of a detector is inversely proportional to the square of the distance of separation between the material and the detector (assuming the radioactive source is a point source) A doubling of the distance of separation will result in a fourfold... 6, 2006 9:53 AM 346 Radionuclide Concentrations in Food and the Environment 10. 2.4 MASKING OF ILLICIT MATERIALS Knowledge of the underlying deficiencies of radiation detection instruments and the inherent difficulties of γ-ray spectrometry can be exploited to circumvent the detection of nuclear and other radioactive materials The intentional use of lead or dense materials to shield the emissions of radiation... while the required approvals for transporting the samples to alternative locations are sought In either case, a temporary storage facility must be secure and meet the mandatory safety requirements needed to handle the level of radioactivity present within the samples Furthermore, the facility must have the required licensing or permits needed to store radioactive materials and must meet the chain-of-custody... ion sputtering a sample of interest The resultant negative ions produced from the sample are then accelerated in a tandem accelerator to energies in the megaelectron volt (MeV) range The negative ions then interact with a terminal stripper, which results in the loss of electrons The positively charged species are then accelerated a second time by the same potential The benefit of the terminal stripper... individual areas of a sample Information obtained from both imaging and electron diffraction can be used to determine the processing history of materials This information is highly valuable in providing clues for tracing the source of the material Excellent examples highlighting the use of the technique to analyze plutonium-bearing samples are detailed in recent review articles [23,42] 10. 3.3.3 Bulk Analysis... emission and mass spectrometry [44] In ICP-AES, the radiation emitted by the analyte is © 2007 by Taylor & Francis Group, LLC DK594X_book.fm Page 356 Tuesday, June 6, 2006 9:53 AM 356 Radionuclide Concentrations in Food and the Environment measured at characteristic wavelengths and this signal is used to identify and quantify the elements present In ICP-MS, the tail of the plasma is extracted into a low-pressure... ongoing development of mass spectrometers The development of multicollector ICP-MS (MC-ICP-MS) enables isotopes of interest, within the limits set by the mass analyzer, to be analyzed simultaneously rather than sequentially The use of a time-of-flight analyzer (ICP-TOF-MS) enables all isotopes to be analyzed simultaneously Both MC-ICP-MS and ICP-TOF-MS are proving to be valuable techniques for situations... 2006 9:53 AM 344 Radionuclide Concentrations in Food and the Environment unacceptably low signal:noise ratio Cooling of the detector is achieved in the laboratory using liquid nitrogen or electronic cooling devices In the field, the use of liquid nitrogen is restricted and in many cases not feasible Recently, however, HPGe-based detectors, cooled via electrically operated Stirling cooling cycles, have... used to determine the extent of the contamination and the establishment of cordon and control areas [14] The use of radiation detection equipment, as described earlier, is vital for locating and identifying the radioactive isotopes The objective of the crime scene expert is to collect evidence for analysis that may provide clues to the origin of the material Hence the radioactive material and related... of the detector and the conversion of this energy into a voltage pulse, the amplitude of which is proportional to the initial energy of the γ ray By sorting the voltage pulses according to the amplitude, a spectrum of different γ-ray energy intensities can be displayed Comparison of the spectrum against reference libraries enables identification of the radionuclides A variety of different types of γ-ray . Radionuclide Concentrations in Food and the Environment 10. 3.2.3 Sample Storage and Transportation 349 10. 3.3 The Nuclear Forensics Laboratory 350 10. 3.3.1 Introduction 350 10. 3.3.2 Imaging. LLC 346 Radionuclide Concentrations in Food and the Environment 10. 2.4 MASKING OF ILLICIT MATERIALS Knowledge of the underlying deficiencies of radiation detection instruments and the inherent. the detector, the length of time of the measurement, and, in the case of a moving item, the speed of the item relative to the detector. In general, the intensity of radiation at the surface of