"No one can solve this problem alone, but together we can change things for the better." 

– Setsuko Thurlow
Hiroshima Survivor
June 6, 2016
Before the Day After: Using Pre-Detonation Nuclear Forensics to Improve Fissile Material Security
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Daniel H. Chivers, Bethany F. Lyles Goldblum, Brett H. Isselhardt, and Jonathan S. Snider

The next U.S. administration will face many daunting challenges, but none of these are likely to be as pressing as combating the threat posed by nuclear terrorism. Twelve years ago, experts identified “nuclear leakage” —the sale, theft, and diversion of nuclear weapons and weapons-usable fissile materials—as the highest priority in U.S. nonproliferation policy.[1]

Widespread proliferation of weapons-related information and technology in recent years means that the construction of a crude nuclear device is within terrorists’ reach if they are able to acquire sufficient weapons-usable fissile material and are adequately organized.[2]

A global campaign leading to unambiguous physical protection standards for states in possession of weapons-usable material, therefore, is urgently needed to prevent any leakage. Although expanding current tactical efforts such as the Cooperative Threat Reduction program might be helpful, it is unlikely to be sufficient. A more strategic approach is needed that would seek to ensure adequate minimum standards for nuclear security among all states. A movement toward broad adherence to appropriate security levels would benefit from using pre-detonation nuclear forensics to help locate and plug fissile material leaks. Greater sharing of nuclear forensics information and capabilities is necessary if the international community is to promote and enforce a new international norm stressing that fissile material accountability ultimately rests with states.

The Role of Forensics in Deterring and Preventing Nuclear Terrorism

Doing so would apply nuclear forensics in a way different than many security thinkers are now considering. The Domestic Nuclear Event Attribution program, launched by the Department of Defense in 2000, established the policy agenda for nuclear attribution that prevails today: nuclear forensics and attribution capabilities must be improved to assist in determining the state origin of fissile material used in a nuclear attack. By doing so, defense planners hope to patch the hole that terrorists punch in traditional nuclear deterrence strategies. Because terrorists do not control territory that can be held at risk and may be more than willing to die as long as they are able to carry out their initial attack, such deterrence strategies are inadequate today. U.S. defense planners have therefore sought to update traditional deterrence to new realities by threatening any state with retaliation should it be seen as participating in or abetting a nuclear attack.

This approach is supported by a wide spectrum of policymakers. Senate Foreign Relations Committee Chairman Joseph Biden (D-Del.) recently advocated that a nuclear forensics capability allows for “a new type of deterrence” and would “bring deterrence into the 21st century.”[3] Testifying before a House subcommittee in October 2007, Vayl Oxford, director of the Department of Homeland Security’s Domestic Nuclear Detection Office, explained that nuclear forensics “is a critical nuclear deterrence capability to demonstrate that we can hold perpetrators accountable and also to help find and prevent follow on attacks.”[4] Oxford’s testimony was an elaboration of President George W. Bush’s cryptic statement in October 2006 that the United States would hold North Korea “fully accountable” for any consequences resulting from Pyongyang’s transfer of nuclear weapons or materials.

Still, even an updated deterrent strategy simply may not be effective for some situations because it is not a means of thwarting terrorists from acquiring fissile materials or nuclear weapons, only from using them. Although some states could intentionally transfer nuclear weapons or materials to nonstate actors, others might be the victims of theft. Retaliating against a state that acted in good faith to prevent nuclear theft is not likely to be a productive response; cooperation is inclined to be a more prudent strategy in preventing follow-on attacks. Of course, it is likely that even a culpable state will declare that the fissile materials used in a terrorist attack were stolen. Given this, some policymakers have suggested shifting the burden of proof so that any country that claims theft will be held accountable in a manner similar to a state that is believed to have directly transferred fissile material.[5]

A deterrent strategy supported by post-detonation nuclear forensics does not make explicit the actions states must take to ensure adequate nuclear security, nor does it take full advantage of the ability to use nuclear forensics to prevent terrorists from acquiring nuclear material. To be sure, those affiliated with the Nuclear Smuggling International Technical Working Group have labored for several years to implement pre-detonation nuclear attribution to prosecute illicit material traffickers.[6] However, a comprehensive strategy must also hold states accountable to their international obligation for adequately securing weapons-usable fissile material. Pre-detonation nuclear forensics can play an important role in this regard.

Speaking at a diplomatic conference, Linton Brooks, the former head of the National Nuclear Security Administration, pressed that states must accept full “sovereign responsibility over activities under their jurisdiction and control—whether that is trade and border controls or regulation of nuclear materials or nuclear facilities that are in conformance with international regimes.”[7] Adequately securing weapons-usable fissile material is among the foremost sovereign responsibilities of states. Poor security of these materials can be revealed by a nuclear terrorist attack or loose fissile material. Credibly holding states responsible in either of these instances rests on using nuclear forensics capabilities to determine the likely source of nuclear materials. These capabilities rely on scientists’ ability to distinguish material formed through different processes and in different parts of the world.[8]

Pre-detonation nuclear attribution can be used to identify the state source of loose weapons-usable fissile material. If such material should escape a state’s control, the state should be forced to establish truly effective physical protection measures or face international condemnation and corrective action. Weapons-usable fissile material found outside of state control would present clear evidence that robust physical protection measures are not in place. Adequate physical protection should mean that all weapons-usable fissile materials remain under state control at all times.

In addition to determining the material’s source, ongoing nuclear attribution research could help identify the “last legal owner.” Determining the production source of fissile material may not be the most important finding for assessing accountability. Many states now possess fissile material produced by other states or could enrich as well as reprocess nuclear fuel purchased from producer states.

The Need for Performance-Based Physical Protection

How is the international community to be assured that a state’s physical protection standards are sufficient? Currently, the international community lacks clear, enforceable standards for the domestic physical protection of fissile material and facilities. This is troubling considering that more than 3,730 tons of fissile materials are stored under widely divergent national standards.[9] Despite several UN Security Council resolutions identifying loose fissile material as a threat to international peace and security, no specific physical protection standards exist.[10]

The Convention on the Physical Protection of Nuclear Material (CPPNM)[11] obligates states to meet certain standards for the protection of nuclear materials, but these largely relate to the international transport of materials. A 2005 diplomatic conference sought to address this deficiency via an amendment to the CPPNM in which states agreed that the “peaceful domestic use, storage and transport” of fissile material and nuclear facilities are subject to physical protection standards.[12] To date, only nine states have ratified the amendment, which requires adoption by two-thirds of the 136 CPPNM member states before it enters into force. Even if the amendment were adopted, its coverage would be incomplete as it does not apply to fissile materials and facilities used for military purposes. More than one-half of all fissile materials worldwide are stored in military stocks.

Growing concern regarding the poor security of fissile materials led to the passage of UN Security Council Resolution 1540, which mandates that all states establish and enforce “appropriate effective” physical protection and control measures relating to fissile materials. This qualitative standard of physical protection is unfortunately subject to multiple interpretations.[13] In a UN Security Council meeting prior to the passage of the resolution, the United Kingdom’s representative explained that the resolution “leaves up to Member States to decide exactly what steps they need to take.”[14] This status quo is simply insufficient in combating contemporary threats, and some suggest has even failed.[15] Several incidents of loose fissile material following the passage of Resolution 1540 in 2004 suggest that physical protection remains a serious problem.[16]

The International Atomic Energy Agency (IAEA) plays an important role in protecting fissile materials from terrorists. It provides guidelines for states inexperienced with physically protecting nuclear facilities, but such guidelines are only recommendations and not binding.[17] George Bunn recently suggested that the IAEA should play a greater role verifying state compliance with Resolution 1540,[18] recommending that IAEA inspectors check the adequacy of a state’s physical protection measures during their routine inspections. It is difficult to see how a state would permit a direct external review of its nuclear security practices absent any clear indication of gross security infractions. An indirect technical review of a state’s nuclear security measures, where nuclear forensics helps identify states with a nuclear leakage problem through attributing loose fissile material, may lead states to request IAEA assistance in reviewing their practices to avoid future leaks.

Experts at Stanford University recently argued the need to go beyond Resolution 1540’s reporting requirements.[19] They propose a series of questions, termed “implementation indicators,” to vigorously assess how states are implementing their Resolution 1540 obligations. This involves garnering additional information from states regarding their overall systemic approach to material security, including law enforcement capabilities and the effectiveness of accounting measures, among other metrics. Nonetheless, this constructive suggestion is likely not enough. Moving forward, a more quantifiable standard is required to assess the effectiveness of actions states are taking to protect fissile material. Although the Stanford team does not make the recommendation in its report, nuclear attribution would constitute the ultimate implementation indicator.

Building an International Nuclear Forensics Capability

The ability to determine the source of interdicted fissile material or material collected after any attack inherently relies in part on the robustness of information previously collected and stored in a materials database. In other words, source attribution requires reference data against which to compare the characteristics of any sample material. Calls for the development of an international database of fissile materials mainly refer to voluntary submission of materials by states to a central repository. A comprehensive global catalogue of fissile material, including sensitive information about weapons-grade material, would constitute the ideal deterrent.[20] Figure 1 (see print edition) depicts a scheme for dividing nuclear forensic signatures and data into at least two classes, sensitive and nonsensitive information, to aid in classification within states and to encourage and control sharing between partner countries.

Full realization of a comprehensive database is highly unlikely, as states will resist voluntarily sharing such data. Although some useful data can be collected involuntarily,[21] movement toward sharing nonsensitive information is important in building a nuclear forensics database in the near term. Broad access to such data would generate more manageable levels of analytic uncertainty than currently exist. U.S.-Russian cooperation on nonsensitive information sharing would pave the way for wider disclosure. The onus for leadership rests with these two states, as the in-country stocks of separated plutonium and both separated and irradiated highly enriched uranium under Russian and U.S. control amount to nearly 87 percent of the global total.[22] Catalogued information from these two states alone would constitute a sizeable database.

Several states, including Russia and the United States, and international organizations such as the European Commission’s Joint Research Centre and the IAEA maintain independent inventories of commercial nuclear material samples, safeguards data, and information on seized illicit materials that could be leveraged to make an attribution finding if voluntary state submissions to a central database remain unlikely. Bush’s threat to hold North Korea “fully accountable” was reportedly made public because its credibility rested on the U.S. ability to access the IAEA’s collection of North Korea’s fissile materials.[23] Catalogued materials can also be used to eliminate possible sources of leaks quickly. Discovery that a material does not belong to the United States or one of its allies may be as informative as an implicating result.

Domestic resistance to a centralized database of materials and their characteristics will likely be fierce. The United States may resist the idea of exchanging details or samples of domestic nuclear materials because of the asymmetric advantage it maintains by having such a high level of expertise in its nuclear complex. Any agreement to risk the exposure of this expertise would have to be outweighed by the gain in security the United States received through international collaboration. Still, a reassessment of the existing line drawn between sensitive and nonsensitive information is appropriate in today’s threat environment.

The creation of an international database of fissile material characteristics will necessarily involve a host of challenging procedural issues related to the veracity of catalogued materials. Some important questions remain unanswered. Who is to formally undertake analysis and authenticate any material collected for entry into the database? How is this analysis to be vetted so that the material’s characteristics can be confirmed? It is likely, depending on the sensitivity of the information ultimately collected and stored, that nuclear data will be shared selectively across the database’s participants. General identity characteristics of fissile materials are likely to be shared in a multilateral arrangement, whereas more detailed information would be reserved for bilateral review. The need for a domestic nuclear forensics board to be established has been effectively argued elsewhere.[24] Members of this board would be responsible for interpreting and debating the evidence collected and, more importantly, reaching formal attribution decisions.

Construction of an international nuclear forensics database presupposes agreements between states on the details of how the effort to collect material samples should proceed. These details are only beginning to be discussed among international scientists associated with the Global Initiative to Combat Nuclear Terrorism (GICNT) and the Nuclear Smuggling International Technical Working Group.[25] The GICNT, launched by Russia and the United States in 2006 to differentially address and aid in the detection, prevention, protection, and response components of U.S. national defense policy through international collaboration, is emerging as one possible mechanism, whereby participants agreed to “develop technical means to identify nuclear or radioactive materials that could be involved in a terrorist incident.” Despite the stated goals of the GICNT, the primary emphasis of its working agenda remains on detection and response. There is currently no nuclear forensics panel situated under the GICNT and no information in the public domain that suggests a major role for nuclear forensics under the GICNT. Just recently, though, the United States-Russia Working Group on Counterterrorism concluded a framework agreement for bilateral cooperation on nuclear forensics, but the details of this agreement are not clear.[26]

A core component of the ongoing foundational work required to build an international database is the standardization of nuclear forensics methods for various types of fissile materials, as well as attribution and related intelligence procedures. These efforts will require the formalization of protocols to transport, distribute, and analyze interdicted materials or collected debris following a nuclear detonation, so that testing and verification of the material can be accomplished as quickly as possible.

Building a robust technical attribution capability among a network of states is distinct from mechanisms that credibly communicate and act on attribution findings. Embedding aspects of the preventative global campaign proposed here under the aegis of a respected international institution will serve to legitimize any attribution finding and subsequent international action by providing a forum for interaction between states. The IAEA, with expertise in assisting states with nuclear security, is well positioned to aid in response when nuclear leaks are identified. Recent recommendations for the future of the agency to 2020 and beyond, commissioned by Director-General Mohamed ElBaradei, propose that the IAEA be given a precise mandate to confirm global nuclear material security standards fixed by member states.[27] ElBaradei has also supported the idea of his agency contributing to efforts to internationalize nuclear forensics and work directly with member states to construct an international database for nuclear material characteristics.[28]

Toward International Implementation

Efforts to implement this approach will likely be met with strong resistance by some states and strong support by those states who perceive that they may be the target of a nuclear terrorist attack. At a minimum, it is necessary to garner international consensus on clear and specific standards relating to the physical protection of fissile materials and elevate these standards to a formal legal obligation. Given that a sufficient amount of fissile material might be unaccounted for at present, national inventories of these materials must be taken to determine when strict state accountability should start. Those states with large fissile material stocks have an important stake and responsibility in taking this first step.

Several states voiced concern in the open debates preceding the Security Council’s adoption of Resolution 1540 that it would be used as a means to institute sanctions against states. France’s UN representative noted that some states were under the impression that they could be forced to implement certain measures. In response to these concerns, the British UN representative stated that “the draft [of Resolution 1540] was not about coercion or enforcement.… [T]he draft did not authorize enforcement action against State or non-State actors in the territory of another country. Any enforcement action would likely require new Security Council measures.”[29] This diplomatic history suggests states will strongly resist being held accountable for fissile material leaks.

Promoting state accountability of weapons-usable fissile material protection in all cases need not require explicit enforcement. Singling out a state for lax nuclear security may bring international condemnation. A “designated nuclear facility watch list” could be established under the auspices of the 1540 Committee, identifying nuclear facilities from which leaked fissile material was discovered outside state control. Placement on this list could entail substantial state fines or other appropriate measures. In instances of grave security infractions, the matter should be referred to the Security Council.

Specific resistance is also likely considering that some states with a history of poor fissile material security, such as Russia, may feel as if they are being targeted. Experts tracking recent incidents of loose fissile material assert that the majority of interdicted material to date is of Russian origin.[30] Yet, an adverse Russian reaction might be tempered for several reasons. If Russia considers itself vulnerable to a nuclear terrorist attack, as suggested by its leadership role in the GICNT, then it would be prudent to support more robust preventative measures. In addition, as mentioned, Security Council resolutions identify loose fissile material as a clear threat to international peace and security.[31] It will be difficult for Russia not to take action against such a widely recognized threat, especially a threat the country has worked with the United States to address in the recent past.

An international scheme outlining state accountability of weapons-usable fissile material could be crafted to give wide deference to any state in resolving issues associated with its own fissile material as long as the material remains within the state’s jurisdiction. Consequently, appropriate international action would not be triggered until fissile material escapes a state’s jurisdiction. The 2005 International Convention for the Suppression of Acts of Nuclear Terrorism serves as a model for this sort of arrangement.[32] It gives states broad latitude in managing domestic terrorist threats before such threats can be characterized as “international,” thereby constituting a violation of the convention. Until then, the matter remains an issue to be resolved through domestic law enforcement. At a minimum, any domestic efforts pertaining to loose fissile material should generate a requirement to report such matters.

The dire international consequences of an unattributed nuclear detonation anywhere in the world are clear motivation for all countries to work together to prevent such a tragedy. It is unsettling that many states view loose fissile material as a significant threat to international peace and security but continue to take no specific global action to address this hazard. Present tactics do not constitute an adequate long-term approach to preventing a nuclear terrorist attack, and immediate action should be taken to establish clear international standards regarding the physical protection of fissile material. The new international standard to be pursued is clear and simple: all weapons-usable fissile materials are to be under state control at all times. This standard can be supported and enforced by the promise of pre-detonation nuclear attribution. Moving forward, the policy proposal outlined here is not intended to replace a policy to deter nuclear terrorism but to complement it. Locating and plugging fissile material leaks will demonstrate the strength of existing capabilities and work to ensure that the government need never implement its response the day after a nuclear explosion.

Daniel H. Chivers is an assistant research scientist and Bethany F. Lyles Goldblum is a postdoctoral scholar in the Department of Nuclear Engineering at the University of California-Berkeley. Brett H. Isselhardt is a doctoral candidate in the Department of Nuclear Engineering at the University of California-Berkeley and a Lawrence scholar at Lawrence Livermore National Laboratory. Jonathan S. Snider is a doctoral candidate in the political science department at the University of California-Davis and an associate in the Institute on Global Conflict and Cooperation’s Public Policy and Nuclear Threats program. The views expressed herein are solely those of the authors and not those of the U.S. government, the Department of Energy, or Lawrence Livermore National Laboratory.

Differentiating Nuclear Materials From Around the World

Fissile material designed and manufactured in different countries, even different facilities and batches, will have distinct atomic and nuclear signatures. Certain fissile material characteristics, such as isotopic composition and concentration of neutron-absorbing isotopes, for example xenon-135 (“neutron poisons”), are precisely controlled because of their significant effect on the ability to sustain a nuclear chain reaction within the material. Other contaminating materials are less tightly controlled because they do not hinder the intended function of the material. The design choices to control certain parameters and neglect others are utilized by nuclear forensics techniques to determine a material’s source.

Several methods may exist for creating a given end product, and each process will leave its imprint within the nuclear material of interest in the shape or form of the material (morphology), trace contaminants, or even small but detectable changes in the relative abundance of important isotopes (isotopic fractionation). In addition to these process differences, the indigenous environment of the raw material may also leave a lasting impression. Isotope abundances for stable elements, such as oxygen and lead, have detectable composition differences around the world. Other materials from differing parts of the globe also will be composed of starting materials that vary in measurable ways.

Finally, another method for distinguishing nuclear materials, even from the same facility or process, is known as age dating. Once nuclear material has been produced or purified, the radioactive decay process continues within the material, generating a chain of decay products that when analyzed in conjunction, form an intricate stopwatch of a material’s age.




1. Graham T. Allison et al., Avoiding Nuclear Anarchy: Containing the Threat of Loose Russian Nuclear Weapons and Fissile Material (Cambridge: MIT Press, 1996), p. 2.

2. Matthew Bunn and Anthony Wier, “Terrorist Nuclear Weapon Construction: How Difficult,” Annals of the American Academy of Political and Social Science, Vol. 607 (September 2006), p. 133.

3. Senator Joseph Biden, “CSI:Nukes,” The Wall Street Journal, June 4, 2007, p.A17..

4. Vayl Oxford, Statement before the House Homeland Security Subcommittee on Emerging Threats, Cybersecurity and Science and Technology, Hearing on H.R. 2631, The Nuclear Forensics and Attribution Act, October 10, 2007.

5. Joseph Biden, “CSI: Nukes.”

6. Sidney Niemeyer and David K. Smith, “Following the Clues: The Role of Forensics in Preventing Nuclear Terrorism,” Arms Control Today, July/August 2007, pp.14-15.

7. Linton Brooks, Remarks prepared for IAEA International Conference on Nuclear Security, London, March 15, 2005.

8. William Dunlop and Harold Smith, “Who Did It? Using International Forensics to Detect and Deter Nuclear Terrorism,” Arms Control Today, October 2006, pp. 6-10.

9. David Albright, “Global Stocks of Nuclear Fissile Materials: Summary Tables and Charts,” Global Stocks of Nuclear Explosive Materials, September 7, 2005.

10. UN Security Council Resolution 1373, S/RES/1373, September 28, 2001; UN Security Council Resolution 1540, S/RES/1540, April 28, 2004.

11. Convention on the Physical Protection of Nuclear Material, March 3, 1980.

12. “Summary Record of the First Plenary Meeting, Conference to Consider and Adopt Proposed Amendments to the Convention on the Physical Protection of Nuclear Material,” CPPNM/AC/Plen/SR.1, July 4, 2005, p. 1.

13. For a discussion of the distinction between qualitative and quantifiable obligations, see Rudolf Avenhaus and Nicholas Kyriakopoulus, “Conceptual Framework,” in Verifying Treaty Compliance: Limiting Weapons of Mass Destruction and Monitoring Kyoto Protocol Provisions, eds. Rudolf Avenhaus et al. (Berlin: Springer, 2006), pp. 17-21.

14. UN Security Council 4950th Meeting, S/PV.4950, April 22, 2004, p. 12.

15. Anne-Marie Slaughter and Thomas J. Wright, “Punishment to Fit the Nuclear Crime,” The Washington Post, March 2, 2007, p. A13.

16. “Combating Illicit Trafficking in Nuclear and Other Radioactive Material (Reference Manual),” IAEA Nuclear Security Series, No. 6 (2007), pp. 128-131.

17. “The Physical Protection of Nuclear Material and Nuclear Facilities,” INFCIRC/225/Rev.4 (corrected), 1998.

18. George Bunn, “Enforcing International Standards: Protecting Nuclear Materials From Terrorists Post 9/11,” Arms Control Today, January/February 2007, pp. 14-17.

19. Allen S. Weiner et al., “Enhancing Implementation of U.N. Security Council Resolution 1540,” Center for International Security and Cooperation, September 2007.

20. Michael May, Jay Davis, and Raymond Jeanloz, “Preparing for the Worst,” Nature, Vol. 443, No. 26 (October 26, 2006), pp. 907-908.

21. Interdicted loose fissile material can be used, once it is properly attributed, to assist in building the requisite international database even if states do not formally submit their material. This indirect means of building a fissile material repository provides incentives for states to participate directly in order to closely manage the distribution of information relating to their nuclear data.

22. Albright, “Global Stocks of Nuclear Fissile Materials.”

23. David E. Sanger and Thom Shanker, “U.S. Debates Deterrence for Nuclear Terrorism,” International Herald Tribune, May 7, 2007.

24. Jay Davis, “The Attribution of WMD Events,” Journal of Homeland Security, April 2003.

25. Tim Katsapis, Project on Nuclear Issues meeting, April 11, 2008; Niemeyer and Smith, “Following the Clues.”

26 “Fact Sheet: The United States-Russia Working Group on Counterterrorism,” U.S. Embassy, Moscow, June 20, 2008.

27. “Reinforcing the Global Nuclear Order for Peace and Prosperity: The Role of the IAEA to 2020 and Beyond,” GOV/2008/22-GC(52)/INF/4, 2008 (prepared by an independent commission at the request of the director-general of the IAEA).

28. Peter Zimmerman and Hans Binnendijk, “New Nuclear Deterrents,” The Washington Times, August 19, 2007.

29. UN Security Council Press Release SC/8070, April 22, 2004.

30. “Overview of Confirmed Proliferation-Significant Incidents of Fissile Material Trafficking in the NIS, 1991-2007,” CNS Report, 2007.

31. UN Security Council Resolutions 1373 and 1540.

32. “International Convention on the Suppression of Acts of Nuclear Terrorism,” UN General Assembly Resolution 59/290, April 13, 2005.