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Nuclear Forensics

By Michael May

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Nuclear forensics is the technical means by which nuclear materials, whether intercepted intact or retrieved from post-explosion debris, are characterized (as to composition, physical condition, age, and other characteristics) and interpreted (as to provenance, industrial history and implications for nuclear device design).

Nuclear forensics has a long history. During the first fifty years of the nuclear era, nuclear forensics techniques were developed and used to determine the characteristics (such as yield, materials used, design details) of nuclear explosions carried out by the US and by other countries. That application can still come into play if a nuclear explosion is detonated and debris are recovered. But the principal emphasis today is on the application of nuclear forensics techniques to help attribute either intercepted materials or an actual explosion to its originators. This different emphasis places different and new requirements on the technical analysis. In particular, it makes the availability of databases and sample archives from various countries much more important than was the case when the principal application was diagnosing an explosion from a known source.

According to International Atomic Energy Agency (IAEA) data, there have been 1340 reported incidents of lost or stolen radioactive material intercepted between 1993 and 2007. Most of those have not been recovered. Among the material intercepted, a significant number involved highly enriched uranium (HEU) or plutonium, in amounts ranging from grams to hundreds of grams as shown in the picture above, also from IAEA data.

If intact material is recovered, the shape, surface finish, impurities, chemical and isotopic compositions, and other features can lead to identification of some of the industrial history of the material and identify its age since it was last chemically separated. While most plutonium-producing reactors and uranium enrichment facilities fall into a few generic types, individual facilities and processes used for uranium-rich materials differ in a number of potentially telltale details. Whole fuel elements have been recovered and identified and a number of other such identifications have been made.1

If a nuclear detonation of unknown origin takes place, analysis of the radioactive debris can again establish the age and point to the processes used to make the plutonium or HEU. In time, possible nuclear device designs can be inferred by using reverse engineering computer codes. The procedure used, obstacles and time pressure will of course be entirely different from the cases of interceptions of small quantities of material. The overall situation after a detonation and the location of the detonation, whether in the US or abroad, will determine a great deal of what can be done and on what time scale. Ash Carter, Bill Perry and the present author have delved into what would happen and what should happen the “Day After” a nuclear explosion in a city, in a report available on the web and in print.2

The two relatively most accessible places to collect debris from a nuclear explosion are from the fallout downwind from the detonation point and the radioactive cloud drifting with the prevailing winds. Sample collection from the crater will be very difficult for some period of time because high radioactivity will inhibit access to the crater. But even collection from the fallout area (which will need to take place at a number of sites since the materials of interest will not condense and fall uniformly) will require special precautions both for safety of personnel involved and to preserve evidence. Time in the high fallout area must be tracked and limited. Rapid transport suitable for transporting radioactive evidence must be available. All this will require coordination with the FBI, which would be in charge overall in the US, and with the federal and local agencies in charge of response and recovery. Collection of airborne debris requires specially equipped aircraft. Much of what would need to be done can be speeded up and improved. 

Nuclear forensics is part and parcel of the overall attribution process; it may be more or less helpful, depending on circumstances. One of the main features of attribution, including forensics, is that results are only available over time. This is not of great importance in cases of material intercepts, unless an entire weapon or material in amount sufficient for a weapon is intercepted, which has not happened. In the case of a nuclear detonation, this time delay and the uncertainties of the initial interpretations assume major political importance and there would be great pressure to obtain firm results to guide policy decisions as soon as possible. It is essential that mechanisms be in place to avoid wrong decisions. The only way to assure partially that those mechanisms will be in place is for the organizations and policy makers that would be involved to carry out realistic exercises that test coordination, operational readiness and that involve participation from the leaders that will have to make relevant attribution decisions.

Last year, a Working Group of the American Physical Society’s (APS) Panel on Public Affairs (POPA), in conjunction with the American Association for the Advancement of Science (AAAS) Center for Science, Technology and Security Policy, was charged to produce an unclassified report describing the state of the art of nuclear forensics, assessing its potential for preventing and identifying unattributed nuclear material intercepts and nuclear attacks, and identifying the policies, resources and human talent to fulfill this potential. The APS/AAAS Working Group report was released on February 16 of this year at the annual meeting of the AAAS in Boston. It is available at http://cstsp.aaas.org/content.html?contentid=1546 and includes the charter of the working group and the biographies of its members.

On the basis of the facts summarized above, the Working Group came to five recommendations.

R&D to Develop Advanced Lab and Field Equipment and Numerical Modeling: There is considerable room for improving the equipment that would have to be used following a nuclear detonation. Much of it dates to the Cold War. More up-to-date equipment would allow for more substantial early field measurements and more rapid and accurate laboratory analysis. A program should be undertaken to develop and manufacture advanced, automated, field-deployable equipment that would allow the necessary measurements to be made rapidly and accurately at a number of sites. Such field equipment is not now readily available. Advances in numerical simulations that provide design information are also needed.

Workforce Development: There are approximately 35-50 scientists working on nuclear forensics at the national labs, not enough to deal with an emergency. A number of them would be double-booked in case of a nuclear emergency. In addition, as things stand, the present numbers will not be maintained: some will move to other responsibilities and many will reach retirement age. Unless a new program is funded, some will not be replaced: the pipeline is nearly empty. A program to develop trained personnel should be undertaken that should include funding research at universities, graduate scholarships and fellowships, internships at the labs, and incentives that stimulate industrial support of faculty positions. The program should be sized to produce at least 3-4 new PhDs per year in the relevant disciplines for the first ten years, and to maintain skilled personnel level thereafter. Scientists with such training could also go into (and be drawn from) the related fields of geochemistry, nuclear physics, nuclear engineering, materials science, and analytical chemistry.

International Cooperation and Sample-Matching Database Development: Doing nuclear forensics on either intercepted or detonated material is inherently an international enterprise: the material (so far) has all come from abroad, key facilities, databases and sample archives are located abroad, the cooperation of other governments and government institutions is essential, and, in the event of a nuclear explosion, the radioactive cloud and fallout will go all over the world, so that many institutions abroad will analyze and interpret it. The US government should extend its ongoing initiatives to counter WMD terrorism to include provisions for prompt technical and operational cooperation in the event of a nuclear detonation anywhere in the world. Such cooperation should most importantly include enlarging and providing for prompt access to international and other databases and linking them electronically under suitable precautions to protect state and commercially sensitive information in normal times. The wider the participation in this effort, the more confident the processes of nuclear forensics will be. The present Global Initiative, co-chaired by the United States and Russia, could be a vehicle for undertaking this effort. The effort will involve the IAEA, which has much relevant data and capabilities. However desirable, the effort nonetheless will encounter a number of obstacles stemming from differing classification rules in different countries, commercial concerns over competitive advantage, and reluctance of some countries to release potentially compromising information. None of those obstacles in the view of most working group members constitute showstoppers, but the program must of necessity be considered a long-term one.

Exercises: Two types of exercises can be carried out: technical exercises, which test operational capabilities, coordination, communication and policies that would be needed at all levels of the organizations concerned in the event of a nuclear detonation anywhere in the world, and war-game types of exercises, structured to involve senior decision-makers in some approximation of what the real situation would be. To date, mainly technical exercises have been carried out. While no exercise can fully simulate the possibly chaotic situation that could prevail in the wake of a nuclear detonation in a city, nevertheless much can be done to make sure top-level leadership is prepared to promulgate realistic decisions in the areas of public health, foreign policy, and military action. Exercises should be structured so as to illustrate the strengths and limitations of nuclear forensics as well as to test capability and coordination in light of both the time-urgent needs of the situation and also the ability to communicate to the public and manage expectations.

Review and Evaluation Groups: Neither the ongoing program to deal with nuclear material intercepts, nor the ongoing exercises are made full use of from the standpoint of incorporating their lessons into the culture of the relevant organizations. In addition, to the working group’s knowledge, there is no expert panel to advise top level leadership of the meaning of developing events in case of an emergency. The US government should establish two groups: one to systematically review, evaluate and keep records of both the results of intercepts and the exercises recommended above; the other to advise the US government in real time on the results of nuclear forensics and what they mean in the event of an emergency. The second group would provide independent assessment of developing forensic and other technical information in case of a nuclear emergency. Its function would be somewhat similar to that of the Cold War Bethe Panel, which advised the US government as to the physical results of foreign nuclear tests and the implication of those results. Both groups should have international participation, as appropriate.

No one knows if a terrorist group is likely to set off a nuclear explosion. We know that there is a black market in nuclear weapons materials. We know that there are huge quantities of these materials stored in the United States, Russia, Pakistan and other countries, and we know that the security in many cases is not as good as it could be. We know that a small crew that includes some specialists and has some time in a protected location could assemble a primitive nuclear weapon from stolen or otherwise acquired materials, and we know that the weapon could be transported in a small truck. A terrorist group would encounter many obstacles–guards, border crossings, intelligence operations from several countries, technical countermeasures, but a nuclear detonation is possible. We believe the recommendations made above would improve US ability to deal with it. A strong international program aimed at strengthening forensics capabilities may also help dissuade a state from cooperation with terrorist groups and encourage it to improve the security of the nuclear material it owns.

Michael May was the Chair of the APS/AAAS working group on nuclear forensics. He is Professor Emeritus (Research) in the School of Engineering, and a Senior Fellow with the Center for International Security and Cooperation of the Freeman-Spogli Institute for International Studies at Stanford University. He is Director Emeritus of the Lawrence Livermore National Laboratory.

¹ In a historically curious incident, a 5x5x5 cm cube of pure natural uranium was recovered in 2007 from a forested area in Germany and traced with near certainty to the 1940s, perhaps falling from Werner Heisenberg’s pocket as he bicycled away from an allied detachment nearing his laboratory. I am indebted to Dr.  Klaus Luetzenkirchen of the Institute for Transuranium Elements in Karlsruhe, Germany, for this example.
² For a more detailed overview of “The Day After,” see links at Stanford University and Harvard University.