I will address the threat from nuclear terrorism, the components of a strategy to counter that threat, and the specific role that nuclear materials detection and related capabilities play in that strategy. I will conclude with specifics about what the U.S. and especially my organization within DOE’s National Nuclear Security Administration is doing today to strengthen national capabilities for detection, interdiction, and attribution.

First, let me provide a short answer regarding nuclear detection. Detection of weapons-usable nuclear materials - that is, plutonium and highly enriched uranium - by their radioactive decays is not a “silver bullet.” Rather, nuclear materials detection is but one tool in the broad array of ongoing activities and emerging capabilities, systems, and architectures that comprise an overall strategy to counter nuclear terrorism.

Nuclear Terrorist Threats

In this post-Cold War world, nuclear terrorism may be the single most catastrophic threat that any nation faces - we must do everything we can to ensure against its occurrence. We are focused on two principal scenarios. First, state sponsors of terrorism could seek to employ indigenously developed nuclear weapons covertly in any country because of an inability, or an unwillingness, to deliver them via more traditional delivery means. Second, covert delivery by sub-national terrorist groups, either at the bidding of a state sponsor supplying the nuclear warhead or on their own via purchasing or stealing a warhead, is also a concern.

With regard to terrorist activities, there are three main threat variants we identify in decreasing order of likelihood, but increasing order of consequence in terms of deaths, injuries, cleanup costs, etc.:

• Terrorists could acquire radioactive materials and construct devices for dispersal:  so-called radioactive dispersal devices or RDDs (not a nuclear yield);
• Terrorists could acquire special nuclear materials (SNM) - plutonium or highly enriched uranium (HEU) - and build an improvised nuclear device of a few kilotons of nuclear explosive power; and
• Terrorists could acquire a nuclear weapon from a nuclear weapons state (few 10’s to few 100’s of kilotons).

I’m going to focus first on the latter two threats both involving nuclear yields: the threats involving plutonium or HEU and the nuclear warheads or improvised nuclear explosive devices that employ these materials.  These scenarios present the greatest threat because of the potential harm that could be done and the greatest challenge in terms of detection.

• The overall strategy to protect a country from terrorist nuclear weapons threats has five components:
• Prevent acquisition of nuclear weapons and special nuclear materials;
• Deter the threat if possible;
• If prevention and deterrence fail: detect, interdict and render safe the nuclear device;
• Identify the nature and source of the nuclear device; and
• Prepare for and respond to possible use.

We are working hard to prevent acquisition by:

• Strengthening physical security of U.S. nuclear weapons and weapons usable materials;
• Providing assistance to Russia to strengthen protection, control, and accounting of its nuclear weapons and materials;
• Working with countries and allies to secure weapons-usable nuclear materials worldwide, and to strengthen security at civil nuclear facilities; and
• Taking more aggressive steps to interdict commerce in weapons-usable nuclear materials and related technologies via strengthened export controls, cooperation with  countries through initiatives such as: The Global Initiative to Combat Nuclear Terrorism, NNSA’s Second Line of Defense and Megaports programs, and the Proliferation Security Initiative.

The Global Initiative to Combat Nuclear Terrorism is aimed at strengthening cooperation worldwide on security for nuclear materials and the prevention of terrorist acts involving nuclear or radioactive substances. We continue to believe that keeping nuclear and radioactive materials out of the hands of terrorists - and where possible, eliminating potentially vulnerable weapons-usable materials - is the most effective means of prevention.

Barriers to acquisition also provide an important element of deterrence. If terrorists believe that it will be extremely risky, or impossible, to acquire weapons or materials, they may seek other avenues of attack. While we of course want to prevent all types of terrorism, deterring a devastating nuclear detonation has particular urgency.

A key component of an overall strategy to counter nuclear terrorism is the ability to rapidly characterize and identify the source of nuclear warheads and weapons usable nuclear materials - either before or after an attack -. A state sponsor of terrorism may be deterred from conducting a covert nuclear attack or providing nuclear weapons to terrorist organizations if it believes that a credible capability to attribute such devices to their source and that there is a will to retaliate against both the state sponsor and any terrorists. An attribution capability will be critical to actions taken in response to prevent follow-on attacks, and provide as well a means for law enforcement agencies to bring perpetrators to justice. A lot of hard work remains in fleshing out both the technical and policy dimensions of attribution. At NNSA, we are working with partners within the U.S. and with other governments to put in place the necessary technical tools and protocols.

But what if terrorists succeed in acquiring a nuclear device despite our best efforts? We cannot expect that they will be deterred by threats of retaliation. Indeed, the willingness of an organization such as Al Qaeda to sacrifice the lives of its members in suicidal attacks to achieve political objectives suggests that previous concepts of deterrence based on threats of punitive retaliation simply don’t apply. We therefore need to strengthen our capability to interrupt a terrorist attack in the making. This includes both technical means to identify a nuclear weapon, nuclear or radioactive materials, or other key components being transported around the world, and close monitoring of intelligence collected against terrorist organizations interested in conducting a nuclear or radiological attack. A robust nuclear and radioactive material detection system not only protects the country directly, it could also convince our adversaries that any attempt of this sort is likely to fail.

A nuclear materials detection system does not have to be perfect to be useful. And, we should not expect any nuclear detection system to be successful against all potential configurations of materials. Among other things, the low energy gamma rays emitted from U-235 can be easily shielded from radiation detectors - this reduces the standoff capability of detector systems and/or requires much greater detector time to acquire a signal. This may simply not be practical in many transportation scenarios. Of course, the mass of shielding could itself tip off an inspector to examine a shipment more closely. Other approaches - for example, neutron irradiation to cause fissions in U-235, which are more detectable - raise problems and policy issues including adding to the cost and complexity of the system, and possibly safety questions for both operators and the public. A detection system whose sensitivity is set very low in order to have high confidence of detecting nuclear material will have a correspondingly higher false positives rate from commonly occurring sources of radiation.

At this point, I would like to discuss terrorist acquisition of radioactive materials to construct devices for dispersal:  so-called radioactive dispersal devices (RDDs) or “Dirty Bombs”.  I must point out two things in particular: 1) a RDD or dirty bomb will not produce a nuclear yield, and 2) while I specify terrorist acquisition, an RDD could be produced by anyone who has explosives and radioactive material.   Therefore, an RDD is considered generally to be a more likely scenario than a detonation of an IND or a nuclear weapon.  An RDD also has a significantly lower consequence in terms of radioactive contamination.  In fact, as Fred (Harper from NNSA's Sandia National Laboratories) will show later, the impact of the explosion may do more damage than the radioactive material.  However, and this is a big however, an RDD will have its greatest impact in terms of mass hysteria – “public perception” identifies this as their biggest fear, and thus it is a concern that we must address.

The RDD threat is considered a higher threat in many countries throughout the world.  This is based on the belief that there is a greater probability of the terrorist obtaining the necessary materials (radioactive material and explosives) to achieve the end results.  Challenges to making an effective RDD are:

• Radioactive source size varies from very small to large – making it difficult to make an effective RDD
• Due to material properties of sources and device design complications, duds are likely

Because of these variables, if detonated, an RDD has a very wide range of outcomes. But an effective RDD will cause disruption and damage, and we believe that it will be one of the following scenarios:

• Localized dispersal which will result in higher exposure rates.  This presents challenges to first responders, but dispersal would be confined to an area less than a few hundred meters.
• Widespread dispersal which will result in lower exposure rates, but dispersal area would be larger – a few kilometers – presenting potentially a large cleanup problem.
• Combination of localized and widespread dispersal which will result in a wide variation of exposure rates and complex cleanup depending on the chemistry of the source.

The bottom line is that the best strategy is what we have all been working towards: prevention, response and mitigation.  Again, we have no silver bullets and I have none to offer, but we address the RDD, IND and nuclear device threats in the same manner:

• Prevent acquisition
• Detect the threat
• Interdict
• Respond
• Render safe
• Consequence management

Detection of many RDD source materials is easier than detection of nuclear material and many nuclear device render safe and mitigation activities are applicable to the RDD threat.  For example:

Recent developments involving installation of Advanced Spectroscopic Portals are aimed at addressing this challenge. It is important to emphasize that developing appropriate procedures to be followed after an alarm is triggered - the so-called “concept of operations” - is as important to building a successful detection system as the physical characteristics of the detectors themselves.
 
For detection networks consisting of hundreds of thousands of detectors throughout a country, as some have proposed, the false positives problem could easily become cost prohibitive and seriously affect commerce. Detection systems employing gamma-ray imaging technologies, other advanced processing technologies, or technologies that allow rapid identification of specific isotopes offer potential for a reduced false positive rate and could be suitable, if produced cheaply, for widely-deployed detection networks.

With regard to long-term development of advanced nuclear materials detection technology, we must draw on the science base established in multi-faceted research and development programs. Active efforts are underway in such areas as advanced radiation sensors and sensor systems development, identification and detection of alternative signatures for special nuclear materials, and advanced radiation detection materials development. These research and development activities are focused on enabling detection and identification of shielded HEU, standoff detection of SNM, and higher confidence on SNM threat identification.

The world’s best minds at laboratories, academia, and industry are exploring not only technology development for immediate deployment, but also the boundaries of science to determine if there are new technologies, techniques or methodologies that would provide increased nuclear detection capabilities. We are hopeful that these efforts will result in significant technological advances, but we must be mindful that all detection capabilities are constrained by the laws of physics. While we continue to work to extend conventional methods of radiation detection - that is, detection of neutrons and gamma rays from nuclear materials - we are also investing in unconventional and alternative concepts - for example, muon detection - to ensure that we cover areas that have typically been out of the mainstream.
 
When all is said and done, however, we must recognize that there is no single “silver bullet” in preventing acquisition or in detecting and interdicting terrorist nuclear threats. Rather, we believe nations need a comprehensive strategy that includes a broad range of initiatives, capabilities, and supporting research and development.
 
Thank you for your attention.

Location:
International Atomic Energy Agency (IAEA) in Vienna, Austria.