AAAS Expert Proposes 'Layered Defense' To Protect Against Smuggled Nuclear Materials

Tannenbaum, a senior program associate with the AAAS Center for Science, Technology and Security Policy, was invited by members of the Subcommittee on Prevention of Nuclear and Biological Attack and the Subcommittee on Emergency Preparedness, Science, and Technology of the Committee on Homeland Security to provide objective information on efforts to detect nuclear weapons and radiological material.

His remarks were based on research conducted for AAAS by two independent experts -- Professors Frank von Hippel of Princeton University and Steve Fetter of the University of Maryland. The two experts recently completed a detailed report for the Center, at the request of Rep. Edward J. Markey (D-MA) and Rep. Bennie G. Thompson (D-MS).

In a summary letter to the Congressmen, Norman Neureiter, director of the AAAS Center for Science, Technology and Security Policy, noted that "a several-kilogram cylinder of uranium metal, shielded by a few millimeters of lead and steel and placed in a shipping container, is likely to escape detection by portal monitors using current detectors, algorithms, and operational procedures."

What is the best way to protect the United States and its ports from smuggled nuclear weapons components such as enriched uranium?

In his testimony, Tannenbaum proposed a "layered defense," incorporating currently deployed monitors at U.S. and international ports; plus new detectors and scanners for locating radiological and fissile material while a ship is in transit. At the same time, Tannenbaum noted that "it will always be far easier to monitor a lump of uranium at a known location than it will be to detect uranium smuggling."

He suggested expanding the Comprehensive Threat Reduction program, which currently helps to safeguard much of Russia's highly enriched uranium and plutonium, while converting some of it to fuel for use in nuclear power reactors. Converting nuclear research reactors to use low enriched uranium also would improve national security, Tannenbaum noted.

The current generation of passive radiation detectors can identify isotopes such as cesium-137, cobalt-60, or americium-241 -- all potential components of dirty bombs -- by monitoring the rate at which radioactive decays occur near a sensor, Tannenbaum explained.

Highly enriched uranium "is very difficult to detect" using existing passive radiation detectors, he said. Some ports of entry have both active and passive detectors. But, better detection might be achieved by increasing sampling times, decreasing the distance between the container and the detector, decreasing background radiation with additional shielding and adding collimators to the detectors. In addition, future detectors must have better energy resolution. "This will allow one to distinguish harmless radioactive materials, such as kitty litter, from dirty bombs and nuclear weapons," Tannenbaum testified.

Tannenbaum cited several new technologies that are now under development for locating radiological and fissile materials. At Los Alamos National Lab, for example, researchers are using cosmic rays to find very dense materials, such as plutonium and uranium, in kilogram quantities within cargo containers, according to Tannenbaum. At Lawrence Livermore National Lab, researchers use neutrons to "ping" a container, which provides useful data because fissile materials have a very characteristic gamma ray response. The Ohio-based company Quintell also is developing inexpensive detectors that would be placed in cargo containers during transoceanic shipment, Tannenbaum said. These detectors take advantage of the 10 or more day transit time to locate highly enriched uranium before it enters a U.S. port. The U.S. Department of Homeland Security and the Department of Energy's National Nuclear Security Administration, meanwhile, have begun construction of a facility to test portal monitors.

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The AAAS Center for Science, Technology and Security Policy was established by the American Association for the Advancement of Science (AAAS) through generous support from the Science, Technology & Security Initiative at the MacArthur Foundation. The goal of the Center is to encourage the integration of science and public policy for enhanced national and international security. With Director Norman Neureiter, Tannenbaum and other staff work to identify experts who can provide clear, objective, unbiased scientific and technical information to guide policymaking decisions.