About every three days, unknown to most Americans, an elite team of federal scientists hits the streets in the fight against nuclear terrorism.
The deployments are part of an effort since 2001 to ratchet up the nation's defenses. More than two dozen specialized teams have been positioned to respond to threats of nuclear terrorism, and as many as 2,000 scientists and bomb experts take part in the effort. Spending on the program has more than doubled since it was launched.
And a national policy is evolving that aims to create a system of deterrence in which scientific analysis could quickly identify the state sponsors of a nuclear attack or an attempt and enable the U.S. to retaliate. A key report on the approach, known as nuclear forensics, is due next month.
The counterterrorism efforts are becoming routine. Scientists fly over cities in helicopters and airplanes equipped with radiation detectors to search for signs of weapons. They blend into crowds at major sporting events, wearing backpacks loaded with special instruments that can identify plutonium or highly enriched uranium.
So far, they have not found a terrorist. Near the Las Vegas Strip, they investigated a homeless person who somehow had picked up a piece of radioactive material. On the streets of Manhattan, a hot dog vendor fresh from a medical test triggered a police officer's radioactivity sensor.
But the teams have not become complacent. If the federal government's many layers of defense against nuclear smuggling break down, these unarmed weapons designers and physicists, along with experts from the FBI, are the last hope of staving off a catastrophic attack.
Without hesitation, they are supposed to rush up to a ticking nuclear explosive (or a dirty bomb that would disperse radioactive material) and defuse it before it's too late - a situation depicted often by Hollywood, but one that potentially is becoming less fictional every year.
"After everything else fails, we come in," said Deborah A. Wilber, who directs the Office of Emergency Response at the National Nuclear Security Administration. "I don't believe it is a question of if it will happen. It is a question of when."
Since the attacks of Sept. 11, 2001, the office has created 26 rapid-response units. If a device is found, two other specialized teams would rush to the scene, one from a base in Albuquerque, N.M., where a fueled jetliner is on 24-hour alert. Another FBI team would depart from rural Virginia.
The teams would first attempt to disable a bomb's electrical firing system and then quickly transfer the weapon to the Nevada desert. There, it would be lowered into the G Tunnel, a shaft 5,000 feet deep, where a crew of scientists and FBI agents would attempt to disassemble the device behind steel blast doors and log the evidence.
About 1,000 nuclear weapons scientists and 500 to 1,000 FBI professionals take part in the effort, though not full time. Increased investment in the project reflects an acknowledgment that the nation has long been vulnerable to terrorists seeking to plant a nuclear device. But the increased effort is also reaching for something greater than defense: a Cold War style of deterrence.
The same scientists are also experts in the rapidly evolving field of nuclear forensics, which aims to track nuclear materials to their country of origin. Even if a bomb explodes, fallout can be measured and assessed so the terrorists and their state sponsors might be identified and held accountable. A retaliatory strike could be the response.
The idea is to raise the stakes against foreign nations, forcing them to take better care of their own nuclear fuels or else find themselves in the cross hairs of the U.S. nuclear arsenal.
A major technical and policy analysis of this approach is being conducted by some of the nation's top nuclear-weapons experts, sponsored by the American Association for the Advancement of Science and led by Stanford University physicist Michael M. May. The report is due next year.
In the meantime, the U.S. is retrieving and locking down nuclear fuels abroad, has created a line of radiation detectors at foreign and domestic ports and has increased its intelligence efforts. If those and other measures fail, the emergency response teams are the last hope, but one nobody should rely upon, said Charles B. Curtis, president of the Nuclear Threat Initiative, which pushes for stronger efforts to prevent nuclear terrorism.
"It is a very, very, very difficult problem, but not impossible," said Curtis, a former Energy Department deputy secretary.
The full capability of the teams is classified. Bruce Goodwin, nuclear weapons chief at Lawrence Livermore National Laboratory, noted in an interview that the teams now have "some really remarkable tools that can prevent nuclear function," suggesting a device that can foil the arming system or perhaps neutralize its basic operation.
Ralph Vartabedian writes for the Los Angeles Times.