If a terrorist tried to sneak a "dirty" bomb into the United States, would anyone notice?
Possibly. Radiation detectors rushed into service since 9/11 might sound the alarm at seaports, border checkpoints, and mail-handling facilities.
Then again, the sensors have been set off by everything from loads of kitty litter to bananas. And a smart terrorist could hide a basketball-size chunk of highly enriched uranium by using lead shielding less than an inch thick.
That's why the US is set to begin deploying a new generation of radiation detectors intended to be America's "last line of defense" against weapons of mass destruction. By early spring, the Department of Homeland Security (DHS) will pick technologies from among 10 companies, whose newest generation of nuclear detectors was tested in the Nevada desert this summer. Their devices will begin field-testing at a few ports of entry by next June, with a full-production decision expected by 2007.
Some experts are breathing a sigh of relief. "We're now on the cusp of seeing the next generation of [nuclear and radiological] detectors," says Benn Tannenbaum, a physicist and expert on sensor technology at the Center for Science, Technology & Security Policy at the American Association for the Advancement of Science in Washington.
But others say the US is not moving fast enough to install a multilayered defense against one of its biggest security threats. While billions of dollars have been spent on biological countermeasures, nuclear detection efforts have lagged.
"Little steps are being taken that may be in the right direction," says Richard Wagner Jr., a senior staffer at Los Alamos National Laboratory, who served in the Pentagon during the Reagan administration. "It's the rate of progress I'm concerned about."
That pace may be picking up as disturbing evidence accumulates.
About a year ago, the National Intelligence Council warned that "undetected smuggling has occurred, and we are concerned about the total amount of [nuclear and radiological] material that could have been diverted or stolen in the past 13 years" around the world.
The International Atomic Energy Agency (IAEA), which has documented 650 cases of trafficking since 1993, echoed that report.
About $300 million has been spentby the Department of Homeland Security since 1994 to deploy 470 radiation-detection systems at America's border crossings and ports, according to a Government Accountability Office report in June.
But their shortcomings have become obvious.
In March, DHS officials told Congress port detectors were working and had registered at least 10,000 radiation hits.
But questions about the value of those hits arose in a June congressional hearing, when the security manager for the Port Authority of New York and New Jersey reported 150 "false positives" per day.
That amounted to a false alarm - and possibly a time- consuming search - for about 1 in every 40 shipping containers. The resulting delays, in turn, often caused detection sensitivity to be turned down, crippling a sensor's ability to detect weapons material, the Port Authority security manager and other experts say.
Next-generation sensors will generally be far smaller, often mobile, and smarter - networked with other sensors and able to detect the difference between radiation emitted from a nuclear bomb and a load of bananas.
Overseeing the effort is a brand new office within the Department of Homeland Security devoted to one goal: detecting terrorist nuclear material before it can get into the country.
Established by presidential directive in April, its first assignment is to create a network of US nuclear detectors as part of a larger "global architecture" of detectors to be deployed overseas.
"We anticipate mobile detection systems and fixed systems ... that enable us to achieve randomness and screening around the country, in transit zones, aircraft in flight, and container ships," says Vayle Oxford, acting director of the new DHS Domestic Nuclear Detection Office (DNDO).
He envisions detectors that would screen "target areas" like high-risk cities, and some that could alert security forces to investigate. In sum, it's a new concept that will need huge databases to collect and collate data from what could become thousands of WMD sensors on bridges and buildings.
"What we're trying to do with global architecture is to knit this together," Dr. Oxford says. DNDO received $318 million in fiscal year 2006 funding - about $90 million more than President Bush requested from Congress.
Today only a few truly advanced detection systems are actually deployed, including one at MassPort in Boston and another at a border crossing with Mexico near San Diego, Dr. Tannenbaum says.
By 2007, DHS expects to decide on the best technology to put into 2,500 advanced detectors to be rolled out nationwide.
One possible technology, from Lawrence Livermore National Laboratory, is RadNet, a kind of global positioning system married to a radiation detector packed into a cellphone. The idea is that this "cellphone sniffer" could be carried by police officers on their daily routes - all the while detecting radiation and transmitting coordinates to a computer that maps hot zones for investigation.
Another contender: Princeton University's Miniature Integrated Detection System (MINDS), which can distinguish between types of radiation using sophisticated software.
So far, MINDS systems are scanning for suspicious material at a major train station on the East Coast and a military base in New Jersey, as well as being evaluated for airports and mail facilities.
Scientists at the Livermore lab are working on an even more futuristic nuclear detector that could sense a bomb made of highly enriched uranium, which emits little radiation and is easily shielded.
Other countries are coming on board. A year ago, the European Union and the US agreed to cooperate on development of sensor technology.
Canada last year noted that its Ottawa International Airport would be getting detectors that would sense material likely to be in a dirty bomb, a non-nuclear device that uses conventional explosives.
Even local entities are getting involved. Last year several Las Vegas hotels announced deployment of nuclear and chemical sensors.
MetroRail in the nation's capital has been moving to upgrade its chemical and biological sensors.
Few experts, however - Oxford included - believe WMD sensors are enough.
Most agree the primary defensive layer must be locking down and monitoring with new smart detectors the insecure nuclear materials in places like the research reactors of the former Soviet Union.
The next layer would be smart sensors at ports overseas to screen cargo before it is loaded onto a ship bound for the US.
Some critics, though, say the bulk of funds should be spent securing loose nuclear material overseas and creating sensor networks to make sure that it doesn't end up in the wrong hands. If it did, the argument goes, all the sensors in the world might not be enough.
"This could become a Maginot line for us, creating a false sense of security," says Randall Larsen, CEO of Homeland Security Associates, an Arlington, Va., consulting firm. "Anyone smart enough to get this stuff could sneak it past detectors."
Still, other experts say sensor networks abroad combined with a last line of defense in the US are critical.
"If you have a better defensive system, the attacker has to work that much harder, recruit more people, put on more shielding," says Mr. Wagner. "The bigger the operation gets, the better chance our people have of detecting and stopping it."