JUDY WOODRUFF: Next: guarding against the threat and dangers from a so-called dirty bomb.
NewsHour science correspondent Miles O'Brien has been looking into that and filed this report.
MAN: I got you, Chris.
MILES O'BRIEN: It's the start of a long day for the New York City Police Department's anti-terrorism unit.
MAN: A lot of potential targets. Even if you look over to your right here, you can see these container ships. And these other ships there are actually fuel barges.
MILES O'BRIEN: The three queens of the Cunard cruise ship line, Elizabeth, Mary and Victoria, will be steaming out of New York Harbor together. It's an obvious potential target for terrorists, so the unit is out in force, fielding various kinds of radiation detectors over and through the harbor, on and under the streets, on their belts.
High on the list of worries here, the threat of a so-called dirty bomb, an improvised device that couples conventional explosives with radioactive material.
MILES O'BRIEN: How do you assess the risk of something like this?
RAYMOND KELLY, New York City police commissioner: We look at it as a real possibility, and we look at it as being a real possibility every day.
MILES O'BRIEN: It's a big concern for New York City's police commissioner, Ray Kelly, because a dirty bomb is not nearly as difficult to acquire or assemble as an atomic weapon.
How easy is it to make one of these radiological devices?
RAYMOND KELLY: Explosives are available and radiological material are available. You just have to bring the two of them together.
MILES O'BRIEN: Unlike an atomic weapon, the radioactive materials in a dirty bomb do not fuel the explosion itself with nuclear fission or fusion. Instead, a conventional explosion is used as a means to spread a toxic cloud of radioactive dust.
CHARLES FERGUSON, Federation of American Scientists: A real nuclear bomb, like we saw at Hiroshima, Nagasaki, would destroy the heart of a city.
MILES O'BRIEN: Physicist Charles Ferguson is president of the Federation of American scientists. In 2004, he predicted a dirty bomb attack in the U.S. was all but inevitable.
CHARLES FERGUSON: The worst-case radiological dirty bomb would not have those kinds of effects in the least. But I'm not trying to belittle a radioactive dirty bomb, because it could have significant effects, in terms of economic damage, social disruption. So, it's a weapon of mass disruption versus a weapon of mass destruction.
MILES O'BRIEN: But imagine what might happen if a dirty bomb blew up in Times Square, a proven target for terrorists.
Frankly, your job is to think about all of our worst nightmares, right?
Capt. Mike Riggio of the NYPD anti-terrorism unit.
On the tote board of nightmares, how does a dirty bomb rank?
CAPT. MIKE RIGGIO, New York Police Department: It's up there, because I'll tell you what. Any time you take explosives, which can kill one person, five people, 15 people, and you combine it with a radiological material that, like I said, now is a health hazard, but also a long-term possibly closing this area.
MILES O'BRIEN: Closing down Times Square for many months, or even years, so that it can be decontaminated, would cripple the city and cost billions. And who knows what the long-term health effects might be for those exposed to the cloud?
But where might a terrorist find the radioactive material to make a dirty bomb?
I went to Detroit to ask an expert.
DAVID HAHN: They name they call me is The "Radioactive Boy Scout."
MILES O'BRIEN: When David Hahn was young, he was fascinated by science, a well-worn copy of "The Golden Book of Chemistry Experiments" his scientific bible.
He was most fascinated with the story of Pierre and Marie Curie's discovery of radioactive elements. So, on his way to becoming an Eagle Scout, he naturally decided to get his atomic energy merit badge.
What was required for the atomic energy badge?
DAVID HAHN: Required -- one of the requirements was you could build a model of a nuclear reactor or a nuclear core using straws and matches and stuff like that.
MILES O'BRIEN: Which you did?
DAVID HAHN: Yes. And then at -- there was one time when I thought, you know, what if I built the same kind of thing that's in this book and just tried to used the actual kind of material?
MILES O'BRIEN: David Hahn bought hundreds of lantern mantles which used to contain radioactive thorium. He collected old glow-in-the-dark clocks and scraped off the radium. And he purchased hundreds upon hundreds of smoke detectors, which contain a small amount of radioactive americium.
His goal? To build a breeder nuclear reactor in the shed in his backyard. The shed and the radioactive materials are now long gone. When the authorities caught wind of his experiment in 1995, they put his reactor in drums, dismantled the shed, and buried it all in a radioactive waste dump in Utah.
Was it hard or easy to get ahold of these materials?
DAVID HAHN: Extremely difficult, extremely painstaking. I can almost understand what Marie Curie went through in the 1880s, 1890s just to isolate that radium.
MILES O'BRIEN: But that hasn't stopped some would-be dirty-bombers: Jose Padilla, arrested in Chicago in the wake of 9/11. In 2004, an al-Qaida-linked terrorist in London plotted to amass 10,000 smoke detectors for a dirty bomb.
And, in Belfast, Maine, a white supremacist, James Cummings, shot dead by his wife in 2008, had purchased radioactive material and had literature on how to build a dirty bomb.
BOB LAZAR, United Nuclear: We pretty much try and carry everything in the scientific realm.
MILES O'BRIEN: Cummings got some of his radioactive material from this man, Bob Lazar. He owns a company called United Nuclear. Housed in a small storefront in tiny Laingsburg, Mich., he does a good business on the Web selling all kinds of chemicals, equipment and oddities for scientific hobbyists.
BOB LAZAR: These are isotopes.
MILES O'BRIEN: He sells them to the general public, and it's all perfectly legal.
BOB LAZAR: Really, if you want to build a dirty bomb, buying the radio isotopes isn't the route to go.
MILES O'BRIEN: Why not?
BOB LAZAR: Well, first of all, you can't get enough radioactive material. And, to disperse it, you need something water-soluble would be better, because then you can absorb it into something that, with a bomb, you can disperse it over to a large area.
Having big plastic disks with an invisible amount of a speck of radioactive material in it is pretty useless in -- in making a dirty bomb. And -- and you would have to order literally hundreds of thousands of them.
MILES O'BRIEN: You never know where you may find something radioactive. These are the usual suspects, if you will. This is an isotope called strontium-90. It has educational, medical and industrial applications.
This is uranium ore. And that's uranium metal. Here's the surprise, though. This is a piece of fiestaware. That distinctive orange color comes from uranium oxide in the glaze. It's just as hot as those other items.
Ken Sheely is deputy director of the National Nuclear Security Administration. He says they are focused on the bigger radioactive fish, material used in industry, medicine and higher learning. The federal government estimates there are 77,000 sources of radiation that would be useful for a dirty bomb in 2,700 buildings in the U.S.
KENNETH SHEELY, National Nuclear Security Administration: I think it would be pretty easy to find the material.
MILES O'BRIEN: What about getting it?
KENNETH SHEELY: I think it wouldn't be that difficult to get the material.
MILES O'BRIEN: This is scary.
KENNETH SHEELY: These are very soft targets. And I think we have done a lot to further improve the security, but I think, you know, we cannot just rest on our laurels. We have to continue to be one step ahead of the terrorists.
MILES O'BRIEN: Experts from the NNSA and the Los Alamos National Lab are trying to do just that, recovering radioactive material that is no longer in use. So far, they have secured nearly 25,000 sources at about 900 sites around the world.
Among the items they have recovered, flow meters and pumps used in oil production, devices used by schools for radiation experiments, medical scanners and blood irradiators. But this work is by no means done. The NNSA is working with 90 other countries trying to secure radioactive material in about 13,000 buildings.
KENNETH SHEELY: We always feel that we are a race -- in a race against the terrorists. So, as the terrorists are trying to think of new ways to access materials, you know, radiological materials, we're trying to think of new ways to protect them.
MILES O'BRIEN: The NNSA fields nine nuclear radiological advisory teams, first-responders that deploy about 100 times a year. They carry a dizzying array of sensors to big events: inaugurations, Super Bowls and the like. They use devices mounted on vehicles and in backpacks to detect and home in on a radiation threat.
Once the team has found a target, the next task is to figure out precisely what it is. This is a gram of plutonium. They tell me it's OK to stand here, though, but it really is a gram of plutonium. Oftentimes, what they will use is this handheld device. It's called the identiFINDER, a very simple device.
And it is able to make out the radioactive fingerprint. The war against the radiological threat does not come cheap. The total bill is about a billion dollars a year -- $70 million goes to New York City to fund its anti-terror efforts.
CHARLES FERGUSON: I think it's a wise investment. We spent a relatively small amount of money every year for an event -- an event that could have upwards of tens of billions, maybe $100 billion, worth of damage. So, you look at the tradeoff. It's an insurance policy.
MILES O'BRIEN: But Charles Ferguson still believes a dirty bomb attack is a likelihood, eventually.
Do you feel like we have dodged a bullet?
RAYMOND KELLY: We know that we have a lot of intelligence capability that hopefully would detect something like this in the planning stages. But I -- we don't know enough to say that we have - we've dodged the bullet.
MILES O'BRIEN: On this busy day in New York City, the only alarms were false. In this case, the sensor was reading natural gamma radiation that emanates from the granite towers of the Brooklyn Bridge.
They log more than 400 false alarms a year, mostly triggered by innocent New Yorkers who just had a medical procedure of some kind.
I mean, can you make a categorical statement that, if a dirty bomb came into the city, do you think you would detect it?
CAPT. MIKE RIGGIO: I'll tell you one thing. I can -- I can tell you this with 100 percent certainty: that we are tremendously prepared. I think we are -- we give ourselves the best chance to interdict than anybody else.
MILES O'BRIEN: And, by nightfall, the three queens sailed, the tourists gawked, despite the bitter cold, and the only explosions were aimed to thrill not kill.