STEVE INSKEEP, host:
Senior officials from the United States and South Korea met in Seoul today. They discussed the resumption of the six-party negotiations on North Korea's nuclear weapons program, which Pyongyang agreed to last week.
Also on the agenda was the enforcement of United Nations sanctions, which were approved shortly after North Korea conducted an underground nuclear test. That's the test that raised alarms among North Korea's neighbors and drew international condemnation.
RENEE MONTAGNE, host:
The idea of more bombs worries the world's defense strategists. It's not only the threat from the new nuclear nations but the risk that terrorist will get a hold of bombs or the material to make them.
So scientists are working on better ways to trace nuclear materials back to their source. NPR's Christopher Joyce has this story about the growing field of nuclear forensics.
CHRISTOPHER JOYCE: Raymond Jeanloz is a geophysicist who thinks about the unthinkable: a nuclear attack on America. Besides the horrible casualties, he worries about how to find out who did it.
Mr. RAYMOND JEANLOZ (Geophysicist, University of California Berkeley): There will be a huge pressure to understand what was involved. Was it a sophisticated military weapon? Was it an improvised terrorist device? Was it civilian nuclear power material? Where might it have come from?
JOYCE: Jeanloz notes that after the deadly anthrax mailings in 2003, a search for the source failed in part because there are so many laboratories it could have come from. The same is true for the enriched uranium or plutonium to make bombs. Experts say some 40 countries possess these materials in weapons or in power or research reactors.
All that material needs to be catalogued, says Jeanloz, a professor at the University of California at Berkeley. In a recent issue of the journal Nature, he and two former government scientists say such a catalogue could help investigators identify the source of bomb material. The catalogue would list the unique markers left on bomb material during the manufacturing process.
JEANLOZ: In the case of plutonium, which is created in reactors, one learns a lot about the way the processing has been done, how long the material has been in the reactors and so on.
JOYCE: Enriched uranium is made another way in huge and complicated centrifuges, but these too leave unique markers. Even the ore that uranium comes from has its own geological signature.
As it happens, the Department of Homeland Security is beginning to put together its own nuclear database. Vayl Oxford, head of the department's Domestic Nuclear Detection Office, says there are lots of markers to choose from.
Mr. VAYL OXFORD (Director, Domestic Nuclear Detection Office): It is the isotopes, it's the chemical composition, it's actual physical structure. We're essentially trying to come up with a DNA fingerprint for those kind of materials - although it's dramatically different - but to be able to have that kind of library to assess against when we actually get those kind of samples.
JOYCE: Several other nuclear nations have their own small libraries, too. But what's being talked about now is a more comprehensive and global one. It could be useful right away. For example, in tracking down the source of bomb material seized on the black market. Since 1993, there have been 16 seizures.
These nuclear yellow pages could also help trace the source of a dirty bomb if it uses enriched uranium or plutonium. In fact, Oxford says, Homeland Security is setting up procedures for teams to identify material after an actual nuclear blast.
OXFORD: They would go into the debris field, collect the samples. They would very quickly then get that into one of the laboratories to begin the characterization of the material. Our addition to that would be to start to look at the library that already exists to see what the closest matches are.
JOYCE: Nuclear scientists say tracing material after a nuclear explosion would be daunting but possible. Technology for identifying the elemental and chemical nature of materials has improved. Page Stoutland is chemist with the Nuclear Countermeasures Division at the Lawrence Livermore National Laboratory, one of the government's weapons labs.
Mr. PAGE STOUTLAND (Chemist, Lawrence Livermore National Laboratory): Quite recently, within the last few years, instruments that come online that not only give you high sensitivity but we can also look at individual nanometer-sized particle using mass spectroscopy. That gives us a lot of - a totally new handle, if you will, on the forensics.
JOYCE: Stoutland says, in fact, the instruments have improved faster than the ability to store and analyze the information they provide. Matthew Bunn, a nuclear expect at Harvard University's project on Managing the Atom, says countries such a North Korea or Iran are not likely to cooperate in putting together a database, but even a partial library would help narrow the suspects after an attack.
Mr. MATTHEW BUNN (Senior Research Associate, Harvard University): You may, by process of elimination, say, well, it didn't come from any of the known sources in Russia. It didn't come from any of the known sources in France and so on and so on, and greatly increase your ability to focus in on the likely perpetrators.
JOYCE: Bunn says a good nuclear database would also have other benefits right away. Since it would make it easier to track black market material to its original source, it might encourage governments to be more careful with their nuclear stockpiles. Nobody, he says, wants a reputation for being loose with its nukes.
Christopher Joyce, NPR News.
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