The Holes in Nuclear Forensics
by CKR
It's easy in the movies: put some dust the hero has picked up in the street into a machine with gauges and lights, wait a few seconds, and the answer glows on the monitor: North Korea. Or Iran. Or Russia.
If the bad guys explode a nuclear device in New York City, we've been assured, we can track them down. What we do if it's a Russian device (or Pakistani or Israeli), we haven't quite figured out yet. But we'll know where it came from.
Not so much, said Carol Burns and Vayl Oxford to a House Homeland Security subcommittee on Wednesday. Burns is division leader for nuclear and radiochemistry at the Los Alamos National Laboratory. Oxford is head of the Homeland Security Department's Domestic Nuclear Detection Office.
The hearing was on HR 2631, the Nuclear Forensics and Attribution Act. It is a 'sense of Congress' act, urging the president to
(1) pursue international agreements, both bilateral and multilateral, to establish an international framework for determining the source of any confiscated nuclear material or weapon, as well as the source of any detonated weapon and the nuclear material used in such a weapon;
(2) develop protocols for the dissemination of sensitive information relating to nuclear materials and samples of controlled nuclear materials, to the extent required by the agreements entered into under paragraph (1); and
(3) develop expedited protocols for the dissemination of sensitive information needed to publicly identify the source of a nuclear detonation.
Eileen Sullivan of the AP reads this as
a bill that would ask the president for agreements with other countries to share information on the makings of their nuclear materials. Maintaining a database with this information would help identify nuclear material before or after an attack and serve as a deterrent to nations that continue to produce these weapons.
As usual, I'm not sure what Congress has in mind. It's going to be a delicate matter to ask Iran for a chunk of their highly enriched uranium and oh by the way what kind of tamper they're planning to use, that is, if they're actually planning to make nuclear weapons. Or how about Israel?
Putting aside the diplomatic delicacies of such a project*, the witnesses said that the technical side isn't going so well. A number of people have expressed optimism about the technical side over the past few years: Graham Allison (himself and channeled by David Ignatius), Jonathan Medalia of the Congressional Research Service, William Dunlop and Harold Smith in an article in Arms Control Today, and Andrew Foland.
Samples from Soviet tests were relatively easy to analyze. We had a pretty good idea of what they were using and their bomb design. But a bomb that could have come from anywhere in the nuclear weapon universe? As Paul Kerr noted, Dunlop and Smith give some of the particulars. There are three main kinds of evidence that would be available after a nuclear detonation:
* Atoms of fissile material that did not undergo fission. Examining them allows scientists to identify the material used to make the device and, when compared to the number of fission fragments, to measure the efficiency or sophistication of the weapon.During the Cold War, we knew who was setting off the tests and some things about the composition of their fissionable material. That helped to direct the analyses. It's not a matter of one box tells all about the sample; it never is in analytical chemistry. You have to know a bit about what you're looking for. Many of the tests destroy the sample, and most need some minimum amount. But it really, really helps if you have some idea of what the starting material was. Foland notes that the molybdenum signature might help to identify an Iranian bomb, but there's plenty of molybdenum in structural steel. And concentrations of the various components are important, too, and will be scrambled in a nuclear explosion. Heck, concentrations get fuzzy just when you consider enrichment, as in that business about North Korea reportedly supplying uranium hexafluoride to Libya (WhirledView, Arms Control Wonk)
* New atoms created by fission and by other nuclear reactions within the fissile material. When scientists compare these, they can obtain considerable insight into the nuclear processes that were involved during the actual explosion.
* Atoms of material near the fissioning core that were subjected to an intense bombardment of neutrons during the explosion and became radioactive as a consequence. These atoms provide insight into the components of the weapon and the energy of the neutrons that activated the components.
Burns noted that the scientists who analyzed such samples have mostly retired from Los Alamos and the other laboratories. That's a whole nother sad story of how the laboratories and their personnel have been managed, but I won't get into that today.
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* We've now put aside the difficulty of figuring out who set the bomb vis-a-vis who manufactured it and the difficulties of getting nuclear weapons nations to contribute to the data base. Just keeping track of what we're ignoring.
A couple of comments--
As I see it, there are two ways a covert weapon might be tracked back via forensics: either by forensically identifying the remains of a detonated weapon, or by forensically identifying the remains of a failed, or prematurely discovered, undetonated weapon. To my mind, it's the second case that has the highest product of probabilities and the one case where forensics might already serve as a true deterrent to state-based policy makers. I certainly wouldn't want to put any money on the first case ever being reliable. Maybe it will be, but that just seems like a hard problem.
Exemplars, precisely as you say, are the biggest obstacle, especially wrt Pakistan, Israel, and DPRK. If you found a weapon and couldn't fingerprint it, you'd probably be left to choose among two of the three (whether it was Pu/U hopefully helps you eliminate at least one of them). Forensics are why, if you think some nation might be pursuing a breakout capability, you want them to stay in the NPT as long as possible--so IAEA can get as good an idea as possible what idiosycracies their materials have. And why if they are outside it, you'd like some mechanism for bringing them in. Your knowledge starts deteriorating for every day the IAEA is out. It also means it's not in your interest to force the issue prematurely and bomb their nuclear sites five or ten years ahead of when they might possibly think about pulling out of the NPT.
Posted by: Andrew Foland | Friday, 12 October 2007 at 01:35 PM