How Terrorists Might Make a Bomb – Twice

by CKR

Peter Zimmerman, Jeffrey Lewis, and William Langewiesche have given us two articles on how terrorists might make nuclear weapons. Not radiological dispersal devices, but the real mushroom-cloud thing.

Zimmerman and Lewis’s article is in the November/December issue of Foreign Policy and Langewiesche’s in the December Atlantic. (Many thanks to whoever is responsible for sending me a copy of Foreign Policy after my subscription expired.)

Both articles are generally plausible, although more assumptions have been made than are evident at first glance. Langewiesche admits that it isn’t easy:

In the end, if you wanted a bomb and calculated the odds, you would have to admit that they were stacked against you, simply because of how the world works—and that this may be why others like you, if there have been any, have so far not succeeded.

Langewiesche gives a broader view with detail on how fissile material might be procured; Zimmerman and Lewis focus on the fabrication team. It seems as though the two articles together could furnish a detailed plan.

Both articles assume that some terrorists indeed want nuclear weapons, supported by what evidence we have: Al-Qaeda has said so, and setting one off in a major American city would illustrate power and induce fear. They also assume that acquiring a fully-manufactured weapon is unlikely; Langewiesche details why.

They agree that highly enriched uranium, rather than plutonium, is the material to use. They also agree that the highly enriched uranium has not been shown up on the black market in the quantities that would be needed, although Zimmerman and Lewis speculate as much as they dare. Langewiesche opts for stealing the material from a Russian facility. Zimmerman and Lewis would buy it on the black market.

Langewiesche’s acquaintance with smuggling routes across Georgia makes for a good story. We might also consider the nuclear facilities of Israel, India and Pakistan, under less international scrutiny than the Russian facilities. But we also don’t know as much about them as we know about Mayak, for that very reason, so it’s harder to make a plausible story.

Buying highly enriched uranium on the black market has a downside that Zimmerman and Lewis don’t mention: you don’t know what you’re getting. The group would have to analyze the isotopes in each buy. This requires very exacting mass spectrometers, radiation counters, or laser methods. Add another expensive piece of equipment and another expert to Zimmerman and Lewis’s totals.

We’ve been hearing a lot about polonium lately, but neither of these articles mentions it. That’s strange, because nuclear weapons require a neutron generator to start the chain reaction off in good order. Neutron generators come in three types: polonium and beryllium, tritium, and an electronic widget. None of these are mentioned in either article, but any of them will be as difficult to procure as the enriched uranium. Terrorists might chance omitting a neutron initiator, but a nuclear blast requires getting the critical mass together with the neutrons that initiate the chain reaction in an extremely short time. Not knowing the isotopic composition, or dealing with a lower U-235 concentration, would argue for an initiator. On the other hand, a fizzle of a half-kiloton or so would still be impressive.

I’ll note a few overstatements, and then give my major criticism.

Zimmerman and Lewis:

The frightening truth is that fissile material, including nuclear explosive material, is an item of commerce, and moves from place to place.

They themselves admit that there is no evidence that any large trade in fissile material exists. We need logic to evaluate the threat, not fear.

Langewiesche:

…the use of even a single fission device could pose an existential threat to the West.

Oh please. I recognize that existential is a favorite modifier of threat these days, but exactly how could a single fission device destroy the entire West? Given our overreaction to 9/11, the most plausible “existential threat to the West” would be an even more extreme overreaction.

Langewiesche:

Such a reaction [an uncontrolled chain reaction caused by too much U-235 too close together] would not amount to a military-style nuclear explosion, but it could certainly take out a few city blocks.

This relates to the question of an initiator. The strength of the reaction depends on the speed with which the materials are brought together. The criticality accidents that killed Harry Daghlian and Louis Slotin produced no explosion at all.

The biggest problem is people. Fielding the team will be more difficult than procuring the fissile material or polonium. Zimmerman and Lewis list the skills and numbers of people needed: a senior physicist and two postdocs; 3-4 each engineers or highly skilled technicians in metallurgy and casting, precision machining and construction; designing the gun assembly and devising tests that will not destroy the limited amount of equipment; one or two electronics engineers or highly skilled technicians to do the fusing; a draftsman or two will be needed, but some of the foregoing are likely to have that skill; and one or two “procurement specialists.” Langewiesche’s team would need similar skills, but his “procurement team” would be larger.

Zimmerman and Lewis estimate a total of nineteen, not all necessarily working together at the same time. The skills they describe all require years of preparation; learning on this job could destroy limited stocks of material or disclose the operation. The best candidates for some of the jobs would have been trained in governmental nuclear weapons programs.

It would not be impossible to assemble such a group of experts. It would be more difficult to assemble such a group with the purpose of building an underground nuclear weapon. This question goes to motivation: Who would want to build a terrorist nuke? Who would be willing to chance being caught?

Al-Qaeda and similar organizations have the motivation, but they have so far not managed to motivate weapons designers, experienced or incipient. Some may be disaffected, but those who have worked on nuclear weapons understand well the gravity of their special knowledge. Those who have this kind of expertise outside the weapons community are able to hold good jobs, integrated into their societies. There are always a small number of criminals and sociopaths, and recent unhappiness at the weapons labs suggests that some susceptible people might be turned. Recruitment would have to be underground, through contacts that al-Qaeda probably doesn’t have.

And you have to get those people to work together. The physicists will come up with a design, but their belief in their engineering ability has always outstripped the reality. Oppenheimer believed that only a few tens of scientists would be needed at Los Alamos. Even in the very last moments of the Manhattan Project, they hadn’t calculated the thermal expansions of the plutonium and the explosives and almost couldn’t fit the pit into the explosives at Alamogordo.

The skilled engineers and technicians will have their own stores of knowledge that will conflict with some of the things the physicists want to do; tension will be high; things will go wrong; fights will break out. The head guy will have to keep them all working together by threats that may not be plausible.

And then there are the people outside. Langewiesche considers them in greater detail than do Zimmerman and Lewis. There are always neighbors, or people who live in the areas through which material must be smuggled, and they know the people who live nearby. Strangers coming and going to a ranch in Idaho or a garage in Istanbul will be noticed, particularly if they are moving equipment and materials around and making noises. They can inadvertently get in the way or they can demand bribes not to say anything.

As Langewiesche says,

Every move in this venture, every elaboration, increases the chance for something to go wrong.

Both articles together list some, but not all the moves required and don’t even consider mistakes and just plain bad luck.

It’s not impossible, I guess. But I think that al-Qaeda will be seeking its nuclear weapon for some time into the future.

Comments

[Jeffrey Lewis]

On the initiator.

The South African gun type device didn't use an initiator:

A unique feature of South Africa's gun-type design is that it did not use a neutron initiator - a device that generates neutrons to start the chain reaction in the supercritical material. South African devices were designed to use background, or stray, neutrons to initiate the chain reaction. Calculations showed that the chain reaction would start within a few microseconds after the HEU projectile hit the fixed HEU component.

We figured this loss from not using an initiator was outwieghed by the gain from skipping the step.

Could be wrong, of course.

[Paul Guinnessy]

There were a number of assumptions made in Zimmerman's and Lewis's article that I believed overstated the difficulty of making a device. I asked Zimmerman about it at a seminar a couple of weeks ago. He said that they had delibrately made some aspects of their paper obtuse as they didn't want to be accused of designing a primer for a terrorist group. I suspect one other aspect that is not clarfied, is the assumption that it would be a terrorist group and not a state that would carrying out such a task.

[J.]

"Oh please. I recognize that existential is a favorite modifier of threat these days, but exactly how could a single fission device destroy the entire West? Given our overreaction to 9/11, the most plausible “existential threat to the West” would be an even more extreme overreaction."

Good analysis, and especially this quote. I constantly see educated people making statements on how terrorist CB incidents are "the worst imaginable threat to democracy" and like you, I say, how is this possible? They will cause casualties and panic, but they aren't going to seriously disrupt activities for more than a few weeks (in most credible cases). Worst thing that could happen is that the president might suspend habeous corpus and ignore the will of Congress in important non-proliferation legislation.

Oops. Guess that already happened.

[CKR]

Thanks for the link, Jeffrey. Whether to use an initiator is only one of the decisions that the group would have to make, a series of tradeoffs that, when combined in the wrong ways, could result in a dud. That's why you have the physics team, of course, to calculate a design. Anything you get on the free market, including designs from Wikipedia as well as enriched uranium, may have flaws.

Writing an article like this (or this review or even this response) entails walking a fine line between telling the bad guys something they need to know and making a plausible case while informing the general public accurately and adequately, as J. once more makes clear. But I thought that Zimmerman and Lewis's article made it sound too easy, rather than too hard. In all of the tasks, a certain amount of "art" is needed to make things go right. I've found that chemical manipulations that seem straightforward from a journal paper with full instructions can be tricky. And that's on top of general experience with chemical manipulations.

I assumed, too, that it would be a terrorist group, which I think puts added pressures and divisive motivations into the team. States have other options.

[Andrew Foland]

As you say, the one of the hard parts is getting a team together, and keeping it quiet. A project management question: how much easier would it be to assemble the team if you were willing to accept a substantial probability of fizzle? Is it a trade worth making?

[CKR]

I'm not sure that's the trade, Andrew.

The sponsoring organization would accept some probability of fizzle; there wouldn't be much difference in the effect on the public of a headline

Nuke Devastates Lower Manhattan

versus

Nuke Devastates Manhattan.

A dud would be scary,

Mysterious Nuke found on Wall Street

but not damaging.

To accept your challenge, though, I would estimate that the probability of fizzle is inversely proportional to the years of relevant experience on the team. The distribution of that experience is important, too. A gray-bearded physicist's years wouldn't necessarily balance a green electronics team.

[Marie Cannon]

Came accross this on crusademedia titled 'al qaeda has nuclear weapons'

http://www.crusade-media.com/news1.html

[CKR]

The Crusade Media article is based on a number of dicey assertions. I won't go into all of them, but the main one is Alexander Lebed's claim of missing suitcase nukes.

Here's a report from a more reliable source, the Monterey Institute for Nonproliferation Studies. Its conclusions:

First, the probability that any portable nuclear devices were lost prior to or after the breakup of the Soviet Union appears low; the scenarios of loss offered by the special commission in 1996 are actually the least plausible among other possible scenarios. This does not mean that the threat does not exist, but rather that at this moment, it is probably not the most immediate threat to the home security of the United States or to U.S. armed forces abroad.

Second, even if any devices were lost, their effectiveness should be very low or maybe even non-existent, especially if the loss occurred during the period of the greatest risk, in the early 1990s. Without scheduled maintenance, these devices apparently can produce only minimal yield and eventually possibly no yield at all, and can only serve as a source of small amounts of weapons-grade fissile materials.