link target=_blank>Bulletin of the Atomic Scientists: No experience necessary

The Nth Country experiment showed that three post-docs with no nuclear knowledge could design a working atom bomb.

By Dan Stober
March/April 2003 pp. 56-63 (vol. 59, no. 02) © 2003 Bulletin of the Atomic Scientists

Thirty-nine years ago, in the dusty ranch town of Livermore, California, the U.S. government secretly chose three newly minted post-doc physicists, put them off in a corner of a laboratory with no access to classified information, and told them to design a nuclear weapon.

What can the unsettling results of that experiment tell us about the likelihood that today's Al Qaeda, or some other terrorist group, will build the bomb?

[...]

Much of the proliferation debate centered on industrial capabilities for enriching uranium or producing plutonium. But there was a second argument, one with a whiff of elitism and scientific arrogance. Were the scientists from a small, possibly Third World country, smart enough to design an atomic bomb? Or did it require an Oppenheimer?

There was also the myth of the "secret" of the atom bomb, reinforced by the publicity surrounding the Fuchs and Rosenberg spy cases of the 1950s. David Lilienthal, the chairman of the Atomic Energy Commission, had argued as far back as 1948 (in the Bulletin) that the idea of a "secret formula" was "nothing less than a gigantic hoax upon the people of this country." But many still believed that if only the "secret" could be guarded, proliferation might be prevented.

[...]

They were briefed by physicist Art Hudgins, who handed them a copy of the "operating rules," stamped "Secret" on every page. [3] The first paragraph said it all: "The purpose of the so-called 'Nth Country Experiment' is to find out if a credible nuclear explosive can be designed, with a modest effort, by a few well-trained people without contact with classified information. The goal of the participants should be to design an explosive with a militarily significant yield. A working context for the experiment might be that the participants have been asked to design a nuclear explosive which, if built in small numbers, would give a small nation a significant effect on their foreign relations."

Although banned from classified information, Dobson and Pipkorn needed security clearances--and any sketches they drew would be "born secret." As Hudgins put it years later, "It's against the law to design nuclear weapons without a clearance." They were to represent an imaginary Nth Country, assumed to have a good university library, some competent machinists to shape plutonium or uranium, and an explosives team. They envisioned their nameless country having more resources than Ghana, but less than an industrialized nation. They were given no directions on how to proceed.

If they wanted to conduct an experiment, perhaps involving high explosives, they would describe the experiment in great detail, and their memo would be passed on to an anonymous team of experienced bomb designers who would calculate the results and pass them back through Hudgins. They began in isolation, with a simulated technical staff. They worked in a plain office in barracks left behind by the navy after World War II. Dobson had a desk and a filing cabinet protected by a combination lock. Their notebooks were bound and numbered sequentially, to preserve a record of their progress.

[...]

Dobson had never heard the terms Trinity, Little Boy, or Fat Man. Gun design versus implosion was unknown to him. His knowledge of nuclear fission was limited. "I had seen an exhibit with a model of a chain reaction made up of mousetraps and ping pong balls," he wrote in a later report.

By the end of 1964, seven months after they began, Dobson and Pipkorn made their first crucial choice. They opted to design a Nagasaki-style plutonium implosion bomb instead of a Hiroshima uranium gun-assembly weapon. They picked plutonium not because it was easier, but specifically because it would be more difficult. It was a career-enhancing move: The gun bomb was too simple a project to build a reputation on. The implosion method "seemed to be a more sophisticated, challenging, and hence appealing problem," as they later wrote in their report. Designing a mere gun bomb would have been "a pretty crummy showing," Dobson said.

[...]

They continued to mine the open literature. As Selden described it, "You just go to the library and you start looking under all the subjects, you look under plutonium and uranium and high explosives and you look under nuclear physics and you just keep going and you find articles and stumble across things and books and publications."

They learned about uranium and the details of fission chain reactions courtesy of Dwight Eisenhower, whose "Atoms for Peace" program, designed to help the spread of nuclear power plants, scattered technical information around the world. A reactor, after all, is a fission weapon running in slow motion, "kind of like a bomb that goes off in infinite time," Dobson said.

There is an extensive literature on explosives. Commercial explosives are used from oil fields to road construction, mining to munitions. And as the Iraqis would discover in the 1980s, U.S. university libraries were gold mines of information for clandestine bomb designers. [4] As Selden said, "If the university had a school of mines and engineering, then they would have all the stuff on high explosives and detonation that we needed." To talk to the experts, Selden simply went to an explosives conference.

On a shelf in the lab's unclassified technical library they found charts of data that the wizards of Los Alamos had compiled through tedious, dangerous research. Critical mass numbers were readily available. Hugh Paxton's work provided them with a starting point for calculating how much plutonium they would need. [5] "That kind of information greatly reduces the amount of preliminary experimentation you'd have to do," Dobson said.

[...]

The Nth Country scientists quickly found their way to the work of Princeton physicist Henry DeWolf Smyth. Published by the Manhattan Project just weeks after Hiroshima, Smyth's A General Account of the Development of Methods of Using Atomic Energy for Military Purposes Under the Auspices of the United States Government was just what it claimed to be. This 40-cent, 182-page paperback served as a project-management manual for designing and building the bomb. Dobson and Selden quickly deduced from the Smyth report that uranium would work just fine for the tamper of their bomb.

[...]

To model their design, Dobson and Selden wrote their own codes, which they ran on a punch-card computer far more primitive than the cheapest home computer made today. But it was all the computing power they needed. Although the committee usually calculated the results of their proposed explosive tests instead of conducting actual tests, in a couple of cases, a design question was resolved with an actual non-nuclear explosion conducted at the lab's rural testing area, using explosives known as baratol and Comp B. The lab's veteran weapons designers "couldn't calculate precisely what would happen because nobody had built a device like that for such a long time," Selden said. "We were back to pretty rudimentary technology."

And so they progressed, designing the detonators, the explosive lenses, the uranium tamper, the plutonium core, and a polonium-beryllium initiator inspired by the standard neutron source used to start reactors. "All of this just goes on and on until you evolve through and get to the place where you think that you know what you're doing and that we could calculate what the result was going to be," Selden said.

[...]

By December 1965, the team's first rough design of a plutonium bomb was finished. Nine months later, the design was final, with blueprints to guide their imaginary machinists. Their weapon was too big to fit on a missile, but small enough to be carried by airplane or truck. More interested in guaranteeing an explosion than in maximizing yield, they went with a conservative design. ("We weren't trying to get fancy and optimize things," said Dobson.) The same philosophy guided the first nuclear explosives of the United States, Britain, Russia, and China, all of which came in at around 20 kilotons.

[...]

For veteran bomb designers, accurately predicting the yield of their bomb is of great importance. Dobson and Selden had only a vague idea of the power of their bomb, but did it matter? For an aspiring nuclear state (or a terrorist group), a bomb was a bomb was a bomb. "If Iraq had one of those, you would believe [in it]," Selden said in 1995.

Selden and Dobson wrote a detailed report, carefully documenting their research, and also offered a lengthy tape-recorded narrative, providing a solid underpinning for the political point the lab was attempting to make. Their list of useful articles in the open literature ran four pages, and although the articles were unclassified, the list was, and remains, classified.

According to the official chronology, the Nth Country device was tested (hypothetically) in April 1967. But its designers were not told whether their hypothetical bomb exploded or failed. They remained "knowledge virgins," in anticipation of what became known as the "road show."

It was the "summer of love" in San Francisco, a mere hour away from Livermore. But Dobson and Selden packed their bags for a trip to Washington to explain to the government how they'd designed an atom bomb in an old barracks building.

They went to the CIA, the State Department, and the Atomic Energy Commission. They spoke to generals at the Pentagon. They created a hubbub with a command performance before the advisory committee of the Atomic Energy Commission. By the time they arrived at the National Security Council, word had spread, and there was a crowd in the basement of the Old Executive Office Building. A few staff members without the proper security clearance (Secret Restricted Data--mere Top Secret wasn't good enough) were told to leave the room.

Later, the duo performed at Oak Ridge National Laboratory, where weapons uranium was produced, and then made the pilgrimage to Los Alamos, where some of the deities of the Manhattan Project yet reigned. It was a heady experience for a couple of post-docs.

Eager to prove that Selden and Dobson were true representatives of an Nth Country, untainted by inside information, Livermore officials devised a convincing presentation. Armed with 35-millimeter slides and a pointer, the two men--who had still not been told whether their weapon was a success--described their bomb and their calculations.

[...]

The listeners were told to phrase their questions with care in order not to give away classified information or even tip the lecturers as to the triumph or failure of their venture. "They listened, whispered, thanked us, and left the room," Dobson said.

When, finally, the road show was over, Selden and Dobson were told what they had already guessed: Their labor of three years had succeeded. They had designed a working atom bomb. The reaction from audience members was in proportion to their working knowledge of nuclear weapons. Some civilian officials were stunned, Hudgins said, but most scientists were not.

There was talk of a live nuclear test, to really drive home the point. But the expense could not be justified. The bomb had been run through the computers and the brains of the bomb designers--it would explode, it would wipe out a city, it would kill tens of thousands, or hundreds of thousands, of people.

But there was one last surprise for the boys of the Nth Country. "If you guys are up to it we want to do a little add-on," an administrator told Selden. "We want you to do a thermonuclear." They were given only six weeks to work on it, so their design was more theoretical than practical. They did not discover radiation implosion, the key to U.S. hydrogen bombs, but they came up with something that would have worked well enough for a terrorist. "We actually did come up with some thermonuclear yields," Selden said.

[...]

Selden has studied the question of whether terrorists could develop a nuclear weapon, and his answer is "yes." "That's the key question of the time we live in, whether or not that can be done," he said. "It's certainly possible for a terrorist group if they're really technically savvy and have a lot of resources." The terrorists would need a set of skills: physics, chemistry, explosives, electronics, and access to some machine tools. But they wouldn't have to know anything about nuclear weapons in the beginning. Selden and Dobson proved that. There's enough information available on the Internet to put terrorists "in the right ballpark," Selden said, after which they'd still have to do their own design calculations. Ironically, the most trustworthy Web sites may be those of brand-name arms control organizations, whose papers are written by scientists and carefully footnoted.

From his experience, Dobson believes Al Qaeda, if it were not on the run, could attain the world's worst terror weapon. "It seems to me that this Al Qaeda is enough of an organization, with enough people and enough funding that they probably could." He worries about sea-going shipping containers, which are large enough to hold a heavy, conservatively designed weapon that would have a high chance of success.

[...]

In 1976, Selden wrote a set of briefing viewgraphs that opened up a new front on the proliferation struggle and are often cited in discussions of nuclear terrorism. He settled the dispute over whether plutonium extracted from fuel rods in commercial power plants could power nuclear weapons in "Reactor Plutonium and Nuclear Explosives." [8] "All plutonium can be used directly in nuclear explosives. The concept of . . . plutonium which is not suited for explosives is fallacious," he wrote.

Selden knew that in another hands-on experiment, U.S. weapons designers had proven the concept at the Nevada Test Site in 1962, when they blew up a bomb using reactor-grade plutonium. Ichiro Ozawa, the leader of Japan's opposition Liberal Party, underscored the point 40 years later. In a speech last April that sent shock waves across Asia, he said: "We have plenty of plutonium in our nuclear power plants, so it's possible for us to produce 3,000 to 4,000 nuclear warheads. If we get serious, we will never be beaten in terms of military power."

[...]

Metallic plutonium is not the only option for a terrorist bomb. Powdered plutonium or uranium oxide would work as well, and would be easier to handle. In fact, a group of well-known Los Alamos weapon designers concluded that oxide powder of either type "would seem to be the simplest and most rapid way to make a bomb." [11] It has even been suggested that terrorists could simply pour oxide into a container until it began producing neutrons. That level would be, de facto, almost a critical mass, and thus the amount required for a bomb. The potential yield could be tens to hundreds of kilotons. [12]

While any type of plutonium would work for a bomb, the gold standard for terrorists has to be highly enriched uranium. Its lower radioactivity is less hazardous to its handlers and also lessens the complexity of the designer's task by reducing the odds of pre-initiation. Either an implosion or gun-assembly type weapon is possible with uranium.

[...]

Jay Davis, who headed the Pentagon's Defense Threat Reduction Agency during the Clinton administration, and was earlier a U.N. inspector in Iraq, said there is general agreement in the nuclear community that terrorists can build a bomb. "A very small group of people could do that if they could get the material," he said. During the Clinton administration, he tried unsuccessfully to convince the weapons labs to launch a new version of the Nth Country Experiment, this time asking whether terrorists could build the bomb.

Bob Selden thinks he knows why no one was interested: He and Dave Dobson answered the question 39 years ago.

link target=blank>Summary Report of the Nth Country Experiment