No Experience Necessary

Abstract

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

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 todays Al Qaeda, or some other terrorist group, will build the bomb?

In April 1964, only the United States, the Soviet Union, France, and Britain were nuclear powers. The Cold War was on, and the arms control debates that began even before the Trinity test still raged. The chilling experience of the Cuban missile crisis was less than two years old. And there was fear in the air that nuclear weapons would spread to other, perhaps unexpected, countries.

Britain had been the third country, France the fourth. Would China be the fifth? (It would, six months later.) Where would it end? Which would be the Nth Country? One list of potential proliferators contained the names of a staggering 26 countries, from Argentina to Yugoslavia. 1

Even college students entered the public debate. Chris Hohenemser was a 19-year-old kid when he testified before a congressional committee in the spring of 1958. The issue then was the international sharing of nuclear reactor technology, and he was against it. It wasnt going to serve the process of getting nuclear weapons under control, he said recently.

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.

At the Lawrence Radiation Laboratory (later to become Lawrence Livermore National Laboratory), the bomb designers believed there was no secret, just physics. And they knew that designing a bomb wouldnt require Nobel laureates: Unlike rival Los Alamos, Livermore didnt have any. But the lab had been pushing the envelope of weapons design since 1952, beginning with a batch of young physicists out of Ernest Lawrences Rad Lab in Berkeley.

Livermore was driven by experimentalists, Los Alamos by theoreticians, so it was natural for a Liver-more manager to suggest that if they wanted to know if nuclear innocents could design a bomb, somebody ought to just do the experiment and find out. 2

Today, Dave Dobson is an affable, 65-year-old physicist who has enjoyed a long and successful career teaching at Wisconsins Beloit College. In 1964 he was a post-doc at the Rad Lab in the hills above Berkeley. He occasionally made the 40-minute drive to the labs Livermore outpost to use some of the bomb labs equipment for his own unclassified research. He held no security clearance, and what little he knew about nuclear weapons came from reading the newspapers.

He was approached one day by Hans Mark, a Livermore physicist and later a secretary of the air force. Mark offered him a job. The understanding was that he had something special for me to do, Dobson remembered. Mark had made the same promise to another young post-doc, David Pipkorn.

Dobson and Selden worked out of old navy barracks, shown here as they looked during World War II.

The nature of their mysterious assignment became clear soon enough. It was just basically to design a nuclear explosive without classified information, Pipkorn said much later.

The two young men were picked out of the sky, as Dobson put it, because they were nuclear innocents.

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, Its 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.

To the lab, the experiment was a national security issue, but Dobson and Pipkorn had first-job anxiety. I felt like my reputation was on the line, and I would feel like an absolute idiot if I missed anything, Dobson said.

The one big advantage we had over Fermi and Teller and those guys was that we knew it could work, Dobson said, something the U.S. government had published in the skies over Japan, in the words of Jim Frank, the physicist who headed the anonymous Nth Country committee.

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 Pip-korn made their first crucial choice. They opted to design a Nagasakistyle 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.

You just go to the library and you start looking under all the subjects … plutonium and uranium and high explosives …

A few months later, Pipkorn quit the project. He was replaced by a young army lieutenant, Bob Selden, who had a doctorate from the University of Wisconsin, in Madison. He had arrived in Livermore by happenstance, steered that way as a result of sharing drinks in an officers club with an army personnel specialist. You know, the specialist said, I had a buddy, an ordnance officer, who went to this radiator laboratory.

Seldens job interview was conducted in a hotel room in Washington. A Livermore physicist quizzed him on nuclear physics and chain reactions. He kept asking all these questions and I would answer and know that I didnt know the answer and it got worse and worse. I became very discouraged. When I went home that night, I thought, boy, thats it. Selden had no way of knowing he was the perfect candidate. The next day he got a phone call from Art Hudgins.

Selden and Dobson had adjoining offices and hit it off immediately. He and I had a lot of fun together. Wed bounce things off each other, argue, then go away for a while and come back and argue some more.

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 de-signers. 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 labs 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 Paxtons 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 youd have to do, Dobson said.

In a less theoretical situation, preliminary experimentation might prove deadly to would-be bomb makers. Hudgins, who oversaw the experiment, knew that from reviewing some of the amateur bomb designs that came in over the transom to the federal government.

Usually they [would-be designers] used too much uranium, plutonium, he said. They had not given proper attention to what would happen when they assembled their bomb, or even when they were just working with the uranium and plutonium. People just figure theyll use lots of uranium and then theyll have enough.

Dave Dobson in 1964.

Even at the labs, there were accidents. In 1946 a senior physicist at Los Alamos died of radiation poisoning two weeks after accidentally bringing two sub-critical hemispheres of plutonium, each the size of half a cantaloupe, into direct contact. Liver-more had also suffered a serious crit-icality accident the year before Dob-son and Pipkorn arrived–50 pounds of uranium had burned or melted when equipment jammed during another criticality experiment. 6

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, Smyths 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.

Bob Selden at Livermore.

Along the way, Selden discovered that someone had walked down the same path, a few years earlier, in 1960, producing a report, The Nth Country Problem. 7 Three researchers active in the proliferation debate had used the unclassified literature and their own calculations to create not only a crude paper design for bombs, but also a design of the production complex required to build them.

It was a similar sort of thing, Dobson remembered. We got hold of it sort of in the middle of things, and it was helpful. One of the authors was Chris Hohenemser, the 19-year-old kid who had testified before Congress in 1958.

Hohenemser and his co-authors had concluded that designing the bomb was relatively easy. There was no secret. The hard part, they reported, would be getting the plutonium or enriched uranium.

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 labs rural testing area, using explosives known as bara-tol and Comp B. The labs veteran weapons designers couldnt 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 youre doing and that we could calculate what the result was going to be, Selden said.

Their odyssey had its lighter moments. In the middle of the project, Selden gave a talk in southern California on liquid helium, his thesis topic, and unexpectedly found himself in conversation with Manhattan Project physicist Richard Feynman. Feynman regaled Selden with reminiscences of Los Alamos and offered a short course on the theory of safecracking, but spilled no secrets of bomb design.

By December 1965, the teams 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 werent 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.

By December 1965, the first rough design of a plutonium bomb was finished. Nine months later, it was final.

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 theyd 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 wasnt 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.

They described weapons-design concepts using nicknames they had created. Jim Frank, the Livermore physicist who had headed the technical committee, would intervene occasionally from the sidelines to translate from Nth Country nomenclature to the language of the U.S. weapons program. Frank would explain, When they say X, its what we would call Y. There was some surprise when one of the Dobson-Selden nicknames was a perfect match with a phrase created by Manhattan Project scientists 20 years earlier.

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.

Dave Dobson and David Pipkorn left the weapons world not long after the experiment. Pipkorn went into industry. Today, he is retired and lives in Dayton, Ohio. Dobson lives in Beloit, where his stint as a bomb designer has been in the back of my mind all this time. Only Selden stayed in the business, rising through the ranks at Livermore and then Los Alamos, becoming a key manager. For three years he was the chief scientist for the air force and still serves on the U.S. Air Force Scientific Advisory Board.

The cover and an excerpt from the once-classified “Nth Country Report.”

Selden has studied the question of whether terrorists could develop a nuclear weapon, and his answer is yes. Thats the key question of the time we live in, whether or not that can be done, he said. Its certainly possible for a terrorist group if theyre 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 wouldnt have to know anything about nuclear weapons in the beginning. Selden and Dobson proved that. Theres enough information available on the Internet to put terrorists in the right ballpark, Selden said, after which theyd 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 worlds 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.

They could send it up Chesapeake Bay, San Francisco Bay, Puget Sound, or the Mississippi River. You could go any place, almost. Most large cities are either coastal or on a major river, where barge-type shipping goes, Dobson said.

Commercial hydrodynamics codes and machine tools have improved since the experiment and are readily available from commercial sources. Physicist Ted Taylor, who has been arguing for decades that building a fission bomb is almost a garage project, said in 1987 that even pottery equipment is useful. You can shape C4 [the explosive] beautifully on a potters wheel. How easy is it for terrorists to build an atom bomb? Very easy. Double underline. Very easy, Taylor says. At a meeting some years ago, Selden was asked, Bob, could you do it alone? According to Taylor, the answer was Yes.

Selden now says no: Singlehand-ed? Not a prayer. But he agrees it would take only a handful of people, if they were technically competent and could acquire the fissile material.

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 Japans 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 its 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.

For clandestine bomb makers, the high percentage of plutonium 240 in reactor plutonium would pose a radiation risk, require more fuel, and lower the yield of a weapon, but terrorists would likely find those conditions acceptable. Any group sophisticated enough to fabricate a bomb from weapons-grade plutonium could handle reactor plutonium as well, according to Carson Mark, who headed the theoretical division at Los Alamos from 1947 to 1972. By one estimate, the yield of an implosion bomb made from reactor grade plutonium would be one to a few kilotons, and more using an advanced design. 9 Even if the bomb fizzled, its yield could still devastate the center of a city.

And theres a lot of reactor plutonium around for terrorists to try to get their hands on: Worldwide, the power industry produces 24 tons per year of reprocessed plutonium. 10

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 designers task by reducing the odds of pre-initiation. Either an implosion or gun-assembly type weapon is possible with uranium.

With modern weapon-grade uranium, the background neutron rate is so low that terrorists, if they have such material, would have a good chance of setting off a high-yield explosion simply by dropping one half of the material onto the other half, Nobel Laureate Luis Alvarez wrote in his autobiography. Most people seem unaware that if separated, highly enriched uranium is at hand, its a trivial job to set off a nuclear explosion … even a high school kid could make a bomb in short order. 13

A terrorist could expect a yield of 10 to 20 kilotons from highly enriched uranium, roughly the range of the devastating Hiroshima and Nagasaki weapons, according to a congressional study for which Bob Selden was an adviser. 14

Most of the worlds highly enriched uranium that terrorists might seek to procure is in the hands of weapons programs. Selden, who has worked with the Russians to safeguard their stores, says the terrorist problem is taken seriously there, but material security is still far from U.S. standards.

Another potential source of highly enriched uranium is research reactors, where the metal is burned as fuel. Such reactors are scattered around the world. Anti-terrorism concerns prompted the U.S. government to cooperate last August in the emergency evacuation of 48 kilograms of reactor fuel flown safely from Belgrade to Russia.

The dangers of nuclear terror have been obvious since the beginning of the atomic age. Edward U. Condon, having played a major role in the Manhattan Project, wrote in 1946: In any room where a file case can be stored, in any district of a great city, near any key building or installation, a determined effort can secrete a bomb capable of killing a hundred thousand people and laying waste every ordinary structure within a mile. 15

Jay Davis, who headed the Pentagons 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.