What's Left to Protect?

Abstract

The journalist who fought to reveal the “secret” of the H-bomb says there are, in fact, no secrets left

Are there really “vital nuclear secrets?” The presumption to say “yes” is so strong that to challenge the statement is to risk being dismissed before discussion can begin. And in the political climate generated by the China spy scandal and the Wen Ho Lee court case, to propose throwing open the nuclear books is unrealistic.

At the moment, all the political pressure is in the opposite direction: recent declassifications of nuclear-related material has been excessive, congressional critics say, and the trend must be reversed. 1

But in a democracy, public understanding of government activity is essential, especially when the survival of civilization is at stake. In principle, all government secrecy is a disenfran-chisement of the electorate. It provides cover for bad decisions and abuses of power and it promotes passivity and ignorance on the part of citizens.

On March 28, Gen. Eugene E. Habiger, the nation's new nuclear secrets czar, testified before the Senate Appropriations Committee about an audit of 64 million pages of nuclear-related documents that had been declassified. They contained, Habiger said, “significant amounts of sensitive nuclear weapon design information.”

Another 450 million pages will be examined, he added. A thousand reviewers have been trained for this kind of work, and another 500 will be trained in fiscal year 2001. 2 Habiger's remarks left little doubt that he will take a conservative stand regarding declassification.

Chance timing

A national security scheme based on controlling technical information is a losing game. Information flows in only one direction—out—and once out it never goes back in. Furthermore, transparency, the opposite of information control, actually enhances the kinds of nonproliferation strategies that have a chance of really working: control of nuclear facilities and materials, of testing, and of deployments.

After nearly 50 years, it seems implausible that one big secret remains. Whatever it is, it can't be very important.

But nuclear secrecy is a difficult habit to break. The sociological underpinnings of the secrecy business are complex, and largely shaped by chance timing.

The Italian scientist Enrico Fermi first accomplished nuclear fission— without realizing it—in the spring of 1934. It was not until the eve of World War II that a group of German scientists accurately described what happened when uranium was bombarded with neutrons.

If the fission cat had been let out of the uranium bag in the mid-1930s, the world would have known that nuclear explosives a million times more potent than chemical explosives were plausible. 3

Would World War II have been averted by fear of a nuclear holocaust? Or would war have come anyway? That is unknowable. But this much is certain: the world would not have been surprised by the use of an atom bomb. Nuclear technology would have evolved on the public stage one discovery at a time. The scientifically aware populace, which was fascinated by superstars like Marie Curie and Albert Einstein, would have hungered for details, and journalists would have supplied them. Total secrecy would not have been possible.

As it was, four important years elapsed before nuclear fission became the talk of the worldwide physics community, and wartime secrecy quickly divided the international physics community into competing weapons labs. 4 The public would remain virtually clueless until August 6, 1945.

These special circumstances made it possible for the U.S. government to claim ownership of the entire field of atomic energy. At the time, it appeared reasonable for the government to assert that all “atomic energy information,” regardless of its origin, was a permanent state secret until it was declassified. 5

During the 1940s, new discoveries had been made secretly in government-financed labs. No other field of human knowledge has been treated this way. The “born secret” status of atomic energy information is unique, primarily because the 1940s were unique.

A few basics

One result of nuclear secrecy has been a mythology and a bureaucracy which, to this day, are almost impregnable. The secrecy industry can be expected to fight for its survival, but the larger society deserves to know what is being protected, besides vested interests. The belief that keeping secrets will discourage nuclear weapons proliferation is widely held, but is it true? Are the secrets really secret in any practical sense?

Hiroshima revealed the most important secret: that a mass of fissile material could be held together long enough for a significant fraction of it to undergo fission. In comparison, all other nuclear “secrets” are trivial. With that fact alone, any determined group of qualified people could work out the details, from scratch if necessary.

Albert Einstein described the situation and its consequences in a 1947 fund-raising letter for the Emergency Committee of Atomic Scientists: “For there is no secret and there is no defense; there is no possibility of control except through the aroused understanding and insistence of the peoples of the world.” 6

But Einstein's letter, goes the argument, was written before the invention of the H-bomb. When Edward Teller and Stanislav Ulam invented radiation implosion in 1951, they created a new secret, the secret of the H-bomb, something Einstein did not anticipate.

Twenty-one years ago, I revealed the essence of that secret in the Progressive magazine, after a landmark court battle over the right to publish. 7 (The government dropped the case after six months of prior restraint censorship.)

It turns out the secret was overrated. In the end, says Richard Rhodes, author of Dark Sun, the 1995 book on the development of the H-bomb, “for all its sinister reputation [the H-bomb] is really only a fancy way to do fission.” 8

All nuclear bomb designs derive from Fermi's 1934 neutron experiment, the one he misunderstood until 1939. Neutrons plus uranium equals fission. Since fission produces neutrons, fission can generate more fission. In pure fissile materials, the self-sustaining chain reaction is so rapid and energetic that the only design challenge is keeping the fuel together long enough to avoid a “fizzle” caused by premature disassembly.

Compression and neutron supplementation are the basic ways around this problem. Implosive compression, which squeezes uranium metal like a soft rubber ball, speeds up the chain reaction by narrowing the spaces between fissile nuclei and increasing the chance of neutron capture resulting in fission.

It also creates inward momentum that must be stopped before expansion begins, thus buying time before disassembly ends the process. Handily, the tamper used in compression serves as a neutron reflector that redirects stray neutrons back into the mix.

If, in addition, the compressed fissile mass is flooded with neutrons produced by hydrogen fusion, the fission burn will be virtually complete. Using fission to cause fusion turned out to be merely a matter of subjecting the hydrogen fuels to compression and high temperature.

The secondary stage of the bomb, the part subjected to compression by radiation implosion and to intense bombardment by fusion-generated neutrons, is essentially a fuel charge. At equal efficiency levels, the power of the bomb is determined by how much uranium is located in the secondary.

There are three basic elements of a modern thermonuclear weapon: the primary, the secondary, and the connections between the two. On September 20, 1979, a few days after the government dropped its censorship case against the Progressive, Edward Teller described these three elements in an interview: “There was no question in my mind how the super should be made. We needed a primary, we needed a secondary, we needed a spark plug.

“The secondary had to have cylindrical symmetry because that was the symmetry natural to the process. The energy transfer had to go by radiation in order to make it as close to simultaneous as possible. All this was clear to me.” 9

All three elements had been highly refined by 1960, and the refinements were largely a matter of shapes. The primary, for instance, is usually depicted as a plutonium sphere surrounded by many high explosive charges, a miniature version of the implosiontype Nagasaki bomb.

But it was quickly discovered that implosion did not have to be spherical. The two ends of a cylinder, or an ovoid, could be driven toward each other to momentarily create a high-density sphere. This two-point detonation scheme greatly reduced the diameter and the weight of the primary. 10

Another early refinement: levitation—backing the tamper off from the fissile core so that it delivers “shock” pressure—increased the compression. Precision timing of the first triggering neutrons as well as boosting by a flood of fusion-generated neutrons a microsecond later further improved efficiency of the primary.

The secondary is a replica of the primary, but vastly more efficient and powerful, without being much bigger. The early secondaries were cylindrical, as Teller described, because the original goal was to make the largest possible multi-megaton explosion with a device whose diameter was more tightly constrained than its length.

Some rough calculations. The secondary contains three active ingredients: lithium 6, which becomes hydrogen 3 (tritium); deuterium, which is hydrogen 2; and uranium, which is fissioned by the neutrons emerging from the fusion of the two hydrogens. (The deuterium, normally a gas, is stored as solid lithium deuteride.)

From Our Files

“Some diehards in Congress and the press have maintained that we have had not too much but too little secrecy…. However, it seems that this kind of talk has lost its effect on the American mind; that the cult of the Great Atomic Secret has now collapsed … one can hope [there] will not be a revival of the belief in salvation through secrecy.”

Eugene Rabinowitch, December 1949 Bulletin

Optimal efficiency suggests that the secondary should contain equal numbers of atoms of the three ingredients, analogous to the matching of molecular weights for a chemical reaction. A secondary so composed would be about half uranium by volume, but 96 percent uranium by mass, with an average density of 10 kilograms per liter. Calculating from the well-known nuclear energy potential of the three ingredients, a one-liter secondary would yield 100 kilotons of explosion (seven Hiroshima bombs), assuming 50 percent efficiency of uranium fission. The secondary for a one-megaton warhead (70 Hiroshima bombs) would thus be 10 liters in volume, smaller if the fission efficiency were higher.

A 10-liter sphere would be only eleven inches in diameter, easily small enough to fit inside the 20-inch-diam-eter cylindrical casing of the first Polaris missile warhead, the W47, which was tested in 1958 and deployed in the 1960s. Dan Stober, of the San Jose Mercury News, says a version of this warhead contained the first spherical secondary, an arrangement which was soon to become the standard design. 11

If the reported description of the W88 secondary is correct, namely a sphere 172 millimeters (seven inches) in diameter, the implied efficiency of uranium fission is more than 90 percent. 12

The advantage of a spherical secondary is higher compression. For example, if the walls of an 11-inch diameter cylinder are imploded inward four inches, the result is a three-inch diameter cylinder compressed by a factor of 15. On the other hand, if an 11-inch diameter sphere is imploded inward by the same four inches, the result is a three-inch diameter sphere compressed by a factor of 50. And compression is the key to efficiency, for both fission and fusion.

The third element of weapon design is the matter that was dubbed “radiation coupling” in the 1979 court documents of the Progressive case. It is the method by which the primary implodes the secondary.

Public descriptions of radiation coupling are sketchy, but the scientists who have spent their working lives perfecting it have long been eager to publish what they know about radiative energy transfer under conditions resembling the interior of stars. Curiously, whenever their work is declassified and published it shows a strange preoccupation with using X-rays to cook plastic. 13

The trickiest aspect of radiation coupling is probably the channeling of the radiation flow around the secondary to create an implosion based on temperature difference—hot on the outside, cold on the inside. It would be especially tricky for a spherical secondary, because all the energy would initially come from one direction and would tend to reach the near side of the sphere first.

In practical terms, bomb designers ran out of work years ago. The W88 is a quarter-century-old modification of a half-century-old invention.

Presumably, the 1,500 classification specialists who are reading through the 450 million pages of archival documents are looking for any references to opacity studies, the shapes of radiation channels, and the hydrodynamics of radiation flow in the channels.

Computer simulations of this process are called “channel codes.” They seem to be the essence of what remains classified, except for trivia which could fill a small library.

Especially in the area of channel codes, the published literature on nuclear weapon design is lacking in engineering detail. The published drawings are crude illustrations of concepts, not blueprints. And the drawings are said to not closely resemble the real thing.

Mysterious “secret”

I am told that there is still at least one non-trivial piece of the basic H-bomb design concept that has eluded publication in the open press—something that separates “insiders” from “outsiders,” something that makes the feat of the 1951 design team seem legendary and that gives each insider a grave responsibility to avoid being the one who lets this last kitten out of the bag.

But this icon of nuclear secrecy, if it exists, is known to thousands of people in the bomb labs, the federal energy bureaucracy, congressional committee staffs, and defense contracting firms, and to their counterparts in Russia, Britain, France, and China.

Somehow, after nearly 50 years, it seems implausible that one big secret remains. Whatever it is, it can't be very important. We know that in the spring of 1951, the idea of a two-stage, radiation-implosion device was first placed on the design table. Eighteen months later, in November of 1952, the first 10 megaton explosion was set off.

If it took less than two years to go from novel concept to full-scale demonstration a half century ago, the task would surely be easier with today's technology. The channel codes that taxed the limits of the earliest electronic computers can probably run in the background on a modern laptop, with a video game in the foreground.

Meanwhile, much that has been learned and published in astrophysics and laser fusion is relevant. It is simply not possible that the field of high energy density physics was more advanced in 1951 than it is today.

In practical terms, bomb designers ran out of real work decades ago. For example, the W88 warhead at the center of today's “spy” drama is a 1970s design. It is routinely described as the “latest” or “most sophisticated” U.S. warhead. Somehow press accounts rarely note that the W88 is a quarter-century-old modification of a half-century-old invention.

In 1970, a blue-ribbon Task Force on Secrecy stated in its final report to the Pentagon: “Security has limited effectiveness. One may guess that tightly controlled information will remain secret, on the average, for perhaps five years. But on vital information, one should not rely on effective secrecy for more than one year.”

The report illustrated that statement using the H-bomb as an example: “Certain kinds of technical information are easily discovered independently, or regenerated, once a reasonably sophisticated group decides it is worthwhile to do so. In spite of very elaborate and costly measures taken independently by the [United States] and the [Soviet Union] to preserve technical secrecy, neither the United Kingdom nor China was long delayed in developing hydrogen weapons.” 14

In 1979, Edward Teller told me he was the author of that passage.

Stifling debate

Einstein was right. There is no secret. One of the most pernicious effects of secrecy is to cause nuclear weapons to be overvalued. When a battalion of bureaucrats is searching the archives for misplaced secrets, the impression is given that something must be worthy of all this protection.

The United States encourages the world to copy its free-market economy and its democratic institutions, but it quakes in fear that “rogue” nations might copy a tenth of one percent of its nuclear arsenal. The United States, the inventor of nuclear weapons and the only nation to use them, has a moral responsibility to lead the world, by example, away from Armageddon.

Instead, we put our faith in secrecy, and secrecy helps to hide our folly. The most often cited justification for nuclear secrecy is fear of nuclear proliferation. But information is not a constraint in the production of crude A-bombs. The Hiroshima bomb was so simple it was dropped without being tested. Israel reportedly has a large arsenal of untested but presumably reliable A-bombs.

Terrorist groups and “rogue” nations aspiring to join the nuclear club and reap the benefits of being able to threaten nuclear destruction are not likely to set their sights on radiation-imploded secondaries that fission 90 percent of their uranium. A fission fuel efficiency of only 1 percent destroyed Hiroshima.

The best way to prevent A-bomb proliferation would be the international control of fissile materials, enhanced by the nuclear disarmament of the members of the nuclear club. The best block to H-bomb proliferation would be a worldwide ban on nuclear testing, because secondaries must be tested by the full-yield explosion of their associated primaries. There is no other suitable source of X-rays.

The most important factor in promoting nuclear proliferation of any kind is the continued reliance of the United States on its own still-bloated nuclear arsenal. More than 20 industrial nations that could have stockpiled nuclear arsenals have chosen not to do so. Their restraint is the most remarkable nonproliferation story, and it is based on commonsense decisions, not lack of technical information.

America's lack of restraint, dramatically symbolized by the Senate's rejection of the Comprehensive Test Ban Treaty, is a profound insult.

The U.S. political right advances the inverse of the Einstein assessment of no secret and no defense. Their continued belief in nuclear secrets and in the possibility of ballistic missile defense leads to easy rejection of Einstein's call for arms control based on “the aroused understanding and insistence of the peoples of the world.” Their agenda makes a package: security through technical and nuclear supremacy.

Conveniently, the need to keep secrets justifies a security apparatus that excludes from serious policy debate anyone not willing to take the oath and go inside the fence. It also excludes people who are not allowed in as well as those who, like Oppenheimer, are kicked out.

Most people—including opponents of nuclear arms—believe the United States has a duty to keep the remaining secrets in the bag. But people who have taken the oath cannot discuss what those secrets might be, and those who haven't can only imagine what they are.

Meanwhile, any assertion that the remaining secrets are insignificant— and that secrecy is an obstacle to the public consensus necessary for arms control—is easily dismissed with the suggestion, “If you only knew what I know …”

Maybe we do, and maybe we should talk about it, openly.

“If in no doubt, stamp it ‘SECRET;’ if in doubt, ‘TOP SECRET’.”