Nuclear Proliferation and the “Nth County Experiment”

This compilation edited by LRL staffer James Frank provided basic information on the management of the Nth Country experiment. According to the “Operating Rules,” the participants were to design a weapon with an undefined “militarily significant” explosive yield. If “built in small numbers, [the weapon] was to ‘give a small nation a significant effect on their foreign relations.’” In other words, with nuclear arms the “small nation” could enjoy more freedom of action and presumably deter attacks from neighboring states.

The Experiment that began in the spring of 1964 would eventually involve three post-graduate physics students, David N. Pipkorn, David A Dobson, and Robert V. Selden, whose task was to develop a “credible nuclear weapons design.” As noted, they had access to only open-source literature and could receive unclassified computer and other technical support. Monitored by an “informal committee,” the Experimenters could only communicate with the committee in writing “to provide maximum assurance that [non-written communications]” did not “perturb the experiment in a casual or unrecorded manner,” for example through non-verbal gestures [See Document 3]. In addition, the Experimenters were “expected to avoid conscientiously any contact with classified information in order to maintain the integrity of the primary assumption.”

The Experiment was expected to last one year because Dobson and Pipkorn were post-graduate students at the Laboratory on a one-year appointment. With the experiment not yet completed, the Lab reappointed them for a second year, and in March 1965, Robert V. Selden, an LRL Army Research Associate, joined the design team. Pipkorn left the project in 1966 when he became a regular staff member at the Lab. After “three man years” devoted to the project, Dobson and Selden completed their final draft report in December 1966.

With the many restricted data excisions in this report, most of its substance is classified; for example, the major conclusions and the numerous technical appendices, including the bibliography and chronology, are all redacted. Moreover, most of the “early design” and the “final design” sections have been withheld, including the descriptions of the core, the tamper (the natural uranium sphere surrounding the plutonium pit), the detonators, and the explosive lenses. The section discussing the polonium-beryllium initiator is also classified because of the initiator’s key role in making an implosion weapon work by sending out a burst of neutrons to start the chain reaction.[6]

The declassification review left only the bare outlines of the Experiment: for example, the fact that Dobson and Pipkorn decided to develop a plutonium implosion device because the “Nth Country Treasury” ruled that only one fissile material was affordable. The Experimenters acknowledged that they could have turned in a final design based on a “U²³⁵ gun explosive—the type that detonated over Hiroshima—“much sooner than our implosion design.” While the implosion method appeared to be “more difficult because of its unfamiliar technology,” the participants saw it as having “greater potential for future development and more efficiency because the 1945 implosion bombs gave greater yields.” In addition, they saw the “development of the implosion method to be a more sophisticated challenging and hence appealing problem” compared to gun assembly. The critique of the experiment by F. S. Eby and Lawrence S. Germain saw that decision as a “value judgement” that was “certainly a logical one for a scientist to make, [but] the administration of the Nth Country may be less concerned with a scientifically appealing problem and more concerned with quick results.”

The Experimenters made good progress in their design work. According to the report, at the close of 1965 they had prepared “an historically accurate description of our first complete plutonium implosion design.” In April 1967, their implosion weapon had a “hypothetical test.” They believed that their design was realistic enough that it would not require an actual test compared to even more complex weapons. As they wrote, “from our present understanding of nuclear explosives, our Final Design is credible without a test, but we see no way to design a credible thermonuclear explosive without testing.”

A few details on the facilities and their costs survived the declassification review. According to “Appendix L” by C.R. Henry, the Experimenters assumed “laboratory support facilities and a weapon production complex which includes explosive plants, component fabrication shops, and a diagnostic bunker.” The required facilities would have a capacity to produce five to ten weapons annually. According to Henry, “the major expense of the Nth country weapon is the production of the plutonium.” To produce 50 kilograms of plutonium, a 200-megawatt reactor was necessary, along with uranium and plutonium processing plants. According to the report, a typical estimate for such a facility was $60 million. The annual operating costs would “include both the salaries of several hundred people and fuel costs (100 tons of uranium) and would run on the order of $10 million.”

Dobson, Pipkorn, and Selden put the Experiment in the context of U.S. nuclear history. Looking back at the Los Alamos lab during World War II, they noted that the people there “had advantages of manpower and experience (including the presence of some of the world’s outstanding physicists) and the motivational climate in which they worked.” Yet the Experimenters had “the advantages of knowing that a bomb could be built and of having access to a large quantity of literature on shock waves, explosives, nuclear physics and reactor technology which has been published since 1945.” An interesting section in the report [Appendix D] includes discussion of what Dobson and his colleagues knew about nuclear weapons prior to the Experiment, but also what they found to be “possible security leak[s]” both at the lab and in the open literature, although the security reviewers redacted the substance of both.

The compilation’s editor, James Frank, a veteran weapons designer at Livermore, was an appropriate choice. Frank worked at the Manhattan Project’s Oak Ridge laboratory during World War II, after which he received his Ph.D. in physics from the University of California Berkeley. While Frank was in graduate school, Herbert York hired him to work at Lawrence Radiation Laboratory, where he played a central role in developing the Polaris warhead during the 1950s. Leading Livermore’s “US-UK Treaty Office,” Frank presided over U.S.-United Kingdom cooperation to help the British outfit their submarine-launched missiles with Polaris-type warheads.

Staffers at Lawrence Radiation Laboratory took the Nth Country Experiment on the road through briefings to interested U.S. government officials. Robert E. Fulton with the Office of Politico-Military Affairs had already heard a briefing at the AEC and worked with the Arms Control and Disarmament Agency to arrange a presentation for State Department and ACDA officials. He invited the recipients and others to attend the briefing on 13 December, noting that participants needed to have “appropriate AEC clearances” for weapons design information.

Fulton’s brief description of the Experiment characterized it as a success: Using no classified information but having access to LRL computers for making calculations, “three young PhD physicists, working part-time, succeeded in achieving a workable nuclear weapons design in a period of about three years.”

Lasting until the summer of 1968, the Nth Country Experiment road show began with briefings to LRL and the Rand Corporation and continued with presentations to organizations in the Washington, D.C., area, including the JAEC, the CIA, various AEC offices, the Defense Atomic Support Agency, and the U.S. Intelligence Board. The AEC laboratories such as Los Alamos and Sandia but also LRL received final versions of the briefing. Dobson and Selden delivered the briefings “in the form of a Huntley-Brinkley report.” The final version of their briefing dropped “much of the physics … in favor of descriptions of the basic ideas, reasons for various decisions, and comments and observations on the Experiment from the designers’ point of view.”

In his introduction to the briefing, James Frank observed that two basic facts about the briefing and the Experiment were unclassified—the fact that only unclassified sources were involved and that it was a success. But the rest was classified: “any elaboration of these two statements with details of the Experiment [was] classified Secret-Restricted Data.” Like the “Summary Report,” most of the content of the “Post-Shot” report are excised, but massively so. The security reviewers probably went too far; for example, that the Experimenters chose a plutonium implosion design instead of a gun assembly and the reasons why may have been discussed in this document but did not survive the review, even though the “Summary Report” [Document 1] includes a discussion of this issue.

Making a point about what it took to produce a workable nuclear weapon, Frank cited the widely held post-World War II belief that “there was some secret to the atomic bomb that could be transmitted to another country on a few pieces of paper.” Acknowledging that a “purloined set of official blueprints might indeed convey some basic facts about fission weapons,” he argued that “most technical people … would feel that the transfer of knowledge and understanding is much more difficult.” Frank was implying that designing and producing nuclear weapons involved “specific, hard-to-acquire, tacit skills”—what has been called “tacit knowledge”—that are accumulated and developed through practical experience and communications involving personal and social interactions. Moreover, design work involves judgement that is both “communal and hierarchical,” where “proposals by individuals undergo peer review by senior colleagues.” Tacit knowledge also involves skills in electrical and electronic engineering as well as practical knowledge of achieving “blast waves of particular shapes” that make implosion possible.[7]

Related to the tacit knowledge issue was a point that Frank made about the conduct of the Experiment. The lab’s managers isolated the Experimenters from the rest of the lab and ensured that any of the Experimenters’ communications with the lab committee that oversaw their work were in writing only. The purpose was to “avoid … well known security leaks [that could be conveyed through] raised eyebrows or surprised expressions.”

This report includes portions of the Q&As during the briefings, during which Robert Selden observed that “The Experiment was truly a do-it-yourself project.” To the question about whether any three physicists could have succeeded in the Experiment, James Frank suggested no. First, in hiring physicists, the Lab “makes a rather strict selection.” Second, for selecting post-doctoral candidates, its criteria were even stricter. The best candidates would have a “demonstrated ability for independent research.” In fact, the “three experimenters were in the top quartile of US Ph.D. physicists.”