PDF Summary:Dark Sun, by Richard Rhodes

Dark Sun by Richard Rhodes examines the intriguing history of nuclear weapons development in the United States and Soviet Union during the Cold War era. The guide reveals the pivotal role espionage played in accelerating the Soviet nuclear program through the transfer of scientific and engineering secrets. It also describes the monumental technical challenges confronted by both nations in translating nuclear theory into functional bomb designs.

The guide delves into the heated scientific and political debates surrounding nuclear weapons, from the implosion techniques required for plutonium bombs to the radiation implosion concept behind the hydrogen bomb. Rhodes's account illuminates how closely guarded military secrets shaped the trajectory of the nuclear arms race between superpowers.

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At the conclusion of World War II, with Germany in ruins and divided into zones overseen by the American, British, French, and Soviet forces, there emerged a rivalry over the governance of uranium resources. In the aftermath of the war, the Combined Development Trust, which was responsible for overseeing the joint nuclear energy projects of Britain and America, obtained a substantial portion of the world's uranium resources, influenced by the strategic thinking of US General Leslie Groves, who was of the opinion that dominating these resources would deter the Soviet Union from pursuing the development of nuclear arms. Groves knew that the Belgian Congo was home to the most plentiful uranium reserves on Earth. At the onset of World War II, the German military seized control of roughly 1,200 kilograms of uranium originating from the Belgian Congo, which American troops later found in April 1945 in Stassfurt, an area on the brink of Soviet control.

Before the Soviet forces could arrive, nearly half of the world's uranium reserves, approximately 1,100 tons from the Belgian Congo, were swiftly moved by train and dispatched. During the conflict, the Germans had redirected 100 tons, and a meticulous search through card catalogues revealed a portion of this—approximately 130 tons—at a tannery located at the edge of the area under American control, which was detailed by a Soviet physicist involved in the nuclear search team. The Soviets swiftly laid claim to the ore from the Belgian Congo, which was in Germany, before American forces could secure it. Khariton is of the opinion that the Soviet Union's intensified procurement activities hastened the inauguration of their first reactor for plutonium production by nearly a year.

The construction of the Soviet Union's initial nuclear reactor, influenced by the blueprint of the Hanford 305 test reactor, emphasizes the pivotal role espionage played in transferring essential design information.

In late 1945, Igor Kurchatov and his team commenced the building of the first atomic reactor in the Soviet Union. The facility, often referred to as F-1 for "Physics 1," operated with natural uranium and carbon in its core and was conceived by Kurchatov with dual aims: to demonstrate the feasibility of a nuclear chain reaction and to produce the first detectable quantities of what would eventually be recognized as plutonium.

The F-1 reactor reached a state of criticality at Kurchatov's nuclear research facility in Moscow during December 1946, yet this event was not without precedent. The design of the reactor was strikingly similar to that of the Hanford 305 test reactor, built and operated by the Manhattan Project in Hanford, Washington, in 1944, notable for its air cooling system, use of graphite to moderate neutrons, and the use of natural uranium. Kurchatov's reactor, which bore a resemblance to the Hanford 305, shared comparable characteristics such as power output, atomic grid configuration, size, fuel storage capacity, dimensions of fuel elements, and the design of control rods, all of which were critical in assessing the suitability of graphite and uranium in the development of future reactors for mass plutonium production.

build a test reactor to verify their calculations and perfect the complex procedures required for the development of a reactor capable of producing plutonium. Why opt for a design that is devoid of uniqueness? One possible reason could be the lack of diverse design options. The F-1 reactor, constructed beneath the surface, stood upright, while the Hanford 305, which was built above ground, was oriented horizontally; however, both employed a mix of graphite and unenriched uranium for moderation, indicating that their core operational principles were quite alike, with their distinct designs being primarily influenced by the environments in which they were situated.

By 1946, the range of potential designs for Kurchatov's team to consider for their test reactor strategy had expanded, offering them a wider selection of possibilities. As Kurchatov reviewed the intelligence data, it became clear that the Soviets were aware of the successful operation of Chicago Pile 1 (CP-1), the initial device to employ natural uranium and a graphite moderator, which was assembled in Chicago in 1942. Furthermore, espionage had tipped them off that in Oak Ridge, Tennessee, a heavy-water reactor CP-2 had been built, as well as a more intricate device that made use of uranium in its unenriched form and carbon in a solid state, which was water-cooled and known as the X-10, both of which were in use. The team led by Kurchatov opted to build a reactor that was strikingly similar to the Hanford 305.

The conclusive evaluation strongly supports the conclusion that Soviet acquisition of complex reactor design details was significantly aided by acts of espionage. Who was the source of the information? While the historical record does not identify him, Alan Nunn May, a British scientist apprehended in Canada in 1946 and convicted of espionage, is the most probable candidate, since he had been posted to Montreal in 1943 to work on designing a Canadian heavy-water reactor and had visited Chicago and Oak Ridge frequently in 1944 and 1945, where he had access to reports on reactor design and operation.

Other Perspectives

• While espionage certainly played a role in the Soviet nuclear program, it is also true that Soviet scientists and engineers were highly capable and made significant independent contributions to the development of nuclear technology.
• The Soviet Union had a strong foundational knowledge in nuclear physics before the espionage activities, and it is possible that they could have developed nuclear weapons without the stolen information, albeit at a slower pace.
• The role of espionage in hastening the Soviet nuclear program can be debated, as the Soviet Union had already prioritized atomic research before acquiring the secrets from the West.
• The effectiveness of the information provided by the Cambridge Five can be questioned, as not all information may have been of equal value or utility to the Soviet nuclear program.
• The Soviet Union's pursuit of uranium resources was not solely reliant on espionage or seizures from post-war Germany; they also explored and developed their own domestic sources.
• The assertion that the Soviet Union's initial nuclear reactor was heavily influenced by espionage could be challenged by acknowledging the possibility of parallel development or convergent evolution in reactor design.
• The impact of captured German scientists on the Soviet nuclear program might be overstated, as the Soviets already had a strong scientific community capable of processing uranium and developing nuclear technology.
• The narrative that espionage was the primary driver behind the Soviet Union's nuclear advancements may overlook the broader context of the Cold War arms race, where multiple factors, including internal political pressures and international competition, played significant roles.

The creation of atomic arms posed not only scientific and technical challenges but also ignited substantial ethical and political debates.

This part explores the intricate challenges of a scientific and technical nature that were encountered in the development of both fission and fusion weaponry, as well as the substantial political and moral debates they sparked.

The achievement of developing a nuclear weapon powered by plutonium was contingent upon overcoming the issue of early detonation, underscoring the intricate task of translating theoretical physics into practical engineering applications.

The Soviet equivalent of the Manhattan Project also faced considerable obstacles in their pursuit to create a nuclear weapon powered by the more accessible plutonium-239, as opposed to the scarcer uranium-235. This initiative underscores the difficulty of transforming abstract physics principles into tangible engineering solutions.

Before the understanding of how to manage a chain reaction, U-235, an isotope of uranium, was identified as a potential material for bomb creation. Naturally occurring uranium primarily consists of U-238, with U-235 making up approximately 0.7% of the overall composition. U-238 hinders the advancement of chain reactions due to its propensity to capture neutrons. The primary obstacle faced by the Manhattan Project was the separation of U-235 from U-238 to create a form of uranium suitable for use in arms. The separation process necessitated not only a groundbreaking diffusion theory, which clarifies how certain substances selectively move through permeable barriers, but also the creation of sophisticated equipment. This equipment was crucial for managing and directing a significant amount of uranium gas, known for its heavy weight, corrosive nature, and high reactivity, while preventing any accidental critical reactions.

Even in 1941, after nearly two years of research had led to the discovery of an effective separation material for U-235, it was evident to those involved in the Manhattan Project that uranium reserves were depleting. The evaluation resulted in the conclusion that uranium reserves worldwide might be inadequate to sustain continuous development of nuclear weaponry. A technique needed to be devised to make use of both U-235 and U-238. In 1940, Glenn Seaborg and his team at Berkeley succeeded in converting a tiny amount, exactly one microgram, of a newly synthesized element at their laboratory, which they subsequently christened as plutonium. The following year, scientists working on the Manhattan Project determined that plutonium not only had a higher fission probability than U-235 but also could be produced more economically. The method facilitated the creation of materials for bombs independently of raw ore sources.

Unfortunately, the production of plutonium-239 within reactors also results in a smaller amount of the heavier isotope plutonium-240, known for its higher rate of neutron emission compared to plutonium-239. J. Carson Mark, a physicist from Los Alamos, once remarked on the contrary nature of plutonium, noting that the metal's behavior was as contrary as could be imagined. The Pu-240 isotope's instability posed challenges in shaping and preserving the plutonium's structural soundness. The endeavor to manufacture plutonium required a significant commitment of resources, leading to the conclusion that a gun-type assembly would be too dangerous for the configuration of the bomb.

Prioritizing the development of implosion techniques at Los Alamos necessitated the invention of new technology and the acquisition of specialized theoretical insights.

Rhodes offers a thorough examination of the obstacles encountered by the Manhattan Project as they endeavored to process plutonium safely and efficiently, preventing any early detonation in the first atomic bombs. In 1943, General Leslie Groves was responsible for the metamorphosis of the University of Chicago's Metallurgical Laboratory, often referred to as the Met Lab, into the birthplace where Enrico Fermi and his group of physicists demonstrated the practicality of a controlled nuclear chain reaction by running the first man-made nuclear reactors. The Met Lab team recommended building a reactor that used heavy water to manage the nuclear chain reaction because, at that time, the United States lacked the industrial capacity to produce sufficiently pure graphite.

The available uranium supply was insufficient for the needs of a heavy-water reactor. The team at the Met Lab engineered a reactor that operated on natural uranium, which was regulated by a substantial quantity of refined graphite to maintain the nuclear reactions. In November 1943, the X-10 pile reached a critical state in Oak Ridge, having been built with elements comprising graphite and uranium.

In 1943, the Manhattan Project began building a vast plutonium production complex in the secluded area of Hanford, Washington, near the Columbia River, utilizing the crucial hydroelectric power generated by the Grand Coulee Dam. The researchers working at the Metallurgical Laboratory realized the importance of gathering extensive information on the reactor's elements and operations, particularly the uranium and graphite interplay crucial for sustaining a chain reaction in a production reactor, to ensure a secure transition from a nuclear research facility to a full-scale industrial operation. The first model for the advanced and potent reactors built at Hanford was a compact experimental reactor intended to produce a limited amount of plutonium. In 1944, the Hanford site saw the construction of the more compact reactor, which was referred to as the 305. The initial nuclear reactor of the Soviet Union was modeled after the F-1 design.

The Met Lab embarked on a distinct project aimed at developing a strategy to gather enough plutonium to reach the critical mass necessary for a nuclear weapon. Robert Serber, a theoretical physicist and member of the Los Alamos group, acknowledged in his 1994 comments that individuals with a deep understanding of physics could see the possibilities of nuclear energy, yet he was also aware of the substantial obstacles that needed to be overcome. In early 1943, at the Met Lab, Serber and his team acknowledged that a fundamentally different approach was essential for assembling plutonium in a manner that could feasibly succeed, rather than merely hurling one piece of the reactive metal at another. The Metallurgical Laboratory in the United States was mainly focused on the advancement of reactor technology and the production of materials, rather than specifically on the development of explosive weaponry.

In April 1943, the expansion of the Manhattan Project led to the creation of a new research facility in the secluded regions of northern New Mexico. The initiative, referred to as Project Y, encompassed multiple locations, with principal sites being X and W, known respectively as Oak Ridge and Hanford. The development of a functional detonation device using plutonium was assigned to the Los Alamos group, as described by a participant. Los Alamos resolved the challenge of plutonium's early detonation by modifying the essential design of the Little Boy uranium gun; this modification entailed launching a plutonium projectile to collide with a stationary plutonium mass, as opposed to driving a slow-moving uranium projectile toward a uranium target. The gun assembly mechanism would therefore be basically similar; the main engineering challenge would be designing a high-pressure gun that would achieve the necessary muzzle velocity.

Edward Teller, a Hungarian physicist, led a group of theoretical scientists at the Los Alamos laboratory in exploring methods to use high explosives for compressing multiple subcritical mass fragments into a supercritical sphere through the use of shaped charges that would propel the metal inward. The implosion technique's advantage lay in its ability to condense the plutonium at a speed surpassing that of even the quickest high-pressure artillery methods.

Klaus Fuchs was instrumental in the transfer of implosion design secrets to the Soviet Union through his critical involvement at Los Alamos.

Klaus Fuchs joined Hans Bethe's division at Los Alamos in August 1944, where he concentrated on the complex theories surrounding implosion. The team at Los Alamos focused their efforts on developing implosion systems that operated in two dimensions, employing concentric rings of explosives with differing detonation velocities to condense steel pipes.

The results of these experiments resulted in disastrous consequences. The channels were unable to maintain an airtight seal, which led to their rupture and the subsequent leakage of molten metals from their flanks. To grasp the fundamental causes, scientists focused on the internal implosion of substances and employed sophisticated methods of observation that could record occurrences with precision down to millionths of a second, especially the "flash radiography" they developed, along with an extensive comprehension of fluid dynamics to evaluate how fluids behave when compressed, aiding them in deciphering the radiographic data and enhancing their design.

Fuchs played a major role in this project. Over the following two years, the physicist from Germany wrote several academic papers that clarified the unique properties of structures that collapse inward when subjected to intense explosive forces. Rhodes steadfastly ensured that updates on the progress of the implosion design at Los Alamos were regularly communicated to Soviet contacts.

The initial idea of the "classical Super" by Edward Teller presented a considerable obstacle for the development of fusion-based weaponry, demonstrating how a flawed scientific theory can hinder major technological advancements.

Edward Teller had the concept of initiating a thermonuclear blast through the detonation of an atomic bomb. His steadfast adherence to a flawed idea delayed America's advancement in creating thermonuclear weaponry, leading to several years of delay before the hydrogen bomb came to fruition.

In 1942, Teller proposed the concept of a "superbomb," a thermonuclear explosive device that would be initiated by a nuclear detonation, a notion that would significantly and unintentionally guide the direction of America's hydrogen bomb efforts for the following decade. Teller's initial idea was based on an intriguing analogy, proposing that igniting lighter elements through a nuclear blast could potentially unleash a vastly more potent energy discharge, similar to setting off an exceptionally fierce blaze.

A star operates as a celestial entity powered by fusion, with its energy derived from nuclear processes. Hydrogen atoms combine to form helium, releasing energy in the process without producing radioactive waste. In the 20th century, physicists commonly believed that achieving the intense heat and energy necessary to initiate thermonuclear reactions on our planet was beyond reach. The disclosure that nuclear fission, identified in 1939, could lead to the creation of an atomic bomb, profoundly changed this perspective, with the division of specific heavy elements producing extreme heat that soared to about one hundred million degrees in mere microseconds—exceeding the temperatures at the core of the sun and other stars. The nuclear blast seemed to be an appropriate trigger for initiating Teller's idea of a hydrogen bomb.

An atomic bomb must be set off to begin a thermonuclear explosion, which meant that fusion experiments could not be carried out in a lab setting as with fission, where minimal quantities of uranium and plutonium were employed to study the pace of chain reactions, measure interaction likelihoods, determine the necessary quantity of material for a self-sustaining chain reaction, and observe instances of spontaneous fission. Advancements in thermonuclear research depended on the capability to execute mathematical computations of extraordinary intricacy. Understanding the nuclear fission explosion in detail was essential for the calculations since it triggered a series of events that included powerful waves of neutrons, radiation, heat, and pressure. During World War II, physicists at Los Alamos laid the theoretical groundwork that advanced the implosion design, which necessitated complex hydrodynamic computations that were simplified in response to the era's computational constraints.

Teller proposed starting the fusion process by using a technique that propels substantial amounts of uranium. A uranium gun-type device attains a critical mass without requiring elements typical of an implosion, which he thought would interfere with the onset of a fusion process. By 1949, although the war had ended more than four years earlier and most individuals involved in the atomic bomb's creation had returned to civilian life, the U.S. arsenal was devoid of such weapons. Even though they had the technical know-how to build such a device, it was still uncertain whether it would successfully trigger a sustained thermonuclear reaction.

Stanislaw Ulam's calculations cast doubt on the practicality of Teller's Super design, prompting a thorough reassessment of the methods used to develop thermonuclear weaponry.

Teller encountered resistance while advocating for his vision of the Super. Stanislaw Ulam, a Polish mathematician who was enlisted from Harvard University for the Manhattan Project, joined forces with the volatile Hungarian physicist Teller at Los Alamos as 1943 was drawing to a close, and they worked together until the end of the war. Following his recovery from brain surgery, Ulam rejoined the team at Los Alamos to continue his collaborative efforts in the creation of the hydrogen bomb, committing himself full-time to the project starting in 1946. Ulam embarked on the challenge of scrutinizing Teller's fundamental assumption, which suggested that the energy from a fusion explosion could raise the temperature of the Earth's atmosphere enough to possibly start fusion in nitrogen, which could result in the annihilation of all planetary life.

In 1946, Ulam was of the opinion that thermonuclear explosions could play a part in protecting life on Earth, though he was skeptical about Teller's theory. Teller ultimately decided to defer the concept after they collaborated on the computations. In the meantime, Ulam developed a method he characterized as "a more tactile way" to understand physical events, which stood in stark contrast to Teller's analytical methodology; Ulam proposed that by observing how substances behave when compressed, one might gain an instinctive understanding of an explosion's development instead of depending entirely on speculative theory. He called his technique after the renowned city known for gambling because it utilized random factors in its strategy.

During the 1946 Super Conference, Teller proposed initiating the extended deuterium core, an essential element of his Super design, through the attachment of an atomic bomb at one extremity. Teller was of the opinion that the extreme temperatures produced by the fission explosion would set off a chain reaction of thermonuclear combustion that would spread through the cylinder, which led to its unique shape. The accumulation of computational research on combustion processes in 1949 caused several Los Alamos theorists to question the feasibility of Teller's Super design from the beginning. Los Alamos physicist John Manley concisely posed the inquiry as to whether it was at all possible to initiate and sustain a reaction within a pure deuterium blend. The prevailing view held that accomplishing the task was unfeasible.

In 1950, as Los Alamos initiated the construction of a computer for the detailed examination of Teller's Super design, Ulam, together with Cornelius Everett, a mathematician at the facility, chose to conduct hand calculations on a simplified version of the idea. Ulam and his colleagues embarked on a mission to evaluate the practicality of Teller's suggestions, aiming to grasp the project's extent and determine whether it warranted dedicating thousands of hours of valuable computational time for an in-depth analysis. Their manual calculations yielded disheartening outcomes. The Super's design required a quantity of tritium that was a thousand times more than what the Los Alamos reactors could generate.

Teller steadfastly maintained his position, insisting that the lack of progress was due to the deliberate maneuvers of his adversaries rather than any shortcomings in his own design. As 1950 drew to a close, Teller acknowledged the precision of Ulam and Everett's manual calculations after they were corroborated by the results from von Neumann's ENIAC. In January 1951, the United States committed to developing a hydrogen bomb capable of unleashing destruction on a megaton scale, prompting President Truman to direct the Atomic Energy Commission to expedite the creation of this "superbomb," despite the absence of a viable design from American scientists.

The development of the hydrogen bomb took a crucial turn with the move towards a sophisticated, implosion-based nuclear device, diverging from the original concept known as the Super.

In 1951, at Los Alamos, Teller and Ulam devised a novel approach for the configuration and activation of a thermonuclear secondary. They referred to the process as "staging." Rhodes demonstrates the rapid advancement and refinement of the implosion sequence, transforming the idea of the hydrogen bomb into a concrete technical pursuit.

The development of the hydrogen bomb, which operates on the principle of staged radiation implosion, was a collaborative effort between Ulam and Teller, although Teller subsequently attempted to downplay Ulam's role in its invention. Ulam originated the foundational idea. Ulam proposed a concept in which an initial explosive device, referred to as the 'primary,' would initiate the explosion of a separate device, designated as the 'secondary.' Ulam's concept was expansive, imagining a technique in which the shock waves from a nuclear blast would compress the secondary, similar to how the high-explosive lenses concentrated the plutonium core in the Fat Man bomb's implosion mechanism. Teller grasped that the swift nature of radiation, traveling at the speed of light, would lead to a significantly faster condensation of the thermonuclear secondary compared to the slower, mechanical shock waves produced by the explosion of the primary. Teller proposed using the initial device's X-rays to compress the secondary stage.

To carry out this task effectively, the core apparatus was designed to prioritize producing significant radiation over primarily focusing on energy production through nuclear fission. Rhodes details Teller's role in enhancing the war effort by calculating the energy released as radiation during a nuclear fission explosion, recognizing that the bomb's effectiveness would be amplified with an increased radiation output. The Ivy Mike device, Teller and Ulam’s invention as engineered by Marshall Holloway’s team at Los Alamos, therefore depended on the highly purified U-235 and Pu-239 that had just become available in the postwar US weapons program to make an efficient, radiation-transparent primary – a system designed to employ the powerful X rays generated by the initial nuclear detonation to condense a subsequent stage.

The Mike device's secondary stage incorporated a double-walled cylindrical container specifically for containing its deuterium in liquid form. Teller and Ulam placed a plutonium rod along the central axis inside the deuterium-filled cylinder, which acted as the initiator.

Context

• In the development of nuclear weapons, early detonation issues referred to the challenge of preventing the premature explosion of the weapon before it reached its intended target. This problem was particularly crucial in the context of plutonium-based nuclear weapons, where the rapid assembly of critical mass needed to be controlled precisely to avoid accidental detonation. Overcoming early detonation required intricate engineering solutions to ensure the safe and reliable functioning of the nuclear weapon. Scientists and engineers had to devise methods to manage the timing and assembly of the fissile material to achieve a controlled and efficient nuclear explosion.
• The separation of U-235 from U-238 for bomb creation involved isolating the U-235 isotope, which is suitable for nuclear weapons, from natural uranium, which is mostly U-238. This process was crucial as U-235 is more fissile and can sustain a chain reaction necessary for a nuclear explosion. The Manhattan Project faced the challenge of developing methods to enrich uranium to increase the concentration of U-235, a complex and resource-intensive process. This enrichment process required advanced technologies like diffusion and centrifugation to separate the isotopes effectively.
• Implosion techniques for plutonium safety involved compressing subcritical masses of plutonium using high explosives to create a supercritical mass for nuclear detonation. This method was developed to ensure a controlled and efficient implosion process, crucial for preventing premature detonation and achieving a successful nuclear explosion. The implosion technique allowed for the precise assembly of the plutonium core in nuclear weapons, enhancing safety and reliability in the weapon's design. By compressing the plutonium rapidly and uniformly, implosion techniques enabled the efficient utilization of fissile material for maximum destructive impact.
• The staging concept in the development of the hydrogen bomb involved using two separate explosive devices: a primary and a secondary. The primary device would initiate the explosion of the secondary device through a series of shock waves. The shock waves from the primary device would compress the secondary, leading to a more powerful thermonuclear reaction. This approach allowed for a more controlled and efficient release of energy in the hydrogen bomb.