How to Build an Atomic Bomb - WW2 Documentary Special

Summary

The video discusses the development of the atomic bombs Fat Man and Little Boy during World War II. Directed by J. Robert Oppenheimer at Los Alamos, these two bombs differ in design due to their use of different fissile materials—plutonium for Fat Man and uranium for Little Boy. The video explains the scientific principles of nuclear fission, the challenges of bomb design, particularly with the implosion method for Fat Man, and the timeline leading up to the first nuclear test. It also touches on security measures and preparations for the bombs' deployment.

Takeaways

• ⚛️ On October 27, 1944, J. Robert Oppenheimer gave the order to begin construction of the Alamogordo test site for testing the Fat Man bomb.
• 💣 Two bombs were developed at Los Alamos: Little Boy and Fat Man, each with different fissile materials—uranium for Little Boy and plutonium for Fat Man.
• 🔬 Nuclear fission, the process at the heart of atomic bombs, involves splitting uranium-235 and plutonium-239 atoms, releasing enormous energy in a chain reaction.
• ⚠️ Scientists needed to carefully control critical mass to avoid a pre-detonation of the bomb and ensure the reaction was self-sustaining.
• 🔫 Initially, both bombs were designed to use a gun-type assembly method, but complications with plutonium led to changes in the Fat Man design.
• 💥 Spontaneous fission in plutonium, caused by Pu-240 contamination, created the risk of premature detonation, leading to a shift from the gun-type design to an implosion design for Fat Man.
• 🎯 Implosion technology, led by Seth Neddermeyer and enhanced by John von Neumann's shaped charges, replaced the gun-type method for Fat Man.
• 🏗️ The final Fat Man design featured a plutonium core surrounded by a tamper and explosive lenses to create a symmetrical implosion.
• ✈️ The development of the bombs also involved modifying B-29 bombers to deliver them, with special modifications like removing defensive turrets and adding weaponeer seats.
• ⏳ By the end of 1944, research on Little Boy was nearly complete, while testing for Fat Man was contingent on plutonium production, with expectations of a test by mid-1945.

Q & A

What was J. Robert Oppenheimer's role at the Los Alamos Laboratory?

J. Robert Oppenheimer was the director of the Los Alamos Laboratory and was responsible for overseeing the development of atomic bombs, including the designs for 'Fat Man' and 'Little Boy.'

What were the key differences between the 'Little Boy' and 'Fat Man' bombs?

'Little Boy' used uranium-235 as its fissile material and employed a gun-type assembly method, while 'Fat Man' used plutonium-239 and required an implosion method due to its tendency for spontaneous fission.

Why did the Los Alamos team decide not to test 'Little Boy' before using it in combat?

The design of 'Little Boy' was considered so straightforward that a test was deemed unnecessary. Testing would have also consumed precious uranium, which was in limited supply at the time.

Why was 'Thin Man,' the initial bomb design, ultimately abandoned?

The 'Thin Man' bomb design was abandoned because of spontaneous fission in plutonium, which caused a high risk of pre-detonation and could have made the bomb fizzle. This led the scientists to switch from the gun-type assembly to the more complicated implosion method for 'Fat Man.'

What is spontaneous fission, and why was it a problem for the 'Fat Man' design?

Spontaneous fission is when the nucleus of an atom splits without being bombarded by a neutron. It was a problem for 'Fat Man' because plutonium-240, a contaminant in the plutonium-239 core, had a high rate of spontaneous fission, risking a premature chain reaction that could cause the bomb to fizzle and not reach its full yield.

What role did the 'implosion method' play in the development of 'Fat Man'?

The implosion method was crucial for 'Fat Man' because it allowed the sub-critical plutonium core to rapidly increase its density, creating a super-critical mass capable of sustaining an explosive chain reaction. This solved the problem of spontaneous fission that made a gun-type assembly impractical for plutonium.

What was the role of the 'tamper' in both 'Little Boy' and 'Fat Man' bombs?

The tamper, made of materials like uranium-238 or tungsten carbide, surrounded the core and reflected escaping neutrons back into it, increasing the efficiency of the chain reaction. It also delayed the explosion slightly, allowing the reaction to produce more energy.

Why did the United States choose not to use the Avro Lancaster for delivering the atomic bombs?

The U.S. Army Air Forces, led by Hap Arnold, vetoed the use of a non-American plane, even though the Avro Lancaster’s bomb bay could accommodate the long 'Thin Man' bomb. This decision led to the B-29 Superfortress being modified to deliver the bombs.

What was the 'Silverplate' modification program, and why was it necessary?

The 'Silverplate' modification program involved modifying B-29 bombers to carry the atomic bombs. Initially, modifications were made to create a single long bomb bay to accommodate the 'Thin Man,' but after the switch to 'Fat Man' and 'Little Boy,' the planes were instead fitted with additional features like improved bomb release mechanisms and weight reductions.

Who was in charge of the 509th Composite Group, and what was its mission?

Lieutenant Colonel Paul Tibbets was in charge of the 509th Composite Group, which was formed for the top-secret mission of delivering the atomic bombs. The unit trained intensively at Wendover Army Air Field, Utah, with modified B-29s to prepare for the atomic bombing missions in Japan.