The Making of the Atomic Bomb

The Making of the Atomic Bomb
By Richard Rhodes

As the French nuclear scientist Bertrand Goldschmidt once said, "From a laboratory bench in 1939, the Manhattan Project expanded in scale until by the end of the war it was comparable in scale of investment and number of employees to the United States Automobile Industry in 1945."

Main Points:

• Over the years the idea of the making of the atomic bomb has shrunk in scale to one man (Robert Oppenheimer), one bomb (Hiroshima), and one place (Los Alamos). But the point of the book is to expand the view and broaden the perspective of this nuclear age- large, complicated, and expensive an effort it was.
• Critical mass of plutonium is about 5-6 kg and most modern weapons use plutonium cores of about 3 kg. It is a very dense metal, about twice as heavy as lead. Uranium takes a bit more materials (15 kg is the critical mass). We aren't talking about too much, but it was difficult to enrich this material.
• The Manhattan Project cost about $2 billion ($30 billion in today's dollars- which is slightly less than the Apollo program 20 years later). It employed about 150,000 people and they managed to keep the secret of this scientific endeavor. In order to make enough uranium for the bombs, it was necessary to build vast factories.
• Uranium: There is a type of Uranium called U-235 (an isotope) which is very rare. It is about 0.7% and has no chemical difference from other forms of uranium. In order to separate this from the other materials in natural uranium - it required a physical process. The most common one is centrifuge. You convert uranium to gaseous form and spin it at high speed within a tall cylinder. You can bleed off enriched uranium at one time and depleted uranium at the other time. If you repeat this process thousands of time, you get enough for a bomb.  Most bombs have >90% U-235. Uranium hexafluoride (gas) is only gaseous about 130 degrees and is very corrosive and use some process that distinguishes between the two isotopes. The centrifuge technology didn't get to a point for large scale use during the war. Other profligate technologies like gaseous barrier diffusion (a fine screen with fine pores) allowed pressed uranium hexafluoride against screen with high pressure, then the lighter ones will move through faster. In order to make the levels of enrichment you want, the K-25 factory near Oak Ridge National Lab valleys was so large that the supervisors traveled around on bicycles inside. The factory was developed from laboratory scale. It was difficult to make a satisfactory barrier. This was finely resolved by using sintered nickel powder- nickel was able to handle the corrosive gas and bearings on the pumps were corroding. Finally the idea was to use Dupont's new plastic called Teflon which could deal with the gas. 
• The geometry of the bomb: the first uranium bomb was a gun design in which a piece (rings of U-235) were fired up a cannon barrel into another set of target rings which were welded into a muzzle. This would create a supercritical mass. The most efficient way to detonate would be to use a spherical design. Only at the very end at the period of work was there enough material accumulated. 
• Electromagnetic separation: modified work from Berkeley in the cyclotron. Here you gassify the uranium and ionize it with an electric field so that it is capable of being moved by magnets and draw it through a curved linear field. This way the slightly lighter U-235 separates from the U-238. Buckets caught the spatter as it came around the curve. The buckets needed to be rinsed with acid.
• From the plants like K-25, the counter intelligence core army man would grab a test tube worth of uranium, take the Sante Fe chief train, and would deliver the goods to Los Alamos lab. The people worked at Oak Ridge were baffled by the amount of equipment coming in one end and nothing coming out the other side.
• These big electromagnetic separation tanks, Cal-utrons were built as a secondary enrichment process from the big gaseous diffusion. U-235 could be pushed through for highly enriched uranium. 
• Plutonium: discovered in 1941 was more fissile than U-235 (2x fissile and used 1/2 as much). Since it was chemically different that you could separate it chemically than from these oil-refinery scale machines necessary for uranium. When Fermi built his pile (graphite bricks and uranium in a matrix) in the middle of Chicago he was a very confident man. He wanted to prove that there was a chain reaction that could be sustained and wanted to see if he could make plutonium that way. Everything was scaled up, if you run a chain reaction using U-235 some of the neutrons in the reaction doing go into fissioning U-235 atoms and go into the U-238 atoms (neptunium U-239) which decays to plutonium-239 which was necessary for the bombs. You can use the waste of a nuclear reactor (U-238) to make another fissile material (Plutonium-239). A modified pile was built in Oak Ridge (General Grove wanted to put the whole thing), they built an air-cooled pile and sent the plutonium to Los Alamos. Groves realized he needed to put his plutonium somewhere else (Columbia River in Eastern Washington near Grand Coulee Dam which produced tons of electricity). In 1944, large nuclear reactors which were cooled by cold water from the Columbia River (graphite moderated with channels drilled through with uranium slugs could be put into the channels, left for 100 days of operation, which would breed 1 part in 4000 plutonium, and pushed out into a pool of cool water for 60 days) They were then dumped into casks, moved in a railway line over to huge concrete buildings with 8 foot thick walls called "Queen Mary's". inside were a series of concrete cells/tanks where various processes took uranium/plutonium, dissolve in nitric acid, precipitate various materials, blow that onto a precipitation stage, and resulting in pure plutonium nitrate. That was put into a metal container, sealed in a wooden box, put into an army ambulance, and driven from Hanford to Salt Lake City, transferred to another ambulance and driven down to Los Alamos. Note: Could not use the gun design with plutonium, it was so reactive at 3,000 ft/second the piece would melt down. Therefore Los Alamos developed the famous implosion system. Squeezing plutonium to a critical mass, makes it supercritical and starts the chain reaction. In the spring of 1945, the Hanford Engineering works shipped 5kg of plutonium to Los Alamos for the bomb that was tested at Trinity. They shipped 5kg in July for the bomb that was used in Nagasaki. Another 5kg was shipped at the end of July for another bomb which would have been dropped on Japan thereafter. 
• Key Players in the novel
• Leo Szilard- a 35 year old Hungarian-born Jewish refugee from Germany who first envisioned the nuclear chain reaction and breaking of neutrons from the nucleus.
• Niels Bohr- a Danish Nobel laureate known for uncovering the structure of the atom, who helped design the Los Alamos bomb laboratory and talked about the paradox of nuclear peace and an arms race.
• Three Parts of the Novel:
• Scientific Discovery- the foundational period that helped develop the field of nuclear physics and atomic principles.
• The Design of Bombs- explores the time between research and development where the H-bomb, the Hiroshima bomb (gun bomb), and Nagasaki bomb (implosion).
• Cost of the Project- the Manhattan Project was large in scale. So large that scientists asked to borrow silver from the US treasury because they didn't have enough copper.

The Atomic Archive has a concise review and summary of the major milestones of the nuclear age!

Watch Richard Rhodes' interview with the Atomic Heritage Foundation!

Listen to Rhodes give a talk on The History, Science, and Scientists of the Nuclear Bomb at CUNY!

Read the New York Times review of The Making of the Atomic Bomb!

Read Andrej Karapathy's review of the book on Goodreads!