Why Oppenheimer Deserves His Own MovieJul 22, 2023
atomic. At this point, making the atomic bomb did not seem impossible. It seemed likely. On December 2, 1942, a team of physicists from the University of Chicago led by Enrico Fermi created the world's first artificial nuclear reactor, Pile-1. It consisted of 45 tons of uranium and uranium oxide and 330 tons of graphite blocks. Pretty horrible. It was located under the stands of the football field. It generated about half a watt of power, and if you can build a nuclear power plant, you can build a bomb. The only real difference between the two is how many neutrons hit the next atom, causing it to split and release more neutrons.
If on average that number is one, there will be a stable and self-sustaining chain reaction, but it will not grow. If it is less than one, the reaction will decrease, and if it is more than one, the reaction will increase. This is known as the multiplication factor, K. Nuclear reactions are similar to pandemics in this sense. The simplest way to make a nuclear bomb is to bring enough fissile material close together, which creates an uncontrolled chain reaction. That amount is known as critical mass. With uranium-235, about 52 kilograms are needed. Forming a sphere with a diameter of 17 centimeters.
If plutonium-239 is used, the critical mass is much lower, only about 10 kilograms, which would create a sphere only 10 centimeters wide. For the first few years, scientists worked on a bomb with a pistol-type design. Inside a weapon-type bomb, you have two plates of uranium-235, both below critical mass. Then, using a conventional explosive like cordite, you quickly fire one at the other. So the combined mass is greater than the critical mass. When the uranium bullet is about 25 centimeters away, the nuclear chain reaction begins that results in an atomic explosion. Despite the simple design, it is not very efficient.
Only a small percentage of uranium undergoes fission, so the total yield of the bomb is much lower. You also run into some unexpected problems, like how do you make sure the uranium slides smoothly through the barrel? Well, oil is used to lubricate the barrel, but all the synthetic oils the scientists tested would dry out. In the end, the only oil they could find that worked was sperm whale oil. Only about 0.7% of natural uranium is U235, the fissile fuel for nuclear bombs. When U235 absorbs a neutron, it briefly becomes U236, and then splits approximately in half, releasing an average of 2.4 neutrons per fission.
But when uranium is extracted from the earth, most of it is U238, which does not undergo fission. So, to make a nuclear bomb, scientists used giant mass spectrometers to separate and concentrate U235, and the resulting substance was uranium with a much higher concentration of U235. In other words, he became rich. Although there was another option. At the beginning of 1941, a new element was discovered or rather synthesized. When a neutron is absorbed by a uranium-238 nucleus, it becomes uranium-239. U239 is unstable, so it decays into neptunium, which then becomes plutonium. There are three things that matter in this story.
The first is that plutonium-239 is a great fuel for a nuclear bomb. It has a critical mass of only about 10 kilograms. Second, it is cheaper to manufacture than separating uranium-235, and third, it reacts too quickly to be used in a gun-type device. It would fizzle out, meaning that only a small fraction of the fuel would undergo fission. But there is a way to make a bomb using plutonium. The critical mass changes depending on the density of the material. Under normal pressure conditions, six kilograms of plutonium-239 will not explode. But if you compress it, the atoms move closer together and the chance of a permanent neutron hitting the nucleus increases.
So the higher the density, the lower the critical mass. So if conventional explosives are detonated around a ball of plutonium, it can be compressed enough to start a nuclear chain reaction. And this was the idea behind the design of the implosion bomb. There are a couple of ways to cheat by reducing critical mass. For one thing, you surround the sphere with a material that reflects neutrons, which decreases the amount of nuclear fuel you need to start a chain reaction. You can also have a neutron source, something that starts the chain reaction. For the first implosion bomb, scientists created a device called a hedgehog, which was a small ball that weighed only seven grams and would sit at the heart of the bomb.
It was made of beryllium and polonium separated by a layer of nickel and gold. The idea was that when the explosives detonated, the shock wave would mix the beryllium and polonium, and then the alpha particles of the polonium would cause the beryllium to release an avalanche of neutrons, triggering the nuclear chain reaction. At least that was the hope. An atomic bomb had never been made before. Oppenheimer and the rest of the Los Alamos scientists had to act quickly. It was already 1945 and Truman wanted to test the weapon before the start of the Potsdam conference. That's where Truman, Churchill and Stalin would come together to plan the post-war piece.
The conference began on July 17. The earliest date everything could be ready for the bomb was just a day earlier. That's when the test was scheduled. It was codenamed Trinity. The night before Oppenheimer was nervous. There were so many things that could go wrong. The last test firing of the explosives without the actual plutonium core was a failure. To calm himself, he recited a stanza from the Bhagavad Gita, the sacred Hindu poem. In fact, he himself had translated the Gita from the original Sanskrit. In battle, in the forest, on the precipice of mountains, in the great dark sea, amid javelins and arrows, in sleep, in confusion, in the depths of shame, the good deeds that a man has done before they defend it.
Perhaps more terrifying than the thought of the bomb not working was that it would work too well. Around 1942, Oppenheimer discussed with Arthur Compton the terrible possibility that a nuclear test could end the world. The concern was that the nuclear bomb would create temperatures so high that fusion would occur. A small fraction of the atmosphere, just one part in 2 million, is hydrogen gas. But the concern was that at temperatures and pressures high enough that hydrogen could fuse and release energy, this energy would fuse more hydrogen. It could also separate hydrogen from water vapor and cause it to fuse as well.
That would release even more energy and cause even more fusion until Earth's entire atmosphere became one giant fusion bomb. Recalling his conversations with Oppenheimer in 1959, Compton said: "This was not all that Oppenheimer feared. Nitrogen in the air is also unstable, although to a lesser degree. Could it not also be triggered by an atomic explosion in the atmosphere? ". Most scientists quickly realized how unlikely this scenario was and continued with the project, so no one took the idea too seriously. But the idea of starting a fusion reaction with a fission weapon would be very important after the war. (dramatic music) The Trinity test was scheduled for 4:00 a.m. but was delayed due to a storm.
Then, at 5:29 and 21 seconds, the device, the world's first nuclear bomb, detonated and the high explosive compressed the plutonium core inward. The shock wave mixed the beryllium and polonium, releasing an avalanche of neutrons. The urchin worked. It triggered the nuclear reaction and now there was no way to stop it. Just six kilograms of plutonium caused an explosion equivalent to almost 25,000 tons of TNT. The mountains of New Mexico were brighter than during the day. The shock wave was felt more than 160 kilometers away. The mushroom cloud rose to 12 kilometers high. It was so hot that the desert sand melted, forming a glassy mineral, now known as trinitite.
Fortunately, the explosion did not set the atmosphere on fire. On August 6, 1945, the Boeing B29 Flying Fortress dropped Little Boy, a gun-type nuclear bomb containing 64 kilograms of enriched uranium. The nitrocellulose was ignited by pushing the uranium-235 pellets together, tilting them above their critical mass. The explosion, equivalent to 15,000 tons of TNT, killed almost 70,000 people. Another 70,000 people would die in the following months from burns and radiation poisoning. Three days later, an implosion bomb, like the device, was dropped on Nagasaki, killing an estimated 80,000 more people. More than 95% of the 225,000 people who died in the bombings of Hiroshima and Nagasaki were civilians.
The majority were women and children. In 1965, recalling the moments after the Trinity test, Oppenheimer said that he had thought of another verse from the Ghita. - I knew the world would not be the same. Few people laughed, few people cried. Most people remained silent. I remembered the line from the Hindu scriptures, the (speaks in foreign language). Vishnu is trying to persuade the prince that he must do his duty and to impress him, he assumes his many-armed form and says, "Now I have become death, the destroyer of worlds." I guess we all think that in one way or another. - After the war, Oppenheimer was a national hero.
His portrait appeared on the cover of Time magazine and he became a household name. In 1947, he became director of the Institute for Advanced Study at Princeton. He also became chairman of the General Advisory Committee, where he became an advisor on issues related to nuclear weapons. He used his position to advocate for gun control. (dramatic music) In August 1949, the Soviet Union tested its first atomic weapon and the U.S. military quickly decided that the best course of action was to develop a more powerful bomb. Oppenheimer opposed the development of the hydrogen bomb, known as "The Super," on ethical grounds and out of fear that he would start an arms race.
But the Truman administration forged ahead, and three years later, Ivy Mike, the first hydrogen bomb was tested in the Marshall Islands. It had a yield of 10.4 megatons of TNT. That's 400 times more powerful than the Trinity test. A hydrogen bomb is actually three bombs in one: a conventional bomb, a fission bomb, and a fusion bomb. Conventional explosives trigger a fission reaction, which increases temperature and pressure enough to fuse deuterium and tritium, releasing a huge amount of energy. In 1961, the Soviet Union tested the Tsar Bomba, the most powerful explosion ever detonated. He was five times more powerful than Ivy Mike, around 2000 times more powerful than Trinity.
This type of arms race was exactly what Oppenheimer had feared, in part because of his opposition to the hydrogen bomb. And because of his calls to prevent a nuclear arms race, Oppenheimer was essentially tried to revoke his security clearance. He had been surveilled while working for the Manhattan Project, but that surveillance did not stop after he left. Many of the wiretaps were illegal and did not have a warrant. Oppenheimer was questioned about his ties to the Communist Party, including his affair with Gene Tatlock, a member of the Communist Party while he ran the Los Alamos laboratory.
He basically he was accused of treason and espionage. In December 1953, Oppenheimer's security clearance was suspended. His now grim and black and white face was once again on the cover of time. His security hearings made international news. In 1964, German playwright Heinar Kipphardt wrote a play about Oppenheimer's life. Oppenheimer was sent a copy of this script and he hated it so much that he threatened to sue. He especially despised the final scene where Oppenheimer's character realizes the evil of his work. And he quote, "We've been doing the devil's work." For Oppenheimer, it was always more complicated than that. - I think it was probably assumed, certainly it was always assumed at Los Alamos that if the war was not over and could not be clearly concluded through diplomatic means, this weapon would play a role.
At the time, the alternative, the invasion campaign, was undoubtedly much more terrible for everyone involved. I believe that Hiroshima cost far more lives and inhuman suffering than was necessary to have been an effective argument for ending the war. This is easy to say after the fact. - In 1965, he was asked about the recent proposed talks with the Soviet Union to stop the proliferation of nuclear weapons, and his response was: "They should have been held the day after Trinity. Later that year, he was diagnosed with breast cancer. He was a lifelong smoker and died on February 18, 1967, at the age of 62.
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