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How Does A Nuclear Bomb Work?
Basically, a nuclear bomb is made by using radioactive elements Uranium and Plutonium. The word radioactive means that the atoms in the elements are unstable and therefore they release energy. Atoms of elements consist of a nucleus and an electron, which revolves around it.A Nuclear bomb explodes when the energy inside the nucleus of a radioactive atom is released. There are two types of processes in which energy can be released.
- Nuclear Fission
- Nuclear Fusion
The nucleus contains two sub-atomic particles, Protons and Neutrons. In Fission, the reaction occurs when a free Neutron strikes the nucleus of the atom and then it breaks down releasing a huge amount of energy. While in Fusion, atoms of hydrogen fuse together to form an atom of Helium and thus huge amount of energy. This is how the sun works.
In Nuclear fission, highly enriched Uranium and Plutonium are used. Their scientific names are U-235 and Plutonium239. Literally, fission means splitting of heavy nucleus in which energy is released as a reaction, but the inside of fission is quite complicated and can be only understood by people who are studying Physics. I will try to make the context simple and comprehensible. In nuclear fission, there are two types of processes:
A gun-triggered fission process is a process in which highly enriched Uranium is used. Enrichment process is done in highly sophisticated devices and the radioactivity in increased. Initially, the atomic number of Uranium is 232 but after enrichment it becomes 235.
In such a bomb design, there are two different types of Uranium objects. First one is the Subcritical Mass, a mass used to start a gun-triggered fission reaction, containing Neutrons; and the second is the Supercritical Mass, the mass containing the fuel for the explosion, which contains the highly enriched uranium. The Tamper is a coating to prevent loss of energy stored inside the highly enriched Uranium and is made of Uranium-232. The bomb explodes through the following process:
- The Trigger receives the signal to shoot the bullet (Subcritical Mass)
- The bullet shoots and strikes the Supercritical Mass
- The core expands exerting pressure on the Tamper.
- The Tamper starts expansion
- Expansion stops and pressure is exerted on the core.
- Fission takes place
- The bomb explodes
This process sounds very long but, believe it or not, the complete process takes just an 100th part of a second. This process shown through the picture was used in older nuclear devices, but nowadays it's modified and is more sophisticated. This is how Little Boy, the bomb dropped on Hiroshima exploded, releasing an energy equivalent to 15 Kilotons; i.e. 15,000 kg of TNT and only 15 kg of Uranium was used.
Early in the Manhattan Project, secret US programme to develop the atomic bomb, scientists working on the project recognized that compressing the subcritical masses together into a sphere by implosion might be a good way to make a supercritical mass. There were several problems with this idea, particularly how to control and direct the shock wave across the sphere. But the Manhattan Project team solved the problems. The implosion device consisted of a sphere of uranium-235 (tamper) and a plutonium-239 core surrounded by high explosives. When the bomb was detonated, this is what happened:
- The explosives fired, creating a shock wave.
- The shock wave exerted pressure on the Tamper
- The tamper started expansion
- Expansion stopped exerting pressure on the core
- The fission reaction began.
- The bomb exploded.
Fat Man was this type of bomb and had a 23-kiloton yield (power). These bombs exploded in fractions of a second. The fission usually occurred in 560 billionths of a second.
In a later modification of the implosion-triggered design, here is what happens:
- The explosives fire, creating a shock wave.
- The shock wave propels the plutonium pieces together into a sphere.
- The plutonium pieces strike a pellet of beryllium/polonium at the centre.
- The fission reaction begins.
- The bomb explodes.
This process is highly complicated and destructive. The bomb designed through this technique is known as a thermonuclear device as it involves both Fission and Fusion. But this fusion reaction involves other types of fuels known as Deuterium and Tritium. Fission bombs worked, but they weren't very efficient. Fusion bombs have higher kiloton yields and greater efficiencies than fission bombs.
To understand this bomb design, imagine that within a bomb casing you have an implosion fission bomb and a cylinder casing of uranium-238 (tamper). Within the tamper is the lithium deuteride (fuel made by deuterium) and a hollow rod of plutonium-239 in the centre of the cylinder. Separating the cylinder from the implosion bomb is a shield of uranium-238 and plastic foam that fills the remaining spaces in the bomb casing. Detonation of the bomb causes the following events:
- The fission bomb implodes, giving off X-rays.
- These X-rays heat the inside of the bomb and the tamper; the shield prevented premature detonation of the fuel.
- The heat causes the tamper to expand and burn away, exerting pressure against the lithium deuterates.
- The lithium deuterate is squeezed.
- The compression shock waves start fission in the plutonium rod.
- The fissioning rod give off radiation, heat and neutrons.
- The neutrons goes into the lithium deuterate, with the lithium and make tritium.
- The combination of high temperature and pressure are sufficient for tritium-deuterium and deuterium-deuterium fusion reactions to occur, producing more heat, radiation and neutrons.
- The neutrons from the fusion reactions produced fission in the uranium-238 pieces from the tamper and shield.
- Fission of the tamper and shield pieces produce even more radiation and heat.
- The bomb explodes.
All of these events happen in about 600 billionths of a second (550 billionths of a second for the fission bomb implosion, 50 billionths of a second for the fusion events). The result is an immense explosion that is more than 700 times greater than the Little Boy explosion: It has a 10,000-kiloton yield.
Modern nuclear techniques
Nowadays, nuclear warheads are fitted inside a ballistic missile or they're simply dropped off a bomber. But these bombs are so destructive that they can easily destroy the world. The explosion would not only give off heat and radiation, but a long-term problem would occur.
As the bombs would explode, they would produce dust clouds and gases in the atmosphere and will form a thick layer. Eventually they would block sunlight reaching the earth surface and the planet would become frozen and this would cause mass extinction. This theory is known as the Global Glaciating Theory. It is believed that the mass extinction of dinosaurs happened because of a meteoroid striking the Earth. Nuclear bombs are deadly and they should be dismantled or some day it might get into wrong hands.