Wikijunior:How Things Work/Nuclear Bomb
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[edit] Who invented it?
People had the idea that a nuclear bomb could be made for many years but it took the Second World War to push scientists into turning the idea into reality. The United States of America with British help ran the Manhattan Project, under Robert Oppenheimer, to design and build the first nuclear bomb.
[edit] How does it work?
The nuclear bomb works by releasing an enormous amount of energy, released as heat. The energy heats up the air around it, causing it to expand. This creates a shock-wave so strong that it can level entire cities. The heat also causes fires, but most notorious is the radioactivity that unleashes terrible suffering on those nearby, not killed by the shock-wave or the fires.
There are two types of nuclear bombs, fission bombs and fusion bombs. Fission means to break apart and fusion to merge together. The fission bomb works on the principle that it takes energy to put together a nucleus with many protons and neutrons. Sort of like rolling a heavy cart up a hill. Splitting the nucleus up again then releases some of that energy. Some atoms have unstable nuclei which means that they tend to break apart with little or no nudging.
You may have heard of uranium and plutonium and that they are radioactive elements. These two have just such unstable nuclei which causes their radioactivity. When a nucleus breaks into two smaller nuclei, a couple of neutrons shoot out. This is the radiation. Naturally occurring uranium and plutonium have atoms constantly undergoing radioactive decay. These are spaced sufficiently far apart so that the neutrons rarely bump into other unstable nuclei.
When a neutron, however, does hit an unstable nucleus, just like someone bumping into a cart at the top of a hill, it causes that nucleus to break apart and send out another couple of neutrons. By increasing the concentration of these unstable atoms, the probability that a neutron from one decay causes another one increases. The concentration where the reaction sustains itself is called critical mass and the reaction then called a chain reaction.
With each step of the reaction, energy is released and another step or two is started, and so an avalanche of reactions and energy release continues until the fissile (unstable) material is spent.
Actually, any nuclei heavier than that of iron (Fe56 which has 56 nucleons, to be precise) will release energy when broken apart. Lighter nuclei on the other hand usually release energy when they merge, or fuse. The most energy is released when two hydrogen nuclei fuse into a helium nucleus. Unlike the radioactive elements, getting the two helium nuclei to merge already takes a good deal of energy. Sticking with the analogy of the cart, it is like it's sitting in a hole at the top of the hill and needs a considerable push before rolling down.
In a fusion bomb, this initial energy is created by heating the hydrogen up to a tremendous temperature with a fission bomb as the first stage. In the split second between the fission bomb going off and the hydrogen being blown apart, the temperature causes it to fuse into helium, releasing many times more energy.
The energy released from a nuclear weapon exploded in the air is split four ways:
- Blast—40-50% of total energy
- Thermal radiation—30-50% of total energy
- Ionizing radiation—5% of total energy
- Residual radiation—5-10% of total energy
[edit] How dangerous is it?
The bomb in its stored state isn't very dangerous, as it takes some effort to set it off. Once detonated, the explosion is extremely dangerous. Even those that survive the blast and the fires will be subject to varying levels of radiation (mostly depending on how close they were to the bomb) that can cause death, cancer, leukaemia, or harm to reproductive organs resulting in a higher level of birth defects, or even complete sterility.
Only two nuclear bombs have been used in warfare. Toward the end of World War II, the United States dropped bombs on the Japanese cities of Hiroshima and Nagasaki. The death-toll from these bombings was in the hundreds of thousands.
In Hiroshima, the immediate effects of the blast killed about 70,000 people. In the aftermath, between 90,000 to 140,000 more people died from burns, radiation, and related disease.
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[edit] What does it do?
It creates a huge explosion, the force of which flattens buildings and kills people. It causes a massive fireball that can burn people to death even if they are miles away from the point of explosion. The bomb releases radiation that can poison and kill people for years afterwards.
The size of the explosion is dependent on the yield of the bomb. It can vary from a fairly small explosion from a "battlefield" nuclear weapon to an explosion big enough to destroy a whole town.
[edit] How has it changed the world?
Toward the end of the second world war, the United States dropped two nuclear bombs on the Japanese cities, Hiroshima and Nagasaki. The indiscriminate nature and immediate and long-term effects of the bombings have created a strong sentiment against the use of nuclear weapons.
The nuclear bomb is one of the most destructive weapon ever created. For decades, The United States and the Soviet Union were in a gridlocked power struggle known as the Cold War. Both had enough nuclear bombs to completely destroy each other with devastating repercussions on the entire world population. This provided a large incentive against starting a war. This strategy was called mutually assured destruction and was influential on world politics during the Cold War.
[edit] What idea(s) and/or inventions had to be developed before it could be created?
The binding energy, which is how much energy is stored in the heavy nuclei such as uranium and plutonium, had to be discovered. The process of creating material capable of reaching critical mass is very difficult and represents a significant engineering challenge.
