|MadSci Network: Physics|
Nate, As with general questions, the usual answer is "It depends." In this case, it depends on which atoms you are splitting, how many you are splitting, and even on the definition of "splitting" you use. For background, and for a great read, I recommend "From X-Rays to Quarks" by E. Segre. This is a fascinating history of Nuclear Science from the discovery of radioactivity on to today. The equation that governs the amount of energy released when a nuclear reaction takes place is the famous Einsteinian E = mc^2 where E is energy, m is mass, and c is the speed of light (squared). Remember that E can be positive if energy is given off, or negative if more energy must be input than is given off. In the history of nuclear chemistry (also called radiochemistry) Ernest Rutherford is credited with discovering the splitting of atoms. The first part was recognizing that radioactive decay is a form of splitting atoms. In particular, alpha decay is where a nucleus gives of an alpha particle, a helium nucleus, and becomes another element with Atomic Number A - 2 and Mass M - 4 from the original nucleus. Since this reaction goes spontaneously, the E given off is positive, and is reflected in the kinetic energy of the alpha particle. While you might be able to get heat out of radioactive decay, and indeed, alpha and beta radioactive sources have been used as heat sources in space and underwater applications. But in general this spontaneous splitting is not going to give enough energy to "make the building explode." Rutherford also discovered the trasmutation of atoms by nuclear reactions where an atom is bombarded by a moving particle. He found that nitrogen in the air reacts with alpha particles formed by cosmic ray interations and from decay of radionuclides such as radon. The reaction He4 + N14 -> O17 + H1 + Energy (the kinetic energy of the hydrogen nucleus or proton). This reaction is also not going to give enough energy to "make the building explode." We can use the invention of E.O. Lawrence, the cyclotron, to accelerate charged particles to high energy and cause nuclear reactions. Since a lot of energy must be put into the charged particle (proton, helium nucleus, or ionized nucleus such as iron). In almost all cases, the energy given off by the splitting is not enough to raise the temperature enough to form a shock wave and make the building explode. But there is one class of nuclear reactions that does give off enough energy that if we make a device where a large number of atoms are split in a short time, we can release enough energy to not only "make the building explode", but a good part of the city around it. That is the atomic bomb, which gets its energy from the splitting of very heavy atoms. The most stable nuclide in the entire table of nuclides is Fe56. If there were no kinetic barriers, the entire universe would start reacting to form Fe56. You can look up "binding energy of a nucleus" on the web or in a general radiochemistry book such as "Radiochemistry and Nuclear Methods of Analysis" by Ehmann and Vance, or Nuclear and Radiochemistry by Friedlander, Kennedy, Miller, and Macias. There are a few reactions that can be "easily" initiated to split into smaller pieces. One that is used in nuclear reactors and bombs is U235 + neutron --> 2 fission products, about 2 neutrons, and much energy. The fission products are not about half of the U238, but have one group centered around Barium and the other around Krypton. These nuclei have high kinetic energy, are intensely radioactive giving off high kinetic energy particles and gamma rays. Now there are two ways to "make the building explode". The first way with a nuclear reactor is to have the controlled reaction become uncontrolled. This is what happened at Chernoble. The heat of the fission reaction is removed by a coolant--a gas, or liquid--that is heated. This heated medium is used to generate electricity. Helium, Water, and Liquid Sodium metal are all used as coolants. These coolants are circulating under pressure. If the reaction becomes uncontrolled, the coolant is not able to remove all the heat fast enough, and, for example with water, the coolant is flashed to steam and the rapidly rising pressure causes a steam explosion that "makes the building explode." This is not like an atomic bomb because the atoms that are splitting are not forced to stay together. The fuel is melted or blown apart by the steam explosion. Except for the radioactivity of the fuel and fission products, this explosion is just like a boiler explosion. At a real reactor, there may be a large release of radioactivity that can affect large areas (Chernoble radioactivity contaminated a large area around the reactor, and the wind took radioactive materials into other countries, and eventually measurable amounts went around the world). Now to really "make the building explode", we need to keep the fission reaction going as long as possible to build up the maximum energy possible before the fissioning material blows itself apart with the force of an atomic bomb. This is accomplished by using conventional explosives (like dynamite) to form a powerful spherical compression on the uranium or plutonium and force it to stay together in a mass building up energy (in a very short time) until it blows apart as an atomic bomb. Now we have really "made the building explode" and taken out everything for a good distance around the building (several kilometers for a large bomb). You can Google "Nuclear Physics" and the first hit is the Wikipedia for Nuclear Physics, and it is very good. I haven't found any glaring errors in the times I have used it. There will be many more hits, and some of the teaching resources are also very good. The professional society sites are some of the best sources, but they are a bit harder to find than the Wiki site. My recommendation to you is to read about splitting atoms rather than trying it. You can Google "Radioactive Boy Scout" to see what can happen when things get out of control from a Health Physics perspective and create a major radioactive contamination.
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