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No, moderation of neutrons is not always used to slow nuclear fission. In some types of nuclear reactors, such as fast breeder reactors, fast neutrons are intentionally not moderated to slow down the fission process. These reactors operate using fast neutrons to sustain a chain reaction. However, in most commercial nuclear reactors, moderation of neutrons is employed to slow down the fission process and maintain a controlled chain reaction.
in reacter U-235 fission is due to slow neutrons because in reacter the probability of fission from fast neutron is approximatly zero.
Uranium 235 (92U235) and slow Neutrons.
a thermal slow neutrons that will fission by a chain reaction of the nutrons.
a thermal slow neutrons that will fission by a chain reaction of the nutrons.
Neutrons are the important particles of nuclear chain reactions and the reactions depend on them. The neutrons do not really start the fission, reaction, however, because the neutrons come from fission in the fuel.The material in the fuel, typically a mix of 235U and 238U, undergoes fission spontaneously. When a fission event happens, more neutrons, typically two or three, are emitted. These bounce about from atom to atom, until they cause another atom to undergo fission, releasing more neutrons to increase the rate at which atoms undergo fission.But the neutrons needed for the chain reaction are actually produced by the fuel spontaneously, and these are produce in an ongoing manner with or without critical mass. So it is not a particle that starts the chain reaction; it is the act of putting together a critical mass.
1. Energy (heat) 2. Fast neutrons 3. Fission products (atoms of other elements of lower atomic weight, often very radioactive). All three are produced simultaneously, for every fission that occurs.
Yes, in fact for a sustainable nuclear chain reaction to work, you have to slow neutrons down.
Nuclear fission of Uranium-235 is more efficient when hit by neutrons with low energy of the order of electron volts. However, neutrons coming from fission are at high energies around 2 megaelectron volt. Accordingly, the moderator is needed to slow down the neutrons coming from fission to low energy values through scattering process with moderator molecules. This is the concept of the so called "thermal nuclear reactors"
It explodes because it contains a critical mass of unstable atoms of a heavy metal such as Uranium-235 or Plutonium-239. When the nucleus of one of these large atoms is hit by a neutron, the atom splits into two medium-size atoms such as Barium and Krypton or Strontium and Xenon, and also releases 2 or more free neutrons and a burst of energy. This process is called Nuclear Fission. The free neutrons from one nuclear fission can then create more fissions, and a Chain Reaction is begun. More fissions release more neutrons which create more fissions which release even more neutrons, etc. If conditions are right, this chain reaction proceeds explosively to form a Nuclear Fission Bomb or "Atomic Bomb". If this chain reaction is slowed and controlled, then the nuclear fission produces heat energy which can be used to boil water in a Nuclear Power Plant. Rapid fission, nuclear bomb. Slow controlled fission, nuclear power plant.
All thermal reactors, that is those using a moderator to slow down the fission neutrons, use the same reaction. In the US all commercial reactors (104 of them) are either PWR or BWR types.
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