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Explanation of fast neutron and slow neutron in nuclear reaction?
Wiki User
∙ 12y ago
Free neutrons are said to have a speed or a temperature. Both ideas mean pretty much the same thing, which is that they have an amount of energy associated with them. It is specifically measured most commonly, perhaps, in electron volts (eV), or as Million electron volts (MeV). Unfortunately, what is meant by fast or slow depends on the application, and perhaps the author or speaker.
Free neutrons come from different sources and have different speeds when they are produced. As they fly about, they hit the nuclei of atoms, and may bounce, imparting some part of their energy to the atoms if they do. As time passes, they lose energy in this manner getting slower and slower. Please note, however, that not much time usually passes, because the half life of a neutron is a bit less than fifteen minutes.
There are other things that neutrons can do besides bounce. They can cause decay of a radioactive atom, they can cause fission of a fissionable atom, and they can be absorbed. There is a likelihood of any of these events happening by the collision of a neutron with an atom, and the likelihood depends on several things. Of great importance is the isotope of the atom; different isotopes have different cross sections, the cross section being a measurement of how likely it is for the neutron to interact with the atom. Also very important is the temperature of the atom, and the speed of the neutron.
The cross section of the atom will be greater or less depending on the speed of the neutron and the temperature of the atom, but not in a way that is easily predictable. A faster neutron might not cause fission as easily as a slower one in a given situation. The data on the nuclear cross sections of atoms by isotope, temperature, and neutron speed, were largely obtained empirically.
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∙ 12y ago
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Are there fast neutrons?
Yes, in fact for a sustainable nuclear chain reaction to work, you have to slow neutrons down.
Why U 235 is fissioned by thermal neutron while U 238 by a fast neutron?
It's to do with the capture cross-section of the nucleus. It just happens that the U-235 nucleus has a much larger cross-section for neutron capture when the neutrons are slow, and that the subsequent nucleus is unstable and splits into two parts. With U-238, it does not undergo fission at all, it just absorbs the fast neutron and transmutes to Pu-239. As to the fundamental reason for this, it is in the complex nuclear physics field of study
How do you beat the poster duty within 30 seconds in kingdomhearts 2?
It takes a lot of practice. If you use the skateboard and are fast at reaction commands, it goes by fast. Also, if you memorize who to give letters to, it can go by faster. Don't forget about the bird that is flying up high!
How fast is silver?
Silver the Hedgehog is pretty dang fast, but no where near as fast as Sonic
What is the name of the show that goes run fast for your mother fast for your father?
paadhutha thiyyaga shoe that runs my mom fast and dad
How much temperature can be controlled by liquid sodium in nuclear reactors?
Liquid sodium has been used as a coolant in fast reactors, because it does not slow down and absorb fast neutrons. It does not control the nuclear reaction directly, for that variable neutron absorbers are required.
Why you use slow neutrons instead of fast neutrons in nuclear reaction?
in reacter U-235 fission is due to slow neutrons because in reacter the probability of fission from fast neutron is approximatly zero.
Name the element when uranium captures a fast neutron?
The element is determined by the number of protons. When uranium captures a fast neutron it is still uranium but has an increased atomic mass. Fast neutron capture may encourage a further reaction but it depends on which uranium isotope you start with as to the increase in probability some further reaction will occur and which reaction that might be.
What is nuclear reactors?
An assembly of fissile fuel (U-235 or PU-239) arranged in a geometric array. The assembly can be made to go critical such that a chain reaction starts which builds up a neutron flux inside the assembly. The chain reaction is controlled at a steady level using neutron absorbing control rods.The nuclear reactor can classified under:a thermal nuclear reactor, where the majority of fissions are caused by slow neutrons. In these reactors, the fast neutrons produced by fissions are slowed down with a moderator which can be graphite, heavy water or light water, anda fast nuclear reactor where the majority of fissions are caused by fast neutrons
What is a nuclear reactor?
An assembly of fissile fuel (U-235 or PU-239) arranged in a geometric array. The assembly can be made to go critical such that a chain reaction starts which builds up a neutron flux inside the assembly. The chain reaction is controlled at a steady level using neutron absorbing control rods.The nuclear reactor can classified under:a thermal nuclear reactor, where the majority of fissions are caused by slow neutrons. In these reactors, the fast neutrons produced by fissions are slowed down with a moderator which can be graphite, heavy water or light water, anda fast nuclear reactor where the majority of fissions are caused by fast neutrons
Are there more fast breeder or thermal nuclear reactors?
Most nuclear reactors are thermal-neutron reactors. A few fast breeder reactors have been built, but not many.
Why is the moderator important in a nuclear reactor?
The moderator is used to slow down the neutrons present in the core of the reactor. Normally the neutrons produced as the nuclear fuel (e.g. uranium) is fissioned are travelling too fast to produce a sustained chain reaction. Some examples of moderators are cadmium, heavy water and graphite.
Why fission cannot take place with fast neutron?
In order to cause an atomic nucleus to become unstable so that it will undergo fission, you have to add a neutron. If a slow neutron collides with an atomic nucleus, it will be absorbed into the nucleus and become part of it. The nuclear attraction of the nucleus is strong enough to grab a slow neutron. But a fast neutron cannot be captured because it has too much kinetic energy. The attraction of the nucleus is not enough to stop the motion of a fast neutron. Even if a fast neutron makes a direct hit on an atomic nucleus, it is just going to bounce off.
How nuclear decay rates different from chemical reaction rates?
nuclear decay rates take more time and chemical reaction rates could happen fast.
Is uranium 238 a slow or fast neutron absorber?
uranium 238 is a fast neutron absorber the answer is correct but for more explanation:- when uranium 238 is bombard by neutron >>> uranium 238 , undergoes B decay>>>Np 239 ,undergoes B decay >>> Pu 239 finally undergoes alpha decay >>> fissile U
What is the difference between nuclear decay and nuclear transformation reactions?
nuclear decay rates take more time and chemical reaction rates could happen fast.
Why fast neutrons are not captured by nucleus?
The nucleus is very small; if it were the size of a golf ball the outer electrons would be about as far away as the height of the empire state building. If a neutron was moving very fast it probably wouldn't hit a nucleus. When , occasionally, a neutron does hit a nucleus, it might start nuclear fission- especially when the nucleus is heavy like Uranium 235 (U-235). So, to sum it up, most neutrons are not captured by a nucleus because they are both so small relative to the space that they are in, but sometimes a neutron will hit a nucleus.
