Need help Nuclear Fission Question

In summary, the process of nuclear fission occurs when a neutron hits the nucleus of Uranium-235. The neutron can come from a previous fission, and the reaction can produce multiple neutrons that can continue the chain reaction. This process is controlled in nuclear plants by using a moderator to cool down the neutrons and an absorber to control the rate of reactions. Uranium can also spontaneously disintegrate, producing energy that can start natural reactors if there is a high enough concentration of uranium.
  • #1
maccaman
49
0
This is probably an easy question for most of you, but me nor my teacher knew. Today we learned that nuclear fission can occur when a neutron "hits" the nucleus of Uranium-235. What i wanted to know is, where does this neutron come from, and how can they make it hit this uranium-235 atom.

Any help would be greatly appreciated.
 
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  • #2
The incoming neutron generally comes from... a previous fission ! It may seem like the problem of the egg and the cow and which came first :wink:
Look at this schematic reaction. An incoming neutron causes fission of [tex]^{235}U[/tex] in [tex]^{144}Ba[/tex] plus [tex]^{89}Kr[/tex] thus liberating three neutrons : each of them could trigger one reaction, overall producing 9 neutrons... So basically, if you stack more than a critical mass of [tex]^{235}U[/tex], byitself it will radiate energy. Random processes will eventually cause a few neutrons to be liberated, spontaneous fission for instance, and as you can imagine the process is divergent : if you actually stack really too much, it would blow.

This is controlled in nuclear plants, which do not aim at blowing stuff. For instance http://www.npp.hu/mukodes/lancreakcio-e.htm is a drawing illustrating the need for a moderator to cool down the neutrons. An absorber is usually also used to control the rate of reactions.

wikipedia
some critical masses at the end of this page
Lawrence Berkeley National Laboratory
Uni. of Prince Edwards
 
Last edited by a moderator:
  • #3
I'd add, that uranium spontaneously disintegrates producing alpha and gamma radiation, and this is enough energy source to start natural reactors if the concentration of uranium is big.
 
  • #4
Aka, Critical Mass
 
  • #5
cheers people, thanks for that
 

Related to Need help Nuclear Fission Question

1. What is nuclear fission?

Nuclear fission is a process in which the nucleus of an atom is split into two or more smaller nuclei, releasing a large amount of energy. This process is used in nuclear power plants to generate electricity.

2. How does nuclear fission work?

Nuclear fission occurs when a neutron is fired at the nucleus of an atom, causing it to become unstable and split into two smaller nuclei. This releases energy in the form of heat and radiation, which can be harnessed for various purposes.

3. What is the difference between nuclear fission and nuclear fusion?

Nuclear fission involves splitting the nucleus of an atom, while nuclear fusion involves combining the nuclei of two or more atoms. Both processes release large amounts of energy, but nuclear fusion requires much higher temperatures and is still in the early stages of development for practical use.

4. What are the potential dangers of nuclear fission?

The main danger of nuclear fission is the possibility of a nuclear meltdown, which can release harmful radiation into the environment. There is also the risk of nuclear waste, which can remain radioactive for thousands of years and must be carefully stored and disposed of.

5. How is nuclear fission used in nuclear weapons?

Nuclear fission is the process that powers nuclear weapons, such as atomic bombs. By splitting the nuclei of atoms, a chain reaction can be created, releasing a tremendous amount of energy in a short period of time. However, the use of nuclear fission in weapons also poses a significant threat to human life and the environment.

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