Fission: how far from the center of a U-235 nucleus can a neutron strike

In summary, the distance at which a neutron can strike a spherical nucleus and still cause fission depends on the cross-sectional area of the nucleus, which is affected by factors such as the speed of the neutron. For a U235 nucleus, the cross section is approximately 1 barn, but for slower moving neutrons it can be as large as 1000 barns. Therefore, it is not as simple as just nicking the nucleus at a tangent line.
  • #1
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and successfully fission. let's say a neutron approaches the spherical nucleus from a particular distance. its possible route to the nucleus has a conical shape. how far from the center can it strike and still fission? If it just nicks it just inside a tangent line will it fission?
 
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  • #2
It's not quite that simple. The property of interest here is the cross section of fission for the nucleus, and that depends on more than 1 factor.

For example, the the cross-sectional area of a U235 nucleus is about 1 barn. However, for slow moving neutrons, the cross section for fission can be as large as 1000 barns.
 

1. How does fission occur in a U-235 nucleus?

Fission occurs when a neutron strikes the nucleus of a U-235 atom, causing it to split into two smaller nuclei, releasing energy and additional neutrons.

2. How far from the center of a U-235 nucleus can a neutron strike for fission to occur?

A neutron can strike anywhere within the nucleus of a U-235 atom for fission to occur. However, the probability of fission increases as the neutron approaches the center of the nucleus.

3. What is the critical mass for fission to occur in a U-235 nucleus?

The critical mass of a U-235 nucleus is the minimum amount of U-235 required for a chain reaction to occur. This is typically around 52 kilograms for a bare sphere of U-235.

4. Can fission occur in other types of nuclei besides U-235?

Yes, fission can occur in other types of nuclei, such as U-233, Pu-239, and Pu-241. These nuclei also have a critical mass and can undergo chain reactions when struck by a neutron.

5. What is the difference between fission and fusion?

Fission is the process of splitting a larger nucleus into smaller nuclei, while fusion is the process of combining two smaller nuclei to form a larger nucleus. Fission releases energy by breaking apart atoms, while fusion releases energy by combining atoms. Both processes are used in nuclear energy production, but fission is currently more widely used due to technological limitations in achieving fusion reactions.

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