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

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SUMMARY

The discussion centers on the fission process of a U-235 nucleus when struck by a neutron. The critical factor is the cross section for fission, which varies significantly based on neutron speed. The cross-sectional area of a U-235 nucleus is approximately 1 barn, but for slow-moving neutrons, this can increase to as much as 1000 barns. This indicates that the distance from the nucleus at which a neutron can successfully induce fission is influenced by its velocity and the corresponding cross-sectional area.

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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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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.
 

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