U-238 Neutron Capture: Clarifying Misconceptions about Fast and Slow Neutrons

In summary, U-238 requires fast neutrons to be fissioned due to its even-even nature and an activation energy of 6.6MeV. There is no contradiction in Wikipedia's statement that U-238 is better with capturing fast neutrons than slow neutrons, as fast neutrons are needed to transform U-238 into U-239, which then decays into Pu-239. The confusion may arise from the fact that fast neutrons have a higher kinetic energy, but it depends on the specific process being considered, whether it is Pu-239 formation or fission. A diagram of the cross section for these processes as a function of neutron energy would provide a better understanding.
  • #1
morage_key_ri
2
0
Wikipedia said U-238 is better with capturing fast neutrons than slow neutrons. shouldn't it be the other way round? I thought U-238 is not fissile but is fissionble by neutrons with high enough K.E, and doens't fast neutrons have higher K.E.??
 
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  • #2
U-238 is even-even and can't be fissioned by thermal (slow) neutrons, so it requires fast neutrons to be fissioned. The activation energy is 6.6MeV.

Where is the contradiction? You say that wiki claims that U-238 is better to capture fast neutrons than slow. You says that U-238 require neutrons with high enough K.E.

Where is your confusion?
 
  • #3
Thank you for the reply,

wiki said fast neutrons required for U-238 to capture and become U-239, which then decays into Pu-239.

my confusion is: Won't fast neutrons more likely to cause fission than transform 238 to 239?
 
  • #4
It depends on K.E

There is no contradiction since you are talking about two different things.

What you really need is a diagram over cross section for the two processes: "Pu-239 formation" and "fission" as a function of neutron energy.
 

1. What is U-238 neutron capture?

U-238 neutron capture is a nuclear reaction in which an atom of uranium-238 absorbs a neutron, resulting in the formation of an atom of uranium-239.

2. Why is U-238 neutron capture important?

U-238 neutron capture is important because it is the first step in the process of creating fissile material for nuclear reactors and weapons. It is also a key factor in the production of nuclear energy.

3. How does U-238 neutron capture work?

In U-238 neutron capture, a neutron is absorbed by the nucleus of a uranium-238 atom, causing it to become unstable and form uranium-239. This process releases energy and increases the atomic weight of the atom.

4. What are the potential dangers of U-238 neutron capture?

The main danger of U-238 neutron capture is the creation of plutonium-239, a highly radioactive material that can be used to make nuclear weapons. Additionally, the process can release harmful radiation and create radioactive waste.

5. Is U-238 neutron capture a sustainable source of energy?

No, U-238 neutron capture is not a sustainable source of energy. While it can produce energy, it also creates radioactive waste and has the potential for catastrophic accidents. Alternative forms of energy, such as renewable sources, are more sustainable and less harmful to the environment.

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