Discussion Overview
The discussion revolves around the behavior of the cross section for fission of U-235, particularly focusing on the empirical observation that it decreases like 1/v with respect to the velocity of thermal neutrons. Participants explore qualitative explanations for this phenomenon, including the role of resonances and scattering processes.
Discussion Character
- Exploratory
- Technical explanation
- Conceptual clarification
- Debate/contested
Main Points Raised
- Some participants note that the cross section for fission of U-235 is significantly higher for slow, thermal neutrons compared to fast neutrons, which are more similar to geometric area.
- One participant suggests that the presence of resonances in the cross section is a qualitative reason for the 1/v behavior, mentioning competing paths and the sum of these processes.
- Another participant questions whether resonances are primarily located at higher energies, indicating a potential misunderstanding or differing perspective on resonance behavior.
- It is proposed that the 1/v increase in cross-section might apply to all isotopes, with a suggestion that partial wave analysis could provide insight, although the participant expresses uncertainty about the underlying physics.
- A later reply introduces the concept of threshold states in heavy elements, suggesting that these states near zero energy could also be considered a form of resonance.
Areas of Agreement / Disagreement
Participants express differing views on the nature and implications of resonances in the context of the 1/v law, indicating that multiple competing perspectives remain without a clear consensus.
Contextual Notes
Some limitations include the potential dependence on definitions of resonances and the unresolved nature of the relationship between scattering processes and the observed cross-section behavior.