Neutron Fission & Quantum Physics: How Does Gravity Affect Trajectory?

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Discussion Overview

The discussion revolves around the effects of gravity on the trajectory of neutrons released during the fission of uranium-235 (U235). Participants explore whether gravitational forces from nearby nuclei influence neutron behavior at the quantum level, considering both theoretical implications and practical scenarios in nuclear reactors.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions if a neutron traveling at a significant speed (c/10) would have its trajectory affected by the gravitational force from a nearby nucleus, suggesting a need for comparison with quantum effects.
  • Another participant acknowledges that while neutrons are affected by gravity, this influence is typically observed over much longer distances and may not significantly impact fast-moving neutrons in a reactor context.
  • It is noted that the gravitational effects of materials within a reactor are minimal, with even Earth's gravity having little effect on fast neutrons due to their high speed and short distances involved.
  • A participant reiterates the initial question, proposing a calculation of the gravitational force between a U235 nucleus and a neutron, while asserting that nuclear forces are far more significant than gravitational forces in this context.
  • Further, it is mentioned that fast neutrons in a light water reactor (LWR) are more likely to interact with protons in the cooling water rather than being captured by U235 or U238 atoms, emphasizing the role of delayed neutrons from certain radionuclides in reactor control.

Areas of Agreement / Disagreement

Participants express differing views on the significance of gravitational effects on neutron trajectories, with some arguing that these effects are negligible compared to nuclear forces, while others highlight the need for further calculations to understand the interactions better. The discussion remains unresolved regarding the extent of gravitational influence.

Contextual Notes

Participants acknowledge limitations in understanding the gravitational influence on neutrons, particularly regarding the scale of effects and the need for calculations comparing gravitational and nuclear forces.

1907Quarter
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just thinking cross sections here. a neutron that is freed as a result of a fission of pure U235. travels @c/10(fast!) will its trajectory be perturbed by the gravitational force emitted by a nearby nucleus, or do things on the quantum level work differently?
 
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Neutrons are affected by gravity, but over much longer length scales. For ultracold neutrons that can give rise to interesting effects.

http://physicsworld.com/cws/article/news/2002/jan/17/neutrons-reveal-quantum-effects-of-gravity

The effect of gravity on neutrons is also a common problem in neutron small angle scattering.

How much neutrons are affected by the gravitational field of nearby nuclei I don't know. I guess someone will have to do the calculations (compare the kinetic energy of the neutron to the gravitational energy).
 


The gravitational effects of the stuff in a reactor is extremely miniscule in the workings of a reactor. Even the Earth's gravity will have very little effect, since the neutrons are moving quite fast and the distances involved are quite short.
 


1907Quarter said:
just thinking cross sections here. a neutron that is freed as a result of a fission of pure U235. travels @c/10(fast!) will its trajectory be perturbed by the gravitational force emitted by a nearby nucleus, or do things on the quantum level work differently?
One could calculate the force of gravity between a U235 nucleus and a neutron, and then compare to the nuclear force.

The gravitational effect is insignificant. The nuclear effects dwarf the effect of gravity.

A fast neutron in a LWR is more likely to interact with a proton in the cooling water than it is to be captured by a U235 or U238 atom. The slowing down of neutrons takes on the order of milliseconds. Control of the system is actually achieved by virture of delayed neutrons that come from certain radionuclides (e.g., Br-87, 88, 89, I-137, 138, Rb-93, 94) that emit neutrons seconds after the fission event from which they were created.
 

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