What Is the Final Direction of Fusion Products in the XYZ Axis?

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Discussion Overview

The discussion revolves around the final direction of fusion products resulting from the proton-proton (p-p) reaction in stellar environments, specifically in the context of the sun. Participants explore the implications of energy and momentum conservation laws on the trajectories of the resulting particles in the xyz axis.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant inquires about the final direction of fusion products when two protons approach from opposite directions along the x-axis.
  • Another participant notes that there is some degree of freedom in the directions of the products, as long as energy and momentum conservation laws are maintained.
  • A participant explains that since most of the mass is in the deuterium (d), it will move very little, while the other particles can move in various directions, likely opposite to each other.
  • A further elaboration compares the reaction to a collision between cars, suggesting that if the initial momentum is insignificant compared to the energy released in the reaction, the products will scatter in multiple directions, with some influence from their initial directions.
  • A link to a simulation is provided to illustrate the p-p chain reaction and the conservation laws involved.

Areas of Agreement / Disagreement

Participants generally agree on the importance of energy and momentum conservation in determining the directions of the fusion products, but there is no consensus on the specific final directions or the extent to which initial conditions influence the outcomes.

Contextual Notes

The discussion does not resolve the specific final directions of the fusion products, and assumptions regarding the initial conditions and their influence on the final state remain implicit.

sid_galt
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The first step in the nuke reaction of the sun is p-p reaction

p + p = d + e+ + neutrino

My question is, if the two protons are coming say from the -x and +x direction, what is the final direction of the products formed in the xyz axis.
 
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There is some degree of freedom as long as energy and momentum conservation laws are obeyed. Since most of the mass is in the d, it will move very little. The other particles can go off in any direction (presumably opposite from each other).
 
mathman said:
There is some degree of freedom as long as energy and momentum conservation laws are obeyed. Since most of the mass is in the d, it will move very little. The other particles can go off in any direction (presumably opposite from each other).

mathman,

Exactly correct.

Because the reaction gives so much energy to the products - the energy
and momentum of the reactants before the reaction is insignificant compared
to the energy and momentum the products will have.

But the energy and momentum before the reaction is the only way that the
product particles will "remember" anything about the initial directions of the
reactant particles.

Imagine a collision between two cars. If they collided while going roughly
the same direction - a glancing collision - then they will leave the collision
going in the same general direction as before the collision. That's the only
way to conserve momentum.

Now imagine the cars are full of explosives, which detonate upon collision.
The car parts will spew out roughly in all directions [ with the original
direction favored to some extent ]. That's because the initial momentum
and energy is insignificant relative to the final energy / momentum due to
the added energy of the explosion.

Dr. Gregory Greenman
Physicist
 

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