Fusion product direction

1. Mar 28, 2005

sid_galt

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.

2. Mar 28, 2005

sid_galt

3. Mar 28, 2005

mathman

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).

4. Mar 28, 2005

Morbius

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

5. Mar 28, 2005

Staff: Mentor

Sid - here is a simulation.