Fusion Question

[Isaac Scott]

Hey there,

 

I need a bit of help with a project I am working on.  Two parts here that help answer the same question.  First, when fusing H into He, is there a specific energy needed for fusion to occur or can fusion occur at any energy level or velocity.  

Part two:  When creating heavier elements in the lab, they blast a less massive particle at a more massive particle in the hopes that they will fuse to make the desired element.  Is there a specific velocity that the lighter particle is accelerated to? 

Thanks!  

 

Isaac

[Sensei]

The first step of (hot) fusion is to ionize electric neutral Hydrogen-1 into free protons and free electrons. It requires 13.6 eV energy per single H atom. That's 1312 kJ/mol.

Free protons (or other charged particles, the same sign of charge) are repelling each other. Therefor you need to overcome Coulomb's Barrier.

https://en.wikipedia.org/wiki/Coulomb_barrier

Whether there is needed additional energy depends on particles that you intend to fuse together. There might be needed activation energy in some cases.

BTW, fusion of ¹H into ⁴He is not direct process, but it's in several different reactions.

1 hour ago, Isaac Scott said:

Part two:  When creating heavier elements in the lab, they blast a less massive particle at a more massive particle in the hopes that they will fuse to make the desired element.  Is there a specific velocity that the lighter particle is accelerated to? 

That depends on particles you are accelerating.

Edited January 28, 2019 by Sensei

[swansont]

10 hours ago, Isaac Scott said:

Hey there,

 

I need a bit of help with a project I am working on.  Two parts here that help answer the same question.  First, when fusing H into He, is there a specific energy needed for fusion to occur or can fusion occur at any energy level or velocity.  

Strictly speaking, no. Fusion could occur at any energy owing to quantum tunneling, but it is exceedingly unlikely to happen at low energy. Sensei mentioned the Coulomb barrier — this is the energy scale you need to reach, but again, it's still possible with less, since the protons can tunnel through the barrier.

10 hours ago, Isaac Scott said:

Part two:  When creating heavier elements in the lab, they blast a less massive particle at a more massive particle in the hopes that they will fuse to make the desired element.  Is there a specific velocity that the lighter particle is accelerated to? 

Sort of. You have to have a minimum in order for the reaction to occur at a reasonable rate, but too much energy and you might not get the products you want — the extra energy could go to knocking out an extra neutron or proton, for example. But AFAIK, it's not a precise value. There would be a window of energies that gave you good results.

[John Cuthber]

The likelihood of fusion varies with energy (and the nuclei being fused)
https://en.wikipedia.org/wiki/Fusion_power#/media/File:Fusion_rxnrate.svg

[Isaac Scott]

On 1/28/2019 at 2:57 AM, swansont said:

Strictly speaking, no. Fusion could occur at any energy owing to quantum tunneling, but it is exceedingly unlikely to happen at low energy. Sensei mentioned the Coulomb barrier — this is the energy scale you need to reach, but again, it's still possible with less, since the protons can tunnel through the barrier.

Sort of. You have to have a minimum in order for the reaction to occur at a reasonable rate, but too much energy and you might not get the products you want — the extra energy could go to knocking out an extra neutron or proton, for example. But AFAIK, it's not a precise value. There would be a window of energies that gave you good results.

 

Thank you for the response!  I am trying to see if there is some sort of alignment between mass and fusion.  Very long story short, my hypothesis is that the increase velocity, hence increased mass, is directly related to whether fusion occurs.  If there is a "window" of energy levels the seem to work the best, I wonder if that is because it is impossible for us to know the exact velocity.  

 

Do you know where I might find the numbers on what that "window of energies" is?

On 1/27/2019 at 4:57 PM, Sensei said:

The first step of (hot) fusion is to ionize electric neutral Hydrogen-1 into free protons and free electrons. It requires 13.6 eV energy per single H atom. That's 1312 kJ/mol.

Free protons (or other charged particles, the same sign of charge) are repelling each other. Therefor you need to overcome Coulomb's Barrier.

https://en.wikipedia.org/wiki/Coulomb_barrier

Whether there is needed additional energy depends on particles that you intend to fuse together. There might be needed activation energy in some cases.

BTW, fusion of ¹H into ⁴He is not direct process, but it's in several different reactions.

That depends on particles you are accelerating.

 

Thank you for responding!  On part 2, where do I find numbers on this?  

[John Cuthber]

1 hour ago, Isaac Scott said:

Do you know where I might find the numbers on what that "window of energies" is?

Yes.

In the link I posted.

1 hour ago, Isaac Scott said:

I wonder if that is because it is impossible for us to know the exact velocity.  

No, it's not.

[swansont]

19 hours ago, Isaac Scott said:

Do you know where I might find the numbers on what that "window of energies" is?

You could search physics journals for the kind of data John Cuthber provided, only for fusion of heavier elements.