The destruction of particles and antiparticles

[g.lemaitre]

In the First Three Minutes Steven Weinberg wrote:

There are believed to be just three conserved quantities whose densities must be specified in our recipe for the early universe:
1. Electric Charge. We can create or destroy pairs of particles with equal and opposite electric charge, but the net electric charge never changes. (We can be more certain about this conservation law than about any of the others, because if charge were not conserved, the accepted Maxwell theory of electricity and magnetism would make no sense.)

The word "destroy" really throws me off. When I think of destroy I think of complete elimination from existence, such as when you destroy a house it is completely gone, the timber may still remain but the house no longer exists. With particles and antiparticles they really aren't destroyed, they just get changed into different particles when they collide, right?

 

[Bill_K]

In a collision or a decay the original particles are really, truly destroyed and new particles are created. You can't say they just changed their identity into something else, because the result of the collision may be more than just two particles.

 

[g.lemaitre]

ok, that clears things up, thanks.

 

[PaulS1950]

When two particles collide under high heat and pressure they can fuse (fusion) leaving some of the energy or some of the elements making up the original particles as new pieces. If the heat or pressure is too low they can break apart into constituent componets which ultimately reform other particles.
When a positron and an electron meet they annihilate each other. All that is left is energy in the form of gamma and other forms of radiation. If we could produce enough antimater, and find a way to direct gamma waves then we could have a nearly unlimited power source. It might even allow a reasonable method for exploring the stars.

 

[Bobbywhy]

In the First Three Minutes Steven Weinberg wrote:



The word "destroy" really throws me off. When I think of destroy I think of complete elimination from existence, such as when you destroy a house it is completely gone, the timber may still remain but the house no longer exists. With particles and antiparticles they really aren't destroyed, they just get changed into different particles when they collide, right?

g.lemaitre: Weinberg’s use of the term “destroy” is accurate; two particles can really be destroyed completely. This process, called “annihilation” is unlike your example of knocking down a house, where the materials still exist in a pile of rubble.

“Upon the collision of a particle and an anti-particle, e.g. electron and positron, these are "annihilated" as particles and the mass of these particles converted into energy. Electron and positron have a rest mass which is together equal to an energy of 1.02 MeV. Upon the "annihilation" of both particles, two gamma quanta of 0.511 MeV each are generated.”
http://www.euronuclear.org/info/encyclopedia/annihilation.htm

 

[calvinjhfeng]

That's a **** loads of amount of energy.

If we could find a way to contain a kilogram of positrons and a kilogram of electrons, then we let them annihilate each other on Moon, I wonder if that's enough to destroy the entire moon or at least knock it out of orbit.

But then in the processs of annhilation, there's particles created and scatter all around the places, that's not 100% energy efficiency, some still goes into mass.

So actually how much portion of the energy will get convert into mass? (After the collision of electron and positron?)

 

[Nabeshin]

If we could find a way to contain a kilogram of positrons and a kilogram of electrons, then we let them annihilate each other on Moon, I wonder if that's enough to destroy the entire moon or at least knock it out of orbit.

Not even close.

But then in the processs of annhilation, there's particles created and scatter all around the places, that's not 100% energy efficiency, some still goes into mass.

So actually how much portion of the energy will get convert into mass? (After the collision of electron and positron?)

As was said above, if an electron and positron annihilate, all that is produced is two 0.511MeV gamma rays (photons). No mass.

 

[calvinjhfeng]

Not even close.



As was said above, if an electron and positron annihilate, all that is produced is two 0.511MeV gamma rays (photons). No mass.

1 kg is indeed quite far from what I found after plugging in calculator. It takes 10^12~16 kg to give it a considerable push.