How good is antimatter?

Shinova · Post by **Shinova** » 2006-03-20 09:01pm

I read on this board that there's only so much power you can generate from nuclear fusion, and that there's an upper limit.

Does anti-matter also have such an upper limit? How much higher than fusion is it?

Batman · Post by **Batman** » 2006-03-20 09:18pm

E=mc^2 dictates that there is an upper limit on ANY matter-to-energy conversion. In the case of M/AM it's a theoretical upper limit of 9e16 J/kg.
My memory is hazy on what fusion can do but IIRC it's less than a tenth of a percent of that.

Omega-185 · Post by **Omega-185** » 2006-03-20 10:15pm

I may be compleatly wrong on this but I think that fusion could release as little as 0.6% of the energy stored in the mass. But I could be out to lunch on this, after I only know the very basics of a fusion reaction.

SirNitram · Post by **SirNitram** » 2006-03-20 10:39pm

The Main Site's 'Constants' article:

Energy Density (at 100% efficiency)
Matter/antimatter annihilation = 9E16 J/kg
Deuterium fusion = 6.2E14 J/kg
Uranium-235 fission = 8.9E13 J/kg
Hydrogen burning = 1.2E8 J/kg
Methane gas burning = 5.0E7 J/kg
Coal burning ~ 2.3E7 J/kg (depending on grade of coal)
TNT detonation = 4.2E6 J/kg

dragon · Post by **dragon** » 2006-03-20 11:24pm

So deutrim fusion has less than 1% energy of antimatter. Now those are 100% efficiency but what kind of efficiency do most power plants (nukes in particular) get. I know they have alot of energy wasted as heat which is why need tend to be built by rivers for cooling.

Shroom Man 777 · Post by **Shroom Man 777** » 2006-03-21 02:23am

Gotta remember though, the power/energy wasted in creating antimatter far exceeds the energy generated by antimatter annihilation.

SyntaxVorlon · Post by **SyntaxVorlon** » 2006-03-21 12:12pm

Here's how nuclear power works: It causes binding energy to be released from nuclear reactions. So Helium is at a lower binding energy than two separate Deuterium atoms, so energy is released on fusion. Uranium has a higher binding energy than lead so energy is released upon fission.

Here is a graph:

M/AM releases all the energy in the matter being reacted as electro-magnetic particles.

Nuclear reactions release usually <1% of the energy in mass.

kheegster · Post by **kheegster** » 2006-03-21 05:59pm

SyntaxVorlon wrote: M/AM releases all the energy in the matter being reacted as electro-magnetic particles.

Those particles are otherwise known as 'photons'

.

dragon · Post by **dragon** » 2006-03-21 06:17pm

Some quick checking on CERN website revealved something I didn't know. Appearntly we use antimatter in brainscans (PET)

http://livefromcern.web.cern.ch/livefro ... day01.html

At low energies, however, the electron-positron annihilations can be put to different uses, for example to reveal the workings of the brain in the technique called Positron Emission Tomography (PET).

Lord Zentei · Post by **Lord Zentei** » 2006-03-21 06:19pm

kheegan wrote:
SyntaxVorlon wrote: M/AM releases all the energy in the matter being reacted as electro-magnetic particles.

Those particles are otherwise known as 'photons' .

Actually, that is not correct. Electron-positron annihilations do release all their energy as photons, but nucleon-antinucleon reactions release their energy as pions.

The pions eventually decay into neutrinos, electrons, positrons and photons.

kheegster · Post by **kheegster** » 2006-03-21 06:33pm

Lord Zentei wrote:
Actually, that is not correct. Electron-positron annihilations do release all their energy as photons, but nucleon-antinucleon reactions release their energy as pions.

The pions eventually decay into neutrinos, electrons, positrons and photons.

Yes...my bad. I was thinking in terms of e+/e- annihilation since it's by far the most common matter-antimatter reaction.

But if you want to be precise about it, almost any particle in the Standard Model 'zoo' is possible as the product of an annihilation so long as it's allowed by kinematics and conservation laws. Certainly a quark-antiquark reaction involving particles other than up or down would yield mesons other than pions. The initial annihilation is an EM process, but subsequent decays may not be.

kheegster · Post by **kheegster** » 2006-03-21 06:54pm

Ghetto edit:

I'm an astrophysicist, and 'annihilations' in my field usually means e-e+ collisions.

Post by **Surlethe** » 2006-03-21 07:24pm

Is this a good explanation for the energy output of nuclear reactions? The binding energy of a nucleus can be thought of as similar to the gravitational binding energy of a planet. The strong nuclear force holds the particles together, stopping the similarly-charged protons from flying apart. However, nuclei themselves are positively charged, so you have to have energy to push them together.

In fusion, the potential energy of the nuclear bindings once the strong nuclear force takes over is less than the energy you had to expend pushing them together, so the reaction releases energy. However, in iron, the energy is equal before and after; and elements heavier than iron are inefficient to fuse because the energy you'd spend pushing them together would be less than the energy you'd get out -- i.e., they'd be "cold weapons".

In fission, on the other hand, since the potential energy of the strong nuclear force inside the nucleus for heavier elements is higher than the potential energy of the constituents outside the nucleus, if you can move them apart far enough that the electromagnetic force takes over and pushes them apart, their energy state will be lower than before, and so you'll have to have some released energy there. Similarly, for elements lighter than Fe, the energy state of the nucleus is lower than the energy state of a split nucleus, so fission is not feasible.

kheegster · Post by **kheegster** » 2006-03-22 06:34am

kheegan wrote:
But if you want to be precise about it, almost any particle in the Standard Model 'zoo' is possible as the product of an annihilation so long as it's allowed by kinematics and conservation laws. Certainly a quark-antiquark reaction involving particles other than up or down would yield mesons other than pions. The initial annihilation is an EM process, but subsequent decays may not be.

Quark interactions are STRONG processes....

Shouldn't post when I'm sleep-deprived as I was last night.