Possible breakthrough in energy source research!

[Jon Miller]

Originally posted by KrazyHorse
There's no "energy source" breakthrough here. It sounds like they had pumped some energy into the fields somewhere and when they started to turn down the power some of it came back and reheated the plasma.

The only thing that's happening is that they don't quite understand the dynamics of the system, so they don't understand where they had stored the energy

I should have read the link better, that sounds better than my assumption.

JM

[KrazyHorse]

Yeah, if they claim to have seen fusion then I would expect there to be some mention of transmuted elements or something.

As it stands, this just looks like they don't know what the ****'s going on in their machine.

[BlackCat]

Exactly. The fusion note is the journalists.

They actually says that they don't have a clue about what is happening.

[Provost Harrison]

Yeah, but 2 billion K is pretty damn hot, almost hot enough for British cooking

[Urban Ranger]

Originally posted by Jon Miller
Iron (56) is the atom which has the highest binding energy, it is where it is energetically favorable to do fusion towards (for small nuclei), and to do fission towards (for large nuclei).

Wouldn't that be the lowest?

[KrazyHorse]

No. Binding energy is defined to be a positive quantity. It is the difference between the energy of a system of free nucleons (floating around in space) and the nucleus in question.

Ebinding = Efree - Enucleus > 0

When a system of free nucleons condenses to form a nucleus (not that this actually happens in a single step) there is energy released; Efree = Enucleus + Ereleased

Ereleased = Ebinding

The more the binding energy per nucleon the more stable the nucleus; it is energetically preferable for it to stay in its current configuration.

[KrazyHorse]

When a nucleus fissions spontaneously there must also be energy released (otherwise it is energetically verboten). E1 = Binding energy 1 etc

Since binding energy is defined in such a way as to make it positive, the enrgy conservation equation here looks like:

-E1 = -E2 - E3 + (Released Energy)

[snoopy369]

Originally posted by cronos_qc


Anyone can explain to me, how in nuclear reactions, more energy are releasing than the originally put in?

Thanks!

BTW, a simpler lay explanation to this (as referenced above):

Nuclear fission/fusion puts in some energy to release POTENTIAL energy that is already present in the atom, in the form of nuclear binding energy (energy holding nuclear particles, protons/neutrons, together). That energy was put in somewhere in the past, either at the creation of the Earth billions of years ago, or through some other process.

So, it's just like lighting a fire - where we put in a small amount of energy, via a match, to get a lot more potential energy. Just on a rather ... larger ... scale

BTW, thanks, Jon - I'd never heard that explicit of an explanation of the binding energies in relation to Iron and whatnot

[snoopy369]

Originally posted by KrazyHorse
No. Binding energy is defined to be a positive quantity. It is the difference between the energy of a system of free nucleons (floating around in space) and the nucleus in question.

Ebinding = Efree - Enucleus > 0

How is the energy of the system of free nucleons defined?

[KrazyHorse]

Since they are assumed to be free, they sit at 0 potential (actually, you are free to set the potential to any constant there, but since it's only differences in potential which matters, you can just use this as your convention)

Therefore, their energy comes entirely from their rest masses. A system of non-interacting nucleons at rest has energy equal to the sum of the rest energies of the nucleons.

[KrazyHorse]

To give an example of the scale of binding energies versus rest energies, nucleons have a rest energy of ~1 GeV = 1000 MeV = 1 000 000 000 eV

A helium nucleus (aka alpha particle aka 2N + 2P) therefore has a component energy of ~4 000 MeV

The binding energy of this nucleus is ~28MeV

So, instead of weighing 4000 MeV, it weighs 3972 MeV

[KrazyHorse]

On the other hand, deuterium (1P + 1N) has binding energy ~2MeV

So, if I were to take 2 deuterium and make 1 alpha I would be left with an extra 28 - 2*2 = 24 MeV of energy.

Ta da. Fusion.

[snoopy369]

Ah. So, in putting together four free nucleons to make a Helium nucleus, 28 MeV is spent (presumably from those four nucleons), thus lowering their energy/weight?

[KrazyHorse]

No, 28 MeV is RELEASED in putting together 4 nucleons into helium.

The nucleus is at the bottom of a hill. Getting nucleons close together (if you have the right mix of neutrons and protons to avoid blowing up due to excess positive charge) creates a potential well. Pulling the nucleons out again costs energy. But some hills are deeper than others. Helium is a deeper well than deuterium, so turning two deuteriums into a helium frees up energy.

[snoopy369]

Right. I meant "spent" as in "spent from the potential energies of the nucleons", not "spent putting them together"... just not using the right language not being a physicist

I assume you need to put a small amount of energy in to get them together though, don't you? Just much smaller than 28 MeV?