If you go back one step further, there is only one source of energy - fission or fusion of elements generated by the big bang.
The only way to use these is in nuclear reactors. The Sun is one, the earth itself is one, and we have built our own too.
Parts of the earth were some sort of self moderating chain reaction but I thought that was no longer self sustaining and it's just the decomposition of unstable elements formed from then that keeps the middle warm now?
And gives us helium
AJH
identical to the one they have closed.
Adam
The mantle is kept hot by the radioactive decay of elements (mostly uranium I think) which would have sunk down when the whole earth was molten (as the iron did - hence the iron core of the planet).
You may also be thinking of the natural uranium reactor at Oklo, in Gabon, about 2 billion years ago.
And the whole of GB is about 60 million acres, so we all get approx one each.
Actually I best not complain. A third of my income last year was made by a carbon offsetting scheme. I would probably be out of business without them.
Adam
Yes, I guess nuclear reactors implies criticality, which isn't a requirement for nuclear energy generation.
That's it.
So much of the heavier elements were formed in fusion reactions before the earth formed?
One reason for the core to be iron is that decaying elements tend toward iron as the most stable state I think.
AJH
Elements further up the periodic table than iron are all formed in supernovas. Elements from and including iron downwards are formed in ordinary stars. If you fuse elements lower down than iron, you get energy *out*. To fuse elements above iron, you have to put energy *in*.
An ordinary star will firstly fuse hydrogen to helium - the Sun does that. Every second about 650 Mtons of H are fused to form 645 Mtons of Helium. So the Sun gets lighter by about 5Mtons/sec, which is converted into energy according to E=mc2. Even after 4.5Byears of this, the Sun has only converted a few % of its mass to He.
In some Byears time, the Sun will run out of H, and have to start "burning" Helium to heavier elements, progressively up to iron. It is, however, too small to go supernova.
If you're interested in more details, get hold of "Stardust" by John Gribbin - very readable.
No. Firstly, elements higher up the table than iron are quite rare, comparatively. Certainly much more than 99% of the Earth's iron core was iron when the earth formed.
Second, the "bottleneck" at iron is a feature of the strong nuclear force. Radioactive decay is mediated by the weak nuclear force, and as each radioactive isotope decays, at a rate given by its half-life, it gives rise to "daughter" isotopes which themselves may decay - or may not, if the isotope reached is stable. Thus, Uranium decays to Lead which is stable. Lead (atomic number 82) is much higher up the periodic table than iron (26).
Good informative post Tim
Thanks
AJH
The real problem is people living in houses without any cupboards. Surely lightbulbs aren't so huge that they can't be kept somewhere until needed?
Its a moot point as to when natural decay becomes a reactor.
Correct to my knowledge.
IF it were all good agricultural land, its just about enough to eke out an existence..one acre pre person. At the sort of paleolithic level Greenpeace would like us to revert to.
It isn't though, and to survive loss of 'artificial' energy implies sort of 2-5M population levels.
Which would be ideal, If I were one of the 2-5M.And all those fat gits at Tescos were not.
Natural decay will occur however concentrated or dilute the isotope in question is. You get a reactor if you concentrate the material. With uranium you need about 3% or more of U235 (up from the natural 0.7% level). When a U235 atom fissions, out come some fast neutrons (and heat energy). If you slow these down ("moderate" them), these neutrons can themselves act like bullets which fission more U235 atoms.
In a reactor, you need to keep the number of slow neutrons produced per U235 atom-fission at around 1.0. A bit above, and the reactor produces more heat. A bit below and you cool it off. This is done by inserting control rods which absorb the neutrons. If the ratio gets too much above
1.0, then you are in trouble.Obviously with a bomb you want it as much above 1.0 as poss.
No, see my post of yesterday.
I would rather grow food on my acre and use a nuclear power station to keep me warm.
Or how the unified Germay achieved it's targets by simply shutting down the old industrial plants in the East.
It's all greenwash.
MBQ
I agree. It's totally stupid but NPower didn't make the rules and they had shareholders to think about. It's the short sighted idiots who drew up the scheme who we should be complaining about.
Tim
Tim
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