nuke at the earths core

Merlin

Could the center of the earths core be a critical mass of U-235 or other heavy metals, sustaining a fission reaction. (or might fusion be possible with the presures and magentic fields there? ). If not earth what about jupiter or larger exra solar planet?

Merlin

Chemicalsuperfreak

Nuclear fission is what keeps the earths core warm. There's another thread here on the subject. But it is not a critical mass of U-235. I believe some fusion occurs in Jupiter, although not a lot.

Nereid

Fusion reactions require certain minimum conditions to start, and keep going; Jupiter's core is quite a long way from having these.

The coolest/least-dense conditions under which fusion can occur (special cases aside) are those found in the cores of brown-dwarf mass objects under-going gravitational contraction. In these conditions deuterium fusion can occur; however, that's a thin gruel, soon exhausted, leaving the brown dwarf alone to cool, and look pretty much like Jupiter (albeit considerably more massive).

Merlin

Fusion reactions require certain minimum conditions to start, and keep going; Jupiter's core is quite a long way from having these.

The coolest/least-dense conditions under which fusion can occur (special cases aside) are those found in the cores of brown-dwarf mass objects under-going gravitational contraction. In these conditions deuterium fusion can occur; however, that's a thin gruel, soon exhausted, leaving the brown dwarf alone to cool, and look pretty much like Jupiter (albeit considerably more massive).

hmmm' so it would be impossible for fusion ot occur at any form in the core of a Jupiter size mass, save for special conditions? What about fission or just below critical mass at the earths core (or larger rocky planets)?

And special conditions would be? (mag. fields, shear or tidal forces , "other elements than H in the core etc?). Merlin

Nereid

clarification (a.k.a. caveat): fusion and fission here = self-sustaining processes, as in 'fusion reactor', 'nuclear power plant' or Oklo.
yes not while the cores are composed of iron, nickel etc collision with a white dwarf or neutron star, as two examples.

Merlin

clarification (a.k.a. caveat): fusion and fission here = self-sustaining processes, as in 'fusion reactor', 'nuclear power plant' or Oklo.

Im calling fusion like what may happen in a first generation nuke power plant as follows, for example a D-T fusion reaction. Nuclei of two isotopes of hydrogen, deuterium (D) and tritium (T) react to produce a helium (He) nucleus and a neutron (n). In each reaction, 17.6 MeV of energy (2.8 pJ) is liberated: D + T 4He (3.5 MeV) + n (14.1 MeV).

Fission is the term that I use to describe the process that powers today's nukes (or yesterdays Hiroshima bomb). It seems to me that U235, and even the isotope uranium 238 along other naturally occurring radioactive metals would be in the core of rocky planets in copious amounts. I would suspect that some heat generation exist at the earths core (from nuclear process ,maybe even fission!) Some factors such as purity , pressure, etc needed to start and sustain a fission reacation might not be present. But there is enough to produce heat. MERLIN

Chemicalsuperfreak

I'm not saying there's a self sustained fusion reaction going on in Jupiter like you'd find in a star, but I do remember reading that at least some fusion is occuring. What's the lower mass limit for a brown dwarf?

Chemicalsuperfreak

Fusion is not what happens in first generation power plants. It's all fission, fusion has only occured in hydrogen bombs and test facilities. Nobody's generated power from fusion.

Uranium certainly exists in the earth's interior, but most of the hearing is produced by radioactive potassium.

Merlin

Superfreak,...Either we must agree to disagree or, "What we have here is a failure to communicate!" (Jackie Gleason.) I am at a loss when putting my thoughts clearly into words. I should have said the first generation fusion reactors (yet to be). I thought you would make the connection without elaboration. My bad.

I did say fission is for A bombs like those dropped on Japan. And today's nuke plants. Power plants sustain a critical reaction with u 235 at about 2 or 3%. Bombs require a 90% or more enrichment. Most H bombs, of course use fission as a trigger for the Main event,... fusion...hiss bang pop.. to occur. Outside of the said bomb controlled fusion has yet to fulfill its potential for power production etc.

I don't agree that the decay of potassium to argon (or the trace amounts of thorium, etc)., would generate the required heat energy. Also the properties of the potassium mixing with the Fe in the core must be right on, sulfur and a few other elements in the correct amounts and purity would allow it to mix with the cores massive Fe reserves. The simple (and correct, I know, because I've been at the core myself... heh) theory is, ignoring tidal and rotational forces, convection,(anyone got a super computer for sale cheap?) the heavy metals would migrate to the center first. Hmmm, at about .9 to 2.3%,the last more than enough to sustain heat production. No?......MERLIN

Andre

No, it's also a question of abundance. Iron is by far the most abundant of the heavier elements. Moreover, by measurements of all possible seismic properties, it seems possible to test hypotheses based on an iron inner core.

About nuclear fission. For a sustained fission reaction, the critical mass property is exactly that, "critical". The margin of the number of fissable atoms per volume is rather narrow. A few too liitle and the reaction dies. A few too much and you have the nuclair inferno.

Another problem for the heavy fissable molecules to get together is that thermodynamic motions are much stronger than gravity in the core. So it's is impossible for them to clog together, when the tea keeps being stirred (assuming a fully liquid core).

And now, for some humor only:

warning crackpot inside

Nereid

From the site below:
-> above 8% of the mass of the Sun, red dwarf
-> between 1% and 8%, brown dwarf
-> below 1%, no fusion.

All numbers are approximate, and Jupiter has a mass ~0.1% of the Sun's, so a brown dwarf will have at least 10 times the mass that Jupiter has.

http://chandra.harvard.edu/xray_sour...ndwarf_fg.html

Nereid

There seems to be some confusion of terms here, and I may have contributed to it.

Fusion: like what happens in the core of the Sun, an H-bomb, etc. Main fusion reactions are, in summary, conversion of protons (and deuterons) to ⁴He and ³He. This only happens in a sustained way (power out > power in, in bulk, over more than ~1s) in gravitationally confined objects ('stars'), tho' many believe it will be possible in something like ITER. On Earth, the only natural fusion which takes place is (maybe) in cosmic ray collisions with atoms in the atmosphere or oceans.

Fission: the splitting of a heavy nucleus into two (or more?) lighter nuclei (alpha decay excepted). We usually also mean 'with a net production of kinetic energy'. This happens in A-bombs, in nuclear reactors (both man-made and natural*), and in some isotopes ('spontaneous fission').

Spontaneous fission, along with other forms of radioactive decay, generates heat if it occurs in atoms within rocks (and elsewhere). Radioactive decay (including spontaneous fission) is the primary source of the heat which results in the Earth's core being much hotter than its crust; the primary nuclides are ⁴⁰K, ²³⁸U and ²³²Th.

It doesn't matter in what physical form a radionuclide is - pure element, chemically-bound, alloyed; concentrated (e.g. crystalline salt), impurity - it generates the same amount of heat when it decays.

*in the early days of the Earth, ²³⁵U was a more common isotope than it is today. There were some deposits of uranium - in the form of oxides? - in which sustained fission reactions took place, very similar to man-made reactors. Oklo is the best-known example:
http://antwrp.gsfc.nasa.gov/apod/ap021016.html

Such natural reactors are highly unlikely on, or in, the Earth today.

Finally, iron (and nearby elements in the periodic table) cannot undergo exothermic fission or fusion; they are the most stable nuclei.

Andre, that link is just sooo incredible [:D] [8)]

Chemicalsuperfreak

http://www.nature.com/nsu/030505/030505-5.html

NileQueen

Nereid,

That Astronomy Picture of the Day site is really cool. There are some high resolution pictures of Mars, the moon, the sun.
http://antwrp.gsfc.nasa.gov/apod/ap021114.html


I saw a very interesting picture of Mauritania
http://antwrp.gsfc.nasa.gov/apod/ap021028.html
Richat's rings. Not an impact crater..
A circular mystery...

This one is amazing of the observatory in Chile
http://antwrp.gsfc.nasa.gov/apod/ap021109.html
Cerro Tololo Inter-american Observatory

Nereid

It's a remarkable site, isn't it!?

I try to get to it every day, and often spend several minutes clicking on the links ... it's amazing that the two guys who run it can find so much material, and keep it up for some many years now.

NileQueen

Yes. I see there is an index too
http://antwrp.gsfc.nasa.gov/apod/lib/aptree.html

I'll check out the Venus pictures...

NileQueen

some of the Venus links were no longer any good.

APODs of the world, unite! [:D]