Fusion vs. Dissociation

Steve Willner wrote in
http://groups.google.com/group/sci.a...10441b2?hl=en& :
SW At high temperatures, molecules tend to dissociate to form
SW individual atoms. At even higher temperatures, the atoms break
SW up into separate nuclei and electrons. And at temperatures
SW higher still (far above anything relevant to stellar
SW atmospheres), the nuclei themselves break up.

In article .com,
"Radium" writes:
Huh? If that was the case, then there would be nuclear fusion would
require much lower temperatures.


Why would you think that? Fusion means combining nucleons, not
separating them.

Fusion is the combining of nucleons. However, you said nuclei break up
at extremely high temperatures. That is fission, not fusion.

Nuclear fusion in stars occurs when the temperature is sufficient to
overcome the Coulomb barrier: i.e., the electrical repulsion of the
protons in colliding nuclei. For p-p fusion, the necessary
temperature is around 10 million kelvins. For the carbon cycle, the
repulsion is 12 times higher, and temperature needs to be higher by
about the same factor (actually a bit less because 12C + p goes by
the strong interaction, not the weak one).

Okay.

Temperature to dissociate molecules is about 1000 K, to ionize atoms
about 10000 K, and to break up nuclei about 10^11 K.

Once again, breaking up a nucleus is fission, not fusion.

--
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA
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