On 9 m=E4rts, 01:33, Tim Little <t...@[EMAIL PROTECTED]
> wrote:
> On 2008-03-08, Crown-Horned Snorkack <chornedsnork...@[EMAIL PROTECTED]
> wrote:
>
> > Why would the pressure convert into heat?
>
> The pressure doesn't directly convert into heat. The reduction in
> density allows neutrons to decay. The decay energy converts into
> heat.
>
> > Besides, if the density reduction is slow, the heat would be removed
> > by conduction.
>
> I was considering a slow adiabatic expansion. It's all a thought
> experiment anyway: there is no known way to slow expand degenerate
> neutron matter. In colliding neutron stars, the vast majority of any
> core matter that escapes will just expand into a free neutron gas and
> decay into hydrogen plasma.
>
When a neutron star fills and spills over its Roche lobe, some of the
escaping matter falls towards the other neutron star or black hole,
but some escapes outwards. But the part which escapes on the outer
side is not at infinity! It is bound, on a circular orbit, pretty deep
in the gravity well of the (old or new) black hole.
So, when a neutron star is ripped apart, much of the matter would
remain in a disc. At densities which would be appreciable and permit
neutron captures - but low enough to permit beta decay. As for
temperature, photons would easily be radiated away in the directions
across the disc.
> > If you had high pressure, high electron chemical potential and low
> > temperature
>
> Well, that's fundamentally where we differ: you think the temperature
> will drop by at least an orders of magnitude before electron
> degeneracy ceases affecting nuclear reactions. I don't.
>
> But let us suppose you were right, and we started with isolated and
> contained sample of pure tritium at negligible temperature and
> pressure in nuclear terms. As I see it: even with a 12 year half
> life, each day there would be about 3 keV/atom of heat energy from
> decay added to the system.
IIRC, tritium releases 18 keV per decay - half of which goes away with
neutrino. The rest would be split equally between electron and helium
3 nucleus. And some goes to photons in hot plasma.
> It won't be long at all before we get significant fusion
That would be at a few millions of K, or a few hundreds of eV per
particle.
> and an extremely rapid increase in heat up to a few
> MeV/nucleon.
>
> Yes, we will get lead-208 in some equilibrium mix, but it will be
> particularly short-lived with respect to the ongoing reactions.
It takes a lot of energy to induce fission of lead 208. Even thorium
232 is pretty resistant to induced fission!
> As
> the temperature drops (but still while plenty of nuclear interactions
> are taking place), types of nuclei that have very few energetically
> favourable reactions with other nuclei will come to dominate.
>
> Those most common nuclei won't include high-energy types such as
> tritium or lead-208. They may be present in trace amounts.
>
> - Tim
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