On 8 m=E4rts, 13:00, Tim Little <t...@[EMAIL PROTECTED]
> wrote:
> On 2008-03-08, Crown-Horned Snorkack <chornedsnork...@[EMAIL PROTECTED]
> wrote:
>
> > I am not quite sure of that. I suspect that a stable neutron matter
> > would have small, but nonzero, concentration of protons and electrons.
>
> Yes, I solidly agree. If there were no electrons, there would be no
> electron degeneracy pressure keeping the neutrons from decaying.
>
> > If you have a small decrease of density, you will have a small
> > decrease of electron chemical potential - and beta decay will then
> > act to cause a small increase in proton concentration.
>
> Yes, that is the phase transition I mentioned. There is a *lot* of
> energy in the electron degeneracy pressure, which will maintain the
> temperature as the density is slowly reduced.
>
Why would the pressure convert into heat?
Besides, if the density reduction is slow, the heat would be removed
by conduction.
> Even if it were suddenly decreased, the decaying neutrons would add
> free energy back into the matter, increasing the temperature again.
>
> > Of course, this depends on the speed of density reduction, and
> > density itself.
>
> Oh, no question there. That's exactly what I was saying.
>
> At one extreme the neutron matter explodes into a shower of free
> neutrons that (by comparison) take forever to decay into a rarefied
> hydrogen plasma.
>
> At the other extreme the neutron matter gradually enriches in
> electrons (and protons) as the density is lowered. The temperature
> remains approximately constant during this phase transition, and
> nuclear reactions are common.
>
> > This means that as you decrease the density of neutron matter, which
> > starts with low proton concentration, it goes on to be neutron rich
> > and proton poor even when discrete nuclei condense out.
>
> If it were not for a large range of nuclear reaction equilibria, that
> would probably be true. Starting from a neutron-rich state, many of
> these reactions will produce free neutrons or other nuclei that will
> beta decay.
>
> It will be much, much later before the temperature and density drop
> low enough that reactions between nuclei become unimportant.
>
> - Tim
If you consider zero pressure, zero electron chemical potential and
zero temperature, then lead 208 is stable indefinitely. You could gain
a lot of energy by fission of lead into nickel. Nevertheless it does
not happen.
If you had high pressure, high electron chemical potential and low
temperature, you could have stable neutron-rich isotopes which are
also stable against fission and alpha decay, but which at lower
pressures would undergo beta decay into daughters that in their turn
undergo fission or alpha decay.
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