Re: nuclei role in thermodynamics/energy transport?

From: Gregory L. Hansen (glhansen_at_steel.ucs.indiana.edu)
Date: 12/19/04 

Date: Sun, 19 Dec 2004 02:44:05 +0000 (UTC)

In article <1103317601.888053.241820@z14g2000cwz.googlegroups.com>,
 <boo@fractalfreak.com> wrote:
>
>Supposedly most of the mass in an atom is in the nucleus
>(> 99 %). Yet it appears that most of this mass is latent
>and inert - 'frozen'. I mean, despite having most of the
>mass, the electrical charge of the nucleus is balanced by
>the electron 'cloud' about the atom - which comprises something
>like 1/2 % of an atoms total mass
>
>Also, according to most models of energy transport, only
>the electrons - and usually just the 'outer most' ones,
>are involved in most energy transports (at least at earthly
>temps. and pressures). EM radiation 'excites' electrons
>at multiples of planks constant. Normal chemistry also
>supposedly involves just the electrons - the nucleus is not
>directly involved in most chemical reactions, aside from
>balancing charges.

Sure the nuclei are involved. Just not very much. The electrons transfer
energy more easily because they're lighter, and so a little push makes
them gto faster. K=p^2/2m.

As a counter-example, at low temperatures the electrons tend to be frozen
into the Fermi sea, and then ion motion dominates the thermal
conductivity and the heat capacity

>
>My question is, when an atom receives and emits photons (which
>is happening all the time) does any of this energy affect
>the nucleus? If so, how? Extreme high frequency radiation
>certainly does, as it can cause fission of heavy nucei.
>And nuclear reactions release high frequency radiation, in
>addition to particulate radiation, so apparently EM radiation
>can affect nucleii.
>
>Another thing - it's now thought that even normal chemical
>burns involve a loss of mass - just not enough to be measured.

It's not easy to measure, but mass defects have been measured in a Penning
trap for some chemical reactions.

>And in most nuclear reactions (which involve a more significant
>loss of mass), at least fissions, most of the mass lost is
>thought to be the 'binding' energy of the nucleus. Is there
>any explanation of where the missing mass comes from in normal
>chemical burns (which are supposed to be reversable)?

No particles go missing in chemical reactions, they're just rearranged.
The mass of a system of particles depends on the relationship of each
particle to the others.

>
>And more (sorry, i'm rambling) do, or would, extremely low
>temperatures affect the nucleus? Certain 'condensates' which
>occur at extremely low temperatures - are nuclei affected
>in these condensates?

Nuclei contribute their share of spin angular momentum. For an example,
helium-4 forms a superfluid at around 2 or 3 kelvin. Helium-3 differs
only by missing a neutron in the nucleus, and that doesn't form a
superfluid. It actually will form a superfluid in the millikelvin regime
when helium-3 atoms start pairing up to form bosons, but it's clearly
different behavior. 

-- 
"Outside the camp you shall have a place set aside to be used as a 
latrine.  You shall keep a trowel in your equipment and with it, when you 
go outside to ease nature, you shall first dig a hole and afterward cover 
up your excrement." -- Deuteronomy 23:13-14

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