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From: howard@cpocd2.UUCP (Howard A. Landman)
Newsgroups: sci.research
Subject: Re: Army Research
Message-ID: <741@cpocd2.UUCP>
Date: Fri, 19-Jun-87 18:24:08 EDT
Article-I.D.: cpocd2.741
Posted: Fri Jun 19 18:24:08 1987
Date-Received: Tue, 23-Jun-87 00:52:18 EDT
References: <42000001@uicsrd>
Reply-To: howard@cpocd2.UUCP (Howard A. Landman)
Followup-To: sci.research
Organization: Intel Corp. ASIC Systems Organization, Chandler AZ
Lines: 74

I'm cross-posting this into sci.physics, because there are people there
who are more knowledgeable than I and might be able to supply
information I couldn't.  Or even correct any errors in my analysis!

In article <42000001@uicsrd> mcdaniel@uicsrd.CSRD.UIUC.EDU writes:
>= 2-12.  The investigation of a novel material of potentially
>= tremendous significance to ballistics has supported the hypothesis
>= that a collection of triplet helium atoms could be contained and
>= exploited as a medium of energy storage, the capacity of which is
>= three orders of magnitude greater than those of secondary explosives.
>
>What is a "triplet helium atom[s]"?  I know that there have been
>rather unstable chemical compounds made from noble gases (xenon
>hexaflouride?), but they were of atoms with higher atomic weights.

Consider a system containing two electrons (such as a helium atom).
If the electron spins are opposite, the system has net spin 0 and
therefore the projection of that spin on any coordinate axis can only
be 0.  Because there is only one possibility (for some measurements this
will show up as a curve with a single peak), such a state is called
"singlet".

Now suppose the electron spins are parallel, so the total spin is 1.
The projection of this spin onto a coordinate axis can result in
spins of +1, 0, or -1, leading to a triple-peaked curve and the name
"triplet".

For helium, Pauli exclusion prevents the electrons from both being in
the ground state (1S orbital) unless their spins are opposite.  So,
if "triplet helium" is referring to the electronic state, one electron
would have to be excited (to at least the 2S orbital) for triplet helium
to exist.  Such an atom could not easily decay into the ground state for
helium, because the excited electron would have to reverse spin first,
so it might well be quasi-stable.  If you collected a bunch of them all
together with spins +1, there would be no way for them to do spin
reversal solely by interaction with each other because spin is conserved
(if one goes down to 0, the other must go up to +2!).  So the only
source of spin reversal (leading to energy release as the electron drops
from 2S to 1S) is through interaction with something else (walls of
container, magnetic field, ...).  Long term storage might be very tricky.

How much energy could triplet helium store?  Well, I wasn't able to find
a reference to the energy of the first excited state, but it is bounded
from above by the ionization energy of 24.6 eV.  The difference between
ground state and first excited state should be a fair fraction of that;
let's assume about 10 eV or so.  Now 10 eV/atom = 1.6 x 10^-18 J/atom
= 10^6 J/mole = 2.5 x 10^8 J/Kg.  250,000,000 Joules per kilogram, not
bad.

Here's how such stuff might be made, using a setup similar to the
classical Stern-Gerlach experiment:


                       +1 helium (captured + stored)
                      /
excited      strong  /
helium------>magnetic-- 0 helium (recycled to exciter)
atoms        field   \
                      \
                       -1 helium (captured + stored)

Notice from this that you'll be generating equal amounts of +1 and
-1 spin helium triplets, and that all you have to do is mix them
together to balance the spins and allow energy release.  Helium atoms
are also pretty light, so the muzzle velocity could be impressive.

A remoter possibility is that they're talking about a triplet state in
the helium nucleus.  Similar considerations would hold, but the energy
levels would be different.

It is also possible to have triplets due to nuclear spin in biatomic
molecules such as O2.  Such "triplet oxygen" has the nuclear spins of
both oxygen atoms parallel.  I don't think it's possible to store much
energy in such triplets.

	Q:"Dr. Pauli, where did you get your exclusion principle?"
	A:"I made it up!"

	Howard A. Landman
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