On Mon, 27 Apr 1998, Pieter Thomassen wrote:

I'm not too sure about this, I once read a story about using an
anti-nutronium bomb to turn the Earth into another asteriod belt. 

Forgive my ignorance - but I don't remember Neutronium as one of the 
elementary particles.  And if it is a compound on the periodical 
table, it certainly does not have an "anti-" anything to 
atomically react with.

I was under the impression that neutronium is made up of neutron
in a very compressed state, usually formed only under the most
extreme conditions (such as a collapsing heavy star).

As anti-matter is protons/electrons with a reversed electrical charge, 
and neutrons by definition have no such charge, I don't know if
anti-neutrons are not a contradion in terms.

It's different if its sub-atomic, though. Anyone with a recent physics
class on line ?

Non-physics interested people should skip to the next message now. 

Don't say I didn't warn you. 

<begin far too much physics>

Neutronium is a condensed mass of neutrons. The density is approximately
the same as the found in the nuclei of atoms - say around 10^15
grams/cubic centimeter (think of an entire mountain squeezed into a
thimble).

Neutronium is unstable against electron decay (it emits an electron and an
anti-neutrino) outside of the atom normally with a half-life around 1000
seconds. This means that you get a *BIG* boom almost instantly. One big
enough to destroy large mountains if you have more than a gram of it
(remember, at its density, a gram is *much* too small to be visible to the
naked eye - we are talking something roughly the size of bacteria). 

Except.... ;-)

Neutronium is formed when a star with a core massing more than about 1.4
times the mass of our sun dies in a supernova. The core is _so_ massive
that the electrons are crushed into the protons in the center of the atom
(with a neutrino being emitted to satisify various conservation laws).
When this happens the star is crushed down to 10-30 kilometers across.

The immense gravity of the star (we are talking BILLIONS of gravities
here) prevents the neutronium from reverting to protons+electrons. If you
were to take a small piece of neutronium off the surface - it would
explode immediately without the gravity to keep it confined. 

*Anti-neutronium* is exactly (well close enough for here) the same as
neutronium, except it has its 'quantum numbers' reversed. IOW - you can't
tell it apart from 'normal' neutronium from a distance. Except that if
normal matter encountered it - the anti-neutrons composing it would
annihilate with the regular neutrons. About 50% of normal matter's mass
is in the form of neutrons. They are kept stable (mostly) by the immense
power of the strong nuclear force in atom's nuclei. 

Boom. Big boom. *REALLY* *REALLY* big boom. 

A standard hydrogen bomb converts a few *grams* of matter to energy (with
a conversion efficiency of the order of 1% starting from several kilograms
of hydrogen). Anti-Neutronium gets 100% efficiency (this is an *even
larger* boom than the normal decay would produce by a factor of 3 or so).

The long and the short of it - don't even *think* of playing with
neutronium or anti-neutronium unless you use some additional technology
like Larry Niven's stasis fields to keep it from exploding immediately.
Second off - even if you *do*, its density is so high that it will fall
*through* solid rock like it wasn't even there.

</end far too much physics>

Aren't you sorry you asked?

-- 
Benjamin Franz