[LoGH] Technical debate
Justin Ho (jhh14@cornell.edu)
Fri, 13 Oct 2000 17:28:12 -0400
At 01:15 PM 10/13/00 -0500, you wrote:
> > 2. The neutron cannons given for a standard FPA cruiser have a listed
> > power output of 120 MW and a bore diameter of 12.3 cm. The problem is
> that
> > from those numbers it seems that the power at its listed maximum range of
> > 18 light seconds would be incredibly small.
>
>Why is that? A beam of neutrons would experience almost no
>self-interaction causing beam spreading (as is a problem with a charged
>particle beam, the like charges repelling one another and therefore
>causing the focused beam to disperse). Since it is almost impossible
>to make a perfectly coherent particle beam there would still be some
>dispersion though, and probably 18 light seconds is the range at which
>the spreading would mean that the amount of energy delivered per unit
>area at the target is less than that needed to melt battleship armor.
At 18 light seconds at 120 MW initial power, even with a beam
divergence angle of a picoradian, the total energy per square cm is only
sufficient to melt through less than a meter of steel per second (assuming
the steel was at near absolute zero and assuming my specific heat and
density numbers are correct). A meter of steel per second in a circle of
about 13.04 cm diameter.
Assuming a 3 second beam, that's about 2.38 total meters of steel
melted. Edge that figure upwards if hull was warmer than 3 degrees above
absolute zero, and downwards if armor has higher specific heat than steel
(which it probably does). That makes some of the "drill through the ship"
shots seen impossible unless power output is higher, or shot duration is
longer than it seems.
Hope I haven't made any stupid calculation errors in there.
> > 3. How the hell does a magnetic field deflect a stream of uncharged
> > neutrons? The data appears to indicate the shields have at least a
> > magnetic field component, and the main cannons are most definitely listed
> > as neutron cannons.
>
>This one I can go into in more detail. If I may also quote Graeme Lennon's
>response:
>
> > It is perhaps worth noting that a neutron is not *really* a particle with
> > no charge at all. It is a group of quarks with opposing half-charges that
> > average out to a zero net charge. (Fact)
> > Thus, it stands to reason that at a certain scale there is some form of
> > polarization. Given a strong enough (er, very, very strong) magnetic
> > field, some sort of effect must be possible. (Pure, 100% speculation)
>
>Well, yes and no. You don't really have to resort to electrical charge
>of quarks to explain this, although that may be a component of the
>deeper particle physics explanation. The neutron, like the proton and
>electron, has a "spin magnetic moment", which an external magnetic
>field can act on. Unlike the electron and proton, it is not subject to
>the "Lorentz Force", the force felt by a charged particle moving
>through a magnetic field. The force resulting from the interaction of
>an external field with the spin magnetic moment (which doesn't mean the
>neutron is spinning, that's just what the quantum number describing
>this property is called) is much smaller than the Lorentz force
>interaction. So while it is very hard to cause neutron beams to bend,
>for example, one can use this force to magnetically focus such beams.
Are we talking something analogous to a dipole moment? A fleeting
charge that can be manipulated?
PS Are the yields for the Ahsgrimm missiles reasonable? They
definitely appear to be impact missiles and not nuclear detonation pumped
lasers. Nuclear weapon yields are not my forte. :)
Justin
