"Mr. Fusion" (was Re: NANO: Nanonukes (Was: Goo prophylaxis))

Forrest Bishop (forrestb@ix.netcom.com)
Fri, 29 Aug 1997 03:28:32 -0500 (CDT)

Eliezer wrote:

>> > Well, there's a couple of questions I'd pose about nuclear nanotech:
>> A fission bomb is based on the creation of a critical mass, where the
>> growth of neutron flux due to fission is larger than the loss into the
>> surroundings. Unless nanotech could build a neutron reflector (which I
>> doubt is physically possible?)

Probably not possible. It is a matter of nuclear properties rather tham
and molecular structure.

>Okay. Well, it'd take more tech than I thought, but a few points:
>Modern atomic technology goes like this: You have a mass of U235, with all
>the atoms inside being arranged randomly. Atoms fission all the time, but the
>material isn't very dense, so most neutrons escape. Then an implosive
>explosion occurs which condenses the material down to a tiny, tight ball.
>Neutrons collide with other U235 atoms, causing a chain reaction.
>We all know this implicitly, but I'm verbalizing it so we can alter the
R. Feynman quote:"
>they did not know that the neutrons were enormously more effective when they
>are slowed down in water. In water it takes less than a tenth - no, a
>hundredth - as much material to make a reaction that makes radioactivity. It
>kills people around and so on. It was very dangerous, and they had not paid
>any attention to the safety at all."
>So you don't need neutron reflectors; just ordinary water. I'm not sure
>whether "10% to make radioactivity" and "10% to get critical mass" are the same

Not quite. Water acts as a neutron moderator, i. e. it slows "fast' neutrons
increasing the collision cross section, hence the rate of nuclear reactions.

> I'd be surprised to
>find out that they were unrelated, though. Still, it could be that no amount
>of water decreases the size of a critical mass. Let me know if so.

Just so.

>>And, getting a bit speculative, what if you take U235, store it in ordinary
>water, and then use nano to "catch" the slowed neutrons that emerge? Could
>you store the neutrons and use them as a catalyst for the bomb?

Nyet. Free neutron half-life is about 15 minutes. Also, an atom cannot
"grab" a neutron, only a nucleus can, changing the isotope or causing fission.


>Inertial confinement only operates on a single pellet, the fuse. (Ha ha!)
>The problem with inertial confinement is delivering enough energy.
>Quantum-well lasers are something like 10 to 100 times as efficient, and I
>believe they aren't difficult to construct given nano. Englobe the whole
>pellet with lasers instead of using one. Then fire. I think that you could
>probably deliver at least 1,000 times as much energy as in modern inertial
>confinement. It'd take a gigajoule to set the thing off, sure, but then you
>have a fusion explosion and you can use it to set off arbitrarily larger ones.

***Very, very good Mr. Yudkowsky.***

What you have started to describe is a device I
conceived several years ago and have not published, called "Mr Fusion". This in
fact constitutes the first public disclosure. And yes, it is very much like
current laser inertial confinement, except the EMP front is vastly more
structurally refined. Each laser is individually addressable. It may be possible
to convert some portion of the released energy directly to electric by using the
QM well as receivers.
See "The Optical Assembler" interview at the NanoTechnology magazine website for
a description of a similar array.


> Ask
>some fusion researcher: "If you had complete control over the molecular
>structure of matter, and could get anything built of available atoms just by
>wishing for it, could you build a powerful fusion reactor?"

Yes, but this still requires bettter plasma dynamics modeling and the rest of
the things that have been just around the corner for the last forty years.

>> > I'm far from an expert on explosives... but couldn't you get a bit of an
>> > improvement by detonating the ENTIRE bomb with electronic synchronization,
>> > that the entire blast arrives time-on-target?

? This is what the shaped high explosives in an atomic bomb do already.

> sentience@pobox.com Eliezer S. Yudkowsky
> http://tezcat.com/~eliezer/singularity.html
> http://tezcat.com/~eliezer/algernon.html

Forrest Bishop
Institute of Atomic-Scale Engineering