Re: russia_1.html

Peter Trei:
>The plutonium cores of thermonuclear devices have a limited shelf
>life - he claimed 6 years, which jibes with what I've heard from
>other open sources. Fission products build up in the cores which
>can poison a chain reaction. Thus all Pu based devices need to have
>the cores periodically removed and replaced with new ones, while the
>old ones have to go through a non-trivial reprocessing stage to
>remove the fission products.

Decay, rather than fission, I suppose.   I believe there's a treaty
prohibiting nuclear weapons in space.  Not so surprising if they're
inpractical - political points for nothing.

Bill Frantz:
>I think this comment is in error.  Plutonium has a half life on the order
>of 250,000 years, so very little decay products would build up in 6 years.
>The tritium used in thermonuclear weapons has a much shorter half life, and
>would need to be replaced about that often.

Replacement of tritium is certainly the dominant need.
As for the decay products - it depends how close they get to pure 239.

Half-lives: (years)

Pu 238       89
Pu 239    24000
Pu 240     6500
Pu 241       15
Pu 242   400000
D             0.015
T            12.3 

Paul Pomes wrote:
> 
>Even a fizzle with a yield in the hundreds of tons equivalent is respectable.
>Plutonium decay products have a high neutron cross-section and steal the
>fast neutrons necessary for the chain reaction to build.  Sufficient amounts
>can kill off the last three or more re-doublings which is where most of the
>explosive power comes from.

The only books I have to hand contain _thermal_ cross-sections.  :(

If it's an H-bomb I was under the impression you don't care that
desperately about the size of the plute yield - only that it is enough
to start the fusion.

Anybody know what happened to the proposed fissionless H-bomb of the '60s ?
Presumambly it never got working.

Warm&ComfyMonger

On Mon, 6 Oct 1997, Anonymous wrote:
> 
> Anybody know what happened to the proposed fissionless H-bomb of the '60s ?
> Presumambly it never got working.

According to an editorial in the SF Chronicle by Edward Teller from about
a year ago, the folks in Livermore have teamed up with their counterparts
in Russia to develop just that. This is one of marvels of post-cold war
cooperation. Teller failed to understand the need for such a project. 
Clearly, the availability of non-fission (catstrophic)fusion devices
should lead to an increased market penetation of such devices. There are
few products where supply and demand are as missmatched as is the case
with H-bombs. The spot market will welcome this relief. 

 -- Lucky Green <shamrock@cypherpunks.to> PGP encrypted email
preferred.
   "Tonga? Where the hell is Tonga? They have Cypherpunks there?"

Peter Trei:
>The plutonium cores of thermonuclear devices have a limited shelf
>life - he claimed 6 years, which jibes with what I've heard from
>other open sources. Fission products build up in the cores which
>can poison a chain reaction. Thus all Pu based devices need to have
>the cores periodically removed and replaced with new ones, while the
>old ones have to go through a non-trivial reprocessing stage to
>remove the fission products.

Warm&ComfyMonger:
>Decay, rather than fission, I suppose.   I believe there's a treaty
>prohibiting nuclear weapons in space.  Not so surprising if they're
>inpractical - political points for nothing.

No.  Fission, not decay.  Pu239 decays into U235, which explodes just fine.

The problem is that background radiation (cosmic rays, etc) causes the Pu
to fission.  This sets off a chain reaction which fissions other Pu atoms.
If you have less than a critical mass, this will eventually burn itself
out, but it makes a mess of your core in the process.

As for space nukes, well, if you go stick something up in orbit where its
exposed to all sorts of radiation to destabilize the Pu... well you'll be
lucky if it doesn't melt down, much less last very long.  Furthermore,
there is all sorts of junk in low earth orbit, sooner or later something
is going to knock it out of orbit...

- NukeMonger