From: Anonymous <anon@anon.efga.org>
Date: Tue, 7 Oct 1997 09:52:53 +0800
To: cypherpunks@Algebra.COM
Subject: Re: russia_1.html
Message-ID: <5eace64d33bd306e99f854345cd8c95d@anon.efga.org>
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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