[AR] Re: Damascus AR Incident
- From: Keith Henson <hkeithhenson@xxxxxxxxx>
- To: arocket@xxxxxxxxxxxxx
- Date: Wed, 18 Jan 2017 11:53:11 -0800
On Tue, Jan 17, 2017 at 10:09 PM, Jordin Kare <jkare@xxxxxxxxx> wrote:
Not for safety reasons. Gun-type nuclear devices must be made with uranium,
as Pu has too
high a rate of spontaneous decay and has a high probability
of starting a chain reaction part-way through assembly and producing a
low-yield fizzle.
Implosion devices go from below-critical to ready-to-trigger much faster.
That's correct (not that I expect less from Jordin) but I don't think
it catches all the fine points. It's the Pu 240 contaminant that
spontaneously fissions and starts the chain reaction too early. The
Pu 240 is co-produced when a Pu 239 picks up another neutron and
doesn't fission right away.
https://en.wikipedia.org/wiki/Weapons-grade
Pu 240 in weapons grade is ~6.5%. There was some produced at a lower
level for use in submarine ballistic missiles where they wanted to
keep the neutron radiation to a minimum, but the low burn up for
making low Pu 240 material is not very efficient.
There seems to be a process that would make virtually pure Pu 239 out
of U 238. But this is getting way off topic so unless someone is
interested, I won't go into details.
Keith
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