[ExI] found it!

John Clark johnkclark at gmail.com
Sun Aug 13 00:35:48 UTC 2017

On Sat, Aug 12, 2017 at 2:08 PM, spike <spike66 at att.net> wrote:

> ​>​
>  if that flux is high enough and we find ways to tweak Collar’s
> instrument, perhaps we can create a mobile neutrino detector.
> ​His detector only weighs ​
32 lbs
​ so it should be easy to put a thousand ​of them on even the smallest navy
ship, and then it would be a thousand times as sensitive.

> ​> ​
> Going from memory, Pu239 has a half life of about 90 yrs,
>Actually it's 24,100 years for Pu-239 and for U-235, the working material
of most nuclear reactors
it's 700 million years. And you can't really compare a decay process with
fission. When Pu-239 decays after 24,100
​years ​
it just transforms into slightly lighter U-235, but when it undergoes
fission it's much more dramatic, it splits roughly in half producing much
lighter elements like Barium and Krypton and produces far more energy and
neutrinos than a mere decay.
So a reactor that isn't operating isn't going to produce a lot of
neutrinos; it would make some but probably about a million times less than
when its on.

> ​> ​
> figure a subcritical fissile core is about, I don’t know, 20kg?
> ​In a bomb it's 11 kg at
normal density but less than half of that if you cleverly shape the
chemical explosives around the Plutonium so it compress the Plutonium
sphere to more than normal density. The critical mass can also be reduced
by surrounding the sphere with a beryllium neutron reflector.
With North Korea in the news this fact has been on my mind lately.

If you want to make a really big and really hot fission bomb, the sort
needed for the detonator of a fusion H-bomb
you're also going to need U-235 too because it has a much higher critical
mass of 52 kg. The idea is
​to ​
have a hollow sphere of U-235 (stuffed with Lithium Deuteride if you want
to get fancy) surrounded by a larger but much thinner sphere of Pu-239
surrounded by a heavy sphere of common U-238
​to be used as a tamper to slow down the expansion and give the chain
reaction more time, ​
surrounded by a
​aluminium ​pusher sphere to even out the implosion, surrounded by a
chemical explosive.

The Pu-239 will become critical first and so compress the U-235 far more
than a chemical explosive alone ever could
​and that ​
greatly increasing the efficiency and more important
​ the heat​
​ and heat is what what you need ​
if it is to be used as the match to start the fusion reaction in a H-bomb.

If North Korea has reach this point they would't need any additional exotic
material to make a real honest to
god Teller-Ulam style H-bomb, just Lithium and deuterium,
both easy to get. They would need to perform some non-trivial calculations
​figure out a good
way to place the internal components but the Soviets calculated them well
enough in 1961 to set off a ‎57 megatons bomb and they had nothing better
than slide rules
to help them.
North Korea
​claims they already have a H-bomb, maybe they do but they haven't tested
one, we'd certainly know if they had.​

> ​> ​
> John, help us here.  Do we have any data on Collar’s marvelous new
> instrument?  How often it detects a neutrino?
​I don't have that figure but I do know this new neutrino-matter
interaction that Collar has detected for the first time scales with the
the number of neutrons in the nucleus
​ of the target material, he uses
​ (with 88 neutrons)​
 and iodine
​ (with 74)​. And Collar says his new detector might be used for "
non-intrusive nuclear reactor monitoring

> ​> ​
> As I write this, I get thinking and fear that my one in a trillion
> estimate is crazy optimistic: neutrinos don’t care enough about us to
> interact that often.
​That's OK, a
​3000 MW ​
nuclear reactor produces
​about ​
​neutrinos a second (actually ​
​but never mind), so if we miss a few no big deal. ​


 John K Clark​
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