Re: Food Checkout Week

"John Dallman" <jgd@xxxxxxxxx> wrote

In article <YHZAj.65024$w94.36353@pd7urf2no>, karljohanson@xxxxxxx
(Karl
Johanson) wrote:

The Uranium which was part of the material which formed the Earth,
was likely weapons grade (I don't have the math skills to work out
the precise percentage of U235, but considering how many U235 half
lives there been compared to U238 half lives, since the Earth was
formed, I assume it was higher than 20%, which is needed for a crude
device). I was assuming a meteor from outside our solar system, with
Uranium formed more recently than the material which formed the
Earth.

The Earth is about one half-life of U238 old, and about 6.5 half-lives
of U235 old. So U235 was about 90x as common as now, and U238 about
2x.
That makes 2*99.3 + 90*.07 = 2.62 times as much uranium around when
the
Earth formed, of which about 23% was U235. A pretty good guess.

U234 has to be formed by some other reaction that still goes on. Given
its short half-life and the fact that there is still some around,
there's no other possibility.

However, 20%, or 23% will not do for a crude device at all. Getting
that
to go off would need quite a sophisticated implosion device, well
beyond
the capabilities of the Manhattan Project of 1945: put it in a gun
assembly and it will do no more than get warm.

I thought it was easy enough to detonate with a gun type blast, but that
the explosion wouldn't be very efficient. Glad to know it takes a more
sophisticated device than that.

I have no idea what grade the Plutonium which helped form the Earth
was. Extra solar system Plutonium would only have around 24,000 years
to get to Earth, from whatever supernova or neutron star accretion
disc formed it, before half of the Pu 239 would be gone.

Matter from a supernova explosion can be expected to take a billion or
three years to condense into a new star system. so the answer is
"none"
for practical purposes.

It might well be that U235 and U238 are formed in approximately equal
quantities in a supernova, but I don't know if anyone knows for sure.

I assume a spectrographic analysis of a supernova would give some
indication.

The notion of aliens dropping weapons grade material on Earth (at
Tunguska, and at other meteor crater sites for the game) occurred,
possibly with them hoping to spur on nuclear war ...

Now you're starting to make more sense.

I also didn't see any reason for the meteor to have concentrated
heavy water (and again, collecting it would be close enough to
impossible). While brainstorming, I toyed with the idea of
genetically engineered seeds on the meteor, which grew plants that
concentrated heavy water into nodules where it could be easily
collected. Again, you need unnamed aliens for that. Someone in 1938
determining that the water in the nodules was heavy water, stretches
credibility as well. Such a plant would be quite interesting though.

And not totally incredible.

Karl Johanson


.

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