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Author: Subject: Nuclear shaped charge?
OneEyedPyro
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[*] posted on 29-8-2023 at 00:35
Nuclear shaped charge?


An implosion type warhead is essentially a spherical shaped charge. This involves a fairly complex setup as far as achieving the perfect detonation wave all coming together to create the implosion.

What would happen if two cones were simply shot at each other thus requiring only two individual precise detonations coming together rather than a single very precise global detonation? It would be much simpler to achieve I'd assume.

Pointless I know, but having recently watched the Oppenheimer film it crossed my mind.
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pantone159
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[*] posted on 29-8-2023 at 05:55


The weapon that was first used 'Little Boy' did shoot one piece of material at another, and this was indeed a much simpler method. But the assembly in that case is far too slow for Pu-239, which will pre-detonate nearly as soon as the mass becomes just barely critical, so that technique only works for U-235. To use Pu-239 (which is invariably contaminated with Pu-240 which is the trouble), a much faster assembly method, i.e. the implosion, had to be worked out.
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OneEyedPyro
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[*] posted on 29-8-2023 at 15:44


Quote: Originally posted by pantone159  
The weapon that was first used 'Little Boy' did shoot one piece of material at another, and this was indeed a much simpler method. But the assembly in that case is far too slow for Pu-239, which will pre-detonate nearly as soon as the mass becomes just barely critical, so that technique only works for U-235. To use Pu-239 (which is invariably contaminated with Pu-240 which is the trouble), a much faster assembly method, i.e. the implosion, had to be worked out.


As I recall it was a slug of uranium shot into another one like a cannon.
I was implying that the two sources would collide with each other as two conical shaped charges butted up together with no standoff distance. This way you'd only need precise timing from two points which would be easily done.
I wonder if simply launching a conical shaped charge of U235 against a dense non-fissile material like depleted uranium or tungsten would cause a strong enough criticality to be viable. Maybe it would just undergo low efficiency fission during the detonation.
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averageaussie
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[*] posted on 29-8-2023 at 16:22


it probably would, something similar was done for the trinity test and fat man.
they were both implosion type weapons, which effectively use lots of shaped charges to compress a plutonium core. you can read more here; https://en.wikipedia.org/wiki/Nuclear_weapon_design#Implosio... and https://en.wikipedia.org/wiki/Fat_Man#Interior
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Marvin
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[*] posted on 30-8-2023 at 03:30


Under the pressures we are talking about, the material behaves more like a gas than a solid. If there is any location not exposed to high pressure it's going to squirt out. So two masses fired at one another are going to splat without generating meaningful compression.
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OneEyedPyro
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[*] posted on 30-8-2023 at 03:58


Quote: Originally posted by Marvin  
Under the pressures we are talking about, the material behaves more like a gas than a solid. If there is any location not exposed to high pressure it's going to squirt out. So two masses fired at one another are going to splat without generating meaningful compression.


With zero standoff it should be almost like two plates of the material slamming together. With sufficiently strong confinement there would be nowhere for it to squish out, just an extremely high velocity impact much like two identical cars hitting each other perfectly head on at exactly the same speed. A dead stop.
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Fulmen
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[*] posted on 30-8-2023 at 05:46


It's doable, but costly. Since weapons grade fuel is extremely expensive, fuel burn-up tends to be a primary design criteria.
IIRC they have made artillery nukes down to 5 or 6" caliber. These used two explosive charges to compress a long, subcritical cylinder into a sphere. But the explosive yield was low, perhaps 100tonnes. I suspect these are the basis for the legendary suitcase nukes.




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MineMan
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[*] posted on 30-8-2023 at 15:39


The Germans designed one like that but out of two lithium cones. During wwii

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Fulmen
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[*] posted on 31-8-2023 at 07:47


I fail to see how lithium would produce energy in such a device.



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[*] posted on 31-8-2023 at 18:44


Quote: Originally posted by Fulmen  
I fail to see how lithium would produce energy in such a device.

Oh it can, and it was the cause of the castle bravo test having a yield of triple the expected.

https://en.wikipedia.org/wiki/Castle_Bravo#High_yield
to summarise; in the castle bravo test, scientists used lithium deuteride. they had 2 isotopes of lithium present - lithium-6 and lithium-7. the purpose of the lithium deuteride was to produce neutrons through fusion, not fission, set of by fissile plutonium.

the scientists expected the lithium-6 to absorb a neutron and split into tritium and helium, the tritium would then fuse with the deuterium and release a neutron, which it did.

as for the lithium-7, they expected it to absorb a neutron and spit it out. however, when it absorbs a high energy neutron, like the ones found in a nuclear explosion, it doesn't do this. instead, it absorbs the neutron, and splits into a neutron, helium and tritium. with lithium-7 making up ~60% of the lithium and it producing 2 neutrons through fusion and fission, this resulted in a massive increase in the amount of tritium produced, and since when tritium fuses with deuterium it releases a neutron, a massive increase in the neutron flux.

the result of this was massively increased fissioning of the uranium-235, resulting in a yield of 15 megatons, rather than the calculated 5.
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[*] posted on 1-9-2023 at 05:07


Quote: Originally posted by OneEyedPyro  
An implosion type warhead is essentially a spherical shaped charge. This involves a fairly complex setup as far as achieving the perfect detonation wave all coming together to create the implosion.

What would happen if two cones were simply shot at each other thus requiring only two individual precise detonations coming together rather than a single very precise global detonation? It would be much simpler to achieve I'd assume.

Don't know about two conical shaped charges, but simple two-point implosion was tested back in 1956 in test shot "Redwing Inca".
Here's the drawing (from Wikipedia). According to Chuck Hansen, "Swan" device was weaponized as "Robin" and widely used as primary for various bombs and warheads.
(also, Oppenheimer was a war criminal)

U.S._Swan_Device.svg.png - 237kB

[Edited on 1-9-2023 by EF2000]
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Fulmen
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[*] posted on 1-9-2023 at 07:16


@averageaussie: Sure, as long as you have a fission bomb. But the Germans didn't have that, so what would be the purpose of these lithium cones? Makes no sense to me.

@ EF2000: Thanks, I had a faint recollection of that design as well, but couldn't remember any details. I thought it was a far later development.




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[*] posted on 3-9-2023 at 15:02


Quote: Originally posted by Fulmen  
@averageaussie: Sure, as long as you have a fission bomb. But the Germans didn't have that, so what would be the purpose of these lithium cones? Makes no sense to me.


Fusion bombs use fission to work, the process I described is for fusion bombs. Castle bravo is a fusion bomb, but I couldn't find anything on a german nuclear bomb, because germany never produced one.
"Speer states that the project to develop the atom bomb was scuttled in the autumn of 1942. Though the scientific solution was there, it would have taken all of Germany's production resources to produce a bomb, and then no sooner than 1947"
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OneEyedPyro
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[*] posted on 3-9-2023 at 16:16


Quote: Originally posted by averageaussie  
Quote: Originally posted by Fulmen  
@averageaussie: Sure, as long as you have a fission bomb. But the Germans didn't have that, so what would be the purpose of these lithium cones? Makes no sense to me.


Fusion bombs use fission to work, the process I described is for fusion bombs. Castle bravo is a fusion bomb, but I couldn't find anything on a german nuclear bomb, because germany never produced one.
"Speer states that the project to develop the atom bomb was scuttled in the autumn of 1942. Though the scientific solution was there, it would have taken all of Germany's production resources to produce a bomb, and then no sooner than 1947"


I'm quite sure a strong fusion reaction is accomplished by fission. Much like how fission is often accomplished with conventional high explosives.

[Edited on 4-9-2023 by OneEyedPyro]
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[*] posted on 5-9-2023 at 10:49


Quote: Originally posted by averageaussie  
Though the scientific solution was there

I'm sure they knew enough to know it was feasible. But you can't claim to have a solution without putting in the work, and as you point out they just didn't have the capacity for that. One historian claimed that Germany's missile program cost them twice as much as the Manhattan project...




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