WI:Little Boy had a higher percent of enriched uranium?

IIRC, based on my limited knowledge of nuclear weapons, Little Boy contained HEU close to 88%. However, some amounts were only enriched to 50%, with the average enrichment of uranium in the weapon being around 80%. What happens if Little Boy is produced with uranium to be enriched more higher? I know some uranium produced around Oak ridge was around 90% while the remaining had varying percentages of around 20-70%. What if Little Boy's enrichment of uranium was over 90%? Does this increase the weapon yield? I know it wouldn't be a huge yield difference, but I noted that some gun-type nukes in the late 40's by the US had a yield around 25-30 kt. Was this due to a higher percentage of uranium used or a variety of other factors involved? (I am aware that the gun-type was an inefficeint design, but in this scenario, all work is directed toward a gun-type uranium weapon instead, meaning no thin man or fat man at all.)
 
I believe the 'target' rings were 80%, while 'bullet' was 94%

Little Boy was only 1.4% efficient, a change to Beryllium reflector and neutron tube vs the polonium trigger as well as all 94%HEU would result in more neutrons to aid in the fissioning, as would having a higher propellent load for faster assembly. I believe only the last three were done for the mk8 'Elsie' Gun-type bomb
 
I believe the 'target' rings were 80%, while 'bullet' was 94%

Little Boy was only 1.4% efficient, a change to Beryllium reflector and neutron tube vs the polonium trigger as well as all 94%HEU would result in more neutrons to aid in the fissioning, as would having a higher propellent load for faster assembly. I believe only the last three were done for the mk8 'Elsie' Gun-type bomb
Or Oppenheimer makes his post-Trinity recommendation to Groves, that the gun-barrel design be abandoned, earlier and composite pits using the recycled HEU are used in the MK3 bombs from the beginning. This would mean more bombs available earlier.
 
The two things the Gun types had going, was they were 99% sure it would work with Little Boy, and the Mk8 was sure it would work as a 'bunker buster' as the early implosion weapons were not rated to penetrate at mach 1 like the Mk8 was designed for
 
I believe the 'target' rings were 80%, while 'bullet' was 94%

Little Boy was only 1.4% efficient, a change to Beryllium reflector and neutron tube vs the polonium trigger as well as all 94%HEU would result in more neutrons to aid in the fissioning, as would having a higher propellent load for faster assembly. I believe only the last three were done for the mk8 'Elsie' Gun-type bomb

So what if the target rings were 94% as well?

Would you know if this could increase Little Boy's yield to 20, 25 or even 30 kilotons?
 
So what if the target rings were 94% as well?

Would you know if this could increase Little Boy's yield to 20, 25 or even 30 kilotons?

That's probably where most of the gain to the Mk-8 came from, along with propellant.

In 1945, the easiest way would be to use the longer 'Thin Man' design with HEU to get the faster assembly speed to get in the 20-25kt area, but then you need more mods to the Silverplate B-29 to join the two bomb bays
 
If you up the percentage of HEU or the degree of enrichment, you're going to have to make sure the reaction doesn't start prematurely. Which is one reason the Pu bombs were implosion - they couldn't get the masses together fast enough with a gun-type.
 
If you up the percentage of HEU or the degree of enrichment, you're going to have to make sure the reaction doesn't start prematurely. Which is one reason the Pu bombs were implosion - they couldn't get the masses together fast enough with a gun-type.

Little Boy was still almost twice as safe as Thin Man would have been(given no Pu-240 contamination), despite 1/3 the assembly speed. It used four Polonium initiators, just to make sure sufficient neutron were available at the moment of assembly. It was oversafe, really.

It was a 40%/60% split for material. Would need to do the math, but even a nearby nuke going off wouldn't have been enough to cause a fizzle.
The only real problem was if the gun tube would fill with water from a water landing, that would act as a moderator and allow enough slow fission to flash water to radioactive Tritated steam.
 
Little Boy was still almost twice as safe as Thin Man would have been(given no Pu-240 contamination), despite 1/3 the assembly speed. It used four Polonium initiators, just to make sure sufficient neutron were available at the moment of assembly. It was oversafe, really.

It was a 40%/60% split for material. Would need to do the math, but even a nearby nuke going off wouldn't have been enough to cause a fizzle.
The only real problem was if the gun tube would fill with water from a water landing, that would act as a moderator and allow enough slow fission to flash water to radioactive Tritated steam.
The problem with the Pu bomb, iirc, is the fission starts happening as the slug is traveling towards the target, and that's pretty much unavoidable. I don't know if it's a matter of neutron speed or the reactivity of the fissile material or what, but I at least wondered if the same problem would happen with purer U235. Since @Andras has provided a link to a source that talks about more highly enriched gun type U235 bombs, that must not be a problem.
 
93.5% HEU would have doubled Little Boys yield.


http://nuclearweaponarchive.org/Nwfaq/Nfaq4-1.html#Nfaq4.1.5.2
scroll down to 4.1.6.1.1 Single Gun Systems

Damn! I didn't expect that. I thought the yield would only improve around 10-30%, but that is a lot! Do you know if this could be done in time for Hiroshima if they had focused on setting this yield? Or does concentration toward that level of uranium make it so difficult that there was no need to go beyond around 80%?
 
The two things the Gun types had going, was they were 99% sure it would work with Little Boy, and the Mk8 was sure it would work as a 'bunker buster' as the early implosion weapons were not rated to penetrate at mach 1 like the Mk8 was designed for
Reliability and ground penetration were about all they had going. They were terribly inefficient and none too safe.
You could construct four U235 implosion cores using the HEU80 in a MK1 bomb, or supply the HEU for around ten composite cores (about 25kg of plutonium would be needed).

So what if the target rings were 94% as well?

Would you know if this could increase Little Boy's yield to 20, 25 or even 30 kilotons?
Probably somewhat more.

Little Boy was still almost twice as safe as Thin Man would have been(given no Pu-240 contamination), despite 1/3 the assembly speed. It used four Polonium initiators, just to make sure sufficient neutron were available at the moment of assembly. It was oversafe, really.

It was a 40%/60% split for material. Would need to do the math, but even a nearby nuke going off wouldn't have been enough to cause a fizzle.
The only real problem was if the gun tube would fill with water from a water landing, that would act as a moderator and allow enough slow fission to flash water to radioactive Tritated steam.
Yeah the safe abort options were dubious.

93.5% HEU would have doubled Little Boys yield.


http://nuclearweaponarchive.org/Nwfaq/Nfaq4-1.html#Nfaq4.1.5.2
scroll down to 4.1.6.1.1 Single Gun Systems
But it wouldn't have been available for AUG1945.
 
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