Fat Man on target

Not that much: though the primary targets, the Mitsubushi Aircraft Plant and the Mitsubushi Torpedo Works, were severely damaged by the off-target detonation (20 KT). In an on-target detonation, both get totally destroyed, and the shipyard (where the Super-Battleship Musashi was built) is also seriously damaged.
 

Cook

Banned
It hit the city so it’s on target. This was strategic bombing using an atomic bomb, not sending a cruise missile through an office window after all.
 
The attack would mave been a touch more successful; destroyed/damaged more stuff and killed/maimed more people but I doubt the Japanese would have surrendered any earlier or the Russians been any more impressed.
 
For the strike to be more on target there would have to be less clouds. Less clouds at Nagasaki would suggest less clouds at Kokura, perhaps enough to tip the balance to striking there as the primary target that it was.
 
What strategic affect would that have on the war? Would the Japanese surrender earlier, would the Soviets be more impressed?
 
What strategic affect would that have on the war? Would the Japanese surrender earlier, would the Soviets be more impressed?

No change at all. The Japanese War Council (At least the Army Minister Anami) seemed to be trying to believe the US couldn't possibly have another bomb yet when the news of Nagasaki came in. The understanding of the Bomb already existed, but it was believed that just one would take years. U-239 wasn't even imagined, IIRC, by Japanese physicists.
 
No change at all. The Japanese War Council (At least the Army Minister Anami) seemed to be trying to believe the US couldn't possibly have another bomb yet when the news of Nagasaki came in. The understanding of the Bomb already existed, but it was believed that just one would take years. U-239 wasn't even imagined, IIRC, by Japanese physicists.

Fat Man used Plutonium-239. Uranium-239 isn't fissile and decays with a half life of around 23.5 minutes. The decay of U-239 does however produce Neptunium-239 which then goes on to decay to Plutonium-239

The only easily fissile isotope of Uranium is U-235 as used in Little Boy
 
Fat Man used Plutonium-239. Uranium-239 isn't fissile and decays with a half life of around 23.5 minutes. The decay of U-239 does however produce Neptunium-239 which then goes on to decay to Plutonium-239

The only easily fissile isotope of Uranium is U-235 as used in Little Boy

Right. Like I said. I wasn't posting on NuclearPhysicsHistory.com. The whole idea was that with U-239 you can mass produce many such "Fat Man"s eventually where as U-235 bombs were basically a one shot. But because the success of the Fat Man design couldn't be proven until "Trinity" both tracks had to be followed.
 
Right. Like I said. I wasn't posting on NuclearPhysicsHistory.com. The whole idea was that with U-239 you can mass produce many such "Fat Man"s eventually where as U-235 bombs were basically a one shot. But because the success of the Fat Man design couldn't be proven until "Trinity" both tracks had to be followed.

Well yes but U-239 does not occur naturally as it decays so rapidly. U239 is produced in a nuclear pile from U238 by neutron capture and then naturally decays to Plutonium 239.

Neither design could be guaranteed success which was why both tracks were followed. In fact it is somewhat easier to produce Pu239 once you have nuclear reactors running than it is to produce Uranium that has been sufficiently enriched to be able to be made into weapons

Bear in mind that naturally occurring Uranium is more than 99.2% U238 and only about 0.7% U235 (there are also trace amounts of U234). In order to build a bomb from Uranium it needs to be at least 85% U235,. It is also incredibly difficult to separate U235 from U238 as their chemical properties are (virtually) identical. This is why physical methods such as gas centrifuges must be used to enrich the Uranium.

It is therefore far easier to follow the Pu route to building a bomb
 

Blair152

Banned
What if Fat Man hit Nagasaki as precisely as Little Boy hit Hiroshima, rather than being slightly off-target? What implications would this have?
Little Boy, (formerly Thin Man), wasn't as precise as you may think. The aim point was actually a bridge and it hit a hospital. Nagasaki was actually a backup target. The main target was obscured by smog. As for Fat Man being precise, I'll need more information.
 
I didn't think either bomb actually 'hit' anything, I thought they were parachute retarded airbursts. The 'problem' with Nagasaki was that much of the blast power was deflected by hills or mountains between the airburst and the target area of the city.
 
kellineil said:
Well yes but U-239 does not occur naturally as it decays so rapidly. U239 is produced in a nuclear pile from U238 by neutron capture and then naturally decays to Plutonium 239.

Neither design could be guaranteed success which was why both tracks were followed. In fact it is somewhat easier to produce Pu239 once you have nuclear reactors running than it is to produce Uranium that has been sufficiently enriched to be able to be made into weapons

Bear in mind that naturally occurring Uranium is more than 99.2% U238 and only about 0.7% U235 (there are also trace amounts of U234). In order to build a bomb from Uranium it needs to be at least 85% U235,. It is also incredibly difficult to separate U235 from U238 as their chemical properties are (virtually) identical. This is why physical methods such as gas centrifuges must be used to enrich the Uranium.

It is therefore far easier to follow the Pu route to building a bomb

However, a uranium bomb is much simpler to build in terms of triggering. A very simple gun-type mechanism works fine with uranium, but because of unavoidable isotopic contamination in plutonium that same design will always fizzle. That's why they abandoned the "Thin Man" plutonium-gun-type device in '44. Designing and building the precise conventional explosive blocks needed for an implosion device is apparently rather tricky, one of the harder parts of the bomb design.
 
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