Some Interesting Atomic Bomb Facts (WWII)

bergmen

bergmen

Well-known member
I'm now about a third of the way into "The Making of the Atomic Bomb" by Richard Rhodes (excellent book BTW, tedious at times but excellent).

This got me to thinking about the two bombs dropped on Japan in August of 1945.

As a side note I visited Hiroshima in the late 1950s with my family. I will never forget it (a subject for an entirely different thread).

This is the site that I got most of my info from:

https://www.atomicheritage.org/history/little-boy-and-fat-man

On the bombs:

1) Little Boy (Hiroshima, August 6, 1945):

> Weight: 9700 lbs.
> Fuel: Highly enriched uranium; "Oralloy".
> Uranium Fuel: approx. 140 lbs; target - 85 lbs and projectile - 55 lbs.
> Efficiency of weapon: poor.
> Approx. 1.38% of the uranium fuel actually fissioned.
> Explosive force: 15,000 tons of TNT equivalent.

It is astounding to me that less than 2 lbs of the Uranium fuel actually fissioned and created an explosive force equal to about 15,000 tons of TNT.

2) Fat Man (Nagasaki, August 9, 1945):

> Weight: 10,800 lbs.
> Fuel: Highly enriched plutonium 239.
> Plutonium Fuel: approx. 13.6 lbs; approx. size of a softball.
> Plutonium core surrounded by 5,300 lbs of high explosives; plutonium core reduced to size of tennis ball.
> Efficiency of weapon: 10 times that of Little Boy.
> Approximately 1 kilogram of plutonium fissioned.
> Explosive force: 21,000 tons of TNT equivalent.

So about 2.2 lbs of Plutonium produced about 1.4 times the force of Little Boy. Again, astounding.

Here is a detailed timeline of both missions:

https://www.atomicheritage.org/history/hiroshima-and-nagasaki-bombing-timeline

A bunch of amazing details here.

My intention here is to report on the technical details of these incidents. I would prefer that we do not get into the morality of these events and use another thread for that, please.

Dan
 
afm199

afm199

Well-known member
Great book!

Point of further interest. In the Hiroshima bomb, the amount of matter that was fully converted into energy was .7 gram.

That's not a mistake. .7 gram
 
bergmen

bergmen

Well-known member
afm199 said:
Great book!

Point of further interest. In the Hiroshima bomb, the amount of matter that was fully converted into energy was .7 gram.

That's not a mistake. .7 gram
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In reading this book, the investigations into the secrets of the atom are mind boggling. It became apparent to many of the physicists of the time that there was tremendous energy in the nucleus of some atoms. Extremely difficult to peel the onion and prove it, but they were on the hunt for it.

Freakin' amazing to me. From the site mentioned (Little Boy):

> .1 seconds: The fireball has expanded to one hundred feet in diameter combined with a temperature of 500,000°F. Neutrons and gamma rays reach the ground. The ionizing radiation is responsible for causing the majority of the radiological damage to all exposed humans, animals and other biological organisms.

> .15 seconds: The superheated air above the ground glows. A woman sitting on steps on the bank of the Ota river, a half a mile away from ground zero, instantly vaporizes.

> 0.2-0.3 seconds: Intense infrared energy is released and instantly burns exposed skin for miles in every direction. Building roofing tiles fuse together. A bronze Buddha statue melts, and even granite stones. Roof tiles fuse together, wooden telephone poles carbonize and become charcoal-like. The soft internal organs (viscera) of humans and animals are evaporated. The blast wave propagates outward at two miles per second or 7,200 miles per hour.

> 1.0 second and beyond: The fireball reaches its maximum size, approximately 900 feet in diameter. The blast wave slows to approximately the speed of sound (768 miles per hour). The temperature at ground level directly beneath the blast (hypocenter) is at 7,000° F. The mushroom cloud begins to form.

The blast wave spreads fire outward in all directions at 984 miles per hour and tears and scorches the clothing off every person in its path. The blast wave hits the mountains surrounding Hiroshima and rebounds back. Approximately 60,000 out of the city's 90,000 buildings are demolished by the intense wind and firestorm.

Approximately 525 feet southwest from the hypocenter, the copper cladding covering the dome of the Industrial Products Display Hall is gone, exposing the skeleton-like girder structure of the dome. However, most of the brick and stonework of the building remains in place.

The ground within the hypocenter cools to 5,400°F. The mushroom cloud reaches a height of approximately 2,500 feet. Shards of glass from shattered windows are imbedded everywhere, even in concrete walls. The fireball begins to dim but still retains a luminosity equivalent to ten times that of the sun at a distance of 5.5 miles.

Nuclear shadows appear for the first time as a result of the extreme thermal radiation. These shadows are outlines of humans and objects that blocked the thermal radiation. Examples are the woman who was sitting on the stairs near the bank of the Ota River. Only the shadow of where she sat remains in the concrete. The shadow of a man pulling a cart across the street is all that remains in the asphalt. The shadow of a steel valve wheel appears on a concrete wall directly behind it because the thermal radiation was blocked by the outline of the wheel.

When we visited Hiroshima, we saw the shadows of those that were exposed to the intense energy (actually, the granite was bleached except where people and wagons were blocking the radiation).

As a nine year old child, I was forever moved by this experience. I will never forget it. We spent two days touring the city. My Dad set the stage for what we were to experience and it weighed heavily on him as to the profound circumstances of the bombing.

Dan
 
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DataDan

DataDan

Mama says he's bona fide
bergmen said:
I'm now about a third of the way into "The Making of the Atomic Bomb" by Richard Rhodes (excellent book BTW, tedious at times but excellent).
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Great book. Rhodes really did his homework. Much less was publicly available when he wrote it.

For a different (and irreverent) slant on the Manhattan Project, read Richard Feynman's Los Alamos from Below. It originally appeared as an article in the Cal Tech alumni magazine, which I stole from my dad. Later it was edited down as a chapter in his book Surely You're Joking, Mr. Feynman.
 
afm199

afm199

Well-known member
Another great read is John McPhee's "The Curve of Binding Energy."

Imagine the core of the weapon, at detonation, briefly ( milli seconds) changing state from a solid to a mass of insanely hot ( hundreds of millions of degrees) plasma. The same size. That lasts for a shake and then it's gone, encountering the atmosphere. The blast damage from the blast is from that insanely hot heat source hitting the icy cold heat sink of the atmosphere.
 
afm199

afm199

Well-known member
Killroy1999 said:
Efficiency must be:

(explosive force)/ (plutonium or uranium weight). Both bombs are ~10,000 lb in weight.

I wonder which is easier to make uranium or plutonium.
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It's an odd one. U235 ( fissile uranium) makes up around 2-3% of all of the natural uranium on the earth. At one time, billions of years ago, it was mostly U235, but U235, being fissile, is constantly releasing neutrons and becoming U238 or depleted Uranium, the other 97% of the natural uranium.

What is so very hard about making U235 is the process of refining yellowcake (uranium ore). It's very expensive, in fact the hugest expense of the Manhattan project of WWII was making it, and then it ended up not being used in bombs, due to some of its undesirable qualities, mostly expense.

Pu239, on the other hand, is a man made element and quite easy to make, it's a byproduct of fission in reactors. It's made by irradiation of U238, depleted Uranium. It costs almost nothing compared to U235. It's also far more efficient, you need about a tenth of the amount of U235 to have a working atomic bomb.
 
bergmen

bergmen

Well-known member
afm199 said:
It's an odd one. U235 ( fissile uranium) makes up around 2-3% of all of the natural uranium on the earth. At one time, billions of years ago, it was mostly U235, but U235, being fissile, is constantly releasing neutrons and becoming U238 or depleted Uranium, the other 97% of the natural uranium.

What is so very hard about making U235 is the process of refining yellowcake (uranium ore). It's very expensive, in fact the hugest expense of the Manhattan project of WWII was making it, and then it ended up not being used in bombs, due to some of its undesirable qualities, mostly expense.

Pu239, on the other hand, is a man made element and quite easy to make, it's a byproduct of fission in reactors. It's made by irradiation of U238, depleted Uranium. It costs almost nothing compared to U235. It's also far more efficient, you need about a tenth of the amount of U235 to have a working atomic bomb.
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More great information, thanks! I have just begun reading about this subject in technical detail, never knew any of this before. You are adding greatly to the conversation!

One head scratcher for me: The type of bomb that made up Little Boy was never tested - just built and delivered. Fat Man was, the same type tested at Trinity. I wonder what the thinking was?

Dan
 
DataDan

DataDan

Mama says he's bona fide
U-235 for The Bomb was made primarily by centrifuging naturally occurring uranium to stratify the two isotopes, U-238 and U-235, by weight. Much of Rhodes' book is about the various projects to produce fissionable material.

The uranium in Little Boy was all they had. No uranium bomb was tested before August 6. It was a very simple design that depended only upon criticality being reached quickly enough that it didn't expand and fizzle. To persuade themselves that the design would work, they tested by dropping sub-critical balls through sub-critical hoops and measuring the radiation. :eek

The Trinity test was of a plutonium bomb, which was a much more mechanically sophisticated device at higher risk of failing.

Threat of a third bomb on Japan was a short-term bluff because we didn't have one. Rhodes goes into this.
 
afm199

afm199

Well-known member
bergmen said:
More great information, thanks! I have just begun reading about this subject in technical detail, never knew any of this before. You are adding greatly to the conversation!

One head scratcher for me: The type of bomb that made up Little Boy was never tested - just built and delivered. Fat Man was, the same type tested at Trinity. I wonder what the thinking was?

Dan
Click to expand...

You bet, I love this stuff. The U235 to U238 conversion shows us how old the universe is!



Little Boy was a U235 "Gun" type weapon, a much cruder weapon that just about every scientist involved said would work. However, by that time, it was only considered a backup weapon. For technical reason, the implosion (Fat man) weapon was preferred and accepted as the desirable design. However, a problem in Pu239 production created a momentary shortage and so the Little Boy was used. At this time these two were just about all the nuclear weapons we had, and it took several weeks, or longer, to produce more.
 
afm199

afm199

Well-known member
TylerW said:
What the fuck, dude.
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Apparently you are not conversant with the situation in India and Pakistan, where both countries are nuclear powers, and both have many generals who believe that nuclear weapons should be used.

It's a very real and very scary thing for both Pakistanis, and Indians. Show some cultural sensitivity, please.
 
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