1. The Fission Bomb Luke Whittlesey Department of Physics and Astronomy
Stephen F. Austin State University
add. edit. ydp

2. Introduction
In the 1930’s German physicist/chemists Otto Hahn and Fritz Strassman discovered the fission of Uranium 235
Learned the bombardment of neutrons on uranium gave off lighter elements
also saw the possibility of a chain reaction that could release astronomical amounts of energy

3. Introduction
In 1939 it was rumored the Nazi’s were developing an atomic bomb
America needed to build one before them
In mid 1942 an all-out program to develop the bomb was initiated by U.S. under code name Manhattan Project.
in 1943 The Los Alamos Laboratory was organized

4. The Leaders
The Manhattan Project was directed by General Leslie R. Groves
research was directed by physicist J. Robert Oppenheimer
J. Robert Oppenheimer
General Leslie R. Groves

5. The First Try On July 16, 1945 an implosion type bomb was tested
"The Gadget", was placed on a 100-foot tower and successfully detonated in the Alamogordo Desert, 200 miles south of Los Alamos
Los Alamos Director J. Robert Oppenheimer named the site "Trinity" after a poem

6. First Try
First Atomic Bomb Test, July 16, 1945, Alamogordo, New Mexico

7. The Fission Process Fission is the process of splitting atoms
For example, Uranium can be split into Barium and Krypton, or other pairs of elements.
Fission releases large amounts of energy
Most of this energy is due to some of the mass being converted into energy

8. The Fission Process

10. 56Ba-137
U-236
U-235
36Kr-97

11. Critical Mass
For a fission bomb to explode it must have at least a critical mass of fissionable material
If the mass is not critical the bomb will just fizzle out
On the other hand, if the mass is supercritical the chain reactions of fission will grow exponentially

12. Explanation of Critical mass
If the uranium density isn’t high enough
the chain reaction cannot be sustained

13. Types of fission bombs
There were 2 types of fission bombs developed during the Manhattan Project
The first was a gun-type fission bomb
For its fuel it fissions Uranium 235
Uranium 238 occurs in nature but only a small percentage of that is Uranium 235

14. Gun Type Fission Bomb
The explosives fire and propel the bullet down the barrel.
The bullet strikes the sphere and generator, initiating the fission reaction.
The fission reaction begins.
The bomb explodes.

16. Gun-Type Fission Bomb Used In WWII
The gun-type fission bomb was never tested because the developers were so confident in the bomb design
The first bomb detonated over Japan at Hiroshima on August 6, 1945 was a gun-type fission bomb called “Little Boy”
The Bomb had an energy yield estimated at 15 kilotons
It’s efficiency was said to be about 1.38%

17. The Other Type of Bomb
The later developed bomb design was the implosion type bomb
This bomb used plutonium instead of uranium
They needed a faster way to gain supercritical mass because the plutonium would fission quicker and easier
Give Seth Neddermeyer, a scientist at Los Alamos, credit for coming up with this design
Theses bombs exploded much quicker, within a fraction of a second.

18. Implosion Type Fission Bomb
The high explosive surrounding the fissile material is ignited.
A compressional shock wave begins to move inward. As the core density increases, the mass becomes critical, and then supercritical (where the chain reactions grows exponentially).
Now the initiator is released, producing many neutrons, to start the chain reaction.
The chain reaction continues until the energy generated inside the bomb becomes so great that the internal pressure due to the energy of the fission fragments exceed the implosion pressure.
As the bomb disassembles, the energy released in the fission process is transferred to the surroundings.

19. Implosion Type Fission Bomb
“Fat Man” and “The Gadget” were both implosion type fission bombs
“Fat Man” was the second bomb detonated over Japan at Nagasaki three days after the gun-type “Little Boy”.
This bomb had a 23 kiloton yield, much more than “Little Boy’s” 15 kilotons.
This bomb was much more efficient that the gun-type bomb

20. Mushroom Cloud over Hiroshima, Japan, August 6, 1945

21. Mushroom Cloud over Nagasaki, Japan, August 9, 1945

22. Energy Yield of Little Boy
The estimated energy yield of Little Boy was 15 kilotons
Using one example of a fission of the isotope uranium 235, we will calculate an energy yield for Little Boy
We will only be looking at the energy released from mass being converted to energy

23. Calculations Let’s look at the mass loss using percentages
Staring with 236 and ending with gives a loss of .2
Percent of mass loss is then .2 divided by 236 which is about .0847%

24. Actual Mass Converted to Energy
Little boy contained 64.1 kg of nearly 90% uranium 235.
Also the efficiency of the bomb was 1.38%
To find the amount of uranium 235 that actually went through fission we multiply the 64.1 kg by both of these percentages

25. Mass Lost In Fission
This gives us approximately .796 kg of uranium 235 that actually went through fission.
Now using the mass lost percentage we can find about how much mass was converted into energy.
Mass lost percentage %

26. E=mc2
Using Einstein’s mass to energy Equation, we can find the energy produced as
E=mc2
E= kg * (3.00 x 108)2 m2/s2
E = 60.7 x 1012 J
4.1 x 1012 joules = 1 kiloton
E = 14.8 kilotons
matches the predictions that the bombs energy yield was approximately 15 kilotons

27. Actual Destruction of Fission Bomb
A fission bomb gives off 3 types of energy
Heat
Radiation
Blast
This next slide shows the distribution

29. Bomb Blast
We know what radiation and heat are but what exactly is bomb blast
If you have ever heard of a shock wave that’s what it really is.
The bomb produces a shock wave of air that produces
a sudden change in air pressure that can annihilate buildings and
extremely high winds that blow stuff away

30. Nakasaki, 1945

31. Summary Currently, the US has about 7,000 nuclear warheads
the nations of the former Soviet Union have approximately 6,000 nuclear warheads.
There are more than enough nuclear weapons in the world to destroy civilization as we know it
By just plain destruction
By radioactive fall-out
And by what is called a “Nuclear Winter”

32. What Is Nuclear Winter?
This Nuclear Winter is caused by the dust and debris blown up into the atmosphere
Effects
Less Sunlight
Plants will soon die – resulting in lack of food
temperatures plummet
Falling Radioactive material
Causes many health problems – tumors, cancers
These combined make the chances of survival extremely small

33. Look On the Bright Side
we got Nuclear power plants out of this research
they are extremely efficient power sources
in those we actually control the fission
so as long as we don’t blow ourselves up we will be able to use this technology

34. References
The Manhattan Project Heritage Preservation Association, Inc.,
howstuffworks.com
atomicarchive.com
Wikipedia
Atomic Alchemy: Nuclear Processes, Thinkquest 1998