23年 4月 20日

The Fission Bomb

Luke Whittlesey

Department of Physics and Astronomy

Stephen F. Austin State University

add. edit. ydp

23年 4月 20日

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

Introduction

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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

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General Leslie R. Groves J. Robert Oppenheimer

The Manhattan Project was directed by General Leslie R. Grovesresearch was directed by physicist J. Robert Oppenheimer

The Leaders

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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

The First Try

First Try

First Atomic Bomb Test, July 16, 1945, Alamogordo, New Mexico

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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

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The Fission Process

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U-236U-235

56Ba-137

36Kr-97

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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

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Explanation of Critical mass

If the uranium density isn’t high enough

the chain reaction cannot be sustained

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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

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o The explosives fire and propel the bullet down the barrel. o The bullet strikes the sphere and generator, initiating the

fission reaction. o The fission reaction begins. o The bomb explodes.

Gun Type Fission Bomb

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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%

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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.

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.

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“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

Implosion Type Fission Bomb

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Mushroom Cloud over Hiroshima, Japan, August 6, 1945

Mushroom Cloud over Nagasaki, Japan, August 9, 1945

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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

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Let’s look at the mass loss using percentages

Staring with 236 and ending with 235.8 gives a loss of .2

Percent of mass loss is then .2 divided by 236 which is about .0847%

Calculations

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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

Actual Mass Converted to Energy

kgkg

kgkg

796122.0138.*69.57

69.579.*1.64

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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 - .0847%

kgkg 006743.00847.*796.

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Using Einstein’s mass to energy Equation, we can find the energy produced as

E=mc2

E= .0006743kg * (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

E=mc2

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Actual Destruction of Fission Bomb A fission bomb gives off 3 types of

energy Heat Radiation Blast

This next slide shows the distribution

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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

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Nakasaki, 1945

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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”

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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

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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

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References http://www.childrenofthemanhattanproject.org/HISTORY/ERC-1.htm,

The Manhattan Project Heritage Preservation Association, Inc., http://people.howstuffworks.com/nuclear-bomb5.htm,

howstuffworks.com http://www.atomicarchive.com/Fission/Fission7.shtml,

atomicarchive.com http://www.wikipedia.com, Wikipedia http://www.pref.hiroshima.jp/hiroshima/bunka/htmleng/egenbak2.htm http://www.pref.hiroshima.jp/hiroshima/bunka/htmleng/egenbak3.htm http://hslib.stephenville.k12.tx.us/petross03/p1leyend/p1leyend.htm http://library.thinkquest.org/17940/texts/nuclear_weapons/

nuclear_weapons.html?tqskip1=1, Atomic Alchemy: Nuclear Processes, Thinkquest 1998