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The Atomic Bomb

By Douglas Thornton
BOOM! The first detonation of an atomic bomb was on July 16,1945 on Hiroshima, Japan . That was one of the reasons why I picked this topic. Another reason was that there is lots of information on the atomic bomb out there and the last reason is I wanted to know why the atomic bomb has great explosive power. The main part of an atomic bomb is of course an atom. So that is what Im going to say first.

The Atom
Atoms are everything. It is your paper, your house, your clothes, and everything else. Atoms is the smallest thing on earth. You can fit a million atoms in about the width of a piece of paper. You cant see them with the naked eye or with the best microscope in the world. The sciencists use theories and tests to know that they are there. Atoms are made up of three things; electrons, proton(s),and neutrons. If you combined proton(s) and neutrons you get the nucleus of the atom. Then the nucleus is surrounded by a shell. That shell is made by an electron(s) spinning around the nucleus so fast it makes that shell. Each shell can only hold a certain amount of electrons, this graph will show you that.

The proton is positivtly charged while neutrons have no charge. The proton attracts the electron. This pull causes the whirling of electrons which creates the shell.Most of an atom is empty space( the empty space is between the nucleus and the electrons). Neutrons are just slightly larger than protons. An electron is small. Its about 1/1836 of a proton or a neutron.In every atom there is always the same number of protons and electrons.

The Atomic Bomb
Now, what is an atom bomb? The Atomic Bomb is a weapon of mass destruction. It does that by a quick release of splitting or fission of a nucleus of a heavy element like uranium and plutonium.

They send a neutron to strike a nucleus of the isotopes( means the name given to an atom that has acquired or lost one or more neutrons from its nucleus.The atoms structure is relatively the same, but the added or subtracted weight may cause the atom to have new properties such as being fissionable) uranium-235 or plutonuim-239. Then the nucleus splits into two halves. Each half of the nucleus has about the same amount of neutrons and protons. When the nucleus splits a great deal of thermal energy and gamma rays and two or more neutron are given off. Under some conditions those neutrons that were released come back and strike again. Then you two split halves of a nucleus. Then they give off the same thing and the neutrons come back and strike again, and again. This chain reaction results in which almost all the fissionable material is blown up. This cause the great explosion.

All isotopes of uranium are fissionable, but uranium-235 is better than uranium-238 because it goes under fission quicker and gives off more neutrons per fission than Uranuim-238 or any other isotopes of uranium. plutonium-239 has the same characteristics of uranium-239. Both uranium-235 and plutonium-239 are used in the atomic bomb. If you use a small amount say .45 kg(1 lb) of uranium-235 or plutonium-239 it cant under go the chain reaction that is needed and is called subcritical. It cant undergo the chain reaction because the average of the neutrons released by the fission are likely not to hit another nucleus. Then if more of uranium-239 or plutonium-239 is added there is a higher percentage of neutrons hitting the nucleus. At the point when critical mass has been acomblished, and a chain reaction the explosion will be created.

All subcritical fissionable material must be brought up to critical state extremely quick. One way to do that is to take two subcitical masses together at one point. When you combined those two subcritical masses you will achieve critical mass. How you do it is you use two high explosives to shoot the subcrital masses of fissionable material together in a hollow tube. The second way is to use an implosion, which instead of blow up outward it blows up inward, by which the core of fissionable material is very quickly compressed into a smaller size. This makes the fissionable material more dense; which means the nuclei are packed in tighter and have a better chance of the neutrons hitting the nuclei. The outer layer of the implosion-type Atomic Bomb is a sphere or a bunch of concentric shells of fission able material is covered by explosives, are simultaneously detonated, implode the fissionable material under great persure into a denser mass which automacticly achieves critical mass.The use of a tamper;which is a coat of beryllium oxide or some thing else around the fissionable material; reflects some of the neutrons trying to escape and put back to strike more. More help is used by a “boosted fission” devices which incorporate such fissionable material as deuterium or tritium in the core. This boosts the fission by adding a great abundance of neutrons.

When the bomb is done, 1 kg(2.2 lb) of uranium -235 releases the energy equal to 17,000 tons or 17 kilotons of TNT. When the bomb goes off it releases an ambundant amounts of thermal energy, or heat.Temperature becomes several million degrees in the bomb. This thermal energy, a large fire ball, which can ignites the ground and burns up a whole city. Convection currents are created by the explosion, which sucks in dust and other things into a fireball, creating the well-known mushroom shaped cloud. Also shock waves goes out away from the bomb and can go to several miles away and it can destroy buildings. Also large amounts of neutrons and gamma rays are also emitted; this lethal radiation goes out rapidly over 1.5-3 km(1-2 miles). Materials vaporized in the fireball condences into fine particles; this radioactive debris or fallout is carried by the wind in the troposphere or stratosphere. These radioactive contaminates stay for weeks after the explosion and have a lethal effect. The elements are strontium-90 and plutonium-239.

The Manhattan Project
The manhattan project was a code name for the US effort in World War two to create an atomic bomb. It was named after the Manhattan Engineer District of the US Army Corps of Engineers, based in New York City where most of the research was done, but it mainly took place in New Mexico. The history of the Manhattan project remained classified for many years. The project lasted four years, between 1942-1946, and cost about 1.8 billion dollars( today it cost about 20 billion dollars). The project produced three bombs: the first one was known as “Gadget”, was used as a test model; the second was named “Little Boy”, dropped over Hiroshima, and the third was “Fat Man” detonated over Nagasaki.

When World War two started in1940 Germany and Italy were taking over countries in Europe. When Japan saw that they decided to take over countries in the far east and Pacific. Then on December 7, 1941 Japan bombed Pearl Harbor in a surprise attack. That brought the US into war.

The first major challage the Manhattan project had was finding what fuel would be good for the atomic bomb. Neils Bohr said isotopes uranium-235 would be good because it was very unstable and can sustain the chain reaction. Glen Seaborg found out that you cloud also use plutonium-239. It is very hard to get them both. Second challenge was being able to get the uranium and plutonium to go through th fission chain reaction. Third challenge was getting the uranium or plutonium for the atomic bomb. They needed large amounts of that for the atom bomb. uranium-235 is taken from uranium ore. uranium-235 is 1% and uranium-238 is 99% of the ore. They needed to seperate the uranium-235 and the uranium-238. The first way was called magnetic seperation invented by Ernest O. Lawerence who called it a Cyclotron at University of California, Berkeley laboratories. The uranium was passed through a magnet on 180 degree arc. The lighter uranium-235 would pass closer to the magnet and get collected, while the uranium-238 would go to the outside and get disposed. There many problems with the magnet. it had dirt particles contaminating the oil and the silver bands on the the track got rusted. The magnets would have to been sent back and be cleaned. This took too long.They spent about 1 million dollars on this and only collected about a gram of uranium-235.

The Second way was in 1942, Gen. Leslie Groves bought land in Oak Ridge, Tennessee to build a uranium seperation failtiy. The process they used turned uranium it to a gas by spraying uranium Hexafluoride on it. The gas floats up and goes through fliters. Most of the uranium-235 is collected and most of the uranium-238 is stopped by the filters.

Glen Seaborg discovered how to change uranium-238 into plutonium-239. In 1942 Enrico Fermi bulit a small nueclear reactor in Chicago and created the first controllable chain reaction in his lab; which would become a prototype for five other reactors. Gen. Groves moved the reactor to Hanford, Washington where the area was isolated and secure.

Little Boy
Robert Oppenheimer said that a 100kg(220 lb) of uranium-235 was needed because uranium hardly ever comes pure. The center of the bomb is a section that is hollow where they put the uranium in. A conventional explosions was used to propel the center section into the large section. Both sections would be welded together and begin the chain reaction. This bomb is known as an altimeter bomb which means it has a device that figures out the altitude by measuring the air pressure. This lets the bomb explode before it hits the ground. The land striaght under the bomb is called the hypocenter.

Fat Man
Richard Feyman and Hans Bethe said 16kg(35.2 lb)of plutonium was needed, but changed to10kg(22lb) if the plutonium was surrounded by uranium-238. The bomb that was designed was a Beryllium/Polonium mixture of radioactive elements that released neutrons placed in the center of the sphere. The sphere is made up of equal spaced and shaped plutonium sections; it looked like a soccer ball. The bomb worked like this. The sphere imploded making the plutonium to fuse together which reached supercritical mass and starts a chain reaction. The implosion is made by a conventional explosion. It is also an altimeter bomb.

Safety Features
Both bombs had lead shields, fuses, and neutron deflectors. The Lead shield protect people and the workings of the bomb from the radioactivity of the uranium and plutonium. Without the lead shield the electronic devices could be shortcircuitted and people poisoned by the radioactivity and die. The fuses were used to prevent the bomb from going off early. The neutron deflector was made up of uranium 238 had two purposes. In Little Boy the deflector deflected neutrons and in Fat Man it helped the plutonium from losing neutrons and deflected neutrons. There were many questions about the plutonium bomb.

The plutonium bomb was tested. They were very unsure of what would happen. Bainbridge selected a piece of land near Alamogordo, NM. Its the valley between the Rio Grande River and the Sierra Oscura Mountains called Jornada del Muerto. Oppenheimer chose the code name for this test bombing Trinity. Many events caused the people to wonder if they should go on working with this project. The first event was death of President Roosevelt and President Truman took office and learned of the project. The next event was the surrender of Germany. But they decided to keep working on the project.

General Groves approved the test bomb so that President Truman could attend the Potsdam meeting with Stalin and Churchill knowing the results. No one knew what the nuclear fallout would be on this test bombing. So they tested the fallout with instruments using 100 tons of TNT. They were prepared for almost anything that could go wrong. General Groves worried about the valuable plutonium if the bomb was a dud because plutonium was very valuable and scarce. So the test had to be perfect. Thunderstorms on the night of the test on July 16, 1945 postponed the test until 4 am the next morning. They looked at the bomb from 10,000 yards north of the site. People wore welder glasses and suntan lotion for protection from the bomb. Over one hundred thousand photos were taken of the explosion. The explosion was much more powerful than they expected. It equaled 20,000 tons of TNT. In a half a mile radius of the explosion was called the vaporation point. Temperatures got up to 3,000-4,000 degrees. In a one mile radius was the total destruction zone;1.75 mile radius the sever blast zone; 2.5 mile radius the severe damage zone, and the last is a 3 miles radius called severe wind and fire damage area.

How this effects our world today
Today in our world there are many countries trying to threaten people with these mass destruction bombs. They are smaller, better, and can blow up more area than in 1945. There are many people frightened that some enemy might bomb them. Between 1945 and 1990 , the US was threatened by nuclear bombs from the USSR which resulted in the Cold War. Since the Cold War has ended, we dont need as many bombs. We burn them to get rid of them and when we burn them they give off harmful gases which can kill people. If we stop making these bombs then we dont have to worry so much about that and we can live in peaceful and a happy world.

Berger, Melvin, Our Atomic World
New York,London,Tornton,Sydney
Franklin Watts, 1989
Bracchini, Miguel A.

“The Manhattan Project”
The Manhattan Project
April 30, !997 5pg.

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