Nuclear+Fission+-+its+History+and+Science

__What they Knew Before WWII__
In 1919, physicist Ernest Rutherford discovered protons, positively charged particles in the nucleus of the atom, and electrons, negatively charged particles orbiting the atom. During this time, physicists couldn't explain why several elements weighed differently. This remained a mystery until 1932, when James Chadwick, one of Rutherford's colleagues, discovered the neutron, an atomic particle (with no charge) in an atom’s nucleus. While the number of protons equals the number of electrons for any given element, there can be different numbers of neutrons. This explains why elements can weigh different amounts, even though they are essentially the same element. The different weights of atoms are known as isotopes. Before the invention of nuclear power they did not use the knowledge about atoms for anything. It was only used as a reference; it was the center of modern science. Scientists started to work with their knowledge, performing several experiments, which is how they came to the discovery of nuclear fission. After the discovery, they used nuclear fission mainly for making atomic bombs; it was not until later on they started to build nuclear power plants.



__Background and Discovery of the Nuclear Bomb__
Around 1933, scientists began using particle accelerators to attack groups of atoms in the hopes of splitting atoms in order to create energy. At first, they were not very successful. The particle accelerators shot out protons and alpha particles, both positively charged; these particles were easily repelled by the positively charged nuclei. Atomic power was thought to be impossible. Enrico Fermi changed this theory when he started to use neutrons for bombardment. Since neutrons have no charge, they can hit an atom's nucleus without being repelled. He successfully bombarded several elements and created new, radioactive atoms in the process. He discovered nuclear fission without knowing it. In 1938, two German scientists, Otto Hahn and Fritz Strassmann, were the first to officially acknowledge this process when they successfully split uranium atoms into two or more parts.

__WWII: The Manhattan Project__
The Manhattan Project was a code name for U.S. government’s secret project before WWII, used for development of the atomic bombs. The first successful nuclear bomb was controlled by Enrico Fermi; it was called the Chicago Pile 1 or CP-l. This bomb was later exploded at Los Alamos in July, 1945. On August, 1945, two nuclear bombs were used on Japan, a decision made in order to end the war. This action instantly killed 100,000 people, showing the atomic bomb’s capability of mass destruction.



**The Science Behind Nuclear Fission**


__Nuclear Fission__ Science takes a major part in creating these atomic bombs. Nuclear fission is a nuclear reaction in which a heavy nucleus (such as uranium) splits into two lighter nuclei (and possible some other radioactive particles as well).



The two mainly used elements used for nuclear fission are: uranium and plutonium. Uranium is more often used than plutonium due to its availability. Certain isotopes of these elements must be used in order to be successful in a nuclear chain reaction, which is necessary to make a nuclear bomb. Those isotopes are: uranium-235 and plutonium-239.

__Plutonium__ •Isotope used: plutonium-239 •not naturally occurring, created from saturation of U-238 •less fissionable •fast neutron reactors •takes 10 kg of nearly pure plutonium to create chain reaction (and make a bomb)

__ Uranium __ •primary element used in nuclear reactors •heavy, silvery-white metallic element •radioactive and toxic, easily oxidized •14 known isotopes, most abundant: U-238 is the most abundant •occurs in several minerals, extracted from uraninite and carnotite •Atomic number 92, atomic weight 238.03, melting point 1,132°C,boiling point 3,818°C • 50 kg of Uranium needed to create chain reaction (and make a bomb)

__How to Split a Uranium Atom__

 * 1) A stray neutron is absorbed into atom of isotope uranium-235, creating an unstable U-236, causing it to fission (one neutron splitting an atom)
 * 2) One additional neutron is released after one splits the atoms (causing a chain reaction)
 * 3) The 2 neutrons released (neutron that splits the atom and additional neutron released) can affect 2 more atoms. The more uranium present, the bigger chain reaction.
 * 4) Each atom that is affected release one additional neutron, so now there are 4 stray neutrons.
 * 5) This process repeats itself over and over.

__Where does this energy come from?__
__[|Click to view video.]__

According to E = mc 2, energy has a direct relationship with mass, so as a substance’s energy increases, it’s mass also increases. Mass can be turned into energy, and energy can be turned into matter.

A chunk of uranium is very unstable, and atoms of uranium are constantly falling apart. The pieces, which are now new elements because of fewer protons, are less massive than the original uranium atom. The extra mass disappears as energy according to E=mc2. Also, when the uranium atom is split, some of the energy that held it together is released as heat radiation, causing mass to decrease during the reaction. All in all, energy during nuclear fission is released as: kinetic energy, fragments, gamma rays, and a lot of heat. How is Nuclear Fission Used Today?

__Uses of Nuclear Fission__
Nuclear power, nuclear imaging, and nuclear weapons are the three main uses of nuclear fission today.

__1. Nuclear Power__ Nuclear power is used mainly for electricity, however it is also used for power for submarines and other large vessels. Containing about one-third of the world’s nuclear energy, the U.S. is the widest known user of nuclear energy.



__2. Nuclear Imaging__ Nuclear imaging is greatly used by doctors, providing a safe and cheap way to get information of the structure and function of one’s body. Without this, more expensive ways, such as surgery, would be required to find out this information. Nuclear imaging is widely used in the medical field, including pediatrics, cardiology, and psychiatry.



__3. The Nuclear Bomb__ When one hears the word “nuclear”, the idea of a nuclear bomb is immediately thought of. Today, eight countries are known to have nuclear weapons: USA, Russia, UK, France, China, India, Pakistan, and North Korea. Each of these countries have the power to create a mass destruction, having the ability to destroy very large areas.

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[|__http://library.thinkquest.org/17940/texts/timeline/manhattan.html__]