Manhattanproject Essay, Research Paper

The Manhattan Project

The Manhattan Project was the code name of the U.S. s attempt to construct an atomic bomb during

World War II. It was named after the Manhattan Engineer District of the U.S. Army Corps of Engineers,

because a lot of it s earlier research was done in New York City. An atomic bomb is a weapon that uses

the energy from a nuclear reaction called Fission for its destruction.

The idea that mass could be changed into energy was predicted by Albert Einstein in the earlier

part of the 1900 s. John D. Cockcroft and Ernest Walton confirmed this by experiments in 1932. Then in

1938, nuclear fission was discovered by German scientists, and it was feared by many of the U.S.

scientists, that Hitler would try to build a fission bomb. Three Hungarian-born physicists, Leo Szilard,

Eugene Wigner, and Edward Teller asked Albert Einstein to send a letter to Franklin Roosevelt.

Compelled by the letter in late 1939, Roosevelt ordered an effort to obtain an atomic weapon before

Germany.

At first, this program was led by Vannevar Bush, head of the National Defense Research committee

and the Office of Scientific Research and Development. Then it came under control of Leslie Groves of

the Army Corps of Engineers. Groves quickly bought a site in Oak Ridge, Tennessee, as a place for

processing the Uranium-235 from the more common Uranium-238. Uranium-235 is used because it is

fissionable, it releases many neutrons, and does not capture many. However, 99.3% of uranium in nature

is the U-238 isotope, and only .7% is the lighter, more fissionable isotope U-235. Next, he gathered

and combined research from many East Coast universities under direction of Arthur Compton, at the

University of Chicago. He appointed theoretical physicist, J. Robert Oppenheimer as the director of the

weapons laboratory, which was built on an isolated mesa located at Los Alamos, New Mexico.

After much work, a porous barrier that could separate the isotopes of uranium was made, and it

was installed in the Oak ridge gaseous diffusion plant. In 1945, uranium-235, pure enough for use in a

bomb was produce and sent to Los Alamos, where it was made into a gun-type weapon. One small piece of

Uranium-235, which was not big enough to hold a chain reaction itself, was fired at another small

piece. This was done by means of a explosive charge, inside a cylinder shaped tube, which formed a

supercritical mass that exploded instantly. They were so sure that this would work, that they did not

even test it. It s first use was made in military action over Hiroshima, Japan, on August 6, 1945. The

bomb uses a device called an altimeter to measure how far it is from the ground. It sends out radio

frequencies which are bounced back to it. Microchips in the bomb determine how far it still has to fall,

and when to detonate. The bombs also have fuses in the front which arm !

the bomb. They are not inserted until the bomb is ready to be launched.

Before this bomb was developed, another kind was proposed. Uranium-238 could capture a neutron

and become Uranium-239. All uranium has 92 protons. U-238 has 146 neutrons, and the added neutron raised

the mass to 239. But U-239 is very unstable and it decays to neptunium-239 (93 protons, 146 neutrons),

and plutonium-239 (94 protons and 145 neutrons). Plutonium-239 was fissionable, and could be separated

from uranium by chemical techniques ( much easier than physical process of separating the different

isotopes of 235 and 238 of the same element).

The first successful reactor was made at the University of Chicago under the Italian physicist

Enrico Fermi. On December 2, 1942 it made a controlled chain reaction. Five large reactors were built at

Hanford, Washington, where U-238 was blasted with neutrons to make plutonium. It was then sent to Los

Alamos. Since another isotope of plutonium was also fissionable, there was a fear that a chain reaction

could start to soon when the pieces of plutonium where brought together, making it blow apart before it

was consumed. To overthrow this problem, the plutonium would have to be brought together much faster

than the methods use for the uranium bomb.

A technique called implosion was used to make the plutonium bomb work. A noncritical shell of

plutonium was surrounded by chemical high-explosives. When detonated, it squeezed the plutonium into a

very dense supercritical mass, that in chain reaction lasted long enough for a large and destructive

explosion. This type of bomb was tested 60 miles northwest of Alamogordo on what is now the White Sands

Missile Range on July 16, 1945. This bomb was used on Nagasaki, Japan, on August 9, 1945.

When the uranium based atomic bomb, (nick-named Little Boy), was dropped (by the Enola Gay ,

flown by Colonel Paul Tibbets), on Hiroshima, Japan, on August 6, 1945, at 8:15 a.m., five square miles

of the city were completely destroyed in seconds, and most buildings in the city were destroyed or

damaged. The bomb weighed 9,700 pounds. It detonated 1900 feet above the city, and exploded with a force

of 20,000 tons of TNT. About 75,000 people(including 20 American airmen held as POWs)were killed.

Another 70,000 were injured. By the end of the year the death number had risen to 140,000 from radiation

sickness. Five years later it had reached 200,000.

The Peace Memorial park was made in memory of the bombing. It has a monument and a marble tomb,

in memory of the bomb s victims, and the remains of the Industrial Exhibition Hall. The Peace Memorial

Museum in the park has relics of the attack. Nearby is the Atomic Bomb Casualty Commission, which

studies the effects of radiation. Clinics have been set up to fight radiation illness and other effects

of the bomb.

The plutonium-based atomic bomb (nicked-named Fat Man) was dropped (by Bock s Car , flown by

Charles Sweeney) on Nagasaki, Japan on August 9, 1945, at 11:01 a.m. The original target was Kokura

Arsenal on Kyushu Island, but poor weather conditions and antiaircraft artillery forced the pilot to

change to his secondary target, Nagasaki. Fat Man weighed 10,000 pounds. It exploded 1650 feet above

the city, and with a force of 21,000 tons of TNT. Three square miles of the city were destroyed, less

than Hiroshima because of the hills around the city. The U.S. bomber was aiming for the shipyards, and

though it missed the target, it devastated the city and killed about 40,000 people, and injured 60,000

more. By January 1946, 70,000 people died from radiation. The total eventually reached 140,000, with a

death rate similar to Hiroshima s. A Peace Park was set up in memory of the victims.

There is still controversy today on reasons for destroying Hiroshima and Nagasaki, Japan. Those

in favor of using the bomb claim that invasion of the Japanese islands would have caused 1,000,000

military deaths and unknown civilian deaths. Those who opposed dropping the bombs , including many

scientists who built them, argue that the U.S. s use of the bomb was the first act of the cold war.

Even after the bombs had destroyed Hiroshima and Nagasaki, the Japanese leadership was struggling

to come to a decision on whether or not they should surrender. They had military extremists pleading for

a policy of resistance to the end. Word of their surrender finally reached Washington on August 10th.

They would accept the terms of surrender, providing the emperor would retain his position. The U.S.

acknowledged the emperor by stating his authority after the surrender would be exercised under the

authority of the Supreme Commander of Allied Powers. (Gosling 54) The U.S. answered on August 11, with

Russia, China, and Britain in agreement. Japan surrendered on August 14, 1945, ending the war that had

started when the Japanese had attacked Pearl Harbor on December 7, 1941. Formal papers were signed

aboard the U.S.S. Missouri on September 2.

After 1945, the U.S. built thousands of atomic bombs, and different types of smaller of fission

weapons. A much more powerful bomb, the Hydrogen Bomb, became the leader of the U.S. nuclear arsenal.

In general, the Hydrogen Bomb was like an atomic bomb with a Hydrogen fuel. The fuel would fusion

(opposite of fission) from the bomb s fission explosion, which would further strengthen the original

fission, causing a much larger chain reaction. The United States was the only nation that had atomic

weapons in 1945. Then in 1949, the USSR learned how to make them. Great Britain followed in 1952,

France in 1960, the People s Republic of China in 1964, and India (it was claimed that they were for

peaceful purposes only) in 1974. In 1968, the Nuclear Non-Proliferation Treaty which was signed by the

U.S., the USSR, and Britain. It set up precise requirements for any non-nuclear nations that want to

build nuclear energy industries.

However, several other countries are believed to have some nuclear weapons, like Israel and South

Africa. North Korea, Iran , and Pakistan may be on the verge of nuclear discovery. When the Soviet

Union broke up it added to risks of the spreading of nuclear power.