-J.Robert Oppenheimer
The atomic bomb has been long feared and awed. From the day they made their debut in Hiroshima and Nagasaki, the world has trembled in their shoes at the thought of a nuclear war. Being one of the world's biggest breakthroughs in science, we have unleashed a monster upon ourselves. As Americans, we tremble in our own houses. Us, the very mad scientists who created the Frankenstein for the world to exploit.
A nuclear weapon is a device that gets its destructive power from the transformation of matter in atoms into energy. There are two types of nuclear weapons: fission weapons and fusion weapons. (World Book Encyclopedia, 596) Fission weapons, also known as atomic weapons, are those weapons in which a nuclear reaction splits an atomic nucleus into fragments- usually two fragments of comparable mass. This fission creates the evolution of approximately 100 million to several hundred million volts of energy. In an atomic bomb, this energy is expelled violently to create the blast and destructive power of the bomb. Fusion weapons, also known as hydrogen weapons, create their energy in the fusing of hydrogen atoms to make a helium nuclei. (Nuclear Fission, 1)
The atom bomb is generally compromised of two different types of metals. Uranium 235 or Plutonium 239. These metals are used in the making of atom bombs because their atoms are the largest of any element. Because of their size, the atoms can be easily split- the unusually large size makes the atoms very hard to hold together. Uranium 235 also has more neutrons than protons, which is a benificial factor in the metal's capacity to detonate a bomb. Uranium 238 is generally used as a shield in constructing bombs as a neutron reflector. Uranium 238, being neutron heavy, reflects neutrons instead of absorbing them like U-235. Uranium 238, while not essential to the process of making atomic bombs, is the element used for the developing of Plutonium 239. (WBE, 596)
The theory behind the sucess of atom bombs is the chain reaction. The bulky atoms of Uranium 235 will disintegrate into lead after a long period of time. That this process can be accelerated is the basis for the atom bomb. The atoms are forcibly split by neutrons forcing their way into the nucleus. The force of one neutron is enough to split a U-235 atom and force a chain reaction. When a U-235 atom splits it gives off heat and the most deadly form of radiation called gamma radiation. When the atom splits it will also emit two or three extra neutrons; these neutrons will split other atoms which will emit more neutrons and act. This reaction will take place within a millisecond and cause a fission explosion. (atomic elph, 2)
There has to be a certain amount of mass to sustain a self-supporting chain reaction. This amount of mass is called a supercritical mass. (atomic elph, 2) A supercritical amount of mass is essential to the making of the bomb. For Uranium, this amount of mass is 110 pounds. Of course, this figure is for pure Uranium, and because pure Uranium is unavailable, the amount is in reality more than a 110 pounds.
There are two basic types of bomb structures for the atom bomb. Both were used on Japan in World War II. The first type of bomb is the "gun-type" -used on Hiroshima, and the second type of bomb is the "implosion method" -used on Nagasaki. The gun-type bomb contains two pieces of semi-critical metal that when combined will start a chain reaction. The bomb is sealed on both ends and is shaped like the barrel of a gun. An explosion is triggered and the two metals are forced together to start the chain reaction. This type of explosion is less powerful than the implosion method, but is simpler in design. (WBE, 597)
The "implosion method" is a much more technical bomb in its design. There is a ball of supercritical metal in the center made so by compressing it together tightly. The metal is then surrounded in a circle of high explosives. All of the explosives are wired to go off simultaneously and cause a compression of the metal, which sets itself into a self-sustaining chain reaction. The simultaneous explosion is the most complex part of this type of bomb design. It is essential that all of the explosives go off at once or the bomb will not be as effective. The "implosion" bomb is a very powerful bomb, but not much more than the "gun-type" design. (WBE, 597)
An explosion of a nuclear bomb can create a wide range of blast yields. Some older bombs had explosions of about 20 megatons, or 1,540 times the power of the Hiroshima bomb. Today however, the bombs are generally no more than 1 megaton, or less than one million short tons of TNT. The effects of the explosion of nuclear bombs depend on many factors: the weather, terrain, and point of explosion in relation to the earth's surface. There are three basic things that these blasts produce: the blast wave, the thermal radiation, and initial nuclear radiation. A fourth affect, which is delayed, is the residual radiation. (WBE, 597)
The Blast Wave is created from a cloud of high temperature gas and dust under extremely high pressure. This cloud is formed only a split second after the bomb explodes and can travel very fast. From ground zero, the point directly below the explosion of the bomb, the blast wave causes the most destruction of any of the effects of the bomb. As the blast wave moves forward it creates overpressure, the atmospheric pressure above the normal pressure level. The overpressure is what destroys most buildings in an explosion. The overpressure and blast wave are also responsible for the deaths of most all of the people with in about three miles of the blast, and injuries of those within six miles. The blast wave is also accompanied by high winds, which can reach up to 400 miles an hour as far as two miles from ground zero. (WEB, 598)
Thermal Radiation, consisting of ultraviolet, visible, and infared readiation, is what causes severe skin burns called "flash burns." The ultraviolet radiation is quickly absorbed by particles in the air, and therefore, is contained before it does any real harm. The visible and infared radiation can cause eye injuries and severe "flash burns." In Nagasaki and Hiroshima "flash burns" were the cause of twenty to thirty percent of the deaths resulting from the bombings. Thermal radiation is also responsible for the starting of many fires that destroyed much of the remainders of the cities of Nagasaki and Hiroshima. Thermal radiation is hot enough that it can ignite old newspapers and dry leaves. Protection from thermal radiation can be obtained from walls, buildings, trees, light colored clothing, and other landscaping features. Thermal radiation only lasts about ten seconds, but can cause second degree burns and blistering as far away as eleven miles from ground zero. Being that it only lasts about ten seconds, the thermal radiation would only char objects like thick pieces of wood, plastic, and heavy fabrics- it would not burn them up completely. (WBE, 599)
Initial nuclear radiation is deadly given in large doses. The initial radiation, which is emitted within a minute after the intitial explosion, dosen't extend very far away from ground zero, and diminishes rapidly in strength the farther away from ground zero you are. Initial nuclear radiation is composed of neutrons and gamma rays. The neutrons and some gamma rays are emitted from the bomb almost simultaneously. The rest of the gamma rays are given off from the mushroom cloud created by the explosion. The nuclear radiation emitted from the explosion can cause swelling and destruction of human cells. The radiation can also deprive the body of normal cell reproduction, for this reason nuclear radiation can cause death. (WBE, 599)
Residual nuclear radiation is given off after later than a minute after the explosion, and has long-lasting effects on living plant and animal life in an enlarged area of the explosion. The residual radiation is created from the fission of gamma rays and beta particles (electrons). The residual radiation is made up mainly of neutrons that strike other particles which turns them into radioactive particles. As these radioactive particles fall back to earth they are known as fallout. Early fallout consists of heavier particles that reach the ground during the first twenty-four hours and can kill or severely damage living things. Delayed fallout can reach the ground after twenty-four hours and can continue for as long as years later. Delayed fallout consists of light small particles that fall in small amounts, and can cause long-term radiation damage to living things. (WBE, 599)
The atom bomb is a very deadly and threatening form of a mass destruction device. Not only will they kill and injure living things when they explode, but atom bombs can leave lasting scars and silent death in their wake. Because of its extreme power and effects, the world leaders have banded together to attempt to keep nuclear warfare only an ever-present haunting thought. The world knows what it can do- and there are those who would want to use it.
Nuclear Fission/Nuclear Fusion. Pg. 1-2, atomic elph. Obtained Feb4, 1999:http://energy.ca.gov/education/story/story-html/chapter07.html
Nuclear Weapons, World Book Encyclopedia, Vol. 14, N-O, Pg. 596-599, 1995, World Book Inc: London, Chicago, Sydney, Toronto.
