Upper Iowa University
"On July 16, 1945, the United States detonated the fission (atomic) bomb; it was the first nuclear reaction to ever be tested" (pbs.org). In the beginning, an intense flash of light flooded the valley as observers witnessed from their bunkers 10 kilometers away. Within two seconds, a massive fireball expanded 600 meters throughout the sky and boiled 12 kilometers high into the shape of a mushroom. Nearly a minute later, hot air blasted against the observation bunkers with a long, deafening roar. "The explosion was just as predicted and had the force equivalent to the explosive output of 20,000 tons of TNT" (Educator’s Assoc, Inc). Since the discovery of nuclear power it has been responsible for an alternative energy source, radioactive contamination, medical advances, and defensive warfare. A nuclear bomb is an explosive device that derives its destructive force from nuclear chain reactions. There are two basic types: one sustains only nuclear fission reactions (atomic bomb) and the other uses fission to begin nuclear fusion reactions (hydrogen bomb). Although, fusion bombs can produce a much larger yield than the limited explosive force of a fission bomb, they're both created from the Uranium atom. Uranium-238 is the most common isotope (weight) of Uranium found in nature. Once obtained, the mass is enriched by increasing its proportion of Uranium-235 isotopes through a process called isotope separation. Enriched Uranium is a fissile material and is therefore capable of sustaining a nuclear chain reaction. When a 235U atom is induced by a neutron it becomes an excited 236U atom and splits into two smaller parts, emitting several neutrons. If the emitted neutrons induce another 235U, it is referred to as a nuclear chain reaction. The mass is then defined by the growth of this reaction known as criticality.
A subcritical mass has a decreasing (exponentially) chain reaction; the neutrons emitted from each splitting 236U atom must induce less than one 235U atom. The fission (atomic) bomb is two subcritical masses assembled into a supercritical mass--the amount of fissile material needed to have an increasing (exponentially) chain reaction; the neutrons emitted from each splitting 236U atom must induce more than one 235U atom. Assembling is done either by shooting one piece of subcritical material into another (the "gun" method) or by compressing a sphere of material using traditional explosives (the "implosion" method).
The "gun" and "implosion" methods are both used to create uncontrolled nuclear reactions (nuclear bombs). A controlled nuclear reaction is a fissile mass that’s fueled at a controlled rate to sustain a constant sub-criticality. Nuclear power plants use this process to boil water and create electricity. The Navy powers some of their ships and submarines by placing nuclear reactors onboard that act similar to power plants. This method is the most efficient way to generate electricity. "Uranium is as common as tin in nature and is currently being used to generate power for 16% of the world. A single kilogram (2.2 pounds) can produce as much energy as 200 barrels (8,400 gallons or 31.8 m3) of oil or 20,000 kg (44,092 pounds) of coal." (www.wisegeek.org) Although, nuclear waste does not pollute the earth like our natural resources, it is however, radioactive and can contaminate nearby matter. Fission products (waste)--the remains of the split 236U atoms--are either highly radioactive (but short-lived) or moderately radioactive (but long-lived), and as such are a serious form of radioactive contamination if not fully contained. Half-life is the time required for a given amount of radioactive material to be reduced to one-half of its original activity. The half-life values of fission products vary widely and decay at exponential rates unique to each kind. "In example, the half-life of 235U is 700 million years