Nuclear Fission And Fusion Essay

Almost twenty years after this process of combination was discovered, a group of German scientists created a process of separation, not a slow disintegration like radioactive decay, but a much more dramatic reaction. In 1938, Otto Hahn and Fritz Strassmann, working with Lise Meitner, bombarded uranium with neutrons, releasing energy and causing the uranium atoms to split into multiple parts, the nuclei themselves breaking down to create new nuclei with fewer protons, which were the nuclei of smaller atoms. Hahn, Strassmann, and Meitner had produced nuclear fission, the reaction soon to be used in powerful nuclear weapons and power plants. Hahn and Strassmann made other contributions to nuclear chemistry (Hahn identifying an isotope of uranium, and several other “radioactive substances,” while Strassmann played a role in the development of rubidium-strontium dating), but

fission, which has had an impact on many lives, seems to have been their most memorable.

Nuclear Processes: Decay
Radioactive decay, the breaking down of a radioactive element over time, can occur in three forms: alpha decay, beta decay, and gamma decay. When a single atom of an element breaks down through alpha decay, it emits alpha particles at random, but with a greater number of decaying atoms, there is a steady rate of decay. The alpha particles which are given off consist of two protons and two neutrons, forming a helium-4 nucleus, as can be seen in the formula for alpha decay. Using uranium as an example:
U-238 --> He + Th-234
A uranium atom decays into a helium nucleus and an atom of thorium.
Beta decay can occur in two forms: β- and β+. In β-, a neutron breaks down into an antineutrino, a proton, and an electron; the proton remains in the atom, while the antineutrino and electron are expelled from it. β+ decay involves the transformation of a proton into a positron, a neutron, and a neutrino.
β- decay of a neutron: n --> p + e + v¯
β- decay of thorium into protactinium Th-234 --> β + Pa-234
After alpha or beta decay occurs, an atom has “excess energy,” which it reduces by giving off a gamma ray.
Tc-99m --> γ + Tc-99
Where m indicates the “metastable state,” in which the atom has extra energy.
Decay is measured through half-life, which is defined as “the time after which, on average, half of the original material will have decayed.” Half-life varies by element, some decaying slowly, and others very rapidly.

Nuclear Processes: Fission and Fusion

Fission and fusion are opposing nuclear reactions, both of which release enormous amounts of energy and therefore hold attractive potential as energy sources.

Nuclear fission occurs when a neutron collides with an atom, which causes the atom to break apart, giving off “heat and radiation,” as well as two to three fission products and several neutrons. During the reaction, a small amount of matter is converted into a large amount of energy, per Einstein’s formula E = mc^2, where energy is equal to mass times the speed of light squared, the last being a large number which accounts for the high level of energy from the small mass.

Uranium-235 can undergo this transformation during fission:

U-235 + n --> Ba-142 + Kr-91 + 3n

Here, uranium-235 breaks into barium-142, krypton-91, and three neutrons, when struck by a

neutron.
In fission, the neutrons which are a product of the reaction collide with other atoms, causing them to disintegrate, as well, in a nuclear chain reaction. This chain reaction enables the creation of continuous fission reactions to generate power, either in nuclear reactors in power plants and submarines, where the reactions are restricted, or in nuclear weapons, where the reactions are not restricted, but continue at an ever-increasing rate due to the increase of loose neutrons with every fission. Fission products, too, can be useful for applications such as “power[ing] batteries.” While nuclear fission releases energy by splitting atoms, nuclear fusion releases it by combining, or fusing, small atoms into larger ones—for example, hydrogen atoms that undergo fusion combine to form helium. Atoms must be moving extremely quickly in order to come together, in spite of the repelling of their positively charged nuclei, which means that they must be in an extremely hot environment; and when scientists create fusion on Earth (using certain isotopes of hydrogen), the necessary temperature is 150,000,000 °C. The preferred hydrogen isotopes for fusion on Earth are deuterium (H-2, one neutron) and tritium (H-3, two neutrons), used in this fusion reaction:
H-2 + H-3 --> He + n
Some of the mass from the two original atoms is not used in the formation of the helium and the neutron, and this mass is converted into a great amount of energy, based on E = mc^2.
Currently, nuclear fusion occurs in stars and scientific experimentation, but if certain difficulties can be overcome (i.e. the extraordinarily high temperature required), fusion may be a promising source of energy, without the risk of radioactive accidents that comes with fission. Fusion has also been used in hydrogen bombs, where a fission reaction triggers a fusion reaction, which in turn triggers another fission reaction to produce a force of several tens of megatons of TNT (as opposed to a fission bomb’s force of only tens of kilotons of TNT).

Applications of Nuclear Chemistry
Nuclear chemistry has many applications in our modern world, from medicine to warfare, from agriculture to generating electricity. Some of our uses for radioactive materials are relatively harmless, while others carry significant risks, and we must consider carefully whether those risks are justified by the benefits which we derive from using the materials.
Medical diagnoses and treatments can both be accomplished with the use of nuclear chemistry. Gamma decay is used in imaging procedures such as PET scans, for which radioactive positron-emitters are mixed into “chemical compounds that selectively migrate to specific organs in the body,” where the emitted positrons encounter electrons, and the two types of particles “annihilate each other,” in the process giving off gamma rays, which can be tracked and mapped by computers to create images of the organ. These radioisotope diagnostic procedures, effective for imaging of both soft and hard tissues, are a less invasive alternative to exploratory surgery, and although exposure to radiation may increase a patient’s risk of developing cancer, the level of exposure is no higher for radioisotope imaging than it is for CT scans and x-rays. Nuclear medical treatments, too, have an advantage over surgery because they are painless, requiring no anesthetic. Radionucleide therapies often use beta-decaying isotopes, whose medium penetrating radiation “causes the destruction of… damaged cells” in cancer patients. One such treatment is boron capture therapy, in which boron-10 “concentrates in [a] tumor,” and then, when the patient is “irradiated with neutrons,” the boron breaks down by alpha decay, and the tumor is destroyed by the alpha particles, which being short-range radiation do not harm the “surrounding healthy tissue.”
Agriculture also benefits from nuclear chemistry, which can be used to create new varieties of plants, to help farmers to regulate fertilizer use, and to control pest populations. Exposure to radiation (both neutron and gamma) can cause plant cells to mutate, which creates more options for breeding, leading to hardier, higher-yielding, and pest-resistant crops. The fertilizer use of these crops can then be monitored with radioisotopes, so that farmers know how much fertilizer they need to give their plants, which means less frequent overuse of fertilizers, thus less water and ground pollution. Nuclear radiation even allows for the control of harmful insects, when male flies are sterilized with gamma rays so that they fail to create offspring upon mating. This method has proven successful in several instances—against the Mediterranean fruit fly in Central and South America, and against screwworms in Central and North America. Even though all of these processes use radiation, the Canadian Nuclear Association states that they are not dangerous, either to the environment or to people.
In addition to radiation-treated crops, we also have irradiated food, which undergoes a process that “exposes food to gamma rays from cobalt-60, a radioisotope of cobalt. The gamma rays kill bacteria in the food, lowering consumers’ risk of foodborne illness, as well as foreign insects on imported produce, and they extend foods’ shelf lives, without significantly decreasing their nutrient content. Irradiated foods are safe for consumption as well; the FDA states that “irradiation does not make foods radioactive,” and the Canadian Nuclear Association reports that scientists studying irradiation have deemed these foods safe to eat, based on “data accumulated from about 50 years of research.” However, although the foods themselves may be perfectly harmless, there is some risk of accidents with radioactive materials in factories that irradiate foods, and of radioactive pollution that may escape from the facilities.
Yet another use for nuclear science, as mentioned in the “Fission and Fusion” section, is power generation, via nuclear fission. Nuclear reactors, powered by uranium pellets, use fission chain reactions to produce a steady heat. This heat turns the cooling agent of the reactor (often water) into steam, which powers turbines that generate electricity. The chain reactions are controlled by rods of “nuclear poison,” materials like xenon that absorb some of the neutrons produced by fission, thereby preventing the rate of fission from rising. Because it gives off no greenhouse gases or other air pollutants, nuclear is a “clean” source of energy; however, radioactive fission products are produced which must be transported and stored, as well as radioactive waste, consisting of tools and clothing used in environments with “radioactive dust.” There is also the possibility of a nuclear meltdown, such as the Chernobyl incident, which causes widespread pollution via toxic, potentially cancer-causing radioactive material.
Finally, nuclear science has been applied to weapons, to build atomic bombs (like those dropped on Japan) and hydrogens bombs, which are even more powerful. These weapons use the nuclear fission and fusion reactions of elements such as uranium, plutonium, lithium, and hydrogen. The advantages of nuclear weapons are questionable (some people suggest that because we have these weapons of mass destruction, we are unlikely to use them or even to engage in war), while the advantages of nuclear warfare seem fairly nonexistent, unless one desires to destroy one’s enemy entirely, and perhaps injure one’s own forces. A speaker at the Monterey Institute of International Studies cited a 1970s study which reported that “even [in] an attack where you try to use nuclear weapons surgically, the radiation spreads all across the country,” which would pose potential danger to any of the attacker’s army which might be within that large area. So far, the only problem which nuclear warfare has solved has been the Pacific Theater of WWII—and it solved that problem rather one-sidedly, destroying two Japanese cities.