C3: Nuclear Fusion & Fission
The source of energy for the sun is the fusion of hydrogen nuclei into helium. This process releases much more energy than the fission of U-235 or Pu-239, the fuels that are used in nuclear reactors. This process releases a tremendous amount of heat and almost no nuclear waste. However, it takes a vast amount of energy to initiate the reaction. Hydrogen bombs use a nuclear fission reaction (a small atomic bomb) to provide this energy. The heat released comes from nuclear fusion, but it has associated nuclear fallout from the fission reaction.
There is an abundance of fuel for nuclear fusion and the lack of waste makes it an attractive prospect for energy generation. However, there are technological issues involved. Fusion takes place at high temperatures and there is no material that can contain it. In the sun, hydrogen converts to helium, but there is a difference in the mass of a helium nucleus and the sum of the masses of 2 protons and 2 neutrons. This is known as mass defect. The missing mass is converted directly into energy, which can be predicted using E = mc2. This is energy calculated per atom, and the unit is the electron volt (eV).
There is an abundance of fuel for nuclear fusion and the lack of waste makes it an attractive prospect for energy generation. However, there are technological issues involved. Fusion takes place at high temperatures and there is no material that can contain it. In the sun, hydrogen converts to helium, but there is a difference in the mass of a helium nucleus and the sum of the masses of 2 protons and 2 neutrons. This is known as mass defect. The missing mass is converted directly into energy, which can be predicted using E = mc2. This is energy calculated per atom, and the unit is the electron volt (eV).
Many different chain reaction mechanisms can occur to produce the helium nucleus and most of them occur in the sun and stars. On Earth, the process incorporates the fusion of deuterium and tritium. Deuterium is a hydrogen isotope with 1 proton and 1 neutron. Tritium is a hydrogen isotope with two neutrons. The reaction is shown on page 668 in your text. There is a difference in the binding energy per nucleon between helium and the two hydrogen isotopes. This means there is a mass defect and that mass is converted directly into energy.
Fusion of lighter elements into heavier ones increases the binding energy and the mass defect is converted into energy. The heavier transuranium elements (Z=92+) can undergo fission to form lighter nuclei. The binding energy of the two lighter elements is greater than the binding energy of a uranium isotope and therefore, the mass defect is converted into energy. Controlled nuclear fission is the process that powers nuclear plants nowadays.
Read about critical mass on page 669.
Fusion of lighter elements into heavier ones increases the binding energy and the mass defect is converted into energy. The heavier transuranium elements (Z=92+) can undergo fission to form lighter nuclei. The binding energy of the two lighter elements is greater than the binding energy of a uranium isotope and therefore, the mass defect is converted into energy. Controlled nuclear fission is the process that powers nuclear plants nowadays.
Read about critical mass on page 669.
Fission and/or fusion involve the capture or emission of subatomic particles. The conversion of one element into another is called transmutation. Familiarize yourself with the above chart from the Pearson textbook.
Some heavier atoms are radioactive, which means they undergo spontaneous decay to produce daughter products, releasing alpha, beta, and/or gamma radiation in the process. Radioactive decay is a first-order reaction, which means that they have a constant half-life. The half-life refers to the time it takes for one half of the number of atoms in a sample to decay. There is an equation for half-life in your text on page 671.
Some heavier atoms are radioactive, which means they undergo spontaneous decay to produce daughter products, releasing alpha, beta, and/or gamma radiation in the process. Radioactive decay is a first-order reaction, which means that they have a constant half-life. The half-life refers to the time it takes for one half of the number of atoms in a sample to decay. There is an equation for half-life in your text on page 671.
The following material is for Advanced Higher Level.
Uranium-235 is the only natural occurring uranium that is fissionable. However, there is only 0.72% of naturally occurring U-235. In order to obtain fissile material, U-235 must be enriched so that the percentage of U-235 is large enough. To do this, the U-235 isotope must be separated from the U-238 isotope. Pages 704-705 goes into detail how this is done.
Graham's Law of Effusion allows you to calculate the relative rates of diffusion of the uranium hexafluoride.
Uranium-235 is the only natural occurring uranium that is fissionable. However, there is only 0.72% of naturally occurring U-235. In order to obtain fissile material, U-235 must be enriched so that the percentage of U-235 is large enough. To do this, the U-235 isotope must be separated from the U-238 isotope. Pages 704-705 goes into detail how this is done.
Graham's Law of Effusion allows you to calculate the relative rates of diffusion of the uranium hexafluoride.
Radioactive decay is a first order process. The time it takes for half a sample to decay is called half-life. The decay constant is related to the half-life (see page 706). The level of radioactive decay decreases in proportion to the quantity of material remaining.
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