Natural Background (cosmic rays, earth minerals) 81% Medicine and Diagnostics 15% Consumer Products (televisions sets, smoke detectors) 4% Origins of radiation exposure
Human Exposure to Radiation
Uses of Nuclear Radiation/Energy Radioactive Dating Medicine –Chemotherapy –Power pacemakers –Diagnostic tracers Agriculture –Irradiate food –Pesticide –Fertilizer evaluation Energy –Fission –Fusion
22,920 years ago Carbon-14 dating
17,190 years ago
11,460 years ago
5730 years ago
Radioisotopes in Medicine Radioisotopes like Tc-99 can be used to detect bone cancer. The Tc-99 accumulates in areas of abnormal bone metabolism and then detection of the nuclear radiation (gamma rays) show the location of the cancer.
Radioisotopes in Agriculture -Radioactive tracers used to determine the effectiveness of fertilizers. - Cobalt-60 produces gamma rays that are used to irradiate food.
Fission Nuclear fission occurs when scientists bombard a large isotope with a neutron. This collision causes the larger isotope to break apart into two or more elements. These reactions release a lot of energy. You can calculate the amount of energy produced during a nuclear reaction using an equation developed by Einstein: E=mc 2
Chain Reaction Figure
Nuclear Power Plants If the neutrons can be controlled, then the energy can be released in a controlled way. Nuclear power plants produce heat through controlled nuclear fission chain reactions. The fissionable isotope is contained in fuel rods in the reactor core. All the fuel rods together comprise the critical mass. Control rods, commonly made of boron and cadmium, are in the core, and they act like neutron sponges to control the rate of radioactive decay.
Nuclear Reactors The reaction is kept in check by the use of control rods. These block the paths of some neutrons, keeping the system from reaching a dangerous supercritical mass.
Nuclear Power Plants (cont) In the U.S., there are approximately 100 nuclear reactors, producing a little more than 20% of the countrys electricity. Advantages –No fossil fuels are burned. –No combustion products (CO 2, SO 2, etc) to pollute the air and water. Disadvantages –Cost - expensive to build and operate. –Limited supply of fissionable Uranium-235. –Accidents (Three Mile Island & Chernobyl) –Disposal of nuclear wastes
Nuclear Reactors In nuclear reactors the heat generated by the reaction is used to produce steam that turns a turbine connected to a generator.
What is Nuclear Fusion? Nuclear Fusion is the energy-producing process taking place in the core of the Sun and stars The core temperature of the Sun is about 15 million °C. At these temperatures hydrogen nuclei fuse to give Helium and Energy. The energy sustains life on Earth via sunlight
Energy from Fusion H 2 1 + He 4 2 + n 1 0 H 3 1 + Energy
Nuclear Fusion Fusion would be a superior method of generating power. –The good news is that the products of the reaction are not radioactive. –The bad news is that in order to achieve fusion, the material must be in the plasma state at several million kelvins. –Tokamak apparati like the one shown at the right show promise for carrying out these reactions. –They use magnetic fields to heat the material.