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Nuclear Reactions.

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Presentation on theme: "Nuclear Reactions."— Presentation transcript:

1 Nuclear Reactions

2 n Energy Nuclear Fission E = mc2
Nuclear Fission is when a large nucleus splits into two smaller nuclei, releasing neutrons and energy Heavier nuclei tend to be more unstable n 1 Energy In this process, a small amount of mass changes to energy according to the equation: E = mc2 Matter and energy are interchanged in a nuclear reaction (the mass of the products is slightly less than the mass of the reactant) All nuclear power generation is accomplished through nuclear fission.

3 Nuclear reactions vs Chemical reactions
mass is conserved, and energy changes are relatively small. There are no changes to the nuclei in chemical reactions. Nuclear reactions: the actual nucleus of atoms changes. Protons, neutrons, electrons, and/or gamma rays can be lost or gained. Small changes of mass = huge changes in energy The nuclear fission of 1 g of uranium-235 produces the same amount of energy as burning 2 tonnes of coal!

4 Induced Nuclear Reactions
In addition to natural radioactive decay, scientists can also create nuclear reactions by smashing nuclei with alpha, beta and gamma radiation or other subatomic particles.

5 Nuclear Fission of U-235 It is much easier to crash a neutral neutron than a positive proton into a nucleus to release energy. Most nuclear fission reactors and weapons use this principle. A neutron crashes into an atom of stable U-235 to create unstable U-236, which then undergoes radioactive decay. After several steps, atoms of krypton and barium are formed, along with the release of three neutrons and huge quantities of energy.

6 Chain Reactions Once the nuclear fission reaction has started, it can keep going. The neutrons released trigger more reactions on other U-235 atoms. This chain reaction can quickly get out of control. materials that absorb neutrons help to control the chain reaction. eg: Cadmium Rods Nuclear bombs are uncontrolled reactions Ping Pong Ball chain reaction:

7 CANDU Reactors Hazardous wastes CANadian Deuterium Uranium reactor
safe and easy to shut down in an emergency. produces a lot of heat to generate steam to drive a turbine that produces electricity. Hazardous wastes Some waste products, like fuel rods, can be re-used. Some products are very radioactive, however, and must be stored away from living things. Most of this waste is buried underground or stored in concrete. It will take 20 half-lives (thousands of years) before the material is safe.

8 Nuclear Fusion Nuclear Fusion is when two small nuclei join together into one larger nucleus, releasing large amounts of energy Energy Nuclear Fusion produces much more energy for a given mass of fuel than Nuclear Fission. e.g.: The Sun and other stars Hydrogen Bomb the basic source of energy in the universe (how all elements are formed)

9 Nuclear Fusion continued
As an energy source it is clean and plentiful, however it is very hard to control as it needs very high temperatures (100,000,000°C) Scientists cannot yet find a safe, manageable method to harness the energy of nuclear fusion. So-called “cold fusion” would occur at temperatures and pressures that could be controlled.

10 Practice Workbook Pages


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