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Fusion

Fusion. When 2 light nuc particles combine / ‘FUSE’ together – energy is released. Why? Because the product nuclei have less mass than the original particles. How can such fusion be caused? By bombarding particles with charged particles – using an accelerator; or

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Fusion

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  1. Fusion • When 2 light nuc particles combine / ‘FUSE’ together – energy is released. • Why? • Because the product nuclei have less mass than the original particles.

  2. How can such fusion be caused? • By bombarding particles with charged particles – using an accelerator; or • By raising the temperature of a gas to a high enough level for nuc reactions to take place. [thermonuclear reaction  a nuclear fusion reaction occurring at a very high temperature: responsible for the energy produced in the sun, nuclear weapons, and fusion reactor]

  3. Fission  can be controlled • Fusion  so far uncontrolled • Need more research for controlled ‘fusion’ so that more energy can be produced

  4. The most promising reactions make use of the isotope – deuterium • 1 D for every 6700 atoms of Hydrogen. • Plenty of water – so almost inexhaustible amount of D in nature.

  5. 41H2  22He4 + 47.7 MeV • The energy yield per atomic mass unit [AMU] of D fuel is ~6MeV • The same of U235 burned is only 190/235 = 0.86MeV

  6. Thermonuclear reactions in ionic plasma • The most promising medium in which to obtain the high particle energies that are needed for practical fusion is – the plasma • It consists of a completely ionized gas as in an electrical discharge created by the acceleration of electrons. • Equal no. of electrons & deuterons [nuclei of deuterium] r present – making the medium electrically neutral.

  7. How can u increase the temp? • Through the injection of enough energy – into the plasma – its temp can be increased, & • The deuterons reach the speed for fusion to be favorable. The term thermonuclear is applied to reactions induce by high thermal energy.

  8. The temp to which the plasma must be raised r extremely high. • Lets express the avg particle energy in terms of temp, E = [3/2]kT

  9. E = [3/2]kT Even if E is as low as 10 KeV, the temp is – T = [2/3][(104 eV)(1.6 x 10-19 J/eV)]/[1.38 x 10-23 J/0K] = 77,000,000 0K.

  10. Such a temp greatly exceeds the temp of the surface of the sun! • Fusion is the process that powers active stars.

  11. The fusion of two nuclei with lower masses than iron (which, along with nickel, has the largest binding energy per nucleon) generally releases energy, • while the fusion of nuclei heavier than iron absorbs energy.

  12. The opposite is true for the reverse process, nuclear fission. • This means that fusion generally occurs for lighter elements only, and likewise, that fission normally occurs only for heavier elements.

  13. http://reactor.engr.wisc.edu/tour/fission.htm

  14. Next • Particle accelerator

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