Fusion When 2 light nuc particles combine FUSE

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 – 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]

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

• 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.

41 H 2 22 He 4 + 47. 7 Me. V - The energy yield per atomic mass unit [AMU] of D fuel is ~6 Me. V - The same of U 235 burned is only 190/235 = 0. 86 Me. V

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.

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.

• 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]k. T

E = [3/2]k. T Even if E is as low as 10 Ke. V, the temp is – T = [2/3][(104 e. V)(1. 6 x 10 -19 J/e. V)]/[1. 38 x 10 -23 J/0 K] = 77, 000 0 K.

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

• 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.

• 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.

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

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