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FUSION AND FISSION INTRODUCTION to FUSION AND FISSION

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There are 1200 students in a hall. A student starts talking. If each talking student starts 3 others to talk each second,... … what is the minimum time required for all students to be talking? Warm-up

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Sec. No. of talking students 01 11 + 1 3 = 4 24 + ____ 3 = ____ 3____ + ____ 3 = ____ 4____ + ____ 3 = ____ 5____ + ____ 3 = ____ 6____ + ____ 3 = ____ Warm-up The time required = 6 s How to stop it from being out of control? 416 64 256 1024 4096 Ask teachers responsible for discipline to patrol around the hall.

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Nuclear Reactions splits up, When a heavy nucleus splits up, join together When 2 light nuclei join together to form a heavy nucleus, huge amount of energy is released. E.g. atomic bomb huge amount of energy is released. the Sun E.g. the Sun

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Nuclear Fission Fission is the process of splitting a nucleus into two nuclei with smaller masses. Large amount of energy is releases A chain reaction is an on-going series of fission reactions. Critical mass Critical mass is the amount of fissionable material required to continue a reaction at a constant rate Exothermic Reaction

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Nuclear fission neutron U-235 nucleus Ba-144 nucleus Kr-90 nucleus neutron uncharged not repelled on approaching nuclei U 235 92 144 56 Ba+Kr 90 36 + n 1 0 n 1 0 + n 1 0 + energy+ neutron

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Nuclear fission Naturally-occurring uranium consists of 2 isotopes, U-238 (99.3%) & U-235 (0.7 %). (U-235) It is the rare isotope (U-235) which undergoes fission. less The total mass of the fission products is found less than the total mass before fission takes place. U 235 92 144 56 Ba+Kr 90 36 + n 1 0 n 1 0 + n 1 0 + energy +

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Chain reaction uranium nucleus When a uranium nucleus splits, 2 or 3 neutrons are emitted. neutron U-235 nucleus splits If these neutrons carry on splitting other uranium nucleus...

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Chain reaction neutron U-235 nucleus splits self-sustaining chain reaction escapes

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Chain reaction the fraction of neutrons escaping. small piece If a small piece of uranium is used, the chain will break very quickly. If the mass of uranium is below a critical mass,

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Nuclear fission

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Neutrons may: 1 - Cause another fission by colliding with a U 235 nucleus 2 - Be absorbed in other material 3 - Lost in the system If sufficient neutrons are present, we may achieve a chain reaction Each split (fission) is accompanied by a large quantity of E-N-E-R-G-Y Creates two smaller nuclides and free neutrons The free neutrons potentially collide with nearby U 235 nuclei May cause the nuclide to split as well

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Nuclear FUSION DEUTERIUM TRITIUM HELIUM NEUTRON http://fusioned.gat.com

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Nuclear Fusion Fusion occurs when two nuclei with low masses are combined to form one nucleus of larger mass. Can only happen when the nuclei are moving fast enough to get close to each other Temperature in stars are high enough for fusion to occur (millions of degrees Celsius) FUSION FUSION video clip

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Nuclear fusion HUGE AMOUNT light nuclei A HUGE AMOUNT of energy is also released when two light nuclei join together to form a heavy nucleus. This process is called nuclear fusion.

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Nuclear fusion hydrogen-3 nucleus hydrogen-2 nucleus neutron helium-4 He 4 2 + H 2 1 n 1 0 + + energy H 3 1 fusion

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Nuclear fusion Since nuclei carry + charges, they repel each other. 2 hydrogen very high speed. For fusion to occur, the 2 hydrogen nuclei must approach each other with very high speed. He 4 2 + H 2 1 n 1 0 + + energy H 3 1 hydrogen gas of high temperature (10 8 C)!

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Nuclear fusion Sun Nuclear fusion occurs in the core of the Sun, giving out heat and light. The reaction takes place continuously for billions of years.

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Q1Which of the following… AU-235 BU-238 CHydrogen DHelium Which of the following elements is used in nuclear fission?

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Q2According to Einsteins… According to Einsteins mass-energy equation E = mc 2, what is the amount of energy produced if 1 kg of a certain element completely changes into energy? A3 10 8 J B3 10 16 J C6 10 16 J D9 10 16 J

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Q3In nuclear… (U) In nuclear ___________, nuclei of uranium are split into smaller pieces and large amount of energy will be released. In order to maintain the ___________ reaction, mass of uranium used should exceed the __________ mass. critical fission chain

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Q4In nuclear… (H) In nuclear __________, nuclei of hydrogen are joined together and ____________ nucleus is formed. helium fusion

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Every second, the sun converts 500 million metric tons of hydrogen to helium. Due to the process of fusion, 5 million metric tons of excess material is converted into energy in each second. This means that every year, 157,680,000,000,000 metric tons are converted into energy. THE SUN

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Complete the Reaction 1H 4 Be 1H1H 8O8O 2 He 1H1H 6C6C 1 H element atomic number (protons) 6C6C

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Nuclear Fission Neutron induced in U 235 Fission is Exothermic The sum of the masses of the resulting nuclei is less than the original mass (about 0.1% less) The missing mass is converted to energy according to E=mc 2

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U.S. Electrical Power Production by Source Source: EIA (2004)

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Nuclear Fuel Costs Nuclear Fuel Costs Include –Uranium –Enrichment –Manufacturing –Waste Disposal Total Nuclear Fuel Cost is Only About 0.5 cents per kilowatt-hour –Uranium accounts for only about 20% of this cost or 0.1 cents per kilowatt-hour –Increasing Uranium Cost has Minimal Impact

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Review Nuclear fission: A large nucleus splits into several small nuclei when impacted by a neutron, and energy is released in this process Nuclear fusion: Several small nuclei fuse together and release energy.

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