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Nuclear Chemistry Chapter 23 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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X A Z Mass Number Atomic Number Element Symbol Atomic number (Z) = number of protons in nucleus Mass number (A) = number of protons + number of neutrons = atomic number (Z) + number of neutrons A Z 1p1p 1 1H1H 1 or proton 1n1n 0 neutron 0e0e 0 or electron 0e0e +1 0 or positron 4 He 2 4 2 or particle 1 1 1 0 0 0 +1 4 2 23.1

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Balancing Nuclear Equations 1.Conserve mass number (A). The sum of protons plus neutrons in the products must equal the sum of protons plus neutrons in the reactants. 1n1n 0 U 235 92 + Cs 138 55 Rb 96 37 1n1n 0 ++ 2 235 + 1 = 138 + 96 + 2x1 2.Conserve atomic number (Z) or nuclear charge. The sum of nuclear charges in the products must equal the sum of nuclear charges in the reactants. 1n1n 0 U 235 92 + Cs 138 55 Rb 96 37 1n1n 0 ++ 2 92 + 0 = 55 + 37 + 2x0 23.1

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212 Po decays by alpha emission. Write the balanced nuclear equation for the decay of 212 Po. 4 He 2 4 2 or alpha particle - 212 Po 4 He + A X 84 2Z 212 = 4 + AA = 208 84 = 2 + ZZ = 82 212 Po 4 He + 208 Pb 84 282 23.1

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Nuclear Stability and Radioactive Decay Beta decay 14 C 14 N + 0 + 6 7 40 K 40 Ca + 0 + 19 20 1 n 1 p + 0 + 0 1 Decrease # of neutrons by 1 Increase # of protons by 1 Positron decay 11 C 11 B + 0 + 6 5 +1 38 K 38 Ar + 0 + 19 18 +1 1 p 1 n + 0 + 1 0 +1 Increase # of neutrons by 1 Decrease # of protons by 1 and have A = 0 and Z = 0 23.2

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Electron capture decay Increase # of neutrons by 1 Decrease # of protons by 1 Nuclear Stability and Radioactive Decay 37 Ar + 0 e 37 Cl + 18 17 55 Fe + 0 e 55 Mn + 26 25 1 p + 0 e 1 n + 1 0 Alpha decay Decrease # of neutrons by 2 Decrease # of protons by 2 212 Po 4 He + 208 Pb 84 282 Spontaneous fission 252 Cf 2 125 In + 2 1 n 98 490 23.2

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n/p too large beta decay X n/p too small positron decay or electron capture Y 23.2

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Nuclear Stability Certain numbers of neutrons and protons are extra stable n or p = 2, 8, 20, 50, 82 and 126 Like extra stable numbers of electrons in noble gases (e - = 2, 10, 18, 36, 54 and 86) Nuclei with even numbers of both protons and neutrons are more stable than those with odd numbers of neutron and protons All isotopes of the elements with atomic numbers higher than 83 are radioactive All isotopes of Tc and Pm are radioactive 23.2

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Nuclear binding energy (BE) is the energy required to break up a nucleus into its component protons and neutrons. BE + 19 F 9 1 p + 10 1 n 9 1 0 BE = 9 x (p mass) + 10 x (n mass) – 19 F mass E = mc 2 BE (amu) = 9 x 1.007825 + 10 x 1.008665 – 18.9984 BE = 0.1587 amu 1 amu = 1.49 x 10 -10 J BE = 2.37 x 10 -11 J binding energy per nucleon = binding energy number of nucleons = 2.37 x 10 -11 J 19 nucleons = 1.25 x 10 -12 J 23.2

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Nuclear binding energy per nucleon vs Mass number nuclear stability 23.2 nuclear binding energy nucleon

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Kinetics of Radioactive Decay N daughter rate = - N t rate = N N t = N - N = N 0 exp(- t)lnN = lnN 0 - t N = the number of atoms at time t N 0 = the number of atoms at time t = 0 is the decay constant ln2 = t½t½ 23.3

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Kinetics of Radioactive Decay [N] = [N] 0 exp(- t) ln[N] = ln[N] 0 - t [N] ln [N] 23.3

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Radiocarbon Dating 14 N + 1 n 14 C + 1 H 716 0 14 C 14 N + 0 + 6 7 t ½ = 5730 years Uranium-238 Dating 238 U 206 Pb + 8 4 + 6 0 92822 t ½ = 4.51 x 10 9 years 23.3

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Nuclear Transmutation Cyclotron Particle Accelerator 14 N + 4 17 O + 1 p 7 2 8 1 27 Al + 4 30 P + 1 n 13 2 15 0 14 N + 1 p 11 C + 4 7 1 6 2 23.4

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Nuclear Transmutation 23.4

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Nuclear Fission 23.5 235 U + 1 n 90 Sr + 143 Xe + 3 1 n + Energy 92 54 3800 Energy = [mass 235 U + mass n – (mass 90 Sr + mass 143 Xe + 3 x mass n )] x c 2 Energy = 3.3 x 10 -11 J per 235 U = 2.0 x 10 13 J per mole 235 U Combustion of 1 ton of coal = 5 x 10 7 J

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Nuclear Fission 23.5 235 U + 1 n 90 Sr + 143 Xe + 3 1 n + Energy 92 54 3800 Representative fission reaction

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Nuclear Fission 23.5 Nuclear chain reaction is a self-sustaining sequence of nuclear fission reactions. The minimum mass of fissionable material required to generate a self-sustaining nuclear chain reaction is the critical mass. Non-critical Critical

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Schematic Diagram of a Nuclear Reactor 23.5

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Annual Waste Production 23.5 35,000 tons SO 2 4.5 x 10 6 tons CO 2 1,000 MW coal-fired power plant 3.5 x 10 6 ft 3 ash 1,000 MW nuclear power plant 70 ft 3 vitrified waste Nuclear Fission

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23.5 Nuclear Fission Hazards of the radioactivities in spent fuel compared to uranium ore From Science, Society and Americas Nuclear Waste, DOE/RW-0361 TG

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Chemistry In Action: Natures Own Fission Reactor Natural Uranium 0.7202 % U-235 99.2798% U-238 Measured at Oklo 0.7171 % U-235

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23.6 Nuclear Fusion 2 H + 2 H 3 H + 1 H 1 1 1 1 Fusion ReactionEnergy Released 2 H + 3 H 4 He + 1 n 1 1 2 0 6 Li + 2 H 2 4 He 3 1 2 6.3 x 10 -13 J 2.8 x 10 -12 J 3.6 x 10 -12 J Tokamak magnetic plasma confinement

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23.7 Radioisotopes in Medicine 1 out of every 3 hospital patients will undergo a nuclear medicine procedure 24 Na, t ½ = 14.8 hr, emitter, blood-flow tracer 131 I, t ½ = 14.8 hr, emitter, thyroid gland activity 123 I, t ½ = 13.3 hr, ray emitter, brain imaging 18 F, t ½ = 1.8 hr, emitter, positron emission tomography 99m Tc, t ½ = 6 hr, ray emitter, imaging agent Brain images with 123 I-labeled compound

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23.7 Radioisotopes in Medicine 98 Mo + 1 n 99 Mo 42 0 235 U + 1 n 99 Mo + other fission products 92042 99m Tc 99 Tc + -ray 43 99 Mo 99m Tc + 0 + 42 43 Research production of 99 Mo Commercial production of 99 Mo t ½ = 66 hours t ½ = 6 hours Bone Scan with 99m Tc

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Geiger-Müller Counter 23.7

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23.8 Biological Effects of Radiation Radiation absorbed dose (rad) 1 rad = 1 x 10 -5 J/g of material Roentgen equivalent for man (rem) 1 rem = 1 rad x QQuality Factor -ray = 1 = 1 = 20

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Chemistry In Action: Food Irradiation DosageEffect Up to 100 kilorad Inhibits sprouting of potatoes, onions, garlics. Inactivates trichinae in pork. Kills or prevents insects from reproducing in grains, fruits, and vegetables. 100 – 1000 kilorads Delays spoilage of meat poultry and fish. Reduces salmonella. Extends shelf life of some fruit. 1000 to 10,000 kilorads Sterilizes meat, poultry and fish. Kills insects and microorganisms in spices and seasoning.

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