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1 Nuclear Chemistry Chapter 9 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Atomic number (Z) = number of protons in nucleus Mass number (A) = number of protons + number of neutrons = atomic number (Z) + number of neutrons Mass Number Atomic Number A ZX Element Symbol proton p or H neutron 0 n electron 0 e - or 0 β - positron or 0 β + 0 e + α particle 4 He 2 or 4 α 2 A Z

2 Balancing Nuclear Equations. Conserve mass number (A). The sum of protons plus neutrons in the products must equal the sum of protons plus neutrons in the reactants Cs + Rb U 0 n 37 n = x 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 Cs + Rb = x0 235 U 0 n 37 n Po decays by alpha emission. Write the balanced nuclear equation for the decay of 22 Po. alpha particle - 4 He 2 or 4 α 2 22 Po 4 He + A X 84 2 Z 22 = 4 + A A = = 2 + Z Z = Po 4 He Pb

3 23. Beta decay Nuclear Stability and Radioactive Decay 4 C 4 N + 0 β + ν K 40 Ca + 0 β + ν Decrease # of neutrons by Increase # of protons by n p + 0 β + ν 0 - Positron decay 6C B + 0 β + ν K 38 Ar + 0 β + ν 8 + Increase # of neutrons by Decrease # of protons by p n + 0 β + ν 0 + ν and ν have A = 0 and Z =

4 Nuclear Stability and Radioactive Decay Electron capture decay 37 Ar + 0 e 37 8 Cl + ν Fe + 0 e Mn + ν - 25 Increase # of neutrons by Decrease # of protons by Alpha decay p + 0 e n + ν 0-22 Po 4 He Pb Decrease # of neutrons by 2 Decrease # of protons by 2 Spontaneous fission 252 Cf 2 25 In + 2 n n/p too large beta decay X Y n/p too small positron decay or electron capture

5 Nuclear Stability Certain numbers of neutrons and protons are extra stable n or p = 2, 8, 20, 50, 82 and 26 Like extra stable numbers of electrons in noble gases (e - = 2, 0, 8, 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

6 Nuclear binding energy (BE) is the energy required to break up a nucleus into its component protons and neutrons. BE + 9 F 9 p + 0 n E = mc BE = 9 x (p mass) + 0 x (n mass) 9 F mass BE (amu) = 9 x x BE = amu amu =.49 x 0-0 J BE = 2.37 x 0 - J binding energy binding energy per nucleon = number of nucleons = 2.37 x 0- J 9 nucleons =.25 x 0-2 J 23.2 Nuclear binding energy per nucleon vs Mass number nuclear binding energy nucleon nuclear stability

7 Kinetics of Radioactive Decay N rate = - ΔN Δt ΔN - Δt N = N 0 exp(-λt) daughter rate = λn = λn lnn = lnn 0 - λt N = the number of atoms at time t N 0 = the number of atoms at time t = 0 λ is the decay constant λ ln2 = t½ 23.3 Kinetics of Radioactive Decay [N] = [N] 0 exp(-λt) ln[n] = ln[n] 0 - λt [N] ln [N]

8 Fig Radiocarbon Dating 4 N + n 4 C + H C 4 N + 0 β + ν t ½ = 5730 years Uranium-238 Dating 238 U Pb α β t ½ = 4.5 x 0 9 years

9 Fig Nuclear Transmutation 4 N + 4 α 7 O + p Al + 4 α 30 P + n N + p C + 4 α Cyclotron Particle Accelerator

10 Page 040 Nuclear Transmutation

11 Nuclear Fission 235 U + n 90 Sr + 43 Xe + 3 n + Energy Energy = [mass 235 U + mass n (mass 90 Sr + mass 43 Xe + 3 x mass n )] x c 2 Energy = 3.3 x 0 - J per 235 U = 2.0 x 0 3 J per mole 235 U Combustion of ton of coal = 5 x 0 7 J 23.5

12 Nuclear Fission 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 23.5 Nuclear Fission Schematic diagram of a nuclear fission reactor

13 Nuclear Fission 35,000 tons SO 2 Annual Waste Production 4.5 x 0 6 tons CO x 0 6 ft 3 ash 70 ft 3 vitrified waste,000 MW coal-fired power plant,000 MW nuclear power plant 23.5 Nuclear Fission Hazards of the radioactivities in spent fuel compared to uranium ore From Science, Society and America s Nuclear Waste, DOE/RW-036 TG

14 Radioisotopes in Medicine out of every 3 hospital patients will undergo a nuclear medicine procedure 24 Na, t ½ = 4.8 hr, β emitter, blood-flow tracer 3 I, t ½ = 4.8 hr, β emitter, thyroid gland activity 23 I, t ½ = 3.3 hr, γ ray emitter, brain imaging 8 F, t ½ =.8 hr, β + emitter, positron emission tomography 99m Tc, t ½ = 6 hr, γ ray emitter, imaging agent Brain images with 23 I-labeled compound 23.7 Geiger-Müller Counter

15 Biological Effects of Radiation Radiation absorbed dose (rad) rad = x 0-5 J/g of material Roentgen equivalent for man (rem) rem = rad x Q Quality Factor γ-ray = β = α = Chemistry In Action: Food Irradiation Dosage Up to 00 kilorad kilorads 000 to 0,000 kilorads Effect Inhibits sprouting of potatoes, onions, garlics. Inactivates trichinae in pork. Kills or prevents insects from reproducing in grains, fruits, and vegetables. Delays spoilage of meat poultry and fish. Reduces salmonella. Extends shelf life of some fruit. Sterilizes meat, poultry and fish. Kills insects and microorganisms in spices and seasoning. 5