Nuclear Chemistry

1. Nuclear Chemistry Chapter 23

2. n/p too large n/p too small 23.2

3. Types Of Radioactive Decay • An alpha (a) particle has the same composition as a helium nucleus: two protons and two neutrons (positive charge) • Beta (b-) particles are high-energy electrons (from the nucleus, not from the electron cloud). • Gamma (g) rays are a highly penetrating form of electromagnetic radiation. No charge. • Positrons are particles having the same mass as electrons but carrying a charge of 1+. • Electron capture (EC) is a process in which the nucleus absorbs an electron from an inner electron shell, usually the first or second, with the release of an X-ray. • Most radionuclides undergo one specific type of decay, though some can undergo two or more types.

4. How Far Will Radiation Penetrate?

5. Summary Of Decay Types

6. A X Mass Number Element Symbol Z Atomic Number a particle proton neutron electron positron or or 1H 1p 0b 0e or 1 1 +1 1n 0e +1 0b 0 -1 -1 4a 4He or 2 2 Atomic number (Z) = number of protons in nucleus Mass number (A) = number of protons + number of neutrons = atomic number (Z) + number of neutrons A 1 1 0 0 4 1 0 -1 +1 2 Z 23.1

7. + + + + + 2 + 2 1n 1n 1n 1n 96 96 0 0 0 0 Rb Rb 37 37 138 235 138 235 Cs Cs U U 92 55 92 55 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. 235 + 1 = 138 + 96 + 2x1 • 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. 92 + 0 = 55 + 37 + 2x0 23.1

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

9. (a) α-particle emission by radon-222 22288Rn  42He + ?? 22288Rn  42He + 21886Po • (b) β-decay of phosphorus-32 3215P  0–1 β + ?? 3215P  0–1 β + 3216S

10. 23.1

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

12. 37Ar + 0e 37Cl + n 18 17 -1 55Fe + 0e 55Mn + n 26 25 -1 1p + 0e 1n + n 1 0 -1 212Po 4He + 208Pb 2 82 84 Nuclear Stability and Radioactive Decay Electron capture decay Decrease # of protons by 1 Increase # of neutrons by 1 Alpha decay Decrease # of neutrons by 2 Decrease # of protons by 2 23.2

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

14. 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 are radioactive 23.2

15. BE + 19F 91p + 101n 0 9 1 binding energy per nucleon = binding energy number of nucleons 2.37 x 10-11 J 19 nucleons = Nuclear binding energy (BE) is the energy required to break up a nucleus into its component protons and neutrons. E = mc2 BE = 9 x (p mass) + 10 x (n mass) – 19F mass 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 10-11J = 1.25 x 10-12 J 23.2

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

17. 37Ar + 0e 37Cl + n 18 17 -1 Electron capture decay - 36.966776amu - .000549amu + 36.965903amu = - 0.001422amu 0.001422amu * 1.4924E-10 J/amu = 2.1222E-13 J E/h = v = 2.1222E-13 J / 6.626E-34 Js = 3.2028E20 1/s 1amu = 931.5MeV 0.001422amu * 931.5 MeV/amu = 1.3246 MeV 23.2

18. N daughter DN rate = - Dt DN - = lN Dt ln2 = l t½ Kinetics of Radioactive Decay rate = lN N = N0exp(-lt) lnN = lnN0 - lt N = the number of atoms at time t N0 = the number of atoms at time t = 0 l is the decay constant 23.3

19. [N] ln [N] Kinetics of Radioactive Decay [N] = [N]0exp(-lt) ln[N] = ln[N]0 - lt 23.3

20. Selected Nuclide Half-Lives

21. 14N + 1n 14C + 1H 0 7 6 1 14C 14N + 0b + n 6 7 -1 238U 206Pb + 8 4a + 6 0b 92 82 2 -1 Radiocarbon Dating t½ = 5730 years Uranium-238 Dating t½ = 4.51 x 109 years 23.3

22. Radiocarbon Dating • 14C is formed at a nearly constant rate in the upper atmosphere by the bombardment of 14N with neutrons from cosmic radiation. • The 14C is eventually incorporated into atmospheric CO2. • Since atmospheric CO2 eventually finds its way into living tissue, the level of 14C in living tissue is constant (about 15 disintegrations per minute per gram of carbon). • When an organism dies, no more 14C is consumed. • The level of 14C decreases as the dead tissue ages. • The half-life for carbon-14 is 5,730 years. This dating method works well for objects up to 50,000 years old.

23. EXAMPLE 19.4 A wooden object from an Egyptian tomb is subjected to radiocarbon dating. The decay rate observed for its carbon-14 content is 7.2 dis min–1 per g carbon. What is the age of the wood in the object (and, presumably, of the object itself)? The half-life of carbon-14 is 5730 years, and the decay rate for carbon-14 in living organisms is 15 dis min–1 per g carbon. SOLUTION First, we can determine the decay constant, λ λ = 0.693/ t1/2 = 0.693/5730 y = 1.21 x 10–4 y–1 Now we can use the decay equation, substituting activity (disintegrations per minute) for N: Nt 7.2 ln = –λ t ln = – (1.21 x 10–4 y–1) t No 15 t = 6.1 x 103 y

24. 14N + 4a17O + 1p 7 2 1 8 27Al + 4a30P + 1n 13 2 0 15 14N + 1p 11C + 4a 7 1 2 6 Cyclotron Particle Accelerator Nuclear Transmutation 23.4

25. Nuclear Transmutation 23.4

26. 235U + 1n 90Sr + 143Xe + 31n + Energy 0 38 0 54 92 Nuclear Fission Energy = [mass 235U + mass n – (mass 90Sr + mass 143Xe + 3 x mass n )] x c2 Energy = 3.3 x 10-11J per 235U = 2.0 x 1013 J per mole 235U Combustion of 1 ton of coal = 5 x 107 J 23.5

27. 235U + 1n 90Sr + 143Xe + 31n + Energy 0 38 0 54 92 Nuclear Fission Representative fission reaction 23.5

28. Non-critical Critical 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. 23.5

29. Nuclear Fission Schematic diagram of a nuclear fission reactor 23.5

30. 35,000 tons SO2 4.5 x 106 tons CO2 70 ft3 vitrified waste 3.5 x 106 ft3 ash 1,000 MW coal-fired power plant 1,000 MW nuclear power plant Nuclear Fission Annual Waste Production 23.5

31. Nuclear Fission Hazards of the radioactivities in spent fuel compared to uranium ore 23.5 From “Science, Society and America’s Nuclear Waste,” DOE/RW-0361 TG

32. Chemistry In Action: Nature’s Own Fission Reactor Natural Uranium 0.7202 % U-235 99.2798% U-238 Measured at Oklo 0.7171 % U-235

33. 2H + 2H 3H + 1H 1 1 1 1 2H + 3H 4He + 1n 2 1 0 1 6Li + 2H 2 4He 2 3 1 Nuclear Fusion Fusion Reaction Energy Released 6.3 x 10-13 J 2.8 x 10-12 J 3.6 x 10-12 J Tokamak magnetic plasma confinement 23.6

34. Radioisotopes in Medicine • 1 out of every 3 hospital patients will undergo a nuclear medicine procedure • 24Na, t½ = 14.8 hr, b emitter, blood-flow tracer • 131I, t½ = 14.8 hr, b emitter, thyroid gland activity • 123I, t½ = 13.3 hr, g-ray emitter, brain imaging • 18F, t½ = 1.8 hr, b+ emitter, positron emission tomography • 99mTc, t½ = 6 hr, g-ray emitter, imaging agent Brain images with 123I-labeled compound 23.7

35. Geiger-Müller Counter 23.7

36. 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 Q Quality Factor g-ray = 1 b = 1 a = 20 23.8

37. Chemistry In Action: Food Irradiation