Nuclear Chemistry

1. Nuclear Chemistry

2. Radioactivity • Emission of subatomic particles or high-energy electromagnetic radiation by nuclei • Such atoms/isotopes said to be radioactive

3. Its discovery • Discovered in 1896 by Becquerel • Called strange, new emission uranic rays • Cuz emitted from uranium • Marie Curie & hubby discovered two new elements, both of which emitted uranic rays • Polonium & Radium • Uranic rays became radioactivity

5. Types of radioactivity • Rutherford and Curie found that emissions produced by nuclei • Different types: • Alpha decay • Beta decay • Gamma ray emission

6. Isotopic symbolism • Let’s briefly go over it • Proton = 11p • Neutron = 10n • Electron = 0-1e

7. Types of decay: alpha decay • Alpha () particle: helium-4 bereft of 2e- • = 42He • Parent nuclide  daughter nuclide + He-4 23892U  23490Th + 42He • Daughter nuclide = parent nuclide atomic # minus 2 • Sum of atomic #’s & mass #’s must be = on both sides of nuclear equation!

9. Alpha decay • Has largest ionizing power • = ability to ionize molecules & atoms due to largeness of -particle • But has lowest penetrating power • = ability to penetrate matter • Skin, even air, protect against -particle radiation

10. Beta decay • Beta () particle = e- • How does nucleus emit an e-? •  neutron changes into proton & emits e- •  10n  11p + 0-1e • Daughter nuclide = parent nuclide atomic number plus 1 13755Cs  13756Ba + 0-1e-

11. Beta decay • Lower ionizing power than alpha particle • But higher penetration power • Requires sheet of metal or thick piece of wood to arrest penetration •  more damage outside of body, but less in (alpha particle is opposite)

13. Gamma ray emission • Electromagnetic radiation • High-energy photons • 00 • No charge, no mass • Usually emitted in conjunction with other radiation types • Lowest ionizing power, highest penetrating power  requires several inches lead shielding

14. Problems • Write a nuclear equation for each of the following: 1. beta decay in Bk-249 2. alpha decay of Ra-224

15. Cont. • In determining nuclear stability, ratio of neutrons to protons (N/Z) important • Notice lower part of valley (N/Z = 1) • Bi last stable (non-radioactive) isotopes • N/Z too high: above valley, too many n, convert n to p, beta-decay • N/Z too low: below valley, too many p, convert p to n

16. Magic numbers • Actual # of n & p affects nuclear stability • Even #’s of both n & p give stability • Similar to noble gas electron configurations: 2, 10, 18, 36, etc. • Since nucleons (= n+p) occupy energy levels within nucleus • N or Z = 2, 8, 20, 28, 50, 82, and N = 126 • Magic numbers

17. Radioactive decay series

18. Detecting radioactivity • Particles detected through interactions w/atoms or molecules • Simplest  film-badge dosimeter • Photographic film in small case, pinned to clothing • Monitors exposure • Greater exposure of film  greater exposure to radioactivity

19. Geiger counter • Emitted particles pass through Ar-filled chamber • Create trail of ionized Ar atoms • Induced electric signal detected on meter and then clicks • Each click = particle passing through gas chamber

20. Radioactive decay kinetics • Half-life = time taken for ½ of parent nuclides to decay to daughter nuclides

21. Devised in 1949 by Libby at U of Chicago Age of artifacts, etc., revealed by presence of C-14 C-14 formed in upper atmosphere via: 147N + 10n  146C + 11H C-14 then decays back to N by -emission: 146C  147N + 0-1e; t1/2 = 5730 years Approximately constant supply of C-14 Taken up by plants via 14CO2 & later incorporated in animals Living organisms have same ratio of C-14:C-12 Once dead, no longer incorporating C-14  ratio decreases 5% deviation due to variance of atmospheric C-14 Bristlecone pine used to calibrate data Carbon-dating good for 50,000 years Radiometric dating: radiocarbon dating

22. Radiometric dating: uranium/lead dating • Relies on ratio of U-238:Pb-206 w/in igneous rocks (rocks of volcanic origin) • Measures time that has passed since rock solidified • t1/2 = 4.5 x 109 years • For ex, if rock contains equal amts of isotopes above, it would be 4.5 billion years old

23. Fission • Meitner, Strassmann, and Hahn discovered fission: splitting of uranium-235 • Instead of making heavier elements, created a Ba and Kr isotope plus 3 neutrons and a lot of energy • Sample rich in U-235 could create a chain rxn • To make a bomb, however, need critical mass = enough mass of U-235 to produce a self-sustaining rxn

24. Nuclear power • In America, about 20% electricity generated by nuclear fission • Imagine: • Nuclear-powered car • Fuel = pencil-sized U-cylinder • Energy = 1000 20-gallon tanks of gasoline • Refuel every 1000 weeks (about 20 years)

25. Nuclear power plant • Controlled fission through U fuel rods (3.5% U-235) • Rods absorb neutrons • Retractable • Heat boils water, making steam, turning turbine on generator to make electricity

27. Comparing • Typical nuclear power plant makes enough E for city of 1,000,000 ppl and uses about 50 kg of fuel/day • No air pollution/greenhouses gases • But, nuclear meltdown (overheating of nuclear core) • Also, waste disposal: location, containment problems?

28. Comparing • OTOH, coal-burning power plant uses about 2,000,000 kg of fuel to make same amt of E • But, releases huge amts of SO2, NO2, CO2

29. Fusion • H-bonds utilize fusion (but needs high-temps to react cuz both positively charged) • As does the sun: 21H + 31H 42He + 10n • 10 x more energy/gram than fission

30. Transmutation • Transforming one element into another • In 1919, Rutherford bombarded N-17 to make O-17 • The Joliot-Curie’s bombarded Al-27 to form P-30 • In ’30’s, devices needed that could accelerate particles to high velocities: • 1. linear accelerator • 2. cyclotron

31. Linear accelerator • Charged-particle accelerated in evacuated tube • Alternating current causes particle to be pulled into next tube • Continues, allowing velocity = 90% speed of light! • 2 miles long 

32. Cyclotron • Similar alternating voltage used • But applied btwn two semicircular halves of cyclotron • Particle spirals due to magnets • Hits target

33. Radiation on life • 3 divisions • 1. acute radiation • 2. Increased cancer risk • 3. genetic effects

34. The first • Quickly dividing cell at greatest risk: • Intestinal lining • Immune response cells • Likelihood of death • Depends on dose/ • duration

35. 2nd • Cancer = uncontrolled cell growth leading to tumors • Dose? Unknown • Cancer is a murky illness

36. 3rd • Causes genetic defects  teratogenic

37. Average American 360 mrem/yr

38. Good site • http://www.deq.idaho.gov/inl_oversight/radiation/radiation_guide.cfm

39. Let’s try the handout

40. More facts • 20 rem  decreased white blood cell count after instantaneous exposure • 100-400 rem  vomiting, diarrhea, lesions, cancer-risk increase • 500-1000  death w/in 2 months • 1000-2000  death w/in 2 weeks • Above 2000  death w/in hours

41. Diagnostic and therapeutic radiation • Radiotracer = radioactive nuclide in brew to track movement of brew in body • Tc-99  bones • I-131  thyroid • Tl-201  heart • F-18  heart, brain • P-31  tumors

42. PET • Positron emission tomography • Shows both rate of glucose metabolism and structural features of imaged organ • F-18 emits positrons • Positron and e- produce two gamma rays • Rays detected • Imaged

43. Radiotherapy • Using radiation to treat cancer • Develop symptoms of radiation sickness: vomiting, diarrhea, skin burns, hair loss

44. Other applications • Irradiating foods • Nuking bugs like fruit flies and screw-worm flies