1. Nuclear Science Minor Program 14 upper division units from the following: CHEM 482 Directed Study in Advanced Topics of Chemistry NUSC 341 Introduction to Radiochemistry NUSC 342 Introduction to Nuclear Science NUSC 344 Nucleosynthesis and Distribution of the Elements NUSC 346 Radiochemistry Laboratory NUSC 444 Special Topics in Nuclear Science NUSC 485 Particle Physics PHYS 385 Quantum Physics

2. What we’ve discussed last time History of radioactivity Interactions and Force Carriers Standard Model and Subatomic Particles Structure of Matter Nucleus Chart of Nuclides

3. Forces in Matter and the Subatomic Particles Chapter 1

4. Natural Decay Chains http://hyperphysics.phy-astr.gsu.edu/

5. (4n + 0) 6 α particles 4 β - particles

6. http://hyperphysics.phy-astr.gsu.edu/ (4n + 2) 8 α particles 6 β particles

7. (4n + 3) 7 α particles 4 β particles

8. The members of this series are not presently found in nature because the half-life of the longest lived isotope in the series is short compared to the age of the earth. < 4.7 10 9 y 7 α particles 4 β - particles

10. Types of Radioactive Decay Chapter 2

11. Radioactive Decay Statistical process Spontaneous emission of particle or electromagnetic radiation from the atom Unaffected by temperature, pressure, physical state, etc Exoergic process Conserves total energy, linear and angular momentum, charge, mass number, lepton number, etc.

12. Units of Energy Mass and energy are interchangeable – E = mc 2 where energy usually expressed in MeV 1 eV = 1.602 x 10 -19 J = 1.60219 x 10 -12 erg 1 MeV = 1.602 x 10 -13 J = 1.60219 x 10 -6 erg 1 u = 931.5 MeV/c 2

13. Decay Modes Alpha decay Beta decay Gamma decay Spontaneous fission Delayed neutron and proton emission Two-proton decay Composite particle emission Double beta decay Prompt proton decay (new)

14. Molecular Rotations and Vibrations (Bjerrum 1912) 0 1 ħ 2 /I 10 ħ 2 /I L= 0 L= 1 L= 2 L= 3 L= 4 L= 5 3 ħ 2 /I 6 ħ 2 /I 15 ħ 2 /I rotation axis r1 r2 r m1 m2 CM Absorption spectrum of HCl (note the double peaking caused by two isotopes of Cl) λ = 3 μm = 3 x 10 -4 cm, IR moments of inertia bond and force length

15. Vibrations http://wwwnsg.nuclear.lu.se

16. Rotation prolate rotor oblate rotor

17. Reflection Asymmetric Shape http://wwwnsg.nuclear.lu.se octupole

18. Gamma-Ray Radiation and Nuclei γ Germanium detector Number of counts Gamma-ray energy (keV) 29 Cu 30 59 γ-ray energy, keV Excitation energy, keV Angular momentum, ħ γ γ

19. Alpha Decay 210 Po  4 He + 206 Pb + γ t 1/2 ( 210 Po) = 138.4 d; E α = 5.304 MeV Typically for A>150; Z > 83 ( 144 Nd, 147 Sm) Geiger-Nuttall rule: 216 Rn; 8.05 MeV, 45μs 144 Nd; 1.83 MeV, 2.1 x 10 15 y

20. Conservation of Energy for Alpha Decay E trans = E α + E recoil E = ½ mv 2 2mE = m 2 v 2 = (mv) 2 p = mv; p 2 = m 2 v 2 = (mv) 2 = 2mE p α = p recoil 2m α E α = 2m recoil E recoil E recoil = (m α /m recoil )E α

21. Alpha Spectrum Parent Daughter α 1 (20%) α 2 (40%) α 3 (40%) γ1γ1 γ3γ3 γ2γ2 5.05.5 6.06.57.07.5

22. What we have learned last time Natural decay chains Excited molecules and nuclei Alpha decay

23. Alpha Decay Parent Daughter α 1 (20%) α 2 (40%) α 3 (40%) γ1γ1 γ3γ3 γ2γ2 5.05.5 6.06.57.07.5 Counts E α (MeV) 238 U  234 Th + 4 He 2+ 238 U  234 Th + 4 He

24. Beta Decay  change a neutron to a proton  change a proton to a neutron EC: electron capture, change a proton to a neutron   is an electron β + is an anti-electron or positron (negatron decay) Unlike alpha decay, which occurs primarily among nuclei in specific areas The periodic table, beta decay is possible for certain isotopes of all elements

25. Negatron (β - ) Decay Daughter β1β1 β2β2 γ Parent Neutron rich nuclei; Large N/Z ratio t 1/2

26. Beta decay – Energy spectrum E max Antineutrino in β - –No charge –No magnetic moment –Near zero rest mass –Spin ½ –Conservation of lepton number β-β- β+β+ Beta-particle energy Number of beta particles E trans = E negatron + E antineutrino + E recoil

27. Antineutrino discovery 1953 by F. Reines and C.L. Cowan Jr.

28. Positron (β + ) Decay  change a proton to a neutron β + is an anti-electron, or positron Proton rich nuclei Similar spectrum as in negatron decay Change a proton to a neutron  positive electron is emitted by the nucleus and an orbital electron originally present in the parent atom is lost to form a neutral daughter atom. equivalent to the creation of a positron-electron pair from the available transition energy 2 x 0.511 MeV = 1.02 MeV necessary to create 2 electrons β + decay is possible only when the energy of the transition is greater than 1.02 MeV

29. The fate of the positron Conversion to pure energy by positron annihilation After the positron slows down to energies comparable to that of surroundings Formation of 1, 3, or 0 annihilation photons, depending on the spin orientation of the electron-positron pair If the spins are parallel  triple state If the spins are anti-parallel  a single state Positronium “atom”  light “isotope” of hydrogen, with the positron substituting for the nuclear proton Ortho positronium; paralell spins 10 -7 s Para positronium; anti-parallel spins 10 -10 s

30. Electron Capture (EC orε) EC: electron capture, change a proton to a neutron excited nucleus + x-rays or Auger electrons + inner bremsstrahlung

31. Gamma Decay Pure γ decay Internal conversion (IC) Pair production (PP)

32. Pure Gamma-Ray Emission γ 99.8% β 1, t 1/2 = 1.17 m 0.2% β 2, t 1/2 = 6.70 h 92 U 91 Pa 234 U 234m Pa 234g Pa 2 keV < E < 7 MeV; monoenergetic

33. Internal Conversion The excited nucleus transfers the energy to an orbital electron, which is then ejected from the atom (monoenergetic). E IC electron = E trans – BE atomic electron IC and gamma decay are competing processes Internal conversion coefficient (α) α= Fraction of decays occurring by gamma emission/Fraction of decays occurring by IC

34. Pair Production E > 1.02 MeV 16m O  16 O E trans = 6.05 MeV t 1/2 = 7 x 10 -11 s

35. Spontaneous Fission Decay Induced Fission Reaction

36. Oklo, Gabon – A natural fission reactor 235 U natural abundance is well known: 0.00720 ± 0.00001 Uranium deposit where self-sustained nuclear chain reactions have occurred. 235 U abundance 0.00717, about 3 standard deviations below the accepted value. The only process which can lead to reduction of U is fission by low- energy neutrons. 2 x 10 9 y, 235 U (~3%) reactor moderated by groundwater. Fission product isotope signatures Nd, Ru Geological Situation in Gabon leading to natural nuclear fission reactors: 1. Nuclear reactor zones 2. Sandstone 3. Ore layer 4. Granite

37. Fossil Reactor 15, located in Oklo, Gabon. Uranium oxide remains are visible as the yellowish rock. Source: NASA

38. Oklo Estimations 5 tonnes of 235 U were fissioned. Total energy released 2 x 10 30 MeV or 10 8 MW∙h. A contemporary power reactor can operate at 10 3 MW. Average power 0.01 MW, operating for 10 6 y. Important feature: the fission products are still in place in the reactor zone and have migrated very little. Despite climate changes, no substantial movement of the fission products has taken place over the past 2 x 10 9 y.

39. Confirmation: Nd signature natural neodymium contains 27% 142 Nd the Nd at Oklo contained less than 6% but contained more 143 Nd the isotopic composition matched that produced by the fissioning of 235 U.

40. Delayed-Neutron Emission Following beta decay of fission products such as 140 Ba and 94 Kr 87 Br  87 Kr  86 Kr + n + β - neutron rich

41. Delayed-Proton Emission Production of precursor: 54 Fe(p,2n) 53 Co Decay by proton emission: 53 Co  52 Fe +p

42. Double-Beta Decay 130 Te, 82 Se stable to ordinary beta decay, but unstable toward 2-beta decay Simultaneous 2 beta emission

43. Two-Proton Decay 22 Al (1960), 54 Zn (2005) 45 Fe (2003, 2007) 48 Ni

44. End of Chapter 2 Questions?