NE 301 - Introduction to Nuclear Science Spring 2012

1. NE 301 - Introduction to Nuclear ScienceSpring 2012 Classroom Session 3: Radioactive Decay Types Radioactive Decay and Growth Isotopes and Decay Diagrams Nuclear Reactions Energy of nuclear reactions Neutron Cross Sections Activation Calculations

2. Reminder • Load TurningPoint • Reset slides • Load List

3. Let’s do some accounting… Mass of Oxygen Atom: Mp=1.007276 amu Mn=1.008665 amu Me=5.48e-4 amu 1 amu = 931.49 MeV Mass Defect = Binding Energy (BE)

4. Chart of the Nuclides Isobars Isotopes Z Isotones N

5. Notice radioactive decay stabilizes atoms: • Question: Do fission products normally have - or + decay?

6. Reaction reactants and products If E is positive: reaction exothermic releases energy If E is negative, reaction endothermic requires energy Endoergic and exoergic is sometimes used Reaction Energetics A + B  C + D + E

7. The Energy Released (or consumed), Q Change in BE: Or since BE is related to mass defect Change in M: A + B  C + D + E Preferred! because we have table B.1. Remember:The Equation Has to BeBALANCED!

8. Please remember… BALANCE! Before starting to work

9. Balancing Reactions nucleons  1 +16 = 16+1 Charges (+)  0 + 8 = 7 + 1 (-)  -0 -8 = -7 -0  e- missing 0 1 So in reality the reaction is: Calculating Q…

10. Q-value for the reaction is: Using atomic mass tables: Endothermic reaction. Only a few fission neutrons can do it

11. A beryllium target is irradiated in a proton accelerator to produce 10B. What is Q of the reaction? • 5.5 MeV • 4.5 MeV • 3 MeV • 6.5 MeV • 85 MeV

12. For clicker

13. Excited Nuclei • Many reactions involve excited nuclei • Sometimes long lived states (isomers) • Excitation energy has to be added to the mass of the excited nuclei when calculating Q e.g. The mass of 22Ne* at 1274 MeV is:

14. Decay Series • The radioactive minerals contain many nuclides • All of them decay by either  or  decay •   A changes by 4, Z by 2 •   A does not change, A by 1 • Th has one long lived isotope 232Th • U has two long lived 235U, 238U • Series identified by relation Parent to Dauthers mass: • A in multiples of 4 There are 3 natural series

16. Notice Branching

18. Series are: A = 4n --- Thorium Series A = 4n+2 -- Uranium Series A = 4n+3 – Actinium Series Which one is missing? A = 4n+1 – Neptunium Series (Artificial)

19. It was there from the beginning… but notice: half life of 237Np is relatively low.

20. Main Radioactive Decay Modes (Table 5.1 -page 89-Shultis)

21. Comments: • , +, - are common modes of decay • Long T1/2 usually are -emitters • n, p emission are rare (excess p+ atoms) •  is predominant for Z>83 (above Bismuth) and atoms away from the line of -stability. • Some high Z atoms (Z>96) have dominant spontaneous fission •  mostly dominates again at Z>105

22. Modes of Decay • , +, - are common modes of decay • Long T1/2 usually are -emitters • n, p emission are rare (excess p+ atoms) •  is predominant for Z>83 (above Bismuth) and atoms away from the line of -stability. • Some high Z atoms (Z>96) have dominant spontaneous fission •  mostly dominates again at Z>105

23. Solving momentum and KE equations • Remember the conditions: • Parent nucleus at rest (usually the case) • Binary products only (not -decay, but OK to Emax) • Calculate the correct Q (excited states are prevalent, and balance) • Finally, there usually reaction paths with many outcomes, therefore multiple Q-values

24. Kinetic Energy of Radioactive Decay Products • Parent nucleus is at rest (Eth~ 0.025 eV~17 oC) • Conservation of Linear Momentum and Kinetic Energy requires products to travel in opposite directions (2 product). v2 m2 m2 m1 m1 m1v1=m2v2 Original atom that will split in 2 pieces v1 Q=½ m1v12+ ½ m2v22 What is the energy of emitted particle? (it is what we measure)

25. Kinematics of radioactive decay… Notice 2:1

26. Warm up:What % of the energy should go to the -particle? • 98% • 2% • 50% • 10% • 1%

27. Example of -spectroscopy? • 237Pa • 237U • 237Np • 237Pu • 237Am • 237Cm

28. Find Q for: • 3.638 MeV • 4.638 MeV • 5.638 MeV • 6.638 MeV • 7.638 MeV

29. For Clicker slide: Q=(241.056823-237.048167-4.002603)*931.494=5.638MeV

30. What is the KE of the  particle in the radioactive decay of 241Am? (3 min) • 0.09 MeV • 0.98 MeV • 5.54 MeV • 5.64 MeV

31. For Clicker slide: KE=5.638*237/(237+4)=5.545 MeV

32. Notice: If alpha particle ALWAYS leaves with exactly the same energy. We would expect to detect a monoenergeticbeam of ’s. In reality…

33. The real alpha spectrum of 241Am is: At least 5 different  energies… Why? Excited Nuclei!

34. The real decay path of 241Am There are actually 6 alpha peaks Last two peaks are too close to be resolved Notice frequencies (%’s) Every decay path happens all the time but not with equal probability Look in your book: Page 578. 241Am Taken from J. K. Beling, et al. Phys. Rev. 87 (1952) 670-671

35. Diagram means: • Energy of the -particle? • Same old same old • But Q is different each time 35

36. 3.6

38. 4.0 By the way Notice also

39. 4.0 There are a lot more hard to see peaks

40. So how is the “real” diagram? For that we need the TABLE OF ISOTOPES

41. Diagram 241Am - 1 of 2

42. Diagram 241Am - 2 of 2

43. The Table also includes a more complete list of particles emitted during decay

45. ’s ’s

46. Main Radioactive Decay Modes (Table 5.1 -page 89-Shultis)