Nuclear Decay

1. Nuclear Decay

2. The Atom- Review • The atom consists of two parts: 1. The nucleus which contains: protons neutrons 2. Orbiting electrons. • Atom of different elements contain different numbers of protons. • The mass of an atom is due to the number of protons and neutrons.

3. The Nucleus • Super dense mass that contains protons and neutrons • Has overall positive charge • Protons and Neutrons together are called a nuclide • But, how does the nucleus stay together? • 4 forces help to explain this!

4. Nuclear Forces (4) in order of strength • Gravity: attractive force that exists between all objects (weakest force) • Weak Nuclear Force: force responsible for radioactive decay of elements (2nd weakest) • Electrostatic Force: repulsive or attractive force based on charge (in nucleus repulsive as + repels +; 2nd strongest force) • Strong Nuclear Force: attractive force that pull nucleus together and acts over very small distances (strongest force)

5. Isotope Symbol Review Mass number = number of protons + number of neutrons X A Element symbol Z Atomic number = number of protons A = number of protons + number of neutrons Z = number of protons N = number of neutrons (A – Z) **Number of neutrons = Mass Number – Atomic Number**

6. 238 235 U U 92 92 Fill in the chart for each isotope 235 238 92 92 92 92 143 146 Isotopes of any particular element contain the same number of protons, but differentnumbers of neutrons.

7. Band of Stability • Strong nuclear force rules the nucleus, but acts over very short distance • As nucleus gets bigger, its stability starts to change depending on number of protons and neutrons present • We can predict this stability based on a chart i.e. the band of stability!

8. Band of Stability: • Charts neutrons (n) vs protons (Z) • Nuclei that fall within the band are considered stable • Based on where on chart point falls, can determine if nuclei is stable or not!

9. Band of Stability Extras • All isotopes with atomic number above 83 have an unstable nucleus • Isotopes with 2, 8, 20, 28, 50, 82, or 126 protons or neutrons in their nucleus are stable (magic numbers) • Isotopes with an atomic number less than 40 are most stable when the ratio of protons to neutrons is 1:1.

10. Band of Stability Practice • Using Band of Stability (pg 662) in your book, determine if the following isotopes are stable: • Uranium -215 • Helium – 4 • Bi - 190 • Calcium – 36 • Yb -120 • Yb - 121

11. Atoms that are unstable are labelled radioactive. (golf ball example) • They undergo 1 of 5 types radioactive decay to stabilize themselves. • The products of this decay process are what we know as radiation or radioactivity! • Different types of radiation have different properties and different strengths (penetrating power).

12. Radioactive Decay Radioactive decay results in the emission/absorption of either: • an alpha particle (a), • a negative beta particle (electron) (b-), • a positive beta particle (positron) (b+), • a gamma ray (g). In a nuclear reaction the MASS and ATOMIC NUMBER must be the SAME on both sides of the equations (think basic algebra)

13. Emission Vs. Absorption: A note • If a particle is emitted: • It is released (it appears on products side) • Generally atom gets smaller (decrease in mass number) • If a particle is absorbed: • It is taken in (appears on reactants side) • Generally atom gets bigger (increase in mass number)

14. 4 He 2 Alpha Decay - α An alpha particle is identical to a helium nucleus. Contains two protons and two neutrons. Can be stopped by paper (weak).

15. 226 222 Ra Rn 88 86 4 He 2 Alpha Decay + Loss of 2 protons & 2 neutrons: Atomic # decreases by 2 Mass # decreases by 4

16. 234 234 230 4 4 U U Th He He + + 92 90 2 2 Write the equation for the alpha decay of Uranium-234

17. A 218 X Po + 214 Pb 84 Z 82 214 4 4 4 Pb He He He + 82 2 2 2 Find the missing starting material

18. 0 e -1 Beta Emission - b- Beta emission occurs when a neutron changes into a proton and an electron, and the electron is emitted. Can be stopped by thin metal (aluminium foil). beta particle (electron)

19. 218 218 Po At 84 85 0 e -1 Beta Emission +

20. 234 A A A 0 0 0 e e e X Th Y Y + + 90 Z Z + 1 Z -1 -1 -1 234 234 Th Pa + 90 91 Write your own Beta Emission What is Y?

21. 14 0 e C + -1 14 14 C N + 7 Write the equation for the beta emission of carbon-14

22. A 214 0 0 e e X Bi + Z 83 -1 -1 214 214 Pb Bi + 82 83 Find the missing starting material

23. 0 e -1 Electron Capture An electron is absorbed, then joined with a proton to turn into a neutron (electron Capture is the opposite of Beta Emission) The electron capture itself does not have penetrating power

24. 218 218 Po At 84 85 0 e -1 Electron Capture +

25. 37 37 A 0 0 0 + + + e e e Ar X Ar -1 -1 -1 18 18 Z 37 A A Y Y Cl 17 Z-1 Z-1 Write your own Electron Capture What is Y?

26. 59 Ni + 59 0 + e Ni -1 28 59 Co 27 Write the equation for electron capture of nickel-59

27. A 14 0 0 + + e e X N -1 -1 Z 7 14 14 C C 6 6 Find the missing starting material

28. 0 e +1 Positron Emission b+ A positron is like an electron but it has a positive charge. During positron emission a proton changes into a neutron and the excess positive charge is emitted. Can be stopped by thin metal (aluminium foil).

29. 218 218 Po At 84 85 0 e +1 Positron Emission +

30. A 8 8 8 A A 0 0 0 e e e X B B Y Be Y + + + 5 5 Z Z - 1 Z 4 +1 +1 +1 Write your own Positron Emission What is Y?

31. 16 0 e O + +1 16 16 O N + 7 Write the equation for the positron emission of oxygen-16

32. A 66 0 0 e e X Cu + Z 29 +1 +1 66 66 Zn Cu + 30 29 Find the missing starting material

33. 0 g 0 Gamma Decay - γ • Atoms that undergo alpha & beta decay may still have too much energy to be completely stable. These atoms will emit gamma rays to release that energy. • Can only be stopped by thick concrete or lead • There is nochange in mass or atomic number

34. Summary

35. Writing Equations Practice • Write the equation for the alpha decay (α) of Radon-198 • Write the equation for the beta decay (β-) of Carbon-14 • Write the equation for the positron emission (β+) of Oxygen-15 • Write the equation if Krypton-81 were to undergo electron capture • Write the equation for the gamma decay (γ) of Cobalt-60 • Name the isotope that is the product of the alpha decay (α) of Polonium-194

36. Nuclear Stability • The strong nuclear force holds all nuclei together • Otherwise protons would repel each other • Neutrons space out protons and make nucleus stable • Not all isotopes are radioactive • Only unstablenuclei decay • In smaller atoms stable isotopes have equal numbers of protons and neutrons • In larger atoms stable isotopes will have more neutrons than protons • Too many or too few neutrons makes the nucleus unstable

37. Nuclear Stability Graph Dark band = stable nucleus Areas off line = radioactive

38. Fission • Fission is when a nucleus splits • This is what happens in nuclear power plants • Neutrons emitted during fission reactions can cause other fission reactions • This is a chain reaction • In a nuclear reactor the chain reaction is controlled with control rods

39. Chain Reaction • Each reaction allows multiple other reactions to occur • Controlled vs Uncontrolled

40. Fusion • When two or more elements fuse (combine) to form one new heavier element • The energy released by the sun and all stars is due to fusion reactions in the core • This process releases more energy than fission • Fusion reactions are hard to contain because the reactants are a plasma and at very high temperatures, no solid material can contain a plasma

41. Fission Fusion Nucleus splits Nuclei combine Energy is released End product is lighter than reactants End product is heavier than reactants Nuclear Change Can’t contain reaction Reaction can be harnessed LOTS of energy released

42. Fission vs. Decay • These are not the same! • Decay is a natural process, whereas fission has to be induced (requires tremendous energy) • This explains why a nuclear bomb (fission) releases so much more energy!!!!!