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. X A Z Isotope Symbol Review A = number of protons + number of neutrons
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. Fill in the chart for each isotopeU
235 92 U
238 92 A Z
# of protons (Z)
# of neutrons (N)
235 A Z
# of protons (Z)
# of neutrons (N)
238 92 92 92 92
143
146
Isotopes of any particular element contain the same number of protons, but different numbers 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. Alpha Decay - α
An alpha particle is identical to a helium nucleus.
Contains two protons and two neutrons.
Can be stopped by paper (weak). He 4 2

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

16. U + He U + Th Write the equation for the alpha decay of Uranium-23492 + Th
230 90

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

18. e Beta Emission - b- -1 beta particle (electron)
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). e -1
beta particle
(electron)

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

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

21. C + C N + e Write the equation for the beta emission of carbon-14 147 + e -1

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

23. 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 e -1

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

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

26. Ni + Ni e + Co Write the equation for electron capture of nickel-59 5928 e -1 + Co 27

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

28. e Positron Emission b+ +1
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). e +1

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

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

31. O + O N + e Write the equation for the positron emission of oxygen-167 + e +1

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

33. 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 no change in mass or atomic number g

34. Summary Reaction What happens? Mass # Atomic # -4 -2 No change +1 -1
Alpha Decay a
Lose Helium Nucleus -4 -2
Beta Decay b-
Lose electron from nucleus
(neutron turns into proton)
No change +1
Electron Capture
Gain electron in nucleus (proton turns into neutron) -1
Positron Emission b+
Lose positron
(proton turns into neutron)
Gamma Decay g
Emit high energy gamma ray

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 Not all isotopes are radioactive
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 unstable nuclei 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!!!!!