1. Nuclear Energy

2. Nuclear Fission
Nuclear fission is the process of splitting a nucleus into two nuclei with smaller masses.
Fission means “to divide”
Remember that fission has 2 s’s, therefore it splits into TWO parts.

3. Fission cont.
Only large nuclei with atomic numbers above 90 can undergo fission.
Products of fission reaction usually include two or three individual neutrons, the total mass of the product is somewhat less than the mass of Uranium-235.

4. Chain Reaction
A chain reaction is an ongoing series of fission reactions. Billions of reactions occur each second in a chain reaction.

5. Chain Reaction cont.
On earth, nuclear fission reactions take place in nuclear reactors, which use controlled chain reactions to generate electricity.

6. Chain Reaction cont.
Uncontrolled chain reactions take place during the explosion of an atomic bomb.

7. Fission Products
The products of nuclear fission reactions are radioactive, but the energy released from these reactions is less harmful to the environment than the use of fossil fuels.
The products are intensely radioactive and must be treated and/or stored.

8. Nuclear Fusion
Nuclear fusion is the combining of two nuclei with low masses to form one nucleus of larger mass.
Nuclear fusion reactions are also called thermonuclear reactions.

9. Nuclear Fusion cont. Fusion reactions exist in stars.
Our sun is a good example of a thermonuclear (fusion) reaction.
It is almost impossible to create fusion reactions on earth since they need temperatures above one million degrees Celsius in order to take place.

10. Nuclear Fusion cont.
Nuclear fusion produces less nuclear waste than nuclear fission and the materials are easier to obtain.

11. Radioactive Isotopes and Half Life

12. Radioactive Isotopes
Radioactive elements are unstable. They decay, and change into different elements over time.
Not all elements are radioactive. Those that are listed below are the most useful for geologic dating of fossils are:
U-238 Half-life = 4.5 Billion Years
K-40 Half-life = 1.25 Billion Years
C-14 Half-life = 5, 730 Years

13. Radioactive Decay and Half Life
Here are some facts to remember:
The half-life of an element is the time it takes for half of the material you started with to decay.
2. Each element has it’s own half-life

14. Radioactive Decay and Half Life
Each element decays into a new element
C14 decays into N14
4. The half-life of each element is constant. It’s like a clock keeping perfect time.
Now let’s see how we can use half-life to determine the age of a rock, fossil or other artifact.

15. The green grid below represents a quantity of C14
The green grid below represents a quantity of C14. Each time you click, one half-life goes by and turns red.
C14 – green N14 - red
Half
lives
% C14
%N14
Ratio of
C14 to N14
100% 0%
no ratio
As we begin notice that no time has gone by and that 100% of the material is C14

16. The grid below represents a quantity of C14. Each time you click,
one half-life goes by and you see red.
C14 – green N14 - red
Half
lives
% C14
%N14
Ratio of
C14 to N14
100% 0%
no ratio 1
50%
1:1
After 1 half-life (5730 years), 50% of
the C14 has decayed into N14. The ratio
of C14 to N14 is 1:1. There are equal
amounts of the 2 elements.

17. The blue grid below represents a quantity of C14. Each time you click,
one half-life goes by and you see red .
C14 – green N14 - red
Half
lives
% C14
%N14
Ratio of
C14 to N14
100% 0%
no ratio 1
50%
1:1 2
25%
75%
1:3
Now 2 half-lives have gone by for a total
of 11,460 years. Half of the C14 that was
present at the end of half-life #1 has now
decayed to N14. Notice the C:N ratio. It
will be useful later.

18. The blue grid below represents a quantity of C14. Each time you click,
one half-life goes by and you see red.
C14 – green N14 - red
Half
lives
% C14
%N14
Ratio of
C14 to N14
100% 0%
no ratio 1
50%
1:1 2
25%
75%
1:3 3
12.5%
87.5%
1:7
After 3 half-lives (17,190 years) only
12.5% of the original C14 remains. For
each half-life period half of the material
present decays. And again, notice the
ratio, 1:7

20. Alpha, Beta, and Gamma Decay
Nuclear Reactions
Alpha, Beta, and Gamma Decay

21. The atom consists of two parts:
1. The nucleus which contains:
protons
neutrons
2. Orbiting electrons.

22. X A Z Mass number = number of protons + number of neutrons
Element symbol Z
Atomic number
= number of protons

23. U U 235 92 238 92 There are many types of uranium: A Z
Number of protons
Number of neutrons A Z
Number of protons
Number of neutrons

24. U U 235 92 238 92 There are many types of uranium: A 235 Z 92
Number of protons
Number of neutrons
143 A
238 Z 92
Number of protons
Number of neutrons
146
Isotopes of any particular element contain the same number of protons, but different numbers of neutrons.

25. Most of the isotopes which occur naturally are stable.
A few naturally occurring isotopes and all of the man-made isotopes are unstable.
Unstable isotopes can become stable by releasing different types of particles.
This process is called radioactive decay and the elements which undergo this process are called radioisotopes/radionuclides.

26. Radioactive decay results in the emission of either:
an alpha particle (a),
a beta particle (b),
or a gamma ray(g).

27. An alpha particle is identical to that of a helium nucleus.
Alpha Decay
An alpha particle is identical to that of a helium nucleus.
It contains two protons and two neutrons.

28. X Y + He A Z A - 4 Z - 2 4 2 unstable atom alpha particle
Alpha Decay X A Z Y
A - 4
Z - 2 + He 4 2
unstable atom
alpha particle
more stable atom

29. Alpha Decay Rn
222 86 He 4 2 Ra
226 88

30. Alpha Decay X A Z Y
A - 4
Z - 2 + He 4 2 Ra
226 88 Rn
222 86 + He 4 2

31. Alpha Decay Rn
222 86 + Y A Z He 4 2 Rn
222 86 He 4 2 + Po
218 84

32. Alpha Decay X A Z + Th
230 90 He 4 2 He 4 2 U
234 92 + Th
230 90

33. Alpha Decay Th
230 90 + Y A Z He 4 2 He 4 2 + Ra
226 88 Th
230 90

34. Alpha Decay X A Z + Pb
214 82 He 4 2 He 4 2 + Pb
214 82 Po
218 84

35. Beta Decay
A beta particle is a fast moving electron which is emitted from the nucleus of an atom undergoing radioactive decay.
Beta decay occurs when a neutron changes into a proton and an electron.

36. Beta Decay
As a result of beta decay, the nucleus has one less neutron, but one extra proton.
The atomic number, Z, increases by 1 and the mass number, A, stays the same.

37. Beta Decay b -1 At
218 85 Po
218 84

38. Beta Decay X A Z Y
Z + 1 + b -1 Po
218 84 Rn 85 + b -1

39. Beta Decay Th
234 90 Y A Z + b -1 Th
234 90 Pa 91 + b -1

40. Beta Decay X A Z Pb
210 82 + b -1 Tl
210 81 Pb 82 + b -1

41. Beta Decay Bi
210 83 Y A Z + b -1 Bi
210 83 Po 84 + b -1

42. Beta Decay X A Z Bi
214 83 + b -1 Pb
214 82 Bi 83 + b -1

43. Gamma rays are not charged particles like a and b particles.
Gamma Decay
Gamma rays are not charged particles like a and b particles.
Gamma rays are electromagnetic radiation with high frequency.
When atoms decay by emitting a or b particles to form a new atom, the nuclei of the new atom formed may still have too much energy to be completely stable.
This excess energy is emitted as gamma rays (gamma ray photons have energies of ~ 1 x J).