1. Nuclear Physics
Spring 2013

2. Intro:
What atom is this?
Where do you find protons?
Where do you find neurons?
Where do you find electrons?
How many protons does it have?
How many neutrons?
Is it a neutral atom, and how do you know?

3. The Atom In the nucleus (nucleons) Proton- (+) charged particle
Neutron- no charge
Outside the nucleus
Electron- (-) charged particle
has almost no mass

4. Nucleons Are particles occupying the nucleus
Consist of + charged protons and neutral neutrons
Have almost 2000 times the mass of electrons

5. Where can you find the number of protons?
It’s the atomic number (found on the periodic table)

6. B Nuclear Notation Atomic Number Atomic Mass 5 10.811
Atomic number = no. of protons
Atomic mass = protons + neutrons
Atomic number is the same as the number of electrons
in an uncharged atom

7. Question 1 1a. How many protons? 1b. How many neutrons?
You may see atomic number written many ways. The smaller number is the atomic number and the larger is the atomic mass
1a. How many protons?
1b. How many neutrons?
1c. How many nucleons?

8. has 13 protons and 14 neutrons for a total of 27 nucleons
The identity of an element depends on the number of protons 28 13

9. Isotopes:
Atoms of the same element with different numbers of neutrons (different masses)
Most common stable isotope of carbon
Unstable radioactive isotope of carbon

10. Question 2 List the four fundamental forces from strongest to weakest1. 2. 3. 4.

11. Review of Fundamental forces
Strongest to weakest
Strong Nuclear Force
Electromagnetic Force
Weak Nuclear Force
Gravity

12. Forces Acting on Nucleons:
Forces of attraction between nucleons
Strong forces
Are independent of the charge of the nucleon
Are short range (exist only between closest neighbors)
Electrical force (electrostatic)
Force of repulsions between positively charged protons
Are long range

13. When are nuclei unstable? (naturally radioactive)
Large nuclei (Z > 82) – electrical forces of repulsion are greater than strong forces of attraction
Wrong neutron : proton ratio
stable nucleus
no. of protons
no. of neutrons 6 13 14 26 30 56 81 82
125

14. When are nuclei unstable?
Bigger atoms require more neutrons per proton to keep the atom stable

15. A radioactive isotope:
Has an unstable nucleus
Spontaneously emits a particle and decays into another element (to become more stable)

16. Transmutation
Changing into another element through radioactive decay

17. Who am I?

18. I worked with my husband and discovered radium, a radioactive material

19. Marie and Pierre Curie
First to discover that compounds containing uranium emitted penetrating rays.
Discovered radioactive polonium and radium

20. Types of Radioactive Emission
Symbol
Composition
Stopped By
Alpha
2p + 2n (helium)
Paper
Beta
1e (electron)
Aluminum
Gamma γ
Energy only
Lead

21. Alpha Decay
Radiation through the loss of 2p + 2n or (helium)

22. Beta Decay
Radiation where a neutron splits, giving off an electron and becoming a proton in the new element

23. Gamma Decay
A change energy state gives off a gamma particle or photon

24. Question 3a
Balance the nuclear equation after alpha decay

25. Question 3a
Balance the nuclear equation after alpha decay

26. Question 3b Balance the nuclear equation after beta decay
Remember in beta decay a neutron changes into a proton by giving off an electron

27. Question 3b Balance the nuclear equation after beta decay
Remember in beta decay a neutron changes into a proton by giving off an electron

28. Extra Question
Which radioactive isotope completes this nuclear decay equation 6

29. Extra Problem
Finish off the equation

30. Half Life and Half Life Calculations
Half Life- time it takes for half of the radioactive sample to decay.
Ranges from a fraction of a second to billions of years
Decay constant- Probability per time that a nucleus would decay

31. Section 2 Intro Rewrite and balance the equation above
What kind of decay is shown above?
What is the particle given off during alpha decay composed of?
What is the particle given off during beta decay composed of?

32. Section 2: Nuclear Physics Math

33. Half Life and Half Life Calculations
y= fraction of radioactive material left n= number of half lives

34. Example 1
How much of the original radioactive material is left after 15 half-lives?

35. Example 1
How much of the original radioactive material is left after 15 half-lives?

36. Half Life and Half Life Calculations
T1/2 = half life
λ = decay constant
The unit for λ and T1/2 will be in the same timeframe

37. Example 2
Cobalt-60, used in radiation therapy, has a half-life of 5.26 y. What is the decay constant for cobalt-60?

38. Example 2
Cobalt-60, used in radiation therapy, has a half-life of 5.26 y. What is the decay constant for cobalt-60?

39. Extra Examples A
A radioactive sample has a mass of 56 mg and a half life of 30 minutes. How much of the sample remains after 60 minutes have passed?

40. Extra Examples B
An unknown radioactive material has a half life of 4000 years. How much of the sample will remain after 20,000 years?

41. Half Life and Half Life Calculations
N = Noe-λt
N = number of radioactive atoms
No = original number of radioactive atoms
t = elapsed time
λ = decay constant
e = 2.72

42. Example 3
Cobalt-60, used in radiation therapy, has a half-life of 5.26 y. A sample of cobalt-60 containing 5.00 x 1012 radioactive atoms sits in a lead case in the medical stockroom for years. How many cobalt-60 atoms remain after this amount of time?
(You already solved for the decay constant in example 2) λ= y-1

43. Example 3
Cobalt-60, used in radiation therapy, has a half-life of 5.26 y. A sample of cobalt-60 containing 5.00 x 1012 radioactive atoms sits in a lead case in the medical stockroom for years. How many cobalt-60 atoms remain after this amount of time?

44. Useful applications of radioactivity
Can be detected and therefore small amounts can be used as tracers for medical diagnosis
Larger amounts can be used as treatments for certain types of cancers (cancer cells are killed before healthy cells)
Can be used to determine the age of rocks and fossils

45. Show what you know

50. Types of Nuclear Reactions
Natural transmutation – Uranium spontaneously decays
Artificial transmutation – bombardment of a stable isotope to force it to decay

51. Question 4
Balance the reaction after the following artificial transmutation.

52. Types of Nuclear Reactions
Artificial transmutation
First done by Earnest Rutherford
When the bullets are positively charged, they are repelled by the nucleus they are bombarding. To overcome the repulsions, they must be accelerated to very high speeds by particle accelerators.

53. Nuclear Fission
Nuclear fission - Heavy nuclei are bombarded with neutrons and split.
plus a tremendous amount of energy

54. Nuclear fission
Mass of particles produced is slightly less than the mass of the reactants. This mass is converted into energy. (E=mc2)

55. Nuclear fission is a chain reaction
Nuclear fission is a chain reaction. Neutrons are needed to start and released as a product which can start more reactions.
Critical mass: minimum mass of fissionable material required for a chain reaction.

56. Problems with Fission
Nuclear fission produces radioactive waste that has a large half life.
U Uranium 235
Half life of U-235 is 713 million years
We cannot get rid of this dangerous product so we store it away from anything it can harm.
We deeply bury
Meltdown if cooling system fails the reactor can overheat and melt releasing radioactive materials

57. Nuclear fusion – combination of small nuclei into larger with release of energy.
Mass of particles produced is much less than the mass of the reactants.
This mass is converted into energy. (E=mc2)
Can release up to 10 times that of fission
Occurs naturally in our sun and other stars
Does not give off radioactive waste

58. Problems with Fusion
Fusion requires high temperatures like those in the stars.
We cannot sustain these temperatures without vaporizing the container of the fusion reaction.
Today many are looking into ways of making fusion work under sustainable conditions