1. Chapter 5 The Atomic Nucleus
Lecture Presentation
Chapter 5 The Atomic Nucleus
Bradley Sieve
Northern Kentucky University
Highland Heights, KY

2. 5.1 Radioactivity Results from Unstable Nuclei
Due to the ratio of protons to neutrons
Unstable Nuclei
Contains an “off-balance” ratio of protons and neutrons
Transforms the nucleus to a more stable composition

3. 5.1 Radioactivity Results from Unstable Nuclei
Radioactive Materials
Material containing unstable nuclei
Radioactivity
Emitted high-energy particles and radiation from unstable nuclei
Radioactive Decay
Process of emitting radioactivity

4. 5.1 Radioactivity Results from Unstable Nuclei
Three types of radiation are emitted
Alpha (α)
Alpha particles carry a positive electric charge
Beta (β)
Beta particles carry a negative electric charge
Gamma (γ)
Gamma particles carry no electric charge

5. 5.1 Radioactivity Results from Unstable Nuclei

6. 5.1 Radioactivity Results from Unstable Nuclei
Alpha Radiation
Releases a stream of alpha particles
Alpha Particle
Contains two protons and two neutrons
The same as a helium nuclei
Low penetrating power due to large mass (2 a.m.u.) and double positive charge (+2)

7. 5.1 Radioactivity Results from Unstable Nuclei
Beta Radiation
Releases a stream of beta particles
Beta Particle
Is simply an electron ejected
Medium-range penetrating power with small mass and a single negative charge

8. 5.1 Radioactivity Results from Unstable Nuclei
Gamma Radiation
High-frequency electromagnetic radiation
Gamma Particle
Is pure energy
Highest penetrating power as there is no mass or charge with the particle

9. 5.1 Radioactivity Results from Unstable Nuclei

10. 5.1 Radioactivity Results from Unstable Nuclei

11. 5.2 Radioactivity Is a Natural Phenomenon
Radioactivity has always been present
Contained in soil, air, the earth’s core
Most radiation is natural background radiation
81% natural sources
15% medical and diagnostic sources
4% consumer products

12. 5.2 Radioactivity Is a Natural Phenomenon

13. 5.2 Radioactivity Is a Natural Phenomenon
Radon-222
Is a common source of radiation
Arises from uranium rocks
Can collect in basements to unsafe levels

14. 5.2 Radioactivity Is a Natural Phenomenon
Mutations
Alterations in genetic information contained in our cells
Normally harmless but may cause conditions such as many types of cancer
May be passed on to offspring if damage is in a person’s reproductive cells

15. 5.2 Radioactivity Is a Natural Phenomenon
Rems are units of radiation
Units measure the ability of radiation to cause harm
Lethal doses of radiation begin at 500 rems
Often measured as millirems

16. 5.2 Radioactivity Is a Natural Phenomenon
Radioactive Tracers
Allow molecules to be traced due to radiation
Generally act the same as nonradioactive molecules

17. 5.2 Radioactivity Is a Natural Phenomenon
Medical Imaging
Isotopes used for the diagnosis of internal disorders
Tracer path not influenced by radioactive properties

18. 5.2 Radioactivity Is a Natural Phenomenon

19. 5.3 Radioactivity Results from an Imbalance of Forces
Strong nuclear force
Very strong force between nucleons
Only effects very short distances
Repulsive electric forces effect over relatively long-ranges

20. 5.3 Radioactivity Results from an Imbalance of Forces
Protons far apart may experience stronger repulsive force than the attractive strong nuclear force

21. 5.3 Radioactivity Results from an Imbalance of Forces

22. Concept Check
Two protons in the atomic nucleus repel each other, but they are also attracted to each other. Why?

23. Concept Check
While two protons repel each other by the electric force, they also attract each other by the strong nuclear force. These forces act simultaneously.

24. 5.3 Radioactivity Results from an Imbalance of Forces
Neutrons act as the “nuclear cement”
Neutrons feel attraction but not repulsion because they do not have a charge

25. 5.3 Radioactivity Results from an Imbalance of Forces
Neutrons can decay to a proton and an electron
This will destabilize the nucleus by increasing the number of protons

26. 5.4 Radioactive Elements Transmute to Different Elements
Transmutation
Changing of one element to another
uranium transmuting into thorium

27. 5.4 Radioactive Elements Transmute to Different Elements
Nuclear Equation
Mass numbers at the top balance
Atomic numbers at the bottom also balance

28. 5.4 Radioactive Elements Transmute to Different Elements
Radioactive particle notations

29. 5.4 Radioactive Elements Transmute to Different Elements
Changes in atomic number by each type of particle release
Alpha: decrease by two
Beta: increase by one

30. 5.4 Radioactive Elements Transmute to Different Elements
U-238 decays to Pb-206 through a
series of alpha and beta decays

31. 5.5 The Shorter the Half-Life, the Greater the Radioactivity
Radioactive isotopes decay at different rates
Decay rate is measured as an element’s half-life
Half-life is defined as the time required for half of the radioactive atoms to decay

32. 5.5 The Shorter the Half-Life, the Greater the Radioactivity

33. 5.6 Isotopic Dating Measures the Ages of Materials
N-14 is converted to C-14 in the atmosphere
C-14 is incorporated into plant life through photosynthesis
Animals also ingest C-14 by eating plants

34. 5.6 Isotopic Dating Measures the Ages of Materials
C-14 decays back to C-12 over time
Plants replenish C-14 while growing to maintain a constant amount
Once plant dies, amount of C-14 decreases

35. 5.6 Isotopic Dating Measures the Ages of Materials
Carbon-14 Dating
Used to calculate the age of carbon-containing artifacts
Half of the C-14 decays in about 5730 years
Exhibits roughly a 15% error rate

36. 5.7 Nuclear Fission—The Splitting of Atomic Nuclei
Splitting a large nucleus into smaller halves
Releases enormous amounts of energy

37. 5.7 Nuclear Fission—The Splitting of Atomic Nuclei
Chain Reaction
When a product of one reaction begins the next reaction
Neutrons propagate the chain reaction for U-235

38. 5.7 Nuclear Fission—The Splitting of Atomic Nuclei
Nuclear Fission Reactors
Produces electrical energy from nuclear reactions
1 kg of U yields more energy than 30 freight-car loads of coal

39. 5.7 Nuclear Fission—The Splitting of Atomic Nuclei
Major components of a fission reactor
Nuclear fuel
U-238 mostly with about 3% U-235
Control rods
Neutron-absorbing material
Moderator
Slows the velocity of the neutrons
Liquid
Transfers the heat from the reactor

40. 5.7 Nuclear Fission—The Splitting of Atomic Nuclei
Radioactive Waste
By-products of nuclear reactions
Half-lives range from short to thousands of years
Disposal of waste is problematic

41. 5.8 The Mass-Energy Relationship. E=mc2
Albert Einstein
Postulated that mass and energy are two sides of the same coin
E=mc2
E = energy
m = mass
c = speed of light

42. 5.8 The Mass-Energy Relationship. E=mc2
Variation of average mass based on the nucleus that contains it
Nucleons lose mass in their transition from uranium to a smaller fragment

43. 5.9 Nuclear Fusion—The Combining of Atomic Nuclei
Combining two light nuclei to form a larger nucleus
Mass is lost during the fusion process
Lost mass is released as energy

44. 5.9 Nuclear Fusion—The Combining of Atomic Nuclei
Thermonuclear Fusion
Fusion brought about by high temperatures
Can be initiated by a fission reaction

45. 5.9 Nuclear Fusion—The Combining of Atomic Nuclei
Controlling fusion can be done using plasmas
Magnetic straitjacket for hot ionized gases
Currently no commercial fusion power plants in use