1. QUANTUM AND NUCLEAR PHYSICS
Mark Lesmeister
Pearland ISD Physics

2. Acknowledgements
Selected graphics obtained from Wikipedia Commons or en.wikipedia. Their use is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license or similar license. Please see the link for each graphic for details.

3. Permissions
Text and original graphics © Mark Lesmeister and Pearland ISD.
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4. Particles of Light

5. Infrared Videos: Bats Emerging from Caves
Videos from Boston University Center for Ecology and Conservation Biology,

6. Blackbody Radiation All objects emit electromagnetic radiation.
The frequencies of this radiation and the amount emitted depend on the temperature of the object.
“Room temperature” objects emit infrared frequencies.
Very hot objects (like glowing coals) emit visible radiation.
The universe, which has a temperature of 3 Kelvin, is awash with microwave radiation.
(1) This radiation is called “blackbody” since it does not depend on reflected light, that is, it is emitted even from perfectly absorbing objects.
Source: Darth Kule, “Black-body.svg”, Retrieved May 14, Graphic is public domain.

7. Quantization of Energy
In the 19th century, experiments were conducted to measure the blackbody radiation emitted at each wavelength of light.
Source: Darth Kule, “Black-body.svg”, Retrieved May 14, Graphic is public domain.

8. Quantization of Energy
The wave-theory of EM radiation did not agree with the experimental results for blackbody radiation.
Source: Darth Kule, “Black-body.svg”, Retrieved May 14, Graphic is public domain.

9. Quantization of Energy
In 1900, Max Planck developed a new theory that assumed energy isn’t emitted in any amount, but only in packets, called “quanta”.
This “quantum” theory agreed with the blackbody experiments.
Experimental data points based on a graph from Wilson,Buffa and Lou, College Physics, Pearson Education Inc., 2010

10. Planck’s Equation
Planck’s equation relates the energy of a quantum of light with the frequency of light.
Energy = Planck’s constant x frequency
In atoms, energy is measured in electron volts (eV)
1 eV = 1.60 x J
h=4.14 x eV-s
Show above, then do Problems 23A, p. 833.

11. Photon Practice 1
A certain radio station broadcasts a radio wave of 100 MHz and 30,000 W power.
How many photons does the station emit per second?
Answer: 4.5 x 1029 photons/second

12. Photon Practice 2
Two monochromatic light beams, one red and one green, have the same intensity and cover the same area. How does the energy of each photon and the number of photons in each beam compare?
Photon Energy # per Second
A) Same Same
B) Greater for red Less for red
C) Greater for red Greater for red
D) Less for red Less for red
E) Less for red Greater for red

13. The photoelectric effect
Here is another example of the particle behavior of light. This photoelectric effect is behind every light sensor, digital camera, etc.
The photoelectric effect

14. The Photoelectric Effect
When light strikes a metal surface, it will give off electrons.

15. The Photoelectric Effect
If light is a wave, then a light beam that has greater intensity (greater energy) should cause the electrons given off to have more energy.
A more intense light beam causes more electrons to be emitted, but they all have the same energy.

16. The Photoelectric Effect
Einstein explained the photoelectric effect by assuming that light was made of particles.
A more intense light beam has more photons, but each carries the same energy.
Thus, more intense light would produce more electrons, with the same energy.

17. The Photoelectric Effect

18. Quantum Theory of Light and the Photoelectric Effect
When a photon strikes a metal plate, it transfers energy to the electrons in the plate.
If an electron acquires enough energy, it can be ejected from the plate.
The energy necessary to eject an electron is called the “work function” of the metal.
The kinetic energy of the electrons will be the energy of the photon minus the work function.

19. Photoelectric Effect: Practice
A certain beam of light has photons with 5 eV of energy. When this light strikes a metal plate, electrons with eV of kinetic energy are released. What is the work function of the metal?
Answer: 2 eV

20. The Cutoff Frequency

21. The Cutoff Frequency
The cut-off frequency is the frequency that produces photons of just enough energy to be emitted, i.e. equal to the work function.
Photons with less energy will not be able to eject electrons.
Work Function = h fCutoff

22. Wave Particle Duality
In some experiments, such as blackbody radiation and the photoelectric effect, light acts like a particle (called a photon).
In others, like double slit interference and thin film interference, light acts like a wave.
Light never appears as both in the same experiment.
Source: “John-” – “Dieselrainbow. Jpg” Wikipedia Commons- Creative Commons Attribution-Share Alike 3.0 Unported license
“God runs electromagnetics by wave theory on Monday, Wednesday, and Friday, and the Devil runs them by quantum theory on Tuesday, Thursday, and Saturday.” - Sir William Bragg

23. The Quantum Theory of Light and the Atom

24. Review- Electrical Potential Energy
An atom’s electrons are attracted to its nucleus.
It requires energy to separate them.
The farther away an electron is from the nucleus, the greater the energy.

25. Energy Levels The electrons in an atom occupy discrete energy levels.
These levels are determined by the type of atom involved.
An electron gains or loses energy when transitioning between levels.

26. Energy Levels
We use an energy level diagram to represent the levels.

27. Absorption
When an atom absorbs a photon of light, an electron “jumps” from a lower energy level to a higher energy level.
Only photons with the right amount of energy will cause an electron to jump to a higher level.

28. Absorption
When an atom absorbs a photon of light, an electron “jumps” from a lower energy level to a higher energy level.
Only photons with the right amount of energy will cause an electron to jump to a higher level.

29. Emission
Electrons at higher levels can jump back to a lower energy level by emitting a photon.
The frequency of the emitted photon is determined by the energy that the electron gave up.

30. Energy Levels
Electrons at higher levels can jump back to a lower energy level by emitting a photon.
The frequency of the emitted photon is determined by the energy that the electron gave up.

31. Emission Spectra
Since the energy levels are different for each type of atom, the wavelengths of light given off by the excited electrons jumping back down are different for each type of atom.
We can thus identify the atoms by the colors of light they emit.
The pattern of colors is called an emission spectrum.

32. Emission Spectra H Fe Source: Adrignola, “Emission spectrum-H.svg”
Yttrium91, “Emission spectrum-Fe.svg”
Wikipedia Commons, public domain

33. Absorption Spectra
When light containing all wavelengths passes through a gas, the same wavelengths of light that appear in that gas’ emission spectrum will be absorbed by the gas.
Source: Maureen Gebruiker, “Fraunhofer lines.svg” Wikipedia Commons, public domain

34. Consequences of Quantum mechanics
View video “BBT: Schrodinger’s Cat” (17:45-)
Consequences of Quantum mechanics

35. Double Slit Experiment for Electrons
We can carry out a double slit experiment for electrons just like Thomas Young did for light.
But electrons are particles, so they won’t produce an interference pattern, right?

36. Double Slit Experiment for Electrons
Source: Belsazar, Double-slit experiment results Tanamura 2.jpg, Wikipedia Commons, Creative Commons Attribution-Share Alike 3.0 Unported license.

37. Double Slit Experiment for Electrons
Electrons interfere with each other, just like waves.
If we cover up one slit, the wave-like behavior goes away.

38. The wave-particle duality of matter
Particles of matter, such as electrons, atoms, etc., can also behave like a wave in some experiments.
These matter waves are called de Broglie waves.
The wavelength of these waves is given by the equation l = h/p .
The frequency is given by the equation f=E/h

39. Nuclear Physics

40. The Nucleus An atomic nucleus consists of protons and neutron.
When we want to specify a specific isotope, we write the mass number and atomic number.

41. Units of Mass and Energy in Nuclear Physics
In nuclear physics, mass is usually stated in terms of atomic mass units, or u.
1 u = X kg
Energy is usually stated in electron-volts, or eV.
Particle
m (kg)
m (u)
Proton
1.673 x 10-27
Neutron
1.675 x 10-27
Electron
9.109 x 10-31
1 eV= X J

42. Mass-Energy Equivalence
Energy and mass are equivalent.
Einstein’s equation shows how much energy a quantity of mass corresponds to.

43. Mass-Energy Equivalence
Particle
m (kg)
E (MeV)
Proton
1.673 x 10-27
938.3
Neutron
1.675 x 10-27
939.6
Electron
9.109 x 10-31
0.5110
Energy and mass are equivalent.
Einstein’s equation shows how much energy a quantity of mass corresponds to.
Have the students calculate the equivalence of a kilogram of mass.
1 u = MeV

44. The Strong Force
The electric force would cause the protons in a nucleus to repel each other.
The strong force is an attractive that overcomes the electric repulsion over small distances.
Both protons and neutrons attract by the strong force.
Neutrons help stabilize the nucleus.
Elements with Z>83 do not have stable nuclei.

45. Fundamental Forces Force Strength* Range Field Particle Strong Nuclear1
~ 1 fm = m
gluon
Electromagnetic
10-2
Infinite (1/r2)
photon
Weak Nuclear
10-13
< 10-3 fm
W+,W-, and Z
Gravity
10-38
graviton
* Since the forces involve different quantities and vary with distance, their strength is not a simple comparison. The answer on the homework reverses the weak nuclear and electromagnetic force relative strength.

46. = + Binding Energy Binding Energy
The total energy or mass of a stable nucleus is less than the mass of the individual nucleons.
The difference is called the binding energy, Ebind =
+ Binding Energy

47. = + Binding Energy Mass Defect
Since mass and energy are equivalent, the difference can also be expressed in terms of mass.
The difference in mass is called the mass defect, Δm =
+ Binding Energy

48. Nuclear Physics Questions 1 & 2
Determine the mass defect and binding energy of deuterium.
Determine the mass defect and binding energy of helium.
Particle
m (u)
E (MeV)
Proton
938.3
Neutron
939.6 D He
1 u = MeV

49. Binding Energy and Nuclear Reactions
Nuclear reactions involve the nuclei of atoms.
If a rearrangement of protons and neutrons in a nucleus or nuclei results in a greater binding energy, the reaction will release energy.
Energy

50. Nuclear Physics Question 3
Determine the energy “released” when 2 deuterium combine to form a helium nucleus.
Particle
m (u)
E (MeV)
Proton
938.3
Neutron
939.6 D He
1 u = MeV

51. Nuclear stability
The attraction of the strong force results in lower energy/nucleon for light nuclei.
Because the range of the strong force is limited, beyond a certain size, binding energy/nucleon increases.
Source: Fastfission, Wikipedia, public domain

52. Fission
In nuclear fission, heavy nuclei split into lighter nuclei.

53. Fission This may result in a chain reaction.
A nuclear reactor uses a controlled chain reaction.
The first “atomic” bombs were fission bombs.

54. Fusion Light nuclei can undergo fusion.
Fusion is the nuclear reaction that powers the sun.
Researchers are trying to develop a fusion reactor that releases more energy than it uses.
Source: Wykis, “Deuterium-tritium fusion.svg” Wikipedia Commons, public domain

55. Nuclear Physics Question 3
Correct statements about the binding energy of a nucleus include which of the following:
I) It is the energy needed to separate the nucleus into its individual nucleons.
II) It is the energy liberated when the nucleus is formed from the original nucleons.
III) It is the energy equivalent of the apparent loss of mass of its nucleon constituents.
A) I only. B) III only.
C) I and II only. D ) II and III only.
E) I, II, and III

56. Nuclear Radiation

57. What is your radiation dose?
Calculate Your Radiation Dose | Radiation Protection | US EPA

58. Nuclear Decay
An unstable nucleus can break apart into other particles, releasing energy.
This process occurs naturally in hundreds of types of nuclei. +
+ Energy

59. Nuclear Radiation
Three types of radiation are emitted in radioactive decay.
Particle
Symbol
Composition
Charge
Effect on Parent
Alpha
2 protons,
2 neutrons
(He nucleus) +2
Less mass, new element
Beta
electron
positron -1 +1
~same mass, new element
Gamma
photon
Energy loss
Based on “Holt Physics, Table 25-3, p. 903

60. Uses of nuclear radiation
Carbon dating
Chemical tracing
Radiation therapy
Food irradiation
Sterilization of medical equipment
Non-destructive testing
Smoke detectors
Security scanning
Nuclear power

61. Carbon Dating
Some atmospheric carbon is C-14, produced by cosmic rays.

62. Carbon Dating
This carbon-14 naturally decays to nitrogen with beta decay. -

63. Radioactive Decay Question 1