Atomic and Nuclear Physics

1
Atomic and Nuclear Physics

• Goals quanta-photons-matter waves, Isotopes,
  Binding Energy, Nuclear Decay and Nuclear
  Reactions

2
Electricity, Magnetism, Light and the
Electromagnetic Spectrum what do they have in
common?

• Moving electrons (electric fields) create
  electromagnetic radiation as exited electrons
  return to ground state
• The moving electron quantizes the energy
• Max Plank energy absorbed and given off in
  multiples quanta and depends on the frequency
  of exited electron
• Energy of quanta E h f h6.63 ee-34Js
• Quantum Mechanics theory deals with energy and
  quantum states

3
Photons

• Calculate energy of a photon of Red light
• E h f c ? f f c/?
• (6.63 ee -34 Js) (4.29 ee14 1/s)
• 2.84 ee -19 J
• Energy of a photon of Violet light 4.97 ee -17
  J
• Much more energy!!!
• Einstein applied quanta to all electromagnetic
  radiation electromagnetic radiation occurs
  in bundles called photons particles of light
• Explained the photoelectric effect where even the
  brightest red light cant produce, violet does!
• so, when the frequency is increased then the
  number of photons produced increases

4

• Compton Shift confirms that photons are
  particle-like because they have momentum
  p m v
• Collisions of photons and electrons produced a
  wavelength shift hence transferring energy
• The Low energy frequencies of the electromagnetic
  spectrum act more wave-like and are sent in
  continuous waves that are easily diffracted AM
  vs Fm
• Light photons are wave-like and particle-like
  reflected, refracted, diffracted, interfere and
  exhibit the photoelectric effect
• Higher frequency electromagnetic waves exhibit
  more photon-like character less interference

5
Wave Model

• deBroglie matter-waves
• Heisenberg uncertainty
• Wave Model of the atom 4 quantum numbers
• Energy Level (period), Sublevel (spdf), Orbital
  and Spin ( o -)
• Why is the electron cloud studied?
• Because that is one way photons are produced
• What about another way that photons are produced
• Electromagnetic energy can also be released from
  the Nucleus of atoms

6
Nuclear Physics

• Elemental Keys show atomic number, symbol and
  average atomic mass
• Atomic number Z number of protons
  identifies the
  element
• N number of neutrons varies
• Isotopes elements with differing number of
  neutrons
• Average atomic mass averaged mass of all
  isotopes of an element (beanium lab)
• Mass Number total amu umu P N
• 1/12 of a C-12 atom 6 P and 6 N

7

• Energy of the nucleus is associated with the
  Strong Force what is a force?
• Transfer or conversion of energywhat energy?
• Binding Energy opposes the repulsive P P
  electromagnetic force (coulomb force)
  default mass
• energy is released when nuclei fuse or split
  matter is not conserved and is converted to
  ENERGY
• Energy and mass, however, are conserved in
  nuclear reactions

8
Calculating Binding Energy

• E m c²
• (Z)(1.007825µ) (N)(1.008665µ) -
  mass bound x
  931.49 MeV / µ
• (problems)

9
Nuclear Decay

• Nuclear Decay an unstable nucleus emits alpha,
  beta particles and gamma photons to become stable
• Alpha He-4 nucleus 2 P 2 N (paper)
• Beta electron or positron N becomes P (Al
  foil)
• Gamma is energy does not affect identity
  (penetrate Pb)
• Decay Series (U-235 series)
• Half-Life time for ½ of a radioisotope to decay
  steady T ½ (1/2)² ex H-Ls

10
Fission and Fusion reactions

• Fission (radioactivity) natural or initiated by
  energetic particles like neutrons
• Heavy nuclei split into smaller nuclei called
  daughter products
• daughter nuclei are more tightly bound and have
  less mass so energy is emitted
• U-235 n -gt Be-140 Kr-93 3n gamma
• nuclear chain reaction but can be controlled by
  Cd rods that absorb neutrons
• U-235 only .7 enriched to sustain reactions
• Ce has the most binding energy Z 58

11

• Fusion lighter nuclei slam together to release
  positrons, neutrinos and gamma
• Thermonuclear reaction
• Stars fuse 4 H to He then He to C
• Proton Proton cycles
• Fusion reactors use deuterium H-2 extreme high
  temperatures plasma contained by magnetic
  fields
• Massive stars fuse nuclei to elements as big as
  Fe then Supernova to produce all otter elements

12

• The End
• Wait..There is more.
• Think of a branch of Physics that considers all
  forms of energy
• What is this fascinating subject?
• Astronomy!
• A Great way to shine
• Shine on Physicists!