PHYS1004: Radiation

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PHYS1004 Radiation

• Bill Tango
• Room 314

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Electromagnetic radiation

• EM waves predicted by Maxwell
• EM waves travel (in vacuum) at c 3x108 m/s.
• The wavelength-frequency relation lf c
• EM waves cover wide range of frequencies
• Continuum line radiation

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Blackbody radiation photoelectric effect

• Blackbody radiationthe predictions of
  classical mechanics are completely wrong.
• The photoelectric effect difficult to explain
  classically.

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Einstein PE Effect

• Einsteins interpretation light consists of
  quanta having energy E hf where h is Plancks
  constant.
• Quanta give up their energy on an all or nothing
  basis.
• This provides an explanation for the PE effect.
• But how can we reconcile wave and particle
  pictures?

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deBroglie Waves

• Photon momentum the wavelength
• deBroglie by analogy there may be matter waves
• Experimentally confirmed.
• Interpretation
• Matter probability waves
• Light and probability waves

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Schrödingers Equation

• Mathematically, the waves are described by
  Schrödingers equation.
• Properties of the wave function and
  interpretation as a probability density
• The Heisenberg uncertainty principle
• Interpretation

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Potential wells

• Electrons/particles in potential wells
• The infinite potential well
• Transition energies absorption/emission of
  photons
• The quantisation of energy states
• Finite wells (qualitative only)
• Tunnelling (qualitative)

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The Hydrogen Atom

• Bohrs theory
• The predictions of quantum mechanics

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Properties of atoms

• Line spectra revisited
• Electron spin
• Quantum numbers n, l, m, s
• The Pauli exclusion principle
• Atom building

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Revision EM radiation

• Electromagnetic radiation
• The EM spectrum
• Line spectra
• Black body radiation qualitative
• Wien displacement law
• The problems with the classical theory

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PE Effect

• No photocurrent when f lt fc
• When f gt fc, current proportional to intensity.
• Stopping potential
• Einstein Light consists of quanta or photons.

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Photons, waves, deBroglie

• Classical EM wave only gives the probability of
  finding a photon somewhere.
• deBroglie extends concept to matter waves
• Wave must be interpreted as a probability density
  function.

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Heisenberg uncertainty principle

• Because we can only predict probabilities, we
  cannot know exact position/momentum
• Uncertainty is intrinsic.

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Schrödingers Equation

• The probability wavesthe wave functionare
  described by Schrödingers equation.
• The square of the wavefunction, ?2(x), gives the
  probability.
• Qualitative interpretation of the waves
  relation to deBroglie waves.

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Potential wells

• What is a potential well?
• Bound states are quantised particles can only
  have certain energy states.
• Transitions between states are quantised hf Ef
  Ei.
• Example infinite potential well.
• Tunnelling qualitative only.

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Atoms

• The Bohr picture for hydrogen.
• The energy levels of hydrogen En
  -13.6/n2 eV.
• Quantum numbers n, l, ml, s
• The Pauli exclusion principle
• Atom building and the periodic table
  (qualitative).

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X-rays

• The continuous X-ray spectrum
• The line spectrum
• Moseley and Rutherfords work atoms contain
  small, dense nuclei
• The size of nuclei

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Properties of nuclei

• Terminology (atomic number, mass number,
  isotopes, nuclides)
• The relation between mass and energy E mc2
• Nuclear masses and the binding energy
• The mass defect fission and fusion

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Radioactive decay

• The decay rate disintegration constant l.
• Activity total decay rate
• Half-life mean lifetime
• SI unit becquerel

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Alpha, beta gamma rays

• The characteristics of alpha radiation
• The characteristics of beta radiation
• Two kinds
• Evidence for the neutrino
• The characteristics of gamma radiation
• Carbon dating
• Other applications of radioactivity

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Dosimetry

• Basic quantities
• Source activity (unit Bq)
• Exposure
• Absorbed dose (unit gray Gy 1 J/kg)
• Biological dose equivalent (unit sievert Sv)
  H Q.D
• The quality factor Q

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Biological effects of radiation

• The biological half-life
• Effective half-life
• Lethal whole-body dose LD50/30.