Intro to radiation physics
NHS University Hospitals Coventry and Warwickshire NHS Trust Introduction to Radiation
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Learning Outcomes:
Review atomic & nuclear structure
What is radiation
Types of radiation
Waves and particles
Interactions between radiation and matter
Page 4: Atomic Scale
Everything is made of atoms
Atoms can combine to make molecules in a highly predictable way
Page 5: Atomic Structure
Bohr Model of the atom
Electrons arranged in shells
Size of atom, nucleus, and their ratio
Comparison with astronomy
Page 6: Sub-atomic particles
Protons: positive charge, mass
Neutrons: neutral charge, mass, holds the nucleus together
Electrons: negative charge, mass
Page 7:Electron Shells
Innermost shell is K shell, can support two electrons
Second shell is L, can support eight electrons
Third shell is M, can support eight electrons (plus an extra 8)
Outermost shell is the valence shell
Page 8: Periodic Table
Groups elements with similar chemical properties together
Nomenclature: Element, Atomic Number, Mass Number
Elements form chemical bonds to create stable molecules
Page 10: Stable Atoms / Molecules
A stable atom has a complete outermost electron shell
Chemical reactions occur when atoms exchange electrons
Elements in column 8 are found naturally, others form chemical bonds
Page 12: Excitation and Ionisation
Electrons closest to the nucleus are most tightly bound
Excited atom: electron moves to another shell, atom has extra energy
Ionisation: electron leaves the atom, atom becomes positively charged
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Brief summary so far:
Quick refresher on atoms and atomic structure
Different types of atoms and their differences
Atomic stability and the role of electrons
How atoms combine to become stable molecules
Excitation and Ionisation
Page 14: Radiation
Definition of radiation
Emission of energy as electromagnetic waves or moving subatomic particles
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Particles:
Moving particles have kinetic energy
Faster and heavier particles have more energy
Waves:
Also carry energy
Page 16 :Electromagnetic Radiation
Cell Phone frequencies
Non-ionizing and ionizing radiation
Page 17: EM Radiation
Electromagnetic waves consist of rapidly oscillating electric and magnetic fields
Transverse wave with oscillations at right angles to the direction of motion
Wavelength, frequency, and velocity of electromagnetic waves
Page 18: Features of waves
Low and high frequency
Speed of light is fixed at 300,000 km/s
If frequency increases, wavelength decreases
Page 19: Dual Nature of EM radiation
EM radiation can be both a wave and a particle
Photons are particles of EM radiation
Photons have discrete bundles of energy called quanta
Photons have no mass and travel at the velocity of light
Page 20: Electromagnetic Radiation - Photons
Increasing frequency leads to increasing photon energy
Page 21: Intensity of EM Radiation
Intensity is the total energy per second flowing past unit area
Inverse Square Law: Energy spreads over an ever-widening area
Page 22: Excitation and Ionisation
Excitation and ionization are processes that occur when radiation passes through matter
Excitation involves raising electrons to higher energy levels
Ionization involves removing electrons from atoms or molecules
Page 23: Attenuation
Radiation passing through matter is attenuated (reduced in intensity)
Attenuation follows an exponential decay law
Equal thicknesses of matter absorb equal fractions of incident radiation
Half value layer (HVL) is the thickness of material required to attenuate X-rays by 50%
Page 24: Scatter and Absorption
X-ray beams passing through matter are attenuated through absorption and scatter
Absorption involves the removal of X-ray photons from the beam and deposition of energy in matter
Scatter involves the removal of X-ray photons from the beam and change in direction, with some absorption involved
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Summary
Identified radiation as particles or waves
Discussed properties of radiation
Discussed interchangeability between particles and waves
Discussed spreading of radiation with distance
Discussed interactions of waves or particles with matter
P
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Interactions between Photons and Matter
No specific details mentioned
Page 28: Coherent or Elastic Scatter
Elastic scatter occurs when an incident photon passes close to an electron, causing it to vibrate and absorb the photon
The vibrating electron re-radiates the photon in a different direction, resulting in scatter without absorption
This process occurs at low photon energies (1-30 keV)
Interaction probability is inversely proportional to energy and proportional to the square of the atomic number (Z)
Page 29: Compton Scatter
Compton scatter occurs when an incident photon bounces off a free electron, reducing its energy and changing its direction
This process results in scatter and absorption
Interaction probability gradually decreases with increasing energy
Interaction probability depends on electron density, which is similar for most materials and independent of atomic number (Z)
Page 30: Photoelectric Effect
The photoelectric effect occurs when an incident photon is totally absorbed by a bound electron, causing ionization
This process results in absorption
Interaction probability is proportional to the cube of the atomic number (Z) and inversely proportional to energy
Page 31: Pair Production
Pair production occurs when a photon turns into an electron and a positron in the presence of a nucleus
This process results in absorption
Requires high energy (1.02 MeV) incident photons
Interaction probability is independent of energy and atomic number (Z)
Page 32: Interaction Probabilities
Interactions between photons and matter are random
Different conditions favour different interactions, including photon energy and tissue type
Rarely, an electron can be fully stopped, releasing all its energy and producing a spectrum of X-ray energies
Page 33: Interaction Probabilities
Lead has a K-edge at 88 keV
Iodine has a K-edge at 33 keV
Page 34: Interactions between Electrons and Matter
Electrons interact with electrons in shells and the nucleus
Electrons in shells repel the incident electron
Protons in the nucleus attract the incident electron
Page 35:Interactions between Electrons and Matter
Electrons are repelled by electrons in the electron cloud, causing deflection and energy transfer
This can result in scatter with some absorption
Incident electrons can occasionally interact with a nucleus, leading to attraction
Page 36:Bremsstrahlung
Bremsstrahlung occurs when an electron is deflected by the electrostatic attraction of a nucleus, resulting in the release of a single X-ray
Rarely, the electron is fully stopped, releasing all its energy and producing a spectrum of X-ray energies
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Overall summary
Review of atomic and nuclear structure
Radiation is the transfer of energy
Types of radiation include waves and particles
Dual nature of radiation
Interactions between radiation and matter include elastic scatter, Compton scatter, photoelectric effect, pair production, and bremsstrahlung
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Learning Outcome
No specific details mentioned