Interaction of radiation with matter
E = h ν ; c = λ ν
h= 6.626 068x10-34 Js = 4.135 667x10-15 eVs
c=299 792 458 m/s
  • Low frequency
    long wavelength
    low quantum energy
Radio Waves Flow of electric charges (electric currents)
No Energy level pairs available
λ: 1 m to 105 m
Microwaves Molecular rotation and torsion
Conductors: electric currents
λ: 1 mm to 1m
Molecular vibration
λ: 700 nm to 1mm
Visible light electronic transitions outer shells electrons
λ: 400 nm (violet) to 700 nm (red)
E: 1.7 eV to 3.3 eV
Ultraviolet Near ultraviolet: electron transitions
Higher frequencies: Ionization
λ: 10 nm to 400 nm
E: 3.3 eV to 124 eV
X-rays Electronic transitions inner shell (core) electrons
Photoinization (Photoelectric effect, Compton scattering, Pair production)
Source: Bremsstrahlung -braking radiation-, Transitions between lower atomic energy levels in heavy elements
λ: 0.01 nm to 10 nm (Φ atom: 0.1 nm to 0.5 nm)
E: 124 eV to 124 KeV
γ rays Ionization (Photoelectric effect, Compton scattering, Pair production)
inverse Compton scattering
Synchroton radiation
Source:Radioactive decay of atomic nuclei
λ < 0.1 nm
E > 124 eV
  • High frequency
    short wavelength
    high quantum energy

Scattering in molecules
Rayleigh scattering Elastic scattering
ground state → Virtual energy state → ground state
Scattered photon has the same frequency and energy of the incident photon
Stokes Raman scattering Inelastic scattering
Ground state → Virtual energy state → Vibrational energy states
Scattered photon has less energy and frequency than the incident photon
Rotational transitions and vibrational transitions in molecules
Anti-Stokes Raman scattering Vibrational energy state → Virtual energy state → ground state
Scattered photon has more energy and frequency than the incident photon

Scattering radiation
Mie Particles sizes are similar or larger than the wavelength of incident photon
The greater the particle size, the more of the light is scattered in the forward direction
size similar to the wavelength: white or grey colour -milk, clouds-
Rayleigh Particles sizes are much smaller than the wavelength of incident photon
The scattering intensity is proportional to ν4 of the incident photon
blue colour of the sky
Brillouin Interaction of light and material waves( quasiparticles:phonons, polarons, magnons) within a medium

Interactions of photons with matter
Elastic scattering Photon frequency do not change
Change direction (deflection) of incident photon
Energy of incident photon (ν) too small
scattered photon frequency (ν')
  • Thomson scattering
    • a photon interacts with charged particles (electrons)
    • Photon energy is much less than the mass energy of the particle hν<<mc2
    • Photon energy is less than the binding of the electron hν<EB
    • γ+e →γ+e
  • Rayleigh scattering
    • a photon interacts with particles (atoms or molecules) much smaller than the wavelength of the incident photon
    • γ+atom→γ+atom
Photoluminescence Inelastic scattering
It is the emission of light when photons interact with matter
The emitted photon has a longer wavelength
  • Fluorescence
    • It inmmediately re-emit the radiation it absorbs
  • phosphorescence
    • It does not inmmediately re-emit the radiation it absorbs
    • it is associated with forbidden energy state transitions (Triplet state → Singlet state)
Photoelectric effect Production of electrons when photons interact with matter
The probatility of PE
    The probatility of PE interaction
  • it is proportional to Z3/E3
  • it is greater when Incident photon energy ≈ Binding energy of inner shell electron
    Steps of PE effect
  • Incident photon (or electron)
  • Excites an atom
  • Photon disappears completely (absorbed)
  • Emits a photoelectron from inner shells (K)
  • left an electron-hole in K shell
  • Atom becomes ionised and unstable (ion +)
  • electron in higher energy shell (L) moves to shell K
  • Emits a characteristic radiation (x ray) or
  • the energy is transferred to an outer electron, ejecting it from the atom (Auger Effect)
  • holes in successive shells are filled by electron transitions from outer shells
Compton scattering It is an inelastic scattering of photons (X-ray or γ ray ) by free electrons
The photon energy is very much larger than the binding energy of the atomic electron
Outer shell electron (almost free) is ejected -recoil electron-
the scattered photon has less energy
λ of scattered photon = 0.024 (1- cos θ by which the photon is scattered)
low energy e- + high energy γ → higher energy e- + lower energy γ
  • Inverse Compton scattering
    • high energy e- + low energy γ → lower energy e- + higher energy γ
Pair production It is the creation of a positron-electron pair at the vicinity of an atom
The incident photon energy (Eγ) must have at least an energy of 2me=1.022 MeV (e-+e+)
The probability of pair production is proportional to Z2log Eγ
  • Triplet production
    • Pair production occurs near of an orbital electron
    • The incident photon disappears
    • creation of an electron-positron pair and the orbital electron is freed from the atom
    • The threshold energy is 2.044 MeV
  • Annihilation reaction
    • The positron combines with an electron
    • the positron disappears
    • two photons of 0.511 MeV in opposite direction are produced
Photonuclear reaction
or Photodisintegration
A photon with extremely high energy interact directly with the nucleus
The photon energy is greater than the binding energy that holds the neutrons an protons together
It can eject a particle (mostly a neutron, proton or on rare occasions even an α particle)
The incident photon energy greater than 7 or 8 MeV (2H 2.22 MeV, 9Be 1.66 MeV, 62Ni 8.79)

Interaction of particles with matter
Ionizing or charged particles
    Energy loss by
  • excitation
  • ionization
  • bremsstrahlung
  • Cherenkov radiation
  • transition radiation(when crossing boundaries of two media with different dielectrical constants)
  • multiple Coulomb scattering

Energy is mainly lost due to interaction of charged particles with the orbitals electrons (mainly ionization)
Elastic collisions with nuclei cause deflection and scattering with very little energy loss
  • Heavy particles (α particles and protons)
    • follow a linear path
    • lose KE very fast and slow down
    • Can cause δ rays (secondary ionization produced by a freed orbital electron)
    • Bragg peak: Before the charged particle comes to rest the interaction cross section increases and more ionizing radiation is produced
  • Coulombic interactions
    • with atomic electrons:
      Inelastic coulombic interactions (lose KE)
      primary proton and ionization electrons
    • with the nucleus:
      A repulsive elastic Coulombic interaction (change in trajectory)
      primary proton and recoil nucleus
  • Nuclear reactions
    • Inelastic interactions
      the nucleus may emit secondary protons, deuterium, tritium, neutrons, α particles, γ rays, nuclides
  • Bremsstrahlung
    • Braking radiation produced by the deceleration of proton near a nucleus
      The proton loses KE
      Produce a photon
  • Bremsstrahlung
    • Braking radiation produced by the deceleration of a charged particle when deflected by another charged particle
      The charged particle loses KE
      Produce a photon
  • Cherenkov effect
    • When a charged particle is emitted with velocity greater than the speed of ligh in the medium a shock wave of photons is generated (blue light in water by e- and e+)
Uncharged particles
Neutrons They are indirectly inonizing particle
they lose energy by collisions that transfer KE
They interact primarily with the small atomic nuclei
They can penetrate very deeply into matter
They do not interact with the orbital electrons of atoms
They interact directly with the nuclei of atom
  • Elastic scattering
    • A sharing of KE between target nucleus and neutron
    • Maximum energy transfer occurs when the neutron collides with a nucleus of equal mass (hydrogen atom)
  • Inelastic scattering
    • When a neutron collide with a heavier nucleus
    • Part of the KE is converted into excitation energy of the nucleus (internal process)
    • This energy is released as γ ray photons
  • Neutron capture
    • Slower neutrons
    • New nucleus is formed (nucleosynthesis)
    • An excited state (radiactive isotope) is produced
    • Emits a particle and γ ray photon
  • Neutron-induced fission reaction
    • The nucleus of an atom splits into smaller parts (lighter nuclei)
    • Leading to two or more fission fragments and a few neutrons and γ rays photons, and releases a large amount of energy

Radioactive decay
Nucleus of an unstable atom loses energy by emitting radiation
Nuclear transmutation: The parent (radionuclide) and the daughter nuclides are different chemical elements
Alpha radiation (α) the nucleus ejects an α particle (4He nucleus: 2 protons and 2 neutrons)
Nuclear transmutation:AZX → A-4Z-2X + α
Nuclides heavier than nickel (maximum binding energy per nucleon)
Nuclides which have more number of protons
Speed of 15 000 Km/s
Electromagnetic forces (unlimited range) ∝ Z2 and Nuclear force (range 1 fm) ∝ Z
α particle has a high binding energy
It has a penetration of matter of very short range (<0.1 mm inside the body, 70 μm in Silicon)
Beta radiation or beta minus (β-) electron emission and an electron antinuetrino
n → p + e- + νe
n → W- ; W- + d → u ; W- → e- + νe
Nuclear transmutation:AZX → AZ+1X
An unstable atomic nucleus with an excess of neutrons
This process is mediated by the weak interaction
Speed of 160 000 to 240 000 km/s
positive beta decay or beta plus (β+) positron emission and an electron neutrino
p → n + e+ + νe
Nuclear transmutation:AZX → AZ-1X
An unstable atomic nucleus with an excess of protons
the binding energy of the daughter nucleus is greater than that of the parent nucleus
Gamma radiation (γ) High penetration power (0.15 m of steel)
Electron capture An inner atomic electron is captured by a proton in the nucleus, transforming it into a neutron, and an electron neutrino is released
p+e → n+νe
Proton-rich nuclides if not have enough energy to β+
Internal conversion Excited nucleus interacts electromagnetically with one of the orbital electrons which is emitted (ejected)
In the process emit an orbital electron, characteristic X-rays, Auger electrons
Emits inner shell electron (1s, 2s, 3s, 4s) and occasionally 2p and higher
Protons Nucleus ejects protons
Nulei of other elements