Podcast
Questions and Answers
Which factor(s) do the photoelectric atomic attenuation coefficients depend on?
Which factor(s) do the photoelectric atomic attenuation coefficients depend on?
For which type of photons is the photoelectric effect the major contributor to mass attenuation at relatively low energies?
For which type of photons is the photoelectric effect the major contributor to mass attenuation at relatively low energies?
What happens at absorption edges in terms of photon energy and binding energy of a shell?
What happens at absorption edges in terms of photon energy and binding energy of a shell?
In the Compton effect, why is the orbital electron considered 'free'?
In the Compton effect, why is the orbital electron considered 'free'?
Signup and view all the answers
What does the Compton electronic attenuation coefficient depend on?
What does the Compton electronic attenuation coefficient depend on?
Signup and view all the answers
What is the half value layer (HVL) of concrete for a 10 MeV photon beam?
What is the half value layer (HVL) of concrete for a 10 MeV photon beam?
Signup and view all the answers
Which property does the energy loss of a charged particle in matter depend on?
Which property does the energy loss of a charged particle in matter depend on?
Signup and view all the answers
What is the total stopping power defined as?
What is the total stopping power defined as?
Signup and view all the answers
What is characteristic of atomic excitation during electron interactions with matter?
What is characteristic of atomic excitation during electron interactions with matter?
Signup and view all the answers
What type of interaction between incident electrons and absorber nuclei results in no energy loss?
What type of interaction between incident electrons and absorber nuclei results in no energy loss?
Signup and view all the answers
Which factor characterizes the loss of kinetic energy through bremsstrahlung during electron-nucleus interactions?
Which factor characterizes the loss of kinetic energy through bremsstrahlung during electron-nucleus interactions?
Signup and view all the answers
What is the energy threshold for nuclear pair production to occur?
What is the energy threshold for nuclear pair production to occur?
Signup and view all the answers
What type of pair production occurs in the Coulomb field of an absorber orbital electron?
What type of pair production occurs in the Coulomb field of an absorber orbital electron?
Signup and view all the answers
Which interaction generally predominates at low photon energies?
Which interaction generally predominates at low photon energies?
Signup and view all the answers
What does the linear attenuation coefficient m depend on?
What does the linear attenuation coefficient m depend on?
Signup and view all the answers
What does the half-value layer (HVL) represent?
What does the half-value layer (HVL) represent?
Signup and view all the answers
Which absorber thickness reduces beam intensity to 10% of the original intensity?
Which absorber thickness reduces beam intensity to 10% of the original intensity?
Signup and view all the answers
How is the linear attenuation coefficient determined experimentally?
How is the linear attenuation coefficient determined experimentally?
Signup and view all the answers
Study Notes
Pair Production
- Production of e- - e+ pair occurs when an incident photon is completely absorbed by an absorber atom
- Requires energy (Eg) greater than 2mec2 = 1.022 MeV, where mec2 is the rest energy of e- and e+
- Two types of pair production:
- Nuclear pair production: occurs when the collision partner is the absorber atomic nucleus, with Eg > 2mec2
- Electronic pair production or triplet production: occurs when the collision partner is the absorber orbital electron, with Eg > 4mec2 = 2.044 MeV
- Pair production probability is zero for Eg < 2mec2 and increases rapidly with Eg > threshold
- Nuclear pair production contributes more than 90% to the pair production attenuation coefficient
Attenuation Coefficients
- Linear attenuation coefficient (m) is the probability per unit path length that a photon will have an interaction with the absorber
- Depends on photon energy (hn) and absorber atomic number (Z)
- Exponential absorption of photon beam in absorber occurs, with intensity decreasing as absorber thickness increases
- Attenuation coefficient (m) is determined experimentally by measuring beam intensity with varying absorber thicknesses
Characteristic Absorber Thicknesses
- Three special thicknesses used to characterize photon beams:
- Half-value layer (HVL or x1/2): absorber thickness that attenuates original intensity by 50%
- Mean free path (MFP or λ): absorber thickness that attenuates beam intensity by e = 36.8%/1
- Tenth-value layer (TVL or x1/10): absorber thickness that attenuates beam intensity to 10% of the original intensity
Photoelectric Effect
- Occurs when an orbital electron is ejected from the atom as a photoelectron, with kinetic energy EK = hν - EB
- Threshold energy: Eg = hν > EB, where EB is the binding energy of the photoelectron
- Photoelectric atomic attenuation coefficients depend on atomic number and energy
- Photoelectric effect is the major contributor to attenuation coefficient at relatively low Eg
Compton Effect
- Occurs when an incident photon interacts with a loosely bound ("free") electron, transferring part of its energy to the electron
- Photon is scattered through a scattering angle, with energy E'g = hn' lower than incident energy Eg
- Basic Compton equation: λ' - λ = λC = 0.024Å, where λC is the Compton wavelength of the electron
- Relationship between scattered and incident energies: Eg' = (Eg / (1 + (Eg / mec2)(1 - cos(θ)))
Electron Interactions with Matter
- Energetic charged particles undergo Coulomb interactions with absorber atoms, resulting in:
- Ionization loss
- Radiation loss
- Interactions characterized by specific cross-section (probability) and stopping power
- Energy loss depends on particle properties and absorber properties
- Total stopping power: stot = scol + srad, where scol is collision stopping power and srad is radiation stopping power
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
Description
Learn about pair production in physics, which involves the creation of an electron-positron pair with the complete absorption of an incident photon by an absorber atom. Explore the conditions and characteristics of nuclear pair production and electronic pair production (or triplet production).
