3.0 Interactions of X-ray with Matter Flashcards
Change in direction of a photon without a loss of energy
Scattering
Deposition of energy, i.e. removal of energy from the beam (total loss of energy)
Absorption
Reduction in the intensity of the main X-ray beam caused by absorption and scattering
Attenuation
Interactions of X-rays at the Atomic level (3)
Photoelectric absorption
Compton scattering
Coherent Scattering
Percentage of
No Interaction,
coherent scattering,
Photoelectric absorption, and
Compton scattering
No Interaction 9%
Coherent scattering 7%
Photoelectric absorption 27%
Compton scattering 57%
This process occurs when an incident photon interacts with an electron in an inner orbital of an atom in the patient.
The incident photon loses all its energy to the electron and ceases to exist.
The energy absorbed by the electron is expended to overcome the binding energy, and the remainder energy remains as the kinetic energy of the electron as it escapes the confines of its orbital.
Photoelectric Absorption
The electron that was interacted by the incident photon
recoil electron or photoelectron
It is the basis of image radiographic information.
Photoelectric absorption
_______________________ - Ejects inner electron and ceases to exist; releases characteristic photon.
___________________ - Ejects outer electron, both scatter
_________________ - Scatters from atom.
_________________ - Passes through patient.
Photoelectric absorption
Compton scattering
Coherent scattering
No interaction
__________________ (a) = The fate of scattered photons resulting from primary Compton, photoelectric, and coherent interactions.
______________ (b) = The sum of the total number of photoelectric interactions and photons that exit the patient equals the total number of incident photons.
Scattered photons
Total photons
» (A) Photoelectric absorption occurs when an incident photon gives up all of its energy to an inner electron, which is ejected from the atom (a photoelectron). The incident electron ceases to exist at this point.
(B) The ionized atom now has an electron vacancy in the inner orbital.
(C) An electron from a higher energy level fills the vacancy and emits characteristic radiation.
(D) All orbitals are subsequently filled, completing the energy exchange.
» Stage 1: X-ray photon interacts with an ________________.
» Stage 2: Inner-shell electron is _______ and the X-ray photon is totally absorbed.
» Stage 3: _________________ cascade in to till the inner- shell vacancy and energy is given out in the form of very low energy radiation (e.g. light)
inner-shell electron
ejected
Outer-shell elections
- The probability of photoelectric interaction is directly proportional to the ____________________________________ of the absorber, and inversely proportional to the ____________________________ (E).
third power of the atomic number (Z)
third power of the energy of the incident photon
(1) * it occurs when a photon interacts with an outer orbital electron.
* Approximately ____ of interactions in a dental x-ray beam exposure involve it.
* it results in the loss of an electron and ionization of the absorbing atom.
* _______________ - ejected electron.
» ____________________ occurs when an incident photon interacts with an outer electron, producing a scattered photon of lower energy than the incident photon and a recoil electron ejected from the target atom. The new scattered photon travels in a different direction from the incident photon.
COMPTON SCATTER
57%
Recoil electron
Compton scattering
» (A) Diagram showing the angle of scatter θ with (i) high- and (il) low-energy scattered photons.
» (B) Typical scatter distribution diagram of a ______ X-ray set. The length of any radius from the source of scatter indicates the relative amount of scatter in that direction. At this voltage, the majority of scatter is in a forward direction.
70 kV
» __________________ that exit the patient can expose the operator.
» Scattered photons travel varying distances within the patient’s tissues and cause ionizations. This internal scatter increases the patient radiation dose and often exposes organs and tissues outside of and distant from the path of the primary beam.
Scattered photons
- Coherent scatter (also known as _____________________________) may occur when a low-energy incident photon (<10 keV) interacts with a whole atom.
- No energy is transferred to the biologic atom and __________________ are caused.
- The biologic effects of coherent scatter are insignificant.
- Has minimal impact on image degradation.
» _____________________ results from the interaction of a low-energy incident photon with a whole atom, causing it to be momentarily excited.
» After this interaction, the atom quickly returns to the ground state and emits a scattered photon of the same energy but at a different angle from the path of the incident photon.
Rayleigh, classical, or elastic scatter
no ionizations
Coherent scattering
- Frequently used units of radiation and radiation detriment.
Summary of Radiation Quantities and Units:
(1) Amount of ionization of air by x- or y-rays; its SI Unit; its Traditional unit; its Conversion
(2) Kinetic energy transferred to charged particles; its SI Unit; its Traditional unit; its Conversion
(3) Total energy absorbed by a mass; its SI Unit; its Traditional unit; its Conversion
(4) Absorbed dose weighted by biologic effectiveness of radiation type used; its SI Unit; its Traditional unit; its Conversion
(5) Sum of equivalent doses weighted by radiosensitivity of exposed tissue or organ; its SI Unit; its Traditional unit; its Conversion
(6) Rate of radioactive decay; its SI Unit; its Traditional unit; its Conversion
DOSIMETRY
(1) Exposure; coulomb/ kg (C/kg); Roentgen (r); 1 C/kg = 3876 R
(2) Kerma; gray (Gy); NA; NA
(3) Absorbed dose; gray (Gy); rad; 1 Gy = 100 rad
(4) Equivalent dose; sievert (Sv); rem; 1 Sv = 100 rem
(5) Effective dose; sievert (Sv); NA; NA
(6) Radioactivity; becquerel
(Bq); Curie (Ci); 1 bq = 2.7 x 10-11 Ci
_________________
o The photon directly interacts with and ionizes a biologic macromolecule.
_________________
o Photons and secondary electrons interact with water and the products of water ionizations cause biologic damage.
Direct actions
Indirect actions
- Biologic molecules absorb energy from ionizing radiation and within 10-10 seconds form unstable free radicals.
- These free radicals quickly re-form into stable configurations by _____________ (breaking apart) or ____________ (joining of two molecules).
- Because the altered biologic molecules differ structurally and functionally from the original molecules, the consequence is a biologic
- What does this pertain to? __________
dissociation; cross-linking
DIRECT ACTION
- In indirect actions, the initial interaction of a photon occurs with a water molecule-which constitutes approximately 70% of mammalian cells. Indirect action are the predominant mode of x-radiation-induced biologic damage.
- Ionizing radiation initiates a complex series of chemical changes in water, collectively referred to as _______________.
- The initial series of interactions of x-ray photon with water produce ____________ (H) and ____________ (OH) free radicals that interact with biologic macromolecules.
- The _______ radical is highly reactive and is estimated to cause two-thirds of the biologic damage to mammalian cells from X-rays.
- free radicals in indirect action (2)
radiolysis of water
hydrogen; hydroxyl
hydroxyl
» Hydroperoxyl
» Hydrogen Peroxide
Deoxyribonucleic Acid and Chromosomal Damage and Damage Response (4)
Base damage
Single-strand breaks
Double-strand breaks
DNA-DNA and DNA-protein cross links
- Most important damage type
- Repaired by nonhomologous end-joining or homologous recombination
- ________________________ - accounts for many of the ionizing radiation-induced mutations.
DOUBLE-STRAND BREAKS
Nonhomologous end-joining
» A single photon may cause multiple ionizations in DNA, resulting in a ________________________________. In this instance, an _______________ causes ionization of a water molecule, and the _______________ causes a cluster of damage to multiple sites in a DNA molecule.
» Such cluster damage is difficult to repair and is believed to be responsible for most radiation cell killing, carcinogenesis, and heritable effects.
cluster of DNA damage/ clustered DNA damage
incident photon
recoil electron
