Basic Interartions Of X-Rays With Matter Flashcards
What is the fate of an x-ray?
Absorption in the patient
Scatter
Transmission through patient*
What does an x-ray interaction depend on?
Atomic number of the element (Ca in bones, H20 in cells)
Energy of x-ray (weak rays absorbed by tissue)
Higher atomic number materials attenuate (reduction in force) a ____________ than low atomic number materials
Greater % of the beam
What do x-ray photons interact with?
Orbital electrons (diagnostic energy range interactions ALWAYS) or nucleus of atoms
Most important ways x-ray photon interact with matter
Photoelectric effect
Compton scattering
Photoelectric effect
When a photon interacts with an inner shell electron in the atom and removes it from the shell
Photoelectric effect process
X-ray photon strikes an electron in the inner (K) shell —> incident photon must have enough energy to remove electrons in shell —> photoelectron removed —> incident photon absorbed
What is the electron removed in the photoelectric effect called?
Photoelectron
How is the atom stabilized during the photoelectron effect?
An electron from the outer shell drops into the inner shell and continues from shell to shell until the atom is stabilized
The energy lost by outer shell electrons filling the vacancies is emitted as____________
characteristic radiation
Compton scatter
Incident photon with high energy strikes a free outer shell electron —> ejects it from orbit —> photon deflected by electron and travels in a new direction as scatter
Results of compton scatter
Recoil electron and a scattered less energetic photon
What does scatter radiation produce?
Fog: produces an overall density to the image —> reduction in radio graphic contrast
Ways to reduce Compton scattering
Collimation to a small field size
Use high energy beam (kVp)
Use grids
Decrease size of patient thickness (no control)
Collimators
X-ray beam restrictors that include the center of the beam for a smaller field of view and less scatter
Adjustment horizontal and vertical shutters
Advantages of collimators
Improve image quality by reducing scatter
Less exposure to patient and personnel by limiting area exposed to radiation
What are the purpose of grids
Absorbs scatter radiation and detracts from image quality
Advantages of grids
Improves image detail by removing x-rays traveling at angles (not carrying representative information)
Disadvantages of grids
Some useful rays are absorbed
Requires increase in mAs to accomplish adequate film exposure
Increased patient radiation exposure
Ionizing radiation: Particulate (alpha and beta particles)
Emitted from nuclei
Short range of travel through matter due to mass and charge
Ionizing radiation: electromagnetic radiation
X-rays (emitted from orbital shell)
Gamma rays (emitted from nucleus)
Alpha particles
Positively charged, made of 2 proteins and 2 neutrons from atoms nucleus
Energetic, heavy and use up energy over short distances (can’t travel far from atom)
Where do alpha particles come from?
Decay of the heaviest radioactive elements: uranium and radium
Beta particles
Small, fast moving, negative charge and emitted from atoms nucleus during radioactive decay
More penetrating, less damaging to living tissue and DNA
