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Reference Reading: Chapter 2, pp 18- end of chapter
General (“Braking”) (Bremsstrahlung) Radiation ◦ Refers the sudden “braking” of the electrons as they hit the tungsten target. ◦ Most x-rays are produced in this manner. (70%) Characteristic Radiation ◦ Produced when a high-speed electron dislodges an inner shell electron from a tungsten atom and causes ionization of the atom. ◦ Very little radiation produced in this manner.
Occurs when an electron hits, or comes close to hitting the nucleus of a tungsten atom. If the electron gets a “direct” hit on the nucleus, then ALL of the energy of that atom is given up. This produces a high energy photon of radiation.
Usually, there is a “near miss”. This slows down the electron and a photon of lower energy is produced. www.youtube.com/.webloc
Inner shell electron is ejected from the atom, and all the other electrons will “rearrange themselves” to fill the vacancy. The rearrangement produces a loss of energy that creates an x-ray photon. Not much radiation is generated in this manner.
Primary ◦ The x-ray beam that exits the tubehead ◦ Also referred to as the Primary Beam or the Useful Beam Secondary ◦ Less penetrating radiation ◦ Secondary radiation is produced when the primary beam interacts with matter. (soft tissues of the head, teeth, bones of the skull, etc.)
Scatter ◦ Scatter is harmful to both the patient and the operator. ◦ It is formed when an x-ray has been deflected from its path.
1. The x-rays can pass through the patient without any interaction 2. The x-rays can be completely absorbed by the patient. (Photoelectric Effect) 3. The x-rays can be deflected and become scatter radiation. (Compton Scatter & Coherent Scatter)
No Interaction Some of these rays will strike the film, and make radiography possible by producing “densities” on the film. Will learn more about this later.
At the atomic level, absorption occurs as a result of the photoelectric effect. Ionization has taken place within the patient’s tissues. This accounts for about 30% of the interactions of the x-ray beam with the patient’s body.
Photoelectric Effect The x-ray interacts with an inner shell electron of the patient’s body. The x–ray is absorbed and ceases to exist.
Compton Scatter Loose, outer shell electron is dislodged from its orbit. Ionization has taken place. Accounts for 62% of the scatter that takes place in radiography.
Coherent Scatter There is interaction of the x-ray with an outer shell electron, but it is NOT dislodged, so ionization does NOT take place. Sometimes called “unmodified scatter”. Accounts for 8% of the interactions of matter with the x-ray beam.