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.

 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.