Radiographic Exposure 1 - X-Ray Tube Physics and Radiation Properties

Vocabulary flashcards covering key terms, component functions, radiation types, and physical interactions from the Radiographic Exposure 1 lecture notes.

Primary Radiation

The portion of the x-ray beam that exits the tube through the port window.

Remnant Radiation

The portion of the x-ray beam that exits the patient's body on a relatively original path and forms the diagnostic image, accounting for approximately $20\%$ of the primary beam.

Secondary Radiation

Radiation that originates in the primary beam, interacts with the patient's body, and hits the image receptor on an inaccurate path, causing film fog.

Scatter Radiation

Radiation that originates as the primary beam, strikes the patient's body, undergoes a change in direction, and does not hit the film, serving as the primary source of technologist exposure.

Indiscriminate Radiation

The weak part of the primary beam that has insufficient energy to reach the patient and holds no diagnostic value.

Leakage Radiation

Any radiation that exits the x-ray tube housing other than through the port window, which must not exceed $1\,mGy_a/h$ at a distance of $1\,m$.

Central Ray (CR)

The theoretical photon that exits from the exact center of the focal spot.

Focal Spot (FS)

The portion of the anode target where the electron stream impacts, also referred to as the focal point, target, or focal track.

Thermionic Emission

The heating of a filament to incandescence to boil off or liberate valence electrons from filament atoms, also known as the Edison effect.

Focusing Cup

A shallow depression in the cathode assembly made of nickel or molybdenum with a low negative charge that converges the thermionic electron cloud toward the anode focal track.

Space Charge Effect

The phenomenon where the buildup of negative charge around the filament opposes the emission of additional electrons, limiting maximum tube current to about $1000 - 1200\,mA$.

Saturation Current

The state reached when all available thermionic electrons are driven toward the anode, such that further increases in kilovoltage ($kV$) will not increase the tube current.

Actual Focal Spot (AFS)

The finite physical area on the tungsten focal track that is directly bombarded by electrons from the filament.

Effective Focal Spot (EFS)

The foreshortened area of the focal spot projected out of the tube toward the patient and image receptor.

Line-Focus Principle

A principle utilizing an angled anode target so that the effective focal spot is smaller than the actual focal spot, improving spatial resolution while maintaining heat capacity.

Anode Heel Effect

A variation in x-ray beam intensity along the longitudinal axis of the tube caused by target angle geometry, resulting in lower intensity at the anode end ($75\%$) and higher intensity at the cathode end ($120\%$).

Off-Focus Radiation

Photons produced away from the focal spot when scattered electrons or photons hit other tube components, accounting for $25 - 30\%$ of the primary beam and causing image ghosting.

Bremsstrahlung Interaction

An interaction occurring when a high-speed electron is decelerated by the nuclear force field of a tungsten target atom, producing braking radiation that accounts for $85\%$ of the primary beam.

Characteristic Interaction

An interaction occurring when an incident electron with at least $70\,keV$ ejects a K-shell electron from a tungsten atom, causing an outer-shell electron to fill the vacancy and emit a characteristic photon, making up about $15\%$ of the primary beam.

Wilhelm Conrad Roentgen

The physicist who discovered x-rays on November 8, 1895.

Stator

An array of electromagnets located outside the glass envelope that induces rotation of the anode rotor.

Rotor

A copper shaft with silver-plated ball bearings located inside the glass envelope that connects to the anode disc via a molybdenum shaft.