Rad Physics-Chapter 8

Vocabulary flashcards covering key terms, circuit components, generator types, and timers in x-ray machine circuitry.

Autotransformer

A transformer component located in the control console circuit that allows selection of major and minor kilovoltage peak ($\text{kVp}$).

Line Voltage Compensator

A circuit device that compensates for fluctuations in incoming electrical line voltage (typically $220\,V$ to $240\,V$ AC) to ensure consistent radiographic exposure techniques.

High-Voltage Step-Up Transformer

A step-up transformer with a turns ratio between $500:1$ and $1000:1$ that converts low voltage from the autotransformer into high kilovoltage required for x-ray production.

Diode

A two-pole electronic rectifying component containing positive ($p$) and negative ($n$) semiconductor materials that allows electric current to flow in only one direction.

Rectifier Bridge

An arrangement of rectifying diodes that converts alternating current (AC) into direct current (DC) before it enters the x-ray tube.

Coolidge Tube

An improved x-ray tube developed by William Coolidge in 1913 that replaced Edison's carbonized cotton filament with a tungsten filament, enabling thermionic emission.

Thermionic Emission

The process of heating the x-ray tube filament wire to extreme temperatures prior to exposure in order to boil off free electrons.

Filament Current

A low-voltage ($\approx 5\,V$), high-amperage ($\approx 5\,A$) current that flows through the filament wire to heat it whenever the rotor button is pressed.

Tube Current

The high-voltage current that propels freed electrons across the x-ray tube gap from the cathode filament to the anode during an exposure.

Filament Step-Down Transformer

A step-down transformer in the filament circuit with a typical turns ratio of $1:44$ that reduces incoming voltage to about $5\,V$ to produce high current amperage.

Ohm's Law

The fundamental electrical relationship stating that voltage ($V$) equals current ($I$) multiplied by resistance ($R$), expressed as $V = I \times R$.

Pre-Reading kVp Meter

A voltmeter connected in parallel before the step-up transformer in the console circuit to safely measure set kilovoltage without shock hazards.

mA Meter

An ammeter positioned in the secondary winding of the high-voltage step-up transformer to measure the true tube current flowing across the x-ray tube.

Voltage Ripple

The percentage variation in voltage waveform amplitude from peak voltage down to minimum voltage during electrical generation.

Single-Phase Generator

A generator utilizing 4 rectifying diodes that results in $100\%$ voltage ripple and an average beam energy of approximately $33\%$ of the set peak kilovoltage ($\text{kVp}$).

Three-Phase 6-Pulse Generator

An x-ray generator producing 6 overlapping electricity pulses per cycle, yielding a $14\%$ voltage ripple and an average energy of approximately $91\%$ of the set $\text{kVp}$.

Three-Phase 12-Pulse Generator

An x-ray generator producing 12 overlapping pulses per cycle, resulting in a $4\%$ voltage ripple and an average energy of approximately $97\%$ of the set $\text{kVp}$.

High-Frequency Generator

An advanced x-ray generator that increases incoming waveform frequency to between $500\,\text{Hz}$ and $25,000\,\text{Hz}$, achieving a voltage ripple of less than $1\%$ and an average voltage essentially equal to peak $\text{kVp}$.

Generator Power Rating

A measurement of maximum generator power expressed in kilowatts ($\text{kW}$), calculated as $\frac{\text{mA} \times \text{kVp}}{1000}$ for three-phase equipment and $\frac{0.7 \times \text{mA} \times \text{kVp}}{1000}$ for single-phase equipment.

Synchronous Motor Timer

A manual exposure timer driven by a synchronous motor spinning at 60 revolutions per second, capable of minimum exposure times of $\frac{1}{60}\,s$.

Electronic Timer

A precision manual exposure timer that terminates exposure when a capacitor reaches a preset charge level, allowing times as short as $1\,\text{ms}$ ($\frac{1}{1000}\,s$).

mAs Timer

A timer circuit commonly used on mobile x-ray units that automatically selects the highest safe $\text{mA}$ and terminates exposure when the preset cumulative $\text{mAs}$ is accumulated.

Automatic Exposure Control (AEC)

An automated exposure termination system that measures radiation reaching detectors behind the patient and automatically terminates the x-ray exposure once a preset electric charge threshold is accumulated.

Gas Ionization Chamber

A thin, rectangular radiation detector chamber containing air between two sheets of plexiglass, typically arranged in a triad configuration beneath the tabletop or upright bucky.

Thyratron

The exposure density control component on the console circuit that presets the required charge limit on an AEC capacitor before triggering the relay switch to shut off exposure.