Bremsstrahlung (“Braking”) Radiation
1. Definition
Bremsstrahlung (German for “braking radiation”) occurs when an incident high-speed electron passes near the nucleus of a tungsten target atom. The strong electrostatic field of the nucleus slows the electron down and deflects it, causing it to lose kinetic energy, which is then emitted as an X-ray photon.
2. High-Yield Characteristics
- The Primary Source: It accounts for the majority (approx. 80–90%) of the total X-ray beam produced in the diagnostic X-ray tube.
- Polychromatic Spectrum: Because the electron can lose any amount of its kinetic energy during the “braking” process, it produces a continuous X-ray spectrum rather than specific energy peaks.
- Energy Limit: The maximum energy of a Bremsstrahlung photon is numerically equal to the peak kilovoltage (kVp) applied to the tube.
3. Key Physics Relationships
| Factor | Impact on Bremsstrahlung |
|---|---|
| Atomic Number (Z) | Directly proportional. Higher Z of the target (e.g., Tungsten, Z=74) increases the efficiency of Bremsstrahlung production. |
| kVp | Increasing kVp increases both the quantity and the average energy of the resulting Bremsstrahlung photons. |
4. Exam Pearls
- Vs. Characteristic Radiation: Characteristic radiation depends on the binding energy of the target material’s electrons and produces “spikes” in the X-ray spectrum. Bremsstrahlung produces the broad “hump” or bell curve of the X-ray emission spectrum.
- Clinical Correlation: Bremsstrahlung is the “workhorse” of the X-ray beam. Because it provides a spectrum of energies, it allows for the varying degrees of tissue penetration necessary for quality diagnostic images.