Bremsstrahlung radiation is electromagnetic radiation produced as a charged particle slows and scatters during interaction with an atomic nucleus.

• Bremsstrahlung is used to generate kV imaging x-ray beams as well as high energy MV beams in linear accelerators.
• Very inefficient process (~1% for kV beams)
• Bremsstrahlung energy efficiency (the ratio of the output energy emitted as x-rays to input energy deposited by electrons) in a linac target may be approximated as in equation \ref{eq: Bremsstrahlung efficiency} where Z is the target atomic number and E is the accelerating energy in volts.
• Note: This relationship breaks down in the MV region. This can be seen by noting that for tungsten targets (Z = 74) the relationship predicts an efficiency exceeding 100% for electron energies greater than 15MeV.

$$\label{eq: Bremsstrahlung efficiency} \textrm{bremsstrahlung energy efficiency} \propto 9 \times 10^{-10} ZE$$

$$\label{eq: Bremsstrahlung probability} \textrm{Probability of Bremsstrahlung interaction} \propto Z^2 E$$

• X-rays are emitted in a continuous energy spectrum
• Maximum energy is equal to the incident electron
• Average energy is 1/3 to 1/2 of the maximum energy