Bremsstrahlung (braking) radiation

Bremsstrahlung interaction between an electron and atomic nucleaus causes emission of high energy photon.

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.

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

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

  • 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