Bremsstrahlung and Characteristic X-rays

• Bremsstrahlung radiation arises when accelerated electrons are decelerated near an atomic nucleus within the target.
• Electrons are affected by the nucleus's positive electric field, changing direction and losing kinetic energy.
• The lost kinetic energy is emitted as an X-ray photon.
• Bremsstrahlung production is affected by the atomic number of the target and the kilovolt peak (kVp).
• A higher atomic number leads to greater electron acceleration, and a higher kVp increases the likelihood of electrons reaching the nucleus.
• Characteristic X-rays are produced when a fast electron ejects a K-electron from a target atom.
• The vacancy in the K-shell is immediately filled by an electron from an outer shell.
• This process emits a characteristic K X-ray photon.
• The emitted radiation is atom-specific due to distinct energy level differences within the atom.
• Diagnostic X-rays have energies between 15 to 150 keV.
• Visible light photons have energies between 2 to 4 eV.
• The amount of electrons accelerated toward the anode depends on the temperature of the filament.
• The accelerating peak voltage (kVp) determines the maximum energy of the produced X-ray photons.
• Bremsstrahlung produces a broad, smooth curve whereas characteristic X-rays are represented by spikes on a energy spectrum.
• One kilo electron-volt (keV) equals the energy gained or lost by an electron across a 1000V potential difference.
• 1 keV = 1.6 * 10^-9 erg = 1.6 * 10^-16 J.
• The kVp in X-ray studies depends on patient thickness and study type.
• Mammography uses 25 to 50 kVp.
• Chest X-rays use approximately 350 kVp.
• Electron current typically ranges from 100 to 1000 mA.
• X-ray energy produced is not monoenergetic but a spectrum of energies up to its maximum.
• Power (P) in watts is calculated as current (I) in amps multiplied by voltage (V) in volts.
• At 1 A and 100 kV, power equals 100 kW, where 99% becomes heat, potentially damaging anodes.

X-Ray Absorption

• Attenuation of an X-ray beam is the reduction of intensity from absorption and scattering of photons.
• Intensity (I) decreases exponentially: I = I₀e^(-μx).
• I₀ represents initial beam intensity.
• I represents unattenuated (transmitted) beam intensity.
• μ signifies the linear attenuation coefficient.
• e is approximately 2.718.
• x is the thickness of the attenuator.
• The linear attenuation coefficient (μ) measures the probability of photon interaction per unit length in a material.
• It depends on the energy of X-rays, the atomic number (Z), and the density (ρ) of the material.
• Half Value Thickness (HVT) is the thickness of material required to reduce radiation beam intensity by half.
• HVT (X₁/₂) = 0.693 / μ.

Bremsstrahlung radiation occurs when electrons decelerate near an atomic nucleus, emitting X-ray photons. Characteristic X-rays are produced when fast electrons eject K-electrons, creating vacancies filled by outer shell electrons. Diagnostic X-rays range from 15 to 150 keV, while visible light photons range from 2 to 4 eV.