What is the primary mechanism by which x-rays are produced in an x-ray tube?

• A. Photoelectric effect in the anode material.
• B. Compton scattering in the tube housing.
• C. Thermal radiation from the filament.
• D. Bremsstrahlung (braking radiation) produced when high-speed electrons are decelerated in the tungsten anode, with a smaller contribution from characteristic radiation.

Answer: (D)

Bremsstrahlung, or braking radiation, is the main way X-rays are produced in an x-ray tube. Here’s how it works: electrons are emitted from the heated filament and accelerated toward the high-voltage tungsten anode. As these high-speed electrons pass near the nuclei in the target, their paths are curved and their speed changes abruptly, causing them to lose energy in the form of photons. That energy loss shows up as a continuous spectrum of X-rays, with the highest energy limited by the tube voltage.

A secondary source adds some X-rays: when an electron knocks out an inner-shell electron of the target atoms, electrons from higher shells drop down to fill the vacancy and emit photons with characteristic energies specific to the target material. But this contribution is smaller compared to Bremsstrahlung.

Other options aren’t how X-rays are produced in the tube. The photoelectric effect describes interactions of X-rays with matter after they’re produced, not their creation inside the tube. Compton scattering is a scattering interaction of existing X-rays, not a production mechanism. Thermal radiation from the filament is heat, not X-ray generation.