How X-Rays Work

What It Covers

Josh Clark and Chuck Bryant from Stuff You Should Know explain how X-rays work, covering Wilhelm Roentgen's 1895 accidental discovery, the electromagnetic spectrum physics behind X-ray generation, how density differences in bone versus soft tissue produce images, and the measurable radiation risks from medical and dental X-ray exposure.

Key Questions Answered

• •X-ray physics — atomic density: Bones contain calcium atoms with high radiological density, absorbing X-ray photons and blocking them from reaching the film plate. Soft tissue, made of smaller, lower-density atoms, allows photons to pass through freely. The resulting negative image shows bones as light areas precisely because those photons never reached the camera.
• •Radiation dosage — cumulative exposure: Annual background radiation exposure ranges from 1–4 millisieverts depending on location and elevation. Medical procedures add measurably: a dental panorama adds 0.01 millisieverts, a chest X-ray 0.1, a mammogram 0.4, and a full abdominal CT scan up to 10 millisieverts — equivalent to 2–3 years of natural background radiation in a single session.
• •Lead shielding — atomic absorption: Lead functions as effective radiation shielding because of its extremely high atomic number and density, allowing it to absorb X-ray photons before they penetrate beyond the shielded area. This same principle explains why lead aprons protect body regions not being imaged during dental or medical X-ray procedures.
• •Radiation risk — ask for alternatives: Because X-ray radiation is ionizing — meaning it knocks electrons off atoms, creating charged ions that can break DNA chains, trigger uncontrolled cell replication, and cause cancer or birth defects — patients should routinely ask medical providers whether a non-ionizing alternative exists before consenting to any X-ray procedure, particularly CT scans.
• •Contrast agents — fluoroscopy imaging: To visualize soft tissue structures like blood vessels or the gastrointestinal tract using X-rays, radiologists introduce barium-based contrast agents orally or by injection. These compounds have higher radiological density than surrounding tissue, absorbing X-ray photons and producing visible outlines of otherwise transparent structures in real-time moving fluoroscopy images.