A security scanner at an airport uses X-rays to image the contents of passengers' luggage. A passenger asks why X-rays are used rather than radio waves, which are also electromagnetic waves. Explain why X-rays are suitable for this purpose and describe the health risk associated with repeated exposure to X-rays for the airport security staff who operate the scanner.

X‑rays have a very short wavelength (≈0.01–10 nm) and high frequency, so they can penetrate the soft materials that make up most luggage and are absorbed by denser objects such as metal or bone. The absorption pattern gives a clear image of the contents. Radio waves, with wavelengths of metres to kilometres, are far too long and have too low energy to penetrate the luggage or to be absorbed differentially by small objects, so they cannot produce a useful image.

X‑rays are ionising radiation. When they pass through tissue they transfer enough energy to break chemical bonds and ionise atoms. This can damage DNA and other cellular structures, leading to mutations. Repeated or prolonged exposure to X‑rays increases the cumulative dose and therefore raises the risk of cancer for the staff who operate the scanners.