X-rays and gamma rays – medical imaging and treatments.

The idea

X-rays and gamma rays are ionising electromagnetic radiation with very short wavelengths and very high frequencies, so their photons carry enough energy to remove electrons from atoms. This property makes them useful in medicine but also hazardous. In imaging, X-rays pass through soft tissue more easily than through bone or metal, so a detector behind the patient records a shadow image; gamma cameras detect gamma rays emitted by a tracer inside the body, giving functional images. In treatment, carefully directed X-rays or gamma rays can kill cancer cells by damaging their DNA, often using multiple beams so the tumour receives a high dose while surrounding tissue receives less.

What earns the marks

• X-rays and gamma rays are ionising electromagnetic radiation with shorter wavelengths and higher frequencies than ultraviolet.
• Their high photon energy allows them to pass through body tissue, so X-rays can form shadow images showing bones or dense materials.
• Gamma rays from a radioactive tracer inside the body can be detected outside the body to produce functional images of organs.
• In radiotherapy, X-rays or gamma rays are directed at cancer cells and damage their DNA, which can kill the cells or stop them dividing.
• Because the radiation is ionising, it can also damage healthy cells, so exposure is limited by using the smallest effective dose, shielding and precise targeting.
• Medical use therefore depends on balancing the benefit of diagnosis or treatment against the risk of causing cancer in healthy tissue.

Common mistakes and how to put them right

• Confusing X-rays with gamma rays by origin only.

  Put it right by noting both are ionising electromagnetic waves and their medical use depends on wavelength, frequency and photon energy.

• Saying X-rays are reflected by bones.

  Put it right by explaining that bones absorb X-rays more than soft tissue, so fewer reach the detector and a shadow forms.

• Treating radiotherapy as harmless because it targets a tumour.

  Put it right by stating that ionising radiation can damage healthy cells, so dose and direction are controlled.

Exam tips

• Link each medical use to a named property, such as high penetration for imaging or ionisation for killing cancer cells.
• When explaining risk, refer to ionising ability and DNA damage rather than saying radiation is simply dangerous.
• Use comparative terms such as shorter wavelength than visible light and higher frequency than ultraviolet to place X-rays and gamma rays correctly in the spectrum.