Gamma rays and X-rays

The two highest-frequency kinds carry the most energy, which is what makes them useful — and dangerous.

Gamma rays

Gamma rays are given out by radioactive elements. Their frequency is very high and so is the energy they carry. They can pass through thick steel and concrete.

Treating cancer

Gamma rays destroy living cells, so they are used to destroy cancer cells.

Sterilising

They are used to sterilise food and surgical instruments.

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Figure 4.14 — a hospital machine that uses gamma rays, with a patient lying on its bed.

X-rays

X-rays are mostly used to take pictures of the inside of the body. They pass easily through soft tissue, but lose much of their intensity passing through bone, so the bones show up in the picture.

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Figure 4.15 — a patient standing at an X-ray machine to have an X-ray picture taken.

X-rays are also used to check the containers brought by aircraft and ships without opening them.

Too much exposure

Too much exposure to X-rays can cause cancer.

How X-rays are made

X-rays are produced by letting fast-moving electrons strike a metal target. Part of the electrons' kinetic energy is changed into X-rays.