Physics

6.9 - X-Rays & Gamma Rays

6 min

X-ray imaging and safety

Sterilising with gammaOutside your course

Risks and benefits

note 1 of 2

X-rays let us see inside the body

X-rays pass easily through soft tissue but are absorbed by denser material such as bone or metal.

Forming an X-ray image

Radiation is directed through the body onto a detector plate.
The result is a negative image: lighter areas show where X-rays were absorbed by dense material (such as bone), while darker areas show where they passed through soft tissue.

Uses of X-ray imaging

Diagnosing broken bones and dental problems - Dense bone shows up clearly against surrounding tissue.
CT scans - Use multiple X-rays taken from different angles to build a 3D image of the body.
Airport security scanners - Detect hidden objects inside baggage.

A green box labelled X-ray source fires green arrows through a standing figure onto a grey picture of ribs, with labels X-rays, pass through soft tissue, absorbed by bone and negative image.

note 2 of 2

Treating cancer and tracing the body

Radiotherapy

High doses of X-rays and gamma rays kill living cells.
In radiotherapy, beams of radiation are aimed precisely at a tumour to destroy cancer cells while minimising damage to surrounding healthy tissue.

Medical tracers

A tracer containing a gamma-emitting source is injected or swallowed, and a gamma camera outside the body detects the emitted gamma rays to build an image.
Gamma rays are used because they pass out through skin, soft tissue and bone without being fully absorbed.
Tracers can be attached to molecules like glucose; cancerous tumours use more energy and take up more glucose, showing up as bright spots on the scan.

A patient lies on a bed at a ring scanner labelled gamma camera, with a syringe labelled tracer injected, beside a body outline with yellow dots labelled tracer shows as bright spots.

key terms

TermDefinition

CT scanA scan that uses multiple X-rays taken from different angles to build a 3D image of the body.

RadiotherapyThe treatment of cancer using high doses of ionising radiation to kill cancer cells.

TracerA radioactive substance put into something, such as a patient's body or a pipe, to show where it goes. The radiation it gives out is detected from outside.

end of notes

Key points to remember

X-rays let us see inside the body

X-rays pass easily through soft tissue but are absorbed by denser material such as bone or metal.

Forming an X-ray image

Radiation is directed through the body onto a detector plate.

The result is a negative image: lighter areas show where X-rays were absorbed by dense material (such as bone), while darker areas show where they passed through soft tissue.

Uses of X-ray imaging

Diagnosing broken bones and dental problems - Dense bone shows up clearly against surrounding tissue.

CT scans - Use multiple X-rays taken from different angles to build a 3D image of the body.

Airport security scanners - Detect hidden objects inside baggage.

Treating cancer and tracing the body

Radiotherapy

High doses of X-rays and gamma rays kill living cells.

In radiotherapy, beams of radiation are aimed precisely at a tumour to destroy cancer cells while minimising damage to surrounding healthy tissue.

Medical tracers

A tracer containing a gamma-emitting source is injected or swallowed, and a gamma camera outside the body detects the emitted gamma rays to build an image.

Gamma rays are used because they pass out through skin, soft tissue and bone without being fully absorbed.

Tracers can be attached to molecules like glucose; cancerous tumours use more energy and take up more glucose, showing up as bright spots on the scan.