Applications, hazards and protection

Key idea: Atomic structure, nuclide notation, random decay, radiation properties, background radiation, half-life, applications and hazards.

SEC G3 Combined Science Physics component 2027

Syllabus and review details

K326 / K327 Science Physics componentK326 / K327 · 2027Checked against the syllabus · partial topic coverageRadioactivity topic 16(a)–(h), PDF pages 23–24

Match a useful property to its purpose

A radioactive source contains unstable nuclei. The radiation is the particles or electromagnetic radiation emitted when those nuclei decay. A use depends on what that radiation does in matter, not simply on the word “radioactive”.

Application	Useful property and reason
Medical tracer	Gamma radiation can leave the body and reach an external detector. A suitably short half-life limits how long the tracer remains active, while allowing time for detection.
Radiotherapy	Ionisation can damage cancer cells. Radiation must be directed because healthy tissue can also be damaged.
Thin-sheet thickness monitoring	Beta radiation is partly absorbed by the sheet. At fixed source and detector positions, a thicker sheet gives a lower detector count. Alpha is absorbed too readily; gamma is usually too penetrating for this thin-sheet comparison.
Sterilising packaged equipment	Penetrating gamma radiation reaches microorganisms through the packaging; ionisation damages them.

These are explanations of established uses, not instructions to select or handle a real source.

Worked reasoning: a thickness signal

Suppose a thin-sheet gauge’s count falls while source activity and detector position are unchanged. A thicker sheet absorbs more beta radiation, so fewer particles reach the detector. The count gives information about thickness, not proof that the source’s half-life has changed. In a working gauge, changes in source activity would also have to be accounted for.

Learner claim

“The shortest possible half-life is always safest for a medical tracer.” Correct the claim and explain why gamma radiation may be chosen.

Try this before viewing the solution

Useful radiation

GammaAlpha

Required balance

Long enough for the procedureAlways the shortest available

View solution step by step

Choose detectable radiation
Method
Select penetrating gamma radiation.
Reason
It can leave the body and reach an external detector.
Working
Gamma supports external imaging or tracking.
Set the half-life boundary
Method
Choose a half-life long enough for the test but short enough to limit later exposure.
Reason
A source that decays too quickly may become undetectable before the procedure ends.
Working
“Relatively short” is a compromise, not simply the minimum value.

Distinguish irradiation from contamination

Irradiation means exposure to radiation. Contamination means radioactive material is on or inside an object or person. Removing an external source ends that source’s irradiation, but contaminated material remains a source until removed or decayed. Ordinary irradiation in the applications described here does not mean radioactive material has been transferred.

Alpha radiation is strongly ionising and is readily stopped by paper or the outer dead layer of skin. An alpha-emitting substance inside the body can therefore be harmful to nearby living cells even though its radiation has low penetration. Gamma radiation can penetrate from an external source. A hazard comparison must state where the source is; “most penetrating” and “most ionising” are different properties.

Ionisation can damage living cells and their genetic material. Match the control to the exposure:

Shorter exposure time reduces accumulated exposure under otherwise unchanged conditions.
Greater distance generally reduces exposure from an external source.
Suitable shielding reduces radiation reaching a person: thin aluminium can absorb typical beta radiation; thick lead or concrete reduces gamma intensity, without guaranteeing zero transmission.
Containment helps prevent radioactive material spreading onto surfaces or entering the body. Distance alone does not remove internal contamination.

Guided hazard–control reasoning

An enclosed gamma source remains outside a person. A shield is placed between them. Has this changed the source’s half-life, or reduced radiation reaching the person? If radioactive dust instead enters the body, which additional issue is present?

Effect of the shield

Reduces radiation reaching the personShortens the source's half-life

Radioactive dust inside the body

Internal contaminationExternal irradiation only

Apply the ideas independently

A sealed package of medical equipment is irradiated from an external source. Radiation must reach microorganisms through the package; no radioactive material enters it. Choose the useful emission, its action, and the correct description of the exposure.

Repair a mixed claim

A learner says: “Alpha has the lowest penetration, so an alpha-emitting contaminant inside the body cannot damage tissue. Moving the original container farther away removes this hazard.” The first error is treating an internal source as though skin were between it and the tissue. Alpha can ionise nearby living tissue strongly. Moving an external container does not remove material already inside the body.

Check the repair in a different setting: radioactive material is on a surface. Does merely standing farther away remove the contamination? Which property explains why an internal alpha source can be harmful?

Does distance remove the radioactive material?

No; the material remains on the surfaceYes; distance removes it

Relevant internal alpha hazard

Strong ionisation near the sourceGreat penetration through the whole body

Practice and next step

Use the Radioactivity topic check for focused practice and feedback. Then continue to Practical requirements.

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Course and syllabus information

Course: SEC G3 Combined Science Physics component
Edition: SEC G3 Combined Science Physics component 2027

Applications, hazards and protection

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