Safety, Hazards and Uses of Radioactivity

Ionising radiation is genuinely useful and genuinely dangerous. Questions here are about matching the right source to the job and justifying the precautions — both of which come straight from the properties of alpha, beta and gamma.

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1. Why ionising radiation is dangerous

Ionising radiation can knock electrons off atoms in living cells, damaging molecules — including DNA.

The consequences:

Exposure	Effect
Low dose	mutations in DNA → increased risk of cancer
High dose	cell death, radiation burns, radiation sickness

Damage to DNA can cause mutations that lead to cancer — that is the key phrase. Saying radiation is “harmful” without naming ionisation, cell damage or mutation rarely earns the mark.

Inside vs outside the body — the crucial distinction:

OUTSIDE the body, GAMMA is the most dangerous, because it penetrates the skin and reaches internal organs. Alpha is stopped by the skin or even by clothing. INSIDE the body, ALPHA is the most dangerous, because it is strongly ionising and deposits all its energy in a small volume of tissue.

This reversal is examined constantly. The reasoning is the same properties table as always: alpha is highly ionising but weakly penetrating, so it is harmless outside and severe inside.

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2. Safety precautions

When handling sources:

• Use tongs or a long-handled tool — never touch a source directly
• Keep your distance — intensity falls rapidly with distance
• Minimise the time of exposure
• Point the source away from people
• Wear a film badge or dosimeter to monitor cumulative dose
• Use shielding — lead or thick concrete

When storing sources:

Keep them in a lead-lined container, in a locked cabinet, with the container labelled with the radiation hazard symbol.

The three principles to quote: time, distance and shielding — minimise time, maximise distance, use appropriate shielding.

Justify each precaution. “Use tongs” earns little; “use tongs to increase the distance from the source, reducing the dose received” earns the mark. Precautions must be linked to why they reduce exposure.

Workers in nuclear industries wear film badges, work behind shielding, and have their cumulative dose monitored against legal limits.

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3. Uses — and matching the source to the job

The choice of source always comes down to penetration, ionising power and half-life.

Medical

Use	Source	Why
Medical tracers	gamma, short half-life	penetrates the body to be detected outside; decays away quickly so it doesn’t stay in the patient
Radiotherapy for cancer	gamma, from outside	penetrates to the tumour; beams rotated so healthy tissue receives less dose
Sterilising equipment	gamma	penetrates sealed packaging to kill bacteria inside
Diagnosis of thyroid problems	iodine-131	absorbed specifically by the thyroid

Industrial

Use	Source	Why
Thickness monitoring (paper, metal foil)	beta	partly absorbed — the amount getting through varies with thickness. Alpha would be stopped completely; gamma would pass through regardless
Smoke detectors	alpha, long half-life	strongly ionises air to create a small current; safely absorbed by the casing; long half-life means no frequent replacement
Detecting leaks in pipes	gamma, short half-life	penetrates the soil to be detected at the surface
Sterilising food	gamma	kills bacteria without opening the packaging

Dating

Use	Source
Carbon dating of organic remains	carbon-14 (half-life ≈ 5730 years)
Dating rocks	uranium isotopes (very long half-lives)

Justify a choice using BOTH the type of radiation AND the half-life. A full answer says why the alternatives don’t work, as well as why the chosen one does — for a tracer: gamma because it penetrates, and short half-life so it doesn’t remain in the body.

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4. Handling nuclear waste

Radioactive waste must be stored safely for a long time, because some isotopes have very long half-lives.

• Low-level waste — sealed and buried in landfill
• High-level waste — encased in glass or concrete, stored deep underground in stable rock

The problem is the long half-life: waste remains dangerous for thousands of years, so storage must remain secure far longer than any human institution has existed.

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5. Mistakes that cost marks

Saying radiation is “dangerous” without naming ionisation or DNA damage.

Saying alpha is the most dangerous outside the body — that’s gamma.

Saying gamma is the most dangerous inside — that’s alpha.

Listing precautions without justifying them.

Choosing beta for a smoke detector, or alpha for a tracer.

Ignoring half-life when justifying a source.

Saying a tracer should have a long half-life.

Forgetting that thickness monitoring needs partial absorption.

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Frequently asked questions

Why is ionising radiation dangerous? It ionises atoms in cells, damaging molecules including DNA, which can cause mutations and cancer.

Which radiation is most dangerous outside the body? Gamma, because it penetrates the skin.

Which is most dangerous inside the body? Alpha, because it is strongly ionising over a short range.

What are the three safety principles? Minimise time, maximise distance, use shielding.

How should sources be stored? In lead-lined, labelled, locked containers.

Why is gamma used for medical tracers? It penetrates the body so it can be detected outside.

Why should a tracer have a short half-life? So it decays away quickly and doesn’t remain in the patient.

Why is beta used for thickness monitoring? It is partly absorbed, so the amount passing through varies with thickness.

Why is alpha used in smoke detectors? It strongly ionises air to create a current, and is safely absorbed by the casing.

Why is high-level waste stored deep underground? Because it stays dangerous for thousands of years.

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Quick revision checklist

• I can explain the danger in terms of ionisation and DNA damage
• I know gamma is worst outside the body
• I know alpha is worst inside the body
• I can explain both, using penetration and ionising power
• I can list handling precautions with reasons
• I know the time, distance, shielding principles
• I know how sources should be stored
• I can justify gamma for tracers, radiotherapy and sterilisation
• I can justify beta for thickness monitoring
• I can justify alpha for smoke detectors
• I always include the half-life in my justification
• I know how nuclear waste is stored and why

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These notes cover the safety, hazards and uses of radioactivity in the Cambridge IGCSE Physics (0625) syllabus and are written for Grade 9–11 / Year 10–11 students. They are based on teaching patterns observed across a large set of one-to-one IGCSE Physics lessons. This was one of the less-covered subtopics in that set, so the page follows the syllabus closely rather than being padded. Always check the current syllabus for your own exam series.