Hazards and Uses of Radioactive Emissions and of Background Radiation

Background radiation comes from many sources. Approximate UK percentages:

Source	% of total	Type	Notes
Radon gas (from uranium in rocks)	50 %	Mostly α	Indoor levels vary by region; high in Cornwall, Devon, Derbyshire
Ground and buildings	14 %	γ from soil/stone	Granite (Aberdeen, Cornwall) is higher
Food and drink	12 %	β/γ from natural isotopes (K-40, C-14)	Bananas contain K-40
Cosmic rays	12 %	High-energy particles from space	Increases with altitude (frequent flyers get more)
Medical	12 %	X-rays, CT, nuclear medicine	The dominant man-made source
Nuclear weapons / industry	<1 %	Various	Small in normal operation

Total UK dose: average about 2.7 mSv per year.

For comparison:

• Single chest X-ray: ~0.02 mSv.
• CT scan: 1–10 mSv.
• UK-USA return flight: ~0.1 mSv.
• Lethal short-term dose: ~5 Sv.

The sievert (Sv) measures radiation dose — the biological effect of absorbed radiation. It accounts for both the energy absorbed AND how damaging the radiation type is (α weighted more heavily than γ).

• 1 Sv = potentially lethal dose if received quickly.
• 1 mSv = 1/1000 Sv.
• 1 μSv = 1/1,000,000 Sv.

Typical doses:

• UK average annual background: 2.7 mSv.
• Dental X-ray: ~0.005 mSv.
• Chest X-ray: ~0.02 mSv.
• Mammogram: ~0.4 mSv.
• CT abdomen: ~8 mSv.
• Banana (one): ~0.0001 mSv (the 'banana equivalent dose' is a popular comparison).

Workers in radiation industries are limited to 20 mSv/year average; public limit is 1 mSv/year ABOVE background.

Medical tracers (e.g. for finding tumours):

• Short half-life — so the patient is not exposed for long.
• Beta or gamma — so the radiation can leave the body to be detected externally.
• Example: technetium-99m (Tc-99m), half-life ~6 hours, γ emitter. Widely used in NHS scans.

Cancer radiotherapy (external beam):

• Powerful, focused γ source.
• Half-life long enough to last years between replacements.
• Example: cobalt-60 (Co-60), half-life 5.3 years.

Smoke alarms:

• Long half-life — alarm lasts decades.
• α emitter — ionises air molecules; smoke particles disrupt the ion current → trigger alarm.
• Example: americium-241 (Am-241), half-life 432 years.

Carbon dating:

• Long half-life relative to the artefact's age (so some still detectable).
• Example: carbon-14, half-life 5730 years.

Industrial thickness gauges:

• β emitter for thin materials; γ for thick.
• Half-life long enough that the source doesn't decay during industrial lifetime.
• Example: Sr-90 for thin steel sheet (β, t½ = 29 years).

Application	Radiation	Half-life requirement
Medical tracer	γ (or β)	Hours to days
Smoke alarm	α	Decades-centuries
Cancer treatment	γ	Years
Industrial gauge	β/γ	Years
Dating	All	Comparable to age being dated

1. Medical imaging (tracers). Inject a γ-emitting tracer; a gamma camera tracks where it accumulates. Diagnoses tumours, thyroid problems, bone disease. Example: Tc-99m for bone scans.

2. Radiotherapy. γ rays (Co-60 or X-rays from a LINAC) focused on a tumour kill cancer cells. Multiple beams from different angles concentrate dose on the tumour while sparing surrounding tissue.

3. Brachytherapy. Sealed radioactive sources (e.g. I-131 for thyroid cancer) placed near or inside the tumour.

4. Sterilisation. γ rays kill bacteria and insects on medical equipment, surgical instruments, even some fruit. Doesn't make the item radioactive — it just damages the bacteria's DNA.

5. Smoke alarms. α-emitting Am-241 ionises air; smoke disrupts the current.

6. Thickness gauges. β (or γ) source on one side of paper/metal sheet, detector on the other. Less radiation = thicker sheet. Used in paper mills and steel rolling.

7. Carbon dating. C-14 in once-living material decays at a known rate; ratio of C-14 to C-12 gives age.

Risks:

• Radiation ionises atoms in cells. If DNA is damaged, the cell may mutate.
• Mutations can cause cancer or hereditary defects.
• High doses (>1 Sv) cause acute radiation sickness (nausea, hair loss, organ failure).
• Low doses (~mSv) carry small statistical cancer risks.

Reducing risk:

• Shielding, distance, time (ALARA principle — As Low As Reasonably Achievable).
• Sealed sources where possible.
• Personal dosimeters for staff.
• Public dose limit: 1 mSv/year above background.

Ethical considerations:

• CT scan for diagnosis: benefit (catching disease) usually outweighs ~8 mSv dose risk — but unnecessary scans should be avoided.
• Cancer radiotherapy: side effects (skin burns, fatigue, secondary cancer risk) vs life-saving treatment.
• Disposal of nuclear waste: radioactive for thousands of years; ethical question of leaving the problem to future generations.
• Nuclear power: low CO₂ but creates long-lived waste; debate continues.
• Sterilising food: safe? Public sometimes resists irradiated food despite scientific safety evidence.

Modern medicine constantly evaluates 'is the benefit greater than the radiation risk?' for each procedure.