Radiation & Health

⚛️ Types of Radiation

α

Alpha (α)

PenetrationStopped by paper or skin

RangeA few centimetres in air

DangerLow externally; VERY dangerous if inhaled/ingested

ExamplePolonium-210 (used to poison Alexander Litvinenko)

β

Beta (β)

PenetrationStopped by thin aluminium or plastic

RangeMetres in air

DangerCan penetrate skin; protective clothing needed

ExampleSr-90, I-131 (causes thyroid cancer)

γ

Gamma (γ)

PenetrationRequires thick lead or concrete

RangeCan travel hundreds of metres

DangerPenetrates the entire body - most dangerous externally

ExampleCs-137, Co-60 (medical radiotherapy)

n

Neutron (n)

PenetrationRequires water, polyethylene, or concrete

RangeCan travel large distances

DangerCan make other materials radioactive (activation)

ExampleInside nuclear reactors; weapons (enhanced radiation)

📏 Radiation Units Explained

Bq

Becquerel (Bq)

Activity - how many atoms decay per second

1 Bq = 1 disintegration per second. A banana emits ~15 Bq from potassium-40.

Gy

Gray (Gy)

Absorbed dose - energy deposited per kg of tissue

1 Gy = 1 joule of energy absorbed per kilogram.

Sv

Sievert (Sv)

Effective dose - biological harm accounting for radiation type

The most important unit for health. A chest X-ray = ~0.1 mSv.

rem

Rem

Older unit of effective dose (1 rem = 0.01 Sv)

Still used in the USA. 100 rem = 1 Sv = radiation sickness threshold.

📊 Dose Comparisons µSv (microsieverts)

Lethal dose 50% (LD50)

4,000mSv

Acute radiation syndrome threshold

1,000mSv

Radiation worker annual limit

20mSv

Working near Fukushima exclusion zone (1 year)

10mSv

CT scan (chest)

7mSv

Annual background radiation (average)

2.4mSv

Chest X-ray

100µSv

Transatlantic flight

80µSv

Background radiation (per day)

8µSv

Dental X-ray

5µSv

Eating one banana

0.1µSv

Bar width shown on logarithmic scale. Sources: IAEA, WHO, UNSCEAR.

🏥 Health Effects by Dose

DoseImmediate EffectsLong-term RiskSurvival

< 100 mSv (0.1 Sv) No detectable immediate health effect No measurable increase in cancer risk 100%

100–500 mSv No immediate symptoms in most people Small statistical increase in cancer risk (detectable in large populations) 100%

500 mSv – 1 Sv Mild radiation sickness; some may experience nausea Measurable cancer risk increase ~100%

1–2 Sv Radiation sickness: nausea, fatigue, temporary hair loss Bone marrow suppression begins >95%

2–4 Sv Severe radiation sickness; suppressed immune system Life-threatening without medical treatment 50–95%

4–6 Sv (LD50) Acute Radiation Syndrome (ARS) - severe ~50% fatal within 60 days without aggressive treatment ~50%

6–8 Sv Severe ARS; GI tract damage Lethal without immediate bone marrow transplant < 10%

> 8 Sv Certain death within days to weeks Central nervous system effects at very high doses Near 0%

Sources: IAEA, WHO, UNSCEAR 2020 report. Individual responses vary significantly.

💡 Putting It In Context

🍌

The Banana Equivalent Dose

Bananas contain potassium-40, a natural radioactive isotope. Eating one banana exposes you to ~0.1 µSv. This isn't a real radiation risk - your body regulates potassium levels - but it illustrates that radioactivity is everywhere in nature.

🌍

Natural Background Radiation

The average person receives ~2.4 mSv per year from natural sources - cosmic rays, radon gas from the ground, and naturally occurring radioactive materials in food and water. People in high-altitude cities or granite-rich regions can receive 5–10× more.

✈️

Frequent Flyers

Airline crew members receive ~3–6 mSv per year from cosmic radiation at altitude - roughly double the average background dose. This is well within safe limits, but makes them among the most radiation-exposed workers in low-risk occupations.

🏥

Medical Uses

Medical imaging is the largest artificial source of radiation exposure. A chest CT scan delivers ~7 mSv - about 3 years of natural background radiation. The benefit (detecting disease) massively outweighs the tiny additional cancer risk.