📖 In-Depth Theory
Contamination vs Irradiation
These two terms are often confused but describe very different situations:
RADIOACTIVE CONTAMINATION:
Unwanted radioactive material is DEPOSITED ON or INSIDE a person or object.
The contaminating material continues to emit radiation over time.
The source stays with the person/object — ongoing exposure.
Example: breathing in radon gas; swallowing radioactive dust; radioactive material on skin.
IRRADIATION:
The person or object is EXPOSED TO RADIATION from a source that is NOT attached to them.
When the person moves away from the source, exposure stops.
Example: standing near a radioactive source; medical X-ray; radiotherapy.
KEY DIFFERENCE:
Contamination = source stays with you.
Irradiation = source is external, exposure ends when you move away.
Hazards of Each Type
CONTAMINATION HAZARDS:
Alpha sources are especially dangerous as INTERNAL CONTAMINANTS:
Alpha particles are highly ionising but very short range.
Inside the body they deposit all their energy in nearby cells → severe local tissue damage.
External alpha contamination (on skin) is less dangerous — alpha cannot penetrate skin.
Beta and gamma internal contamination is also serious — penetrate to internal organs.
IRRADIATION HAZARDS:
Depends on radiation type, dose and duration.
Gamma is most dangerous external source — penetrates deeply into tissue.
Alpha from external source: stopped by skin, relatively safe.
Beta: penetrates skin, can damage underlying tissue.
LONG-TERM EFFECTS:
Ionising radiation damages DNA → mutations → increased cancer risk.
High acute doses → radiation sickness, cell death.
Eyes, bone marrow and gonads particularly sensitive.
Precautions and Safe Use
PRECAUTIONS TO PREVENT CONTAMINATION:
Never touch radioactive materials directly — use TONGS or remote handling.
Wear PROTECTIVE CLOTHING (gloves, lab coat) to prevent skin contact.
WORK IN WELL-VENTILATED areas to prevent inhaling radioactive dust or gases.
No eating, drinking or applying make-up in radioactive areas — prevents ingestion.
Seal radioactive materials in appropriate containers.
PRECAUTIONS TO REDUCE IRRADIATION:
DISTANCE — intensity follows inverse square law; doubling distance reduces dose by ¾.
SHIELDING — appropriate material (paper for alpha, aluminium for beta, lead/concrete for gamma).
TIME — minimise exposure duration.
DOSIMETERS — worn by radiation workers to monitor cumulative dose.
PROFESSIONAL GUIDELINES:
Radiation workers have annual dose limits.
Regular monitoring of workplace radiation levels.
Storage of radioactive sources in lead-lined containers when not in use.
BENEFITS vs RISKS:
Medical uses (X-rays, radiotherapy, tracers) involve balancing dose risk vs diagnostic/treatment benefit.
Risk is managed, not eliminated.
⚠️ Common Mistake
Contamination and irradiation are NOT the same. Contamination: radioactive material on/in you — source travels with you. Irradiation: external source — exposure stops when you move away. Alpha is most dangerous as INTERNAL contaminant (highly ionising, short range → all energy deposits locally).