Hazards and Uses of Radioactive Emissions and of Background Radiation

Solution

1. 1

   Natural sources.

   $\text{(i) Radon gas from rocks; (ii) cosmic rays from space (or food/ground).}$

2. 2

   Man-made.

   $\text{Medical X-rays and CT scans.}$

Solution

1. 1

   Short half-life.

   $\text{6 h: most activity gone within a day, so patient dose is limited.}$

2. 2

   γ radiation.

   $\text{Penetrates body tissue, so a gamma camera outside the body can detect it.}$

3. 3

   Energy.

   $\text{Gamma is non-ionising at low intensities, less damaging than α or β.}$

Solution

1. 1

   Long half-life.

   $\text{Am-241 has half-life 432 years, so the alarm works for decades without replacement.}$

2. 2

   α radiation.

   $\text{α ionises the air between two electrodes; smoke disrupts this current, triggering the alarm.}$

3. 3

   α safety.

   $\text{α cannot escape the metal alarm casing, so it is safe externally.}$

Solution

1. 1

   Benefits.

   $\text{γ kills cancer cells; can target tumours from outside the body; can save lives.}$

2. 2

   Risks.

   $\text{Damages healthy tissue too; causes fatigue, skin burns, raises secondary cancer risk.}$

3. 3

   Reducing risk.

   $\text{Multiple beams from different angles concentrate dose on tumour; ALARA principle.}$

4. 4

   Judgement.

   $\text{For most cancers, the benefit (cure or remission) outweighs the radiation risk.}$