8.2 Radioactivity
What Are Isotopes?
Isotopes are atoms of the same element (same number of protons) but with a different number of neutrons.
Isotopes are atoms of the same element (same number of protons) but with a different number of neutrons.
⚡ Key Concept:
• Same element = same number of protons
• Different isotope = different number of neutrons
• Some isotopes are stable, some are unstable
• Unstable isotopes undergo radioactive decay
• Different isotope = different number of neutrons
• Some isotopes are stable, some are unstable
• Unstable isotopes undergo radioactive decay
Carbon-12
6 protons, 6 neutrons
✓ Stable
Carbon-14
6 protons, 8 neutrons
☢ Unstable (Radioactive)
💡 Radioactive Decay:
An unstable nucleus will try to become stable by emitting radiation.
• This process is called radioactive decay
• It is a random process - we cannot predict when a particular nucleus will decay
• We cannot speed it up or slow it down (not affected by temperature, pressure, etc.)
• This process is called radioactive decay
• It is a random process - we cannot predict when a particular nucleus will decay
• We cannot speed it up or slow it down (not affected by temperature, pressure, etc.)
🎯 Isotope Quiz:
Alpha, Beta, and Gamma
There are three main types of radiation emitted by unstable nuclei.
There are three main types of radiation emitted by unstable nuclei.
Alpha (α)
α
☢️ What: Helium nucleus (2p, 2n)
🛡️ Stopped by: Paper/skin
⚡ Ionising: Very high
📏 Range: A few cm in air
Beta (β)
β
☢️ What: High-speed electron
🛡️ Stopped by: Thin aluminium
⚡ Ionising: Medium
📏 Range: ~1 metre in air
Gamma (γ)
γ
☢️ What: EM wave (energy)
🛡️ Stopped by: Thick lead/concrete
⚡ Ionising: Low
📏 Range: Very long
| Property | Alpha (α) | Beta (β) | Gamma (γ) |
|---|---|---|---|
| What is it? | Helium nucleus (2p, 2n) | High-speed electron | Electromagnetic wave |
| Charge | +2 | -1 | 0 (neutral) |
| Penetration | Low (paper stops it) | Medium (aluminium stops it) | High (lead reduces it) |
| Ionising power | Very high | Medium | Low |
⚡ Ionisation:
Ionisation is the ability of radiation to knock electrons off atoms, creating ions.
• Alpha is the most ionising (biggest, slowest, most interactions)
• Gamma is the least ionising (just energy, passes through)
Remember: High ionising = low penetrating, and vice versa.
• Alpha is the most ionising (biggest, slowest, most interactions)
• Gamma is the least ionising (just energy, passes through)
Remember: High ionising = low penetrating, and vice versa.
🎯 Radiation Type Quiz:
Measuring Radioactivity
The activity of a radioactive source is the number of decays that happen every second. It is measured in becquerels (Bq).
The activity of a radioactive source is the number of decays that happen every second. It is measured in becquerels (Bq).
⚡ Key Definitions:
• Activity = number of decays per second
• 1 Bq = 1 decay per second
• Activity decreases over time as nuclei decay
• Half-life = time for the number of unstable nuclei (or activity) to halve
• 1 Bq = 1 decay per second
• Activity decreases over time as nuclei decay
• Half-life = time for the number of unstable nuclei (or activity) to halve
📉 Half-Life
Starting activity: 800 Bq | Half-life: 2 days
After each half-life, the activity halves.
After each half-life, the activity halves.
Example: Half-Life Calculation
A source has an activity of 800 Bq. Its half-life is 2 days.
After 1 half-life (2 days):
Activity = 800 ÷ 2 = 400 Bq
After 2 half-lives (4 days):
Activity = 400 ÷ 2 = 200 Bq
After 3 half-lives (6 days):
Activity = 200 ÷ 2 = 100 Bq
Pattern: Each half-life, divide by 2.
After 1 half-life (2 days):
Activity = 800 ÷ 2 = 400 Bq
After 2 half-lives (4 days):
Activity = 400 ÷ 2 = 200 Bq
After 3 half-lives (6 days):
Activity = 200 ÷ 2 = 100 Bq
Pattern: Each half-life, divide by 2.
🧮 Half-Life Calculator
Enter values and click Calculate
🎯 Half-Life Practice:
Bq
Bq
Radiation and Health
Radiation can be harmful because it is ionising - it can damage or kill living cells.
Radiation can be harmful because it is ionising - it can damage or kill living cells.
Dangers of Radiation
High doses of radiation can:
- Damage DNA in cells
- Cause mutations
- Lead to cancer
- Cause radiation sickness (very high doses)
- Kill cells (used in radiotherapy)
⚡ Which is Most Dangerous?
Inside the body: Alpha is most dangerous
• Highly ionising, causes lots of damage
• Can't escape, all energy absorbed by cells
Outside the body: Gamma is most dangerous
• Most penetrating, can reach internal organs
• Alpha can't even get through skin.
• Highly ionising, causes lots of damage
• Can't escape, all energy absorbed by cells
Outside the body: Gamma is most dangerous
• Most penetrating, can reach internal organs
• Alpha can't even get through skin.
Safety Precautions
When working with radioactive sources:
- Keep sources in lead-lined containers
- Use tongs/long handles - never touch directly
- Minimise exposure time
- Maximise distance from source
- Use appropriate shielding
- Point sources away from people
💡 Background Radiation:
Background radiation is the low-level radiation all around us. It comes from:
Natural sources (~85%):
• Radon gas from rocks
• Cosmic rays from space
• Food and drink
• Rocks and soil
Man-made sources (~15%):
• Medical scans (X-rays, CT scans)
• Nuclear industry
• Fallout from past nuclear tests
Natural sources (~85%):
• Radon gas from rocks
• Cosmic rays from space
• Food and drink
• Rocks and soil
Man-made sources (~15%):
• Medical scans (X-rays, CT scans)
• Nuclear industry
• Fallout from past nuclear tests
🏔️
Radon Gas
☀️
Cosmic Rays
🍌
Food
🪨
Rocks
🏥
Medical
☢️
Nuclear
🎯 Safety Quiz:
Helpful Applications
Despite the dangers, radiation has many important uses when handled safely.
Despite the dangers, radiation has many important uses when handled safely.
Medical Uses
- Tracers: Gamma sources are injected/swallowed to see inside the body (e.g., thyroid scans)
- Radiotherapy: Gamma rays kill cancer cells
- Sterilisation: Gamma rays sterilise medical equipment
Industrial Uses
- Smoke detectors: Alpha particles detect smoke
- Thickness gauges: Beta radiation checks paper/metal thickness
- Tracing leaks: Gamma sources find pipe leaks underground
⚡ Choosing the Right Type:
The type of radiation used depends on the application:
Alpha (α):
• Smoke detectors - ionises air, changes when smoke enters
Beta (β):
• Thickness monitoring - penetrates paper but not metal
Gamma (γ):
• Medical tracers - penetrates body, detected outside
• Sterilisation - penetrates packaging
• Cancer treatment - reaches tumours deep in body
Alpha (α):
• Smoke detectors - ionises air, changes when smoke enters
Beta (β):
• Thickness monitoring - penetrates paper but not metal
Gamma (γ):
• Medical tracers - penetrates body, detected outside
• Sterilisation - penetrates packaging
• Cancer treatment - reaches tumours deep in body
| Application | Radiation Type | Why This Type? |
|---|---|---|
| Smoke detector | Alpha | Highly ionising, short range (safe) |
| Paper thickness | Beta | Partially absorbed by paper |
| Medical tracer | Gamma | Penetrates body, detected outside |
| Sterilising equipment | Gamma | Penetrates packaging, kills bacteria |
| Cancer treatment | Gamma | Penetrates to reach deep tumours |
🎯 Uses of Radiation Quiz: