Welcome! Radiation can be dangerous – but it’s also used every day to save lives. In this lesson you’ll learn about alpha, beta and gamma radiation and half-life, then take on the job of a hospital radiation officer. It takes about one hour. Work through the steps in order.
Before you start
- You need: your exercise book or paper and a pen.
- Write the title and date: Radioactivity – Hospital Radiation Officer.
- The golden rule: write your answer first, then tap Show answer. Tick what’s right and correct mistakes in a different colour.
- Look out for the blue 📝 boxes. Copy each one into your book neatly – these are your revision notes.
📝 Copy into your book
By the end of this lesson I will be able to:
1. describe alpha, beta and gamma radiation
2. use half-life in calculations
3. explain contamination and irradiation
4. choose the right radioactive source for a job.
Step 1: Starter (5 minutes)
Radiation: helpful or harmful? Write down two ways radiation can harm people and two ways radiation is useful. Guess if you’re not sure!
Show answer
Harmful: it can damage cells and cause mutations that lead to cancer; high doses cause burns and radiation sickness.
Useful: medical tracers to see inside the body; radiotherapy to kill cancer cells; sterilising surgical instruments; smoke alarms; checking the thickness of paper in factories.
📝 Copy into your book
Nuclear radiation can damage cells and cause cancer – but choosing the right type, with the right half-life, makes it safe and useful.
Step 2: Read and write (10 minutes)
First, copy these three questions into your book. Then read the text below carefully and answer them in full sentences.
- What is an alpha particle made of?
- What stops alpha, beta and gamma radiation?
- What does “half-life” mean?
📖 Read: Alpha, beta, gamma and half-life
Some atoms have unstable nuclei. They give out radiation to become more stable – this is called radioactive decay. There are three main types. An alpha particle is made of two protons and two neutrons (the same as a helium nucleus). It is strongly ionising but only travels a few centimetres in air and is stopped by a sheet of paper or by skin. A beta particle is a fast-moving electron that comes from the nucleus. It travels about a metre in air and is stopped by a few millimetres of aluminium. Gamma rays are electromagnetic waves. They are weakly ionising, travel a long way, and are only reduced by thick lead or concrete.
We can’t predict when one nucleus will decay – it’s random. But we can measure the half-life: the time it takes for the number of unstable nuclei in a sample to halve, or for the count-rate to fall to half its starting value.
Show answers
(a) Two protons and two neutrons – the same as a helium nucleus.
(b) Alpha: paper or skin. Beta: a few mm of aluminium. Gamma: reduced by thick lead or concrete.
(c) The time it takes for the number of unstable nuclei in a sample to halve – or for the count-rate to fall to half.
📝 Copy and complete
Half-life is the time it takes for the number of __________ __________ in a sample to __________, or for the __________ to fall to half its starting value.
Check your gaps
unstable nuclei · halve · count-rate
✅ Move on when you’ve answered all three questions and completed the box.
Step 3: Key facts (8 minutes)
Your task: copy this table neatly into your book – you’ll need it for the main task.
| Radiation | What it is | Ionising? | Range in air | Stopped by |
|---|---|---|---|---|
| Alpha (α) | 2 protons + 2 neutrons | Strongly | A few cm | Paper or skin |
| Beta (β) | Fast electron from the nucleus | Moderately | About 1 m | A few mm of aluminium |
| Gamma (γ) | Electromagnetic wave | Weakly | Very far | Reduced by thick lead or concrete |
Now copy these three key words – they come up in the exam every year.
📝 Copy into your book
Ionising: knocks electrons off atoms. This is what damages cells.
Contamination: radioactive atoms get onto or into something, so it becomes radioactive.
Irradiation: something is exposed to radiation but does NOT become radioactive.
Remember: alpha is the most dangerous inside the body, because it’s so strongly ionising – but from outside it can’t get through your skin.
Step 4: Quick check (5 minutes)
Cover your notes and answer from memory.
Q1 Which radiation is stopped by a sheet of paper?
Show answer
Alpha.
Q2 Which radiation is an electromagnetic wave?
Show answer
Gamma.
Q3 Which radiation is the most ionising?
Show answer
Alpha.
Q4 A patient has an X-ray. Are they contaminated or irradiated?
Show answer
Irradiated – they were exposed to radiation but don’t become radioactive.
Q5 Why does a source with a short half-life become safe quickly?
Show answer
Its unstable nuclei decay quickly, so its activity (and count-rate) falls to a low level in a short time.
✅ Score out of 5. 4 or less? Look back at your notes before moving on.
Step 5: Half-life practice (7 minutes)
First, copy the method:
📝 Copy into your book
Half-life calculations: keep halving, one half-life at a time. Count the halvings. Time = number of halvings × half-life.
Q1 A source has a count-rate of 1200 counts per minute and a half-life of 2 hours. What is the count-rate after 6 hours?
Show answer
6 hours = 3 half-lives.
1200 → 600 → 300 → 150 counts per minute
Q2 A source has a half-life of 5 days. How long does its count-rate take to fall from 640 to 40 counts per minute?
Show answer
640 → 320 → 160 → 80 → 40 = 4 half-lives.
4 × 5 = 20 days
Q3 (Higher) What fraction of a radioactive sample is left after 3 half-lives?
Show answer
½ × ½ × ½ = ⅛
Step 6: Main task – Hospital Radiation Officer (12 minutes)
You’re the new radiation officer! Four departments need a radioactive source. You have five to choose from:
| Source | Radiation | Half-life |
|---|---|---|
| P | Alpha | 430 years |
| Q | Beta | 28 years |
| R | Gamma | 6 hours |
| S | Gamma | 5 years |
| T | Alpha | 3 days |
- Medical tracer: injected into a patient so a camera outside the body can see how their kidneys are working.
- Smoke alarm for the hospital corridors: the radiation ionises the air inside the alarm, and it should last for years without being replaced.
- Thickness gauge in the hospital’s paper-towel factory: radiation passes through the paper to a detector – more paper, fewer counts.
- Sterilising sealed packs of surgical instruments by passing radiation through the packaging.
Before you start, copy the two questions every radiation officer asks:
📝 Copy into your book
Choosing a radioactive source:
1. Does the radiation need to get THROUGH something? → choose the type.
2. Should it last a LONG time or disappear QUICKLY? → choose the half-life.
Your task: for each job write: Source chosen · Why this type of radiation? · Why this half-life?
Show model answers
1. Tracer – Source R (gamma, 6 hours). Gamma passes out of the body to reach the camera, and it is weakly ionising so it does less damage. The short half-life means the patient doesn’t stay radioactive for long – but it lasts long enough to do the scan.
2. Smoke alarm – Source P (alpha, 430 years). Alpha is strongly ionising, so it ionises the air well, and it only travels a few cm so it stays safely inside the alarm. The long half-life means it keeps working for many years.
3. Thickness gauge – Source Q (beta, 28 years). Beta partly passes through paper, so a change in thickness changes the count-rate. Alpha would be stopped completely; gamma would pass straight through whatever the thickness. The long half-life means the readings stay steady.
4. Sterilising – Source S (gamma, 5 years). Gamma passes through the sealed packaging to kill bacteria. The instruments are irradiated, not contaminated, so they don’t become radioactive. The long half-life means the source doesn’t need replacing often.
Source T wasn’t needed – alpha can’t get out of the body, and a 3-day half-life is too short for a smoke alarm.
✅ Check: did you give a reason for both the type and the half-life each time? Add anything you missed.
Step 7: Exam practice (10 minutes)
Look at the marks – they tell you how many points to make. Answer in full sentences, then mark yourself.
Q1 (2 marks) Explain why an alpha source in a smoke alarm is safe for people in the room.
Show model answer
Alpha has a range of only a few cm in air / is stopped by the alarm’s casing (1), so it cannot reach people in the room (and couldn’t get through skin anyway) (1).
Q2 (4 marks) A worker handles a gamma source. Describe two precautions they should take and explain how each one reduces the risk.
Hint: 2 precautions × (what + why) = 4 marks.
Show model answer
Use long-handled tongs (1), so the source is kept further from the body and less radiation reaches it (1). Keep the source in a lead-lined container when not in use / stand behind lead shielding (1), because lead absorbs much of the gamma radiation (1). (Also accept: minimise the time of exposure, so the dose received is smaller.)
📝 Copy into your book
Staying safe with radiation – DISTANCE (use tongs), SHIELDING (use lead), TIME (as short as possible).
Q3 (4 marks – Higher) A tracer has a count-rate of 800 counts per minute. Six hours later it is 400 counts per minute. How long after the start will the count-rate be 50 counts per minute? Explain your answer.
Hint: use the method in your 📝 box from Step 5.
Show model answer
The count-rate halved in 6 hours, so the half-life is 6 hours (1).
800 → 400 → 200 → 100 → 50 (1)
That is 4 half-lives (1).
4 × 6 = 24 hours (1)
✅ Add up your marks out of 10 and write the score in your book.
Step 8: Exit ticket (3 minutes)
- The type of radiation I’d least like to swallow is… because…
- A medical tracer needs a short half-life because…
- One thing I’m still not sure about is…
🎉 Well done – lesson complete! Your 📝 boxes are your revision notes for this topic. Want more? Try the Radioactive decay and half-life questions and the Nuclear decay equations practice.
▶ Want to watch a video on this topic? (optional)
These are extra – you don’t need them for any of the questions above.
🖨️ Want this lesson on paper? Download the whole lesson as a printable worksheet – answers are on the last page.
