Properties of nuclear radiation Edexcel International A Level Physics revision
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In plain words
Alpha, beta and gamma don't only differ in what they are. They differ in how far they get. Alpha is a heavyweight that knocks into everything, and a sheet of paper stops it. Gamma barely notices matter, and centimetres of lead only weaken it. And there is always a little radiation about, from rocks, the air and space, that has to be allowed for.
5 things to know
- Alpha: very strongly ionising, so it loses energy quickly. It has a range of a few centimetres in air and is stopped by paper or skin.
- Beta: moderately ionising. It has a range of around a metre in air and is stopped by a few millimetres of aluminium.
- Gamma: weakly ionising. It has a very long range in air. Thick lead reduces its intensity but never stops it completely.
- The more strongly a radiation ionises, the shorter its range, because every ionisation takes energy from it.
- Background radiation is always present, from rocks, radon gas, cosmic rays and other sources. Measure the background count rate with no source nearby, and subtract it from every reading.
Worked example
With no source nearby, a detector records 26 counts per minute. With a source in place it records 446 counts per minute. Find the corrected count rate in counts per second.
- Subtract the background: 446 − 26 = 420 counts per minute.
- Change to counts per second: 420 ÷ 60.
- = 7.0 counts per second.
Tips and tricks
- Subtract the background count before you do anything else with the readings, such as finding a half-life.
- To see how lead absorbs gamma rays, measure the count rate through different thicknesses of lead, keeping the source and detector the same distance apart.
It lands in your notebook with its questions as flashcards.
Properties of nuclear radiation: 5 questions and answers
These are the quiz’s questions. Do the quiz first, then come back here for the ones that got you.
Which radiation is the most strongly ionising?
It has the largest charge and moves the slowest.
Which radiation is stopped by a few millimetres of aluminium but not by paper?
Paper stops alpha; aluminium stops beta.
Why is the range of alpha particles in air so short?
Each ionisation takes a little of their energy.
What should be done with the background count rate?
The readings include background as well as the source.
Which of these is a source of background radiation?
Rocks, cosmic rays and radon all contribute.
Quiz
5 questions
Tap an answer and you’ll see straight away whether it’s right, and why.
Worksheet
3 questions, 7 marks. Write your answers on paper, then check them.
Properties of nuclear radiation
Edexcel International A Level Physics WPH · 7 marks · papermunch.org
Name ______________________________ Date ______________
Explain why alpha particles have a short range in air.[2]
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They are strongly ionising, so they lose their energy over a short distance.
The background count rate is 0.5 counts per second. A detector near a source reads 12.5 counts per second. Find the count rate due to the source.[2]
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12.0 counts per second.
Describe how absorbers can be used to find out which types of radiation a source emits.[3]
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Measure the count rate with nothing between the source and the detector. Then put paper in between: a big fall shows alpha. Then a few millimetres of aluminium: a further fall shows beta. Any count still above background that is only reduced by thick lead is gamma.
Answers: Properties of nuclear radiation
- 1. They are strongly ionising, so they lose their energy over a short distance.
- 2. 12.0 counts per second.
- 3. Measure the count rate with nothing between the source and the detector. Then put paper in between: a big fall shows alpha. Then a few millimetres of aluminium: a further fall shows beta. Any count still above background that is only reduced by thick lead is gamma.