Gamma Radiation
Physics: AQA A Level, topic 8.1.3
Gamma Radiation
Unstable nuclei emit one of three types of radiation. alpha, beta and gamma.
Properties of γ radiation
- Gamma radiation:
- Does not change the proton or nucleon number of a nucleus.
- Makes the nucleus more stable by its emission.
- Is highly penetrative.
- Can be absorbed by several centimetres of lead, many metres of air and can travel through a vacuum indefinitely.
Properties of γ radiation 2
- Gamma radiation is part of the electromagnetic spectrum.
- Gamma radiation follows an inverse square law:
- intensity at distance x from the source
Applications
- Gamma radiation is used extensively in medical imaging, curing cancer by destroying tumourous cells and for sterilising medical equipment.
- It can be used to irradiate food to stop food from going bad.
Investigating the Inverse Square Law
Gamma radiation follows an inverse square law. We can perform an experiment to show that this is true.
1) Find background radiation
- Do a background count with a Geiger-Muller (GM) tube and counter without a source present.
- Repeat this measurement and find an average background count per minute.
2) Experimental setup and method
- Position the source in a holder.
- Position the GM tube at different distances from the source.
- Measure the count rate at each distance several times and find an average for each distance.
3) Calculate corrected count rate
- Calculate the corrected count rate per min:
- Corrected count rate = average count rate at each distance − average background count
4) Plot graph
- Plot a graph of count rate against where x is the distance between the source and the GM tube.
- A straight line through the origin indicates that the inverse square law holds.
- The line might miss the origin if the distance to the source is uncertain.
- E.g. If the source is in the back of the holder, the distance 'x' may not be from the front of the tube but from somewhere inside it.
- Alternatively, plot log(count rate) against log(x) and the gradient should be −2.
Background Radiation
Background radiation is radiation which is always present, even when there is no radioactive source.
Sources of radiation
- Background radiation can come from a large number of sources:
- Radon gas, emitted from the ground.
- Buildings (brick).
- Cosmic rays (from the sun and space).
- Medical procedures.
- Food and drink.
Experimental error
- When measuring the radiation from a source, it is important to get accurate readings.
- The background radiation will skew readings if it is not accounted for.
- It is important to first measure the background radiation in an area and subtract it from the count found from a specific source.
Test yourself on Gamma Radiation
How far can a gamma ray travel through a vacuum?
Types of Radiation
Types of Radiation
Which of these are uses of gamma radiation?
What is the first thing you should always do when doing experiments with radiation?