# Edexcel IGCSE Physics: Double Science 复习笔记：7.1.4 Core Practical: Investigating Radiation

### Core Practical 13: Investigating Radiation

#### Aim of the Experiment

•  The aim of this experiment is to investigate the penetration powers of different types of radiation using either radioactive sources or simulations

#### Variables:

• Independent variable = Absorber material
• Dependent variable = Count rate
• Control variables:
• Distance of GM tube to source

#### Equipment List

• Resolution of measuring equipment:
• Ruler = 1 mm
• Geiger-Müller tube = 0.01 μS/hr

#### Method

1. Connect the Geiger-Müller tube to the counter and, without any sources present, measure background radiation over a one minute period
2. Repeat this three times, and take an average
3. Now place a radioactive source a fixed distance of 3 cm away from the tube and take another reading over a one minute interval
4. Now take a set of absorbers: some paper, several different thicknesses of aluminium (increasing in 0.5mm intervals) and different thickness of lead
5. One at a time, place these absorbers between the source and the tube and take another reading over a one minute interval
6. Repeat the above experiment for other radioactive sources

#### Analysis of Results

• If the count over that interval falls to background levels (allow for a little random variation), then the radiation has all been absorbed
• Note that some sources will emit more than one type of radiation
• If the radiation is stopped by paper, the source will be emitting alpha
• If the radiation is stopped by a few mm of aluminium (about 5 or 6) then the source is emitting beta
• If some radiation is still able to penetrate a few mm of lead (5 or 6) then the source is emitting gamma

Penetrating power of alpha, beta and gamma radiation

#### Evaluating the Experiment

Systematic Errors:

• Make sure that the sources are stored well away from the counter during the experiment
• Conduct all runs of the experiment in the same location to avoid changes in background radiation levels

Random Errors:

• The accuracy of such an experiment is improved with using reliable sources with a long half-life and an activity well above the natural background level

#### Safety Considerations

• When not using a source, keep it in a lead lined container
• When in use, try and keep a good distance (a metre or so) between yourself and the source
• When handling the source, do so using tweezers (or tongs) and point the source away from you

#### Exam Tip

When answering questions about the core practicals you could try to remember the acronym SCREAMS:

• S: Which variable will you keep the same
• C: which variable should you change
• R: what will you do to make your experiment reliable
• E: what special equipment and equations are required
• A: how will you analyse your results
• M: which variable will you measure
• S: what safety precautions will you take?