# Core Practical 15: Investigating Gamma Radiation Absorption(Edexcel A Level Physics)

Author

Ashika

Expertise

## Core Practical 15: Investigating Gamma Radiation Absorption

#### Aim of the Experiment

• To investigate the absorption of gamma rays by different thicknesses of lead

#### Variables:

• Independent variable = Thickness of lead
• 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 five-minute period
• Record this value
• Calculate the average background rate per minute
2. Measure the thickness of the lead absorbers using Vernier calipers at three points on each sheet.
• For each sheet record the average thickness
3. Place the radioactive source a fixed distance of 10 cm away from the tube
4. Record the count rate over one minute
5. Repeat steps 3 and 4 a further two times, recording the count rate each time
6. Place the thinnest absorber directly in front of the gamma ray source
7. Repeat steps 3-5
8. Replace the sheet with another thickness and continue taking three readings per thickness

#### 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
• You will be able to determine the thickness of the lead required to absorb gamma radiation

#### Evaluating the Experiment

Systematic Errors:

• Make sure that the source is 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 a reliable source of radiation 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?

### Get unlimited access

to absolutely everything:

• Unlimited Revision Notes
• Topic Questions
• Past Papers