radioactivity decay & penetration

D-and-C-book_091

D-and-C-book_092

Radioactive decay

The radioactivity sensor is normally connected to a standard Geiger-Muller tube and can produce a radioactive decay curve in ‘real-time’. This is a very convincing display of radioactive decay. Protactinium, with its half life of just 72 seconds, makes an ideal radioactive material for this experiment.

Apparatus
Geiger-Muller tube, clamp stand, source such as a Protactinium generator, interface, radioactivity sensor.
Connect the GM tube to the sensor and the sensor to socket 1 on the interface.

Setting up
Some systems recognize the sensors you attach automatically, in others you do this yourself. If you can adjust the range on the sensor, set it to around 50 cps.
You may be able to get the software to calculate Ln(count rate) and plot this in real time.

Recording the data
If you are using a Protactinium generator, give it a shake and then start recording.
Record for up to 10 minutes. The exact time will depend on the source.

Using the results
How is a decrease in radioactivity shown on your graph?
Does the radioactivity change steadily or is there more to it?
Use the software to calculate Ln (count rate) and plot this against time. How is this graph different?
Use the software to perform a least squares fit on the raw decay curve.
Save your data on disk. Print the graph.

Penetration by radiation

The radioactivity sensor is normally connected to a standard Geiger-Muller tube and provides a measure of radioactivity. In this investigation the intensity of a radioactive source is compared over different distances. The investigation can be extended to show the effect of distance and penetration through various materials in fact this is a particularly helpful demonstration.

Apparatus
Geiger-Muller tube, clamp stand, radioactive sources – alpha, beta and gamma. Metre rule, interface, radioactivity sensor. If required, paper, aluminium and lead of different thicknesses.

Setting up
Connect the GM tube to the sensor and the sensor to socket 1 on the interface.
Some systems recognize the sensors you attach automatically, in others you do this yourself. If you can, set the range on the sensor to cover 0-50 cps. The software also needs to know that you will be entering distances, of between 0 and 100 cm, via the keyboard.

Recording the data
Start recording – you should be prompted to enter a distance at the keyboard. Set the GM tube next to the source and type in 0 for the distance.
Move the GM tube 5cm further away. Type in 5 for the distance. Continue moving the tube and entering the distance.

Using the results
How is a decreasing amount of radioactivity shown on your graph?
How does the radioactivity change with distance?
Use the software to find the relationship between count rate and distance.
Save your data on disk. Print the graph.

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