Radioactive Decay

How radioactive materials decay

Radioactive materials decay, or lose their radioactivity, in a special and predictable way. If you have a fast decaying source, such as Protactinium with a half life of just 72 seconds, you can take a series of radioactivity readings and plot them on a graph. Or you can use a Geiger-Muller tube and radioactivity sensor connected to a computer. This can plot a radioactive decay curve and display it as it forms on the screen. Later you can analyse the results using your software.

What you need

radiodec.jpg (12508 bytes)

Geiger-Muller tube / radioactivity sensor, clamp stand, radioactive source such as a Protactinium generator, data logging interface.

Setting up

Connect the Geiger-Muller tube to the sensor and the sensor to the interface. If the sensor is adjustable, set it to a suitable range.
Start your sensing software.
Set your sensing software to record for around 10 minutes. The exact time will depend the strength of the source. If you are using a Protactinium generator, give it a shake and then start recording.

Questions

How is decreasing radioactivity shown on your graph?
Does the radioactivity change in a steady 'straight-line' fashion?
Is the graph 'noisy'? Why might this be?
Use the software to calculate Ln (count rate) and plot this against time. How is this graph different? What does it tell us?
Use the software to perform a least squares fit on the decay curve.

Teacher question

You may have difficulty in obtaining replacement Protactinium generators as the suppliers have discontinued it because of leakage problems. What alternative could you suggest? Click here to respond.

This activity was adapted by Roger Frost from The IT in Science book of Data logging and Control. This page is � IT in Science. It may be reproduced only for use within your school.