1. Activity - what it is and how to calculate it...
2. ALARA - what it means and how it applies to this lab.
3. The operation of the GM tube & scaler ( a counter!)

What to do:

1. No laptops required!  Use the scaler provided.  Write your data on paper in well labelled tables and make copies for each person in your group.
    
2. Learn how to set up the scaler...
    
3. Connect the GM tube to the scaler, ensure the voltage is set to 400 V, and then take a 120 s background reading. (Record on paper).
    
4. Insert the ²²⁶Ra source into the holder as shown at right (use ALARA!) and take 60 s counts at known distances from the source.  Start as with the sample holder and GM tube holder touching (therefore ~5 cm between the source and GM tube) and then readings at an extra 10 cm further away until you reach 1.2 m away.
    
5. Clean up: put the source back in its lead castle, add the lead top and close the lid.  Leave all equipment on the desk.  Turn off the scaler.
    
6. Homework:
   a) Use your data to produce a graph with activity (in Bq) on the vertical axis and distance from the source (in m) on the horizontal.  Use Graphical Analysis for your graph - keeping data etc in Excel is fine.
   
   b) Fit a best fit curve... (hint: fit the simplest line that has a high R² value in Excel, or lowest RMSE in Graphical Analysis.)
   
   c) Print off and bring your graph to the NEXT CLASS.  This will be checked in class and will then be used to do further analysis.
   
   After next class:
   d) Using your 15cm point as a reference (minus background), use the inverse square law to interpolate what you would expect what your 5cm value should be.  Based on this data, what evidence exists that the GM tube was in partial breakdown at 5 cm?  What is GM Breakdown?
   
   e) Graph your data again, this time without the first 5 cm data point. Include the equation of the best fit line (same as your original graph) and compare the equation for the curves fem each graph with each other and the inverse square law.  Discuss the disparity / similarity between the two graphs and suggest what graph is a better representation of the effects of distance on radiation intensity and why.
   
   f) As you know from class the inverse square law should apply yet I actually expect a power higher than 2 on your curve.  Do some thinking / research and explain why your data does not quite match the inverse square law.
   
   g) Explain what your results have to do with radiation safety.  What are the implications of your findings for our labs, and for nuclear safety in general?

Setup:

Handling the radioactive source:
1. Wear gloves and use pliers to remove the source.
    Keep it pointed away from you at all times.

2. Insert into the holder:

What to hand in:

Answers to the homework questions. Insert your Graphical Analysis graph into a Word document.

Each student must do their own report.

Graph is due next class.  The graph plus the rest of the report must be submitted to the appropriate www.turnitin.com folder by the specified date.