Physics 107 and Science One - Radiation Shielding


In this experiment you will explore various aspects of experiments involving radiation, including; the special statistics that govern radioactive counting measurements and how to shield something from a source of radiation.

Given the probabilistic and random nature in some of what you are measuring, understand that there are no precisely "right" answers. You just have to do the best you can and justify what you have done. Note that this is not a problem with the apparatus: the measurements themselves are fundamentally uncertain.


1. Sign out a Sr-90 Beta-ray source and mount it in the end of your apparatus. Handle it carefully and don't touch the active surface of the source.
2. Your counter is connected to a Geiger tube. Check that the voltage applied to your Geiger tube is set to 450 V and that you have it set to use as a Geiger counter.

Counting Statistics

1. Go back to your notes on Expt.3 ‘More uncertainty’ and record on the board the mean and standard deviation that you obtained in the radiation counting part of that experiment. Is there a discernible pattern in the relationship between the mean and the standard deviation?

Radiation Attenuation

In many situations involving radioactive sources it is of vital importance to know how to block the radioactive particles. The rest of this experiment will explore how well Aluminum does this job.

1. Clamp the radioactive source into position with the plastic slide and move the Geiger counter to the 15 mm position..
2. Pick a time interval that gives about 1000 counts and then stick with that time interval for the remainder of the experiment
3. Now that you have decided on a time interval, measure the number of counts that you get as a function of the thickness of alumnum that you use. Be sure you don't move the Geiger counter or the radioactive source. Use many different thicknesses, including some thick enough to make the number of counts nearly zero.
4. Use the techniques that you have learned so far to linearize this data set and devise a model that fits the experimental results. Does the model adequately fit all of the data? Can you midify the model to fit better?
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Marking Scheme

2 mark for describung your measurement techniques and justifying your uncertainties

2 marks for a full data set with measurements of counts and measurements of the aluminum thickness

2 marks for plotting this in a way that linearizes the data - try to plot as you take the data

2 marks for writing an algebraic expression for the counts versus the thickness of aluminum, including values and units for any parameters in the model

1 mark for noting whether or the model fits all of the data or not.