# Physics 107 - Radiation Shielding

## Learning Goals

• Practice at reflecting on your experimental results.
• Practice at scaling graph axes to uncover functions (models) that fit your data

Before you sign a radiation source out, you need to measure the background radiation in the room, measured by your Geiger counter. Start your counter and a timer to measure the background counted in 20 minutes. Once started, you can work on the LEARNING CATALYTICS QUESTIONS 1-3. When your 20 minute count is done, answer LEARNING CATALYTICS QUESTIONS 4-7.

### First Attenuation Measurements

1. Once you have a source in place, check that the distance is set to 0.8 cm (keep this the same through all measurements).
2. Measure the radiation counts in 2 minutes.
3. Next measure the radiation counts with 3 sheets of aluminum placed over the source (the thickness labelled 'C')
4. Is the thickness of three of these sheets of aluminum  sufficient to make your measured count-rate consistent with the background count-rate? (you will need to divide by the number of minutes to get a rate in counts/minute) LEARNING CATALYTICS QUESTIONS 8-10.

Now that you have established the amount of aluminum needed to reduce the count-rate close to background, measure the count rate (counts per minute) for several different thicknesses of aluminum shielding and use graphical scaling techniques to decide whether the relationship between count rate and shielding thickness is an exponential or a power law model. Note that it is important to plot as you go - use the counting time wisely. LEARNING CATALYTICS QUESTIONS 11-13.

### Fitting a Model to the Data

By adjusting a straight line model on your linearized plot, determine the parameters of the model function that describes your data.

Marking Scheme

2 marks for background measuremnt and comparison
2 marks for first attenuation measurements and comparison to background
3 marks for description of your data-taking strategy, adapted as you work to improve it
4 marks for high-quality data on a linearized plot
2 marks for fit a fit on the linearized plot, and a plot of residuals
3 marks for conclusion, including model with parameters and comments on background