University of Virginia
Physics Department

Protection from Radiation

A Physical Science Activity

Student Activity




  1. Set up the Geiger counter according to the unit's instructions, be sure it is calibrated.
  2. Test each source item by placing the item 5 cm away from the Geiger counter probe. Keep the probe steady for 15 seconds, and find the average reading on the meter. The needle will shift around some, so choose a value in the middle of its oscillations. Record your findings in the data table.
  3. Select the three source items with the highest readings. One at a time, place the source far enough away from the Geiger counter probe so that you will be able to fit the thickest piece of shielding in between the probe and the source. Test each of the shielding materials by placing them between the source and the counter. Follow the same procedure as in step 2 when taking the reading. Remember to keep the probe at the same distance for each measurement. Record your findings in the data table along with the thickness of each type of shielding that you use..
  4. Answer the questions on the worksheet after you have recorded your findings.


Data Sheet

To print out the Data Sheet only, click here.


Data Table


Without Shielding




Jar of Water


Gas lantern mantel








Fiesta ware pottery








Luminescent clock face








Smoke detector










1. Which item had the highest reading?


2. Which item had the lowest reading?


3. Do you think the density of the shield was important? Why?


4. Do you think the thickness of the shield was important? Why?