Stop that Gamma

Gamma rays are high-energy electromagnetic radiation released when a nucleus transitions from a higher energy state to a lower one. These emissions, also known as gamma photons, originate from within the nucleus. Gamma radiation possesses significantly greater penetrating power compared to alpha and beta radiation.

At longer distances, when the event rate is low,  it can be challenging to obtain highly precise measurements when the meter is set to the x1 scale. To improve accuracy, it is recommended to count the audible clicks or beats produced by the detector.

In this experiment, Cesium-137 (Cs-137) serves as the gamma radiation source. Measurements are taken at distances of 8 cm, 16 cm, 24 cm, 32 cm, and 48 cm from the source.

Procedure

1. Place down a short strip of tape and measure out 0cm, 8cm, 16cm, 24cm, 32cm, and 48cm. Mark each point.

2. Place your paddle at the 0cm mark.

3. Put the Geiger counter in a comfortable spot. If your counter has a built-in radiation source, then put it further away to reduce error.

4. Record the background activity before starting.

5. Place your source at the 8cm point.

6. Wait until the counter is stable then record the counts-per-minute performing 3 trials.

7. Repeat steps 5 and 6 while moving your counter to the other points.

8. Calculate the average between the 3 trials for each point.

9. Find the standard deviation of all of the trial averages.

10. Square the distances and divide those by 1 and multiply it by the average rate of the first data point to find the prediction of the average (cpm). 

11.  Lastly, get the difference between the measured average and the predicted. Record all of this using Google Sheets. You can use the formula function with the equal sign (=).

Questions:

1. In what ways are light waves and gamma radiation related?

2. Where does the energy of the photons originate?

3. How are photons and X-rays alike? Different?

4. What happens to the intensity of gamma radiation between 8 cm and 24 cm?

Optional: 

1. What is the speed of gamma rays?

2. Make a graph combining the data of 1/r2 vs. cpm for experiments 1, 2, and 3.

To access data from our own trials, click here.